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doi: 10.11883/bzycj-2024-0109
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For the launch safety problem of typical CL-20 based high detonation velocity pressed explosive (C-1, 94.5% CL-20+5.5% additive), the impact response characteristics of the explosive were studied by a large-scale hammer test with 400 kg, which has an impact loading curve similar to the loading characteristics of artillery chamber pressure. Meanwhile, the improved stress rate characterization method, the lower limit method and the drop height method were used to characterize the drop hammer impact response characteristics of explosives, and compared with the same kind of pressed explosives JO-8 and JH-2. The improved stress rate characterization method is obtained by improving the data processing process based on existing criteria, and weakening the sensitivity of the original criterion formula to oscillatory wave forms. The measured stress curves and characterization parameters of the bottom of three pressed explosives under different drop heights are obtained by tests, and the impact sensitivity differences of three explosives and the influence factors of the impact sensitivity of C-1 are discussed. The results show that the improved stress rate characterization method is certain effectiveness and universality for the characterizing the impact sensitivity of explosives. Meanwhile, the improved stress rate characterization method is consistent with other methods in reflecting the law. The drop height of C-1 (H50) is 1.0 m, which is 62.5% and 50.0% of JO-8 and JH-2, respectively; the peak stress of backseat corresponding to non-detonation (σ0) is 748.90 MPa, which is 85.42% and 64.33% of JO-8 and JH-2, respectively; the safety stress rate parameter (C0) is 0.344GPa2?ms-1, which is 45.87% and 39.14% of JO-8 and JH-2, respectively. The molecular structure of CL-20, the mechanical properties and thermal-chemical characteristics of C-1 explosive cylinder are the main factors that make its impact sensitivity higher than JO-8 and JH-2. The research results can provide a reference for the application and design calculation of CL-20 based high detonation velocity pressed explosive in high overload environment.
For the launch safety problem of typical CL-20 based high detonation velocity pressed explosive (C-1, 94.5% CL-20+5.5% additive), the impact response characteristics of the explosive were studied by a large-scale hammer test with 400 kg, which has an impact loading curve similar to the loading characteristics of artillery chamber pressure. Meanwhile, the improved stress rate characterization method, the lower limit method and the drop height method were used to characterize the drop hammer impact response characteristics of explosives, and compared with the same kind of pressed explosives JO-8 and JH-2. The improved stress rate characterization method is obtained by improving the data processing process based on existing criteria, and weakening the sensitivity of the original criterion formula to oscillatory wave forms. The measured stress curves and characterization parameters of the bottom of three pressed explosives under different drop heights are obtained by tests, and the impact sensitivity differences of three explosives and the influence factors of the impact sensitivity of C-1 are discussed. The results show that the improved stress rate characterization method is certain effectiveness and universality for the characterizing the impact sensitivity of explosives. Meanwhile, the improved stress rate characterization method is consistent with other methods in reflecting the law. The drop height of C-1 (H50) is 1.0 m, which is 62.5% and 50.0% of JO-8 and JH-2, respectively; the peak stress of backseat corresponding to non-detonation (σ0) is 748.90 MPa, which is 85.42% and 64.33% of JO-8 and JH-2, respectively; the safety stress rate parameter (C0) is 0.344GPa2?ms-1, which is 45.87% and 39.14% of JO-8 and JH-2, respectively. The molecular structure of CL-20, the mechanical properties and thermal-chemical characteristics of C-1 explosive cylinder are the main factors that make its impact sensitivity higher than JO-8 and JH-2. The research results can provide a reference for the application and design calculation of CL-20 based high detonation velocity pressed explosive in high overload environment.
, Available online ,
doi: 10.11883/bzycj-2024-0158
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Combined with the actual distribution characteristics of tungsten fiber and metallic glass matrix, the three-dimensional (3D) meso-scale finite element (FE) geometric model of tungsten fiber / metallic glass matrix composite long rod was established, and the coupled thermo-mechanical constitutive model was used to describe the high strength and high shear sensitivity of metallic glass matrix. Integrated with related oblique penetrating tests, the finite element simulations on the oblique penetration / perforation of composite and tungsten alloy long rods into steel target were carried out, and comparative analysis on the deformation and failure characteristics of the projectile and target materials were conducted. Furthermore, the influences of oblique angle and impact velocity on the ‘self-sharpening’ behavior of composite long rod as well as the corresponding ballistic performance were investigated in detail. Related analysis shows that in the oblique impact condition, due to the asymmetrical characteristics of target resistance on the rod, the rod nose gradually sharpens into an asymmetrical pointed configuration, and certain deflection occurs in the trajectory, Consequently, the ‘self-sharpening’ behavior in the composite long rod is weakened at a certain extent, and thus a decay occurs in its penetrating property. Besides, the impact velocity also contributes to the ‘self-sharpening’ characteristics and the corresponding ballistic behavior of composite long rod in the oblique impact condition, and the decay of penetrating capability derived from the oblique angle is more remarkable at the lower impact velocity. When the oblique angle increases to 50°, the composite long rod is hard to penetrate into the target effectively at the impact velocity below 900m/s, and ricochet becomes easy to occur when it impacts under a higher oblique angle. Related investigation is of good significance in predicting the penetrating ability of tungsten fiber / metallic glass matrix composite long rod, and it is beneficial to optimizing its impact attitude.
Combined with the actual distribution characteristics of tungsten fiber and metallic glass matrix, the three-dimensional (3D) meso-scale finite element (FE) geometric model of tungsten fiber / metallic glass matrix composite long rod was established, and the coupled thermo-mechanical constitutive model was used to describe the high strength and high shear sensitivity of metallic glass matrix. Integrated with related oblique penetrating tests, the finite element simulations on the oblique penetration / perforation of composite and tungsten alloy long rods into steel target were carried out, and comparative analysis on the deformation and failure characteristics of the projectile and target materials were conducted. Furthermore, the influences of oblique angle and impact velocity on the ‘self-sharpening’ behavior of composite long rod as well as the corresponding ballistic performance were investigated in detail. Related analysis shows that in the oblique impact condition, due to the asymmetrical characteristics of target resistance on the rod, the rod nose gradually sharpens into an asymmetrical pointed configuration, and certain deflection occurs in the trajectory, Consequently, the ‘self-sharpening’ behavior in the composite long rod is weakened at a certain extent, and thus a decay occurs in its penetrating property. Besides, the impact velocity also contributes to the ‘self-sharpening’ characteristics and the corresponding ballistic behavior of composite long rod in the oblique impact condition, and the decay of penetrating capability derived from the oblique angle is more remarkable at the lower impact velocity. When the oblique angle increases to 50°, the composite long rod is hard to penetrate into the target effectively at the impact velocity below 900m/s, and ricochet becomes easy to occur when it impacts under a higher oblique angle. Related investigation is of good significance in predicting the penetrating ability of tungsten fiber / metallic glass matrix composite long rod, and it is beneficial to optimizing its impact attitude.
, Available online ,
doi: 10.11883/bzycj-2024-0130
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The high reactivity of hydrogen and oxygen poses a huge challenge to the stable propagation of rotating detonation waves. To study the propagation instability of hydrogen-oxygen rotating detonation waves, based on the RYrhoCentralFoam solver developed by OpenFOAM, numerical simulations were conducted on two-dimensional hydrogen-oxygen rotating detonation waves in small scale model by changing the equivalence ratio. The complex and variable propagation characteristics of hydrogen-oxygen rotating detonation waves were revealed, and typical flow field was analyzed. The instability of propagation modes, quenching and re-initiation mechanism of detonation waves were explored. The results show that as the equivalence ratio increases, the flow field exhibits three propagation modes: extinction, single wave, and hybrid waves. The detonation wave velocity increases almost linearly with the increase of equivalence ratio, the velocity deficit is 5% to 8%. The disturbance of shock waves causes significant distortion and wrinkling on the deflagration surface, while the high reactivity of hydrogen and oxygen results in obvious layering on the deflagration surface and different instability at the two interfaces. The upper interface exhibits Kelvin-Helmholt (K-H) instability, while the lower interface exhibits Rayleigh-Taylor (R-T) instability. As for the hybrid waves, the detonation wave is extremely unstable, maintaining a cycle between three states: quenching, single wave, and double waves collision. There are two ways in which detonation waves can be extinguished: firstly, the collision of two waves leads to the quenching of the detonation wave, and secondly, the intensification of combustion on the deflagration surface leads to the downward movement of the deflagration surface, ultimately resulting in the quenching of the detonation wave. The main reason for re-initiation is that the R-T instability induces detonation products and fresh
The high reactivity of hydrogen and oxygen poses a huge challenge to the stable propagation of rotating detonation waves. To study the propagation instability of hydrogen-oxygen rotating detonation waves, based on the RYrhoCentralFoam solver developed by OpenFOAM, numerical simulations were conducted on two-dimensional hydrogen-oxygen rotating detonation waves in small scale model by changing the equivalence ratio. The complex and variable propagation characteristics of hydrogen-oxygen rotating detonation waves were revealed, and typical flow field was analyzed. The instability of propagation modes, quenching and re-initiation mechanism of detonation waves were explored. The results show that as the equivalence ratio increases, the flow field exhibits three propagation modes: extinction, single wave, and hybrid waves. The detonation wave velocity increases almost linearly with the increase of equivalence ratio, the velocity deficit is 5% to 8%. The disturbance of shock waves causes significant distortion and wrinkling on the deflagration surface, while the high reactivity of hydrogen and oxygen results in obvious layering on the deflagration surface and different instability at the two interfaces. The upper interface exhibits Kelvin-Helmholt (K-H) instability, while the lower interface exhibits Rayleigh-Taylor (R-T) instability. As for the hybrid waves, the detonation wave is extremely unstable, maintaining a cycle between three states: quenching, single wave, and double waves collision. There are two ways in which detonation waves can be extinguished: firstly, the collision of two waves leads to the quenching of the detonation wave, and secondly, the intensification of combustion on the deflagration surface leads to the downward movement of the deflagration surface, ultimately resulting in the quenching of the detonation wave. The main reason for re-initiation is that the R-T instability induces detonation products and fresh
, Available online ,
doi: 10.11883/bzycj-2024-0150
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Abstract:
The protection level and domestic standard test level of commonly used passive flexible barrier against rockfall impact are not higher than 5000 kJ, while bridges in mountains and other important transportation infrastructures are facing rockfall disaster threat with higher impact energy level. The analysis and design of 8000kJ-level passive flexible barrier against rockfall impact were carried out at present based on the numerical simulation method. Firstly, by adopting the explicit dynamic software ANSYS/LS-DYNA, quasi-static tests including the tensile test on single wire ring and three-ring chain, net puncturing test, and the dynamic impact test, i.e., 2000 kJ rockfall impacting the full-scale passive flexible barrier, were numerically reproduced, and the reliability of the numerical simulation method was fully verified by comparing with the experimental data, i.e., the maximum breaking force and breaking displacement of the wire ring and its failure characteristics, the whole impact process of rockfall and the cable force-time history curves. The influencing factors, i.e., the inclining angle, span, height of the steel post, and different specifications of energy dissipating devices ranging from 50 kJ to 70 kJ on the dynamic behavior of the passive flexible barrier were further analyzed. The results showed that: the specification of energy dissipating device is the most critical parameter controlling the internal force and displacement of the passive flexible barrier; the inclining angle of the steel post is recommended to be taken as 10°; the increase of the post spacing can reduce the in-plane stiffness of the structure, while having less effect on the transverse anchorage; the increase of the post height will cause a significant increase in the support reaction force at the post bottom; the reasonable adjustment of the anchorage position of each wire rope is required when the post height and spacing are changed. Finally, based on the results of parameter analysis, two design schemes for passive flexible barrier against 8000 kJ rockfall impact were given by adjusting the geometry of the structure, the specification of the energy dissipating device, and the addition of transmission support ropes, and both of them passed the test of the European standard EAD 340059-00-0106.
The protection level and domestic standard test level of commonly used passive flexible barrier against rockfall impact are not higher than 5000 kJ, while bridges in mountains and other important transportation infrastructures are facing rockfall disaster threat with higher impact energy level. The analysis and design of 8000kJ-level passive flexible barrier against rockfall impact were carried out at present based on the numerical simulation method. Firstly, by adopting the explicit dynamic software ANSYS/LS-DYNA, quasi-static tests including the tensile test on single wire ring and three-ring chain, net puncturing test, and the dynamic impact test, i.e., 2000 kJ rockfall impacting the full-scale passive flexible barrier, were numerically reproduced, and the reliability of the numerical simulation method was fully verified by comparing with the experimental data, i.e., the maximum breaking force and breaking displacement of the wire ring and its failure characteristics, the whole impact process of rockfall and the cable force-time history curves. The influencing factors, i.e., the inclining angle, span, height of the steel post, and different specifications of energy dissipating devices ranging from 50 kJ to 70 kJ on the dynamic behavior of the passive flexible barrier were further analyzed. The results showed that: the specification of energy dissipating device is the most critical parameter controlling the internal force and displacement of the passive flexible barrier; the inclining angle of the steel post is recommended to be taken as 10°; the increase of the post spacing can reduce the in-plane stiffness of the structure, while having less effect on the transverse anchorage; the increase of the post height will cause a significant increase in the support reaction force at the post bottom; the reasonable adjustment of the anchorage position of each wire rope is required when the post height and spacing are changed. Finally, based on the results of parameter analysis, two design schemes for passive flexible barrier against 8000 kJ rockfall impact were given by adjusting the geometry of the structure, the specification of the energy dissipating device, and the addition of transmission support ropes, and both of them passed the test of the European standard EAD 340059-00-0106.
, Available online ,
doi: 10.11883/bzycj-2024-0142
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Abstract:
In order to investigate the propagation law of gas explosion in U-ventilated coal mining face and explore the sensitivity of different influencing factors to the overpressure attenuation of gas explosion, numerical simulation was carried out by using Fluent simulation software and combining with the situation of 3906 working face in a mine. By comparing the numerical simulation results with experimental results, and the relative error is less than 15%, which further verifies the reliability of the mathematical model in this paper. Additionally, the key parameters of grid size, iteration time step, and ignition temperature are optimized to 0.2m, 0.05ms, and 1900K, respectively. And the relationship between the peak of the explosion overpressure and the distance of the explosion point of the coal face is exponential, and the explosion overpressure and the distance of the explosion point meets the exponential function relationship. The relationship between the peak explosion overpressure and the distance to the explosion point is in line with the exponential function, and the relationship between the arrival time of the peak explosion overpressure and the distance to the explosion point is in line with the linear function. By designing an orthogonal array, 16 sets of data were obtained through simulation, and the following analyses were conducted based on this data. Using extreme difference analysis to get three main control factors extreme difference value from big to small in order: temperature ? gas concentration ? gas accumulation area pressure, the simulation of the temperature for the explosion overpressure attenuation of the greatest impact, in which the R-value reaches 5.928. ANOVA analysis was applied to study the significance of the main control factors affecting the attenuation rate of explosion overpressure. The range values for the three main control factors is ranked from largest to smallest as follows: temperature ? gas accumulation zone pressure ? gas concentration, with temperature showing a significance level of 31.835, while the other two factors were not significant.
In order to investigate the propagation law of gas explosion in U-ventilated coal mining face and explore the sensitivity of different influencing factors to the overpressure attenuation of gas explosion, numerical simulation was carried out by using Fluent simulation software and combining with the situation of 3906 working face in a mine. By comparing the numerical simulation results with experimental results, and the relative error is less than 15%, which further verifies the reliability of the mathematical model in this paper. Additionally, the key parameters of grid size, iteration time step, and ignition temperature are optimized to 0.2m, 0.05ms, and 1900K, respectively. And the relationship between the peak of the explosion overpressure and the distance of the explosion point of the coal face is exponential, and the explosion overpressure and the distance of the explosion point meets the exponential function relationship. The relationship between the peak explosion overpressure and the distance to the explosion point is in line with the exponential function, and the relationship between the arrival time of the peak explosion overpressure and the distance to the explosion point is in line with the linear function. By designing an orthogonal array, 16 sets of data were obtained through simulation, and the following analyses were conducted based on this data. Using extreme difference analysis to get three main control factors extreme difference value from big to small in order: temperature ? gas concentration ? gas accumulation area pressure, the simulation of the temperature for the explosion overpressure attenuation of the greatest impact, in which the R-value reaches 5.928. ANOVA analysis was applied to study the significance of the main control factors affecting the attenuation rate of explosion overpressure. The range values for the three main control factors is ranked from largest to smallest as follows: temperature ? gas accumulation zone pressure ? gas concentration, with temperature showing a significance level of 31.835, while the other two factors were not significant.
, Available online ,
doi: 10.11883/bzycj-2024-0064
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Abstract:
In open-pit blasting, sympathetic detonation can increase the stress wave, increase the value of peak particle velocity, and cause fly rock to be thrown far away. These phenomena will affect the safety of blasting operation, slope stability and blasting effects. To investigate the mechanism of sympathetic detonation and the method of preventing sympathetic detonation in water-rich fissure open-pit mine, sympathetic detonation is identified by comparing the fluctuation difference of recorded blast-induced vibration signals through the impact detonation mechanism of explosives. Numerical simulation and field tests were adopted to analyze the effects of parameters on occurrence of sympathetic detonation, such as the quantity of donor charge, crack width and distance between charges. These results indicated that the borehole pressure increased with the decrease of decoupled charge coefficient, the increase of the crack width between boreholes (0.25 cm~1 cm) and the decrease of the distance between boreholes. By using wave-blocked tube, filling rock power or setting up air-deck, the impact pressure produced by donor charge was transmitted to the acceptor charge through the water-rich cracks. These methods made impact pressure lower than the critical detonation pressure of the emulsion explosive, which can prevent the sympathetic detonation of accept charge. Based on the field tests and simulated results, filling rock power was the best method of preventing sympathetic detonation when there was a single crack between the boreholes. Meanwhile, using wave-blocked tube with a thickness of 2.6mm was the best method of preventing sympathetic detonation when there were multiple cracks between the boreholes. Above all, the proposed detection method and obtained technologies provide the theory and guidance for preventing sympathetic detonation, which lead to improve the blasting effects and the safety of blasting operations.
In open-pit blasting, sympathetic detonation can increase the stress wave, increase the value of peak particle velocity, and cause fly rock to be thrown far away. These phenomena will affect the safety of blasting operation, slope stability and blasting effects. To investigate the mechanism of sympathetic detonation and the method of preventing sympathetic detonation in water-rich fissure open-pit mine, sympathetic detonation is identified by comparing the fluctuation difference of recorded blast-induced vibration signals through the impact detonation mechanism of explosives. Numerical simulation and field tests were adopted to analyze the effects of parameters on occurrence of sympathetic detonation, such as the quantity of donor charge, crack width and distance between charges. These results indicated that the borehole pressure increased with the decrease of decoupled charge coefficient, the increase of the crack width between boreholes (0.25 cm~1 cm) and the decrease of the distance between boreholes. By using wave-blocked tube, filling rock power or setting up air-deck, the impact pressure produced by donor charge was transmitted to the acceptor charge through the water-rich cracks. These methods made impact pressure lower than the critical detonation pressure of the emulsion explosive, which can prevent the sympathetic detonation of accept charge. Based on the field tests and simulated results, filling rock power was the best method of preventing sympathetic detonation when there was a single crack between the boreholes. Meanwhile, using wave-blocked tube with a thickness of 2.6mm was the best method of preventing sympathetic detonation when there were multiple cracks between the boreholes. Above all, the proposed detection method and obtained technologies provide the theory and guidance for preventing sympathetic detonation, which lead to improve the blasting effects and the safety of blasting operations.
, Available online ,
doi: 10.11883/bzycj-2024-0095
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Abstract:
A novel kind of energy-absorbing material that is frequently utilized in protective structures is shear thickening fluid (STF)，Its attributes include ease of production and protection of the environment. STF was successfully prepared in this work. Then add the STF to the honeycomb sandwich structure to strengthen it against impacts. Low-velocity drop hammer impact experiments investigated the effects of honeycomb aperture diameter, honeycomb wall thickness, and impact velocity on honeycomb sandwich structures. The DIC method was used to determine the strain history and deflection of the structure, and investigations were carried out on the mechanism of low-velocity impact response of honeycomb sandwich panels. The results shows that there are differences in the deformation patterns of the honeycomb sandwich structure's back panel with and without STF filling. In the case of the former, the back panel's center area exhibits bump deformation, while the surrounding area displays significant bulging deformation. In contrast, the back panel with STF filling exhibits bump deformation without bulging deformation, and its localized bump area is larger. The filled STF can lessen the back panel of the structure's deformation deflection and the intrusion depth of the falling hammer in the velocity range (1 m/s–2 m/s) examined in this paper. Increasing the impact velocity is more favorable for STF to produce the thickening effect, the other side, this effect of STF is influenced by the honeycomb's aperture diameter and wall thickness. The larger aperture diameter structure is beneficial to the STF hardening effect because it increases the number of honeycomb cells involved in absorbing energy, expands the structure's local deformation region, and reduces the dimensionless deflection of the structure. On the other hand, the thick honeycomb wall mitigates the impact of the falling hammer, which is detrimental to the STF hardening effect, and the thinner honeycomb wall structure is beneficial to the STF hardening effect. The study's results serve as a certain reference for the application of STF in protective structures. Future research will concentrate on examining the coupling mechanism between STF and protective structures as well as the design techniques that allow the structure under consideration to be lighter.
A novel kind of energy-absorbing material that is frequently utilized in protective structures is shear thickening fluid (STF)，Its attributes include ease of production and protection of the environment. STF was successfully prepared in this work. Then add the STF to the honeycomb sandwich structure to strengthen it against impacts. Low-velocity drop hammer impact experiments investigated the effects of honeycomb aperture diameter, honeycomb wall thickness, and impact velocity on honeycomb sandwich structures. The DIC method was used to determine the strain history and deflection of the structure, and investigations were carried out on the mechanism of low-velocity impact response of honeycomb sandwich panels. The results shows that there are differences in the deformation patterns of the honeycomb sandwich structure's back panel with and without STF filling. In the case of the former, the back panel's center area exhibits bump deformation, while the surrounding area displays significant bulging deformation. In contrast, the back panel with STF filling exhibits bump deformation without bulging deformation, and its localized bump area is larger. The filled STF can lessen the back panel of the structure's deformation deflection and the intrusion depth of the falling hammer in the velocity range (1 m/s–2 m/s) examined in this paper. Increasing the impact velocity is more favorable for STF to produce the thickening effect, the other side, this effect of STF is influenced by the honeycomb's aperture diameter and wall thickness. The larger aperture diameter structure is beneficial to the STF hardening effect because it increases the number of honeycomb cells involved in absorbing energy, expands the structure's local deformation region, and reduces the dimensionless deflection of the structure. On the other hand, the thick honeycomb wall mitigates the impact of the falling hammer, which is detrimental to the STF hardening effect, and the thinner honeycomb wall structure is beneficial to the STF hardening effect. The study's results serve as a certain reference for the application of STF in protective structures. Future research will concentrate on examining the coupling mechanism between STF and protective structures as well as the design techniques that allow the structure under consideration to be lighter.
, Available online ,
doi: 10.11883/bzycj-2023-0260
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Abstract:
Based on the computational fluid dynamics (CFD) numerical methods, a set of reliable and effective numerical methods for investigating the flow field and evolution characteristics of motion during the falling impact of water falling vehicle with boost floatation aids in wave environment was established by coupling with volume of fluid (VOF) multiphase flow model, k-ω SST turbulence model, Schnerr-Sauer cavitation model and Stokes fifth-order nonlinear wave theory. The numerical simulation of the process of falling into water under a horizontal cylinder showed that the difference between the experimental results and the numerical results in falling displacement was small, which verifies the validity of the numerical method of water falling impact. The wave generation results obtained by the velocity boundary numerical wave generation method were in good agreement with Stokes fifth-order nonlinear wave theory. Based on the established numerical method, numerical simulation was carried out on the water falling impact process of the vehicle with boost floatation aids under different wave sea states. The kinematic and dynamic parameters of the vehicle and evolution of water-entry cavity flow field during the impact process were analyzed, and the water falling impact characteristics of the vehicle with boost floatation aids under wave environment were summarized. The results show that the impact of wave environment on the falling impact process is mainly reflected in the motion attenuation section. The horizontal impact is much more affected by the wave environment than the vertical impact and the influence of different sea conditions on the horizontal impact of the vehicle is mainly achieved by influencing the formation and collapse of the water-entry cavity. The calculated displacement, velocity, acceleration and boost floatation aids force during the impact process of vehicle with boost floatation aids can be provided as a reference for the structural design and safety test guidance of the vehicle recovery under wave environment.
Based on the computational fluid dynamics (CFD) numerical methods, a set of reliable and effective numerical methods for investigating the flow field and evolution characteristics of motion during the falling impact of water falling vehicle with boost floatation aids in wave environment was established by coupling with volume of fluid (VOF) multiphase flow model, k-ω SST turbulence model, Schnerr-Sauer cavitation model and Stokes fifth-order nonlinear wave theory. The numerical simulation of the process of falling into water under a horizontal cylinder showed that the difference between the experimental results and the numerical results in falling displacement was small, which verifies the validity of the numerical method of water falling impact. The wave generation results obtained by the velocity boundary numerical wave generation method were in good agreement with Stokes fifth-order nonlinear wave theory. Based on the established numerical method, numerical simulation was carried out on the water falling impact process of the vehicle with boost floatation aids under different wave sea states. The kinematic and dynamic parameters of the vehicle and evolution of water-entry cavity flow field during the impact process were analyzed, and the water falling impact characteristics of the vehicle with boost floatation aids under wave environment were summarized. The results show that the impact of wave environment on the falling impact process is mainly reflected in the motion attenuation section. The horizontal impact is much more affected by the wave environment than the vertical impact and the influence of different sea conditions on the horizontal impact of the vehicle is mainly achieved by influencing the formation and collapse of the water-entry cavity. The calculated displacement, velocity, acceleration and boost floatation aids force during the impact process of vehicle with boost floatation aids can be provided as a reference for the structural design and safety test guidance of the vehicle recovery under wave environment.
, Available online ,
doi: 10.11883/bzycj-2024-0017
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Abstract:
Weathering effect can lead to the development of pores in rock material, which affects its engineering properties seriously. Therefore, studying the influence of weathering effect on the mechanical properties and anti-penetration properties of granite is of great significance to evaluate the damage effectiveness of penetration warheads and analyze the protection capability of underground facilities. The two kinds of granite with different weathering degrees were selected to systematically investigate their physical properties, static/dynamic compressive properties and anti-penetration properties with the experiment methods, such as the X ray diffraction (XRD) test, the static uniaxial compression test, the static triaxial compression test, the dynamic uniaxial compression test, the dynamic triaxial compression test and the two-stage light gas gun test. Finally, the results indicate that weathering effect can cause decrease of biotite and microcline, increase of porosity, loose internal structure, and obvious defects in granite, based on the X ray diffraction analysis technique. Besides, weathering effect also can lead to deterioration in granite’s compressive strength, weakened strain rate effect, and the shift of the failure mode from brittle failure to weak shear failure. Under static and dynamic triaxial compression, as for the two kinds of weathered granite, static and dynamic compressive strength rises significantly with confining pressure increasing meanwhile moderately weathered granite is more sensitive to confining pressure, compared with the slightly weathered granite. Under the condition of high-speed penetration, the speed varying from 873m/s to 1040m/s, there is a little difference in anti-penetration performance for the two kinds of weathered granite, in which case both of the non-dimensional penetration depths are generally no more than 3 times the length of the projectiles. Moreover, no obvious penetration trajectory zones exit in weathered granite targets while there are obvious crushed zones around the projectiles, the length of which can reach up to 5~8 times the diameter of the projectiles.
Weathering effect can lead to the development of pores in rock material, which affects its engineering properties seriously. Therefore, studying the influence of weathering effect on the mechanical properties and anti-penetration properties of granite is of great significance to evaluate the damage effectiveness of penetration warheads and analyze the protection capability of underground facilities. The two kinds of granite with different weathering degrees were selected to systematically investigate their physical properties, static/dynamic compressive properties and anti-penetration properties with the experiment methods, such as the X ray diffraction (XRD) test, the static uniaxial compression test, the static triaxial compression test, the dynamic uniaxial compression test, the dynamic triaxial compression test and the two-stage light gas gun test. Finally, the results indicate that weathering effect can cause decrease of biotite and microcline, increase of porosity, loose internal structure, and obvious defects in granite, based on the X ray diffraction analysis technique. Besides, weathering effect also can lead to deterioration in granite’s compressive strength, weakened strain rate effect, and the shift of the failure mode from brittle failure to weak shear failure. Under static and dynamic triaxial compression, as for the two kinds of weathered granite, static and dynamic compressive strength rises significantly with confining pressure increasing meanwhile moderately weathered granite is more sensitive to confining pressure, compared with the slightly weathered granite. Under the condition of high-speed penetration, the speed varying from 873m/s to 1040m/s, there is a little difference in anti-penetration performance for the two kinds of weathered granite, in which case both of the non-dimensional penetration depths are generally no more than 3 times the length of the projectiles. Moreover, no obvious penetration trajectory zones exit in weathered granite targets while there are obvious crushed zones around the projectiles, the length of which can reach up to 5~8 times the diameter of the projectiles.
, Available online ,
doi: 10.11883/bzycj-2024-0030
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Abstract:
Quantitative investigation of stress wave effects during the elastic compression stage of Split Hopkinson Pressure Bar (SHPB) tests is fundamental for decoupling accurate material elastic curves. This paper, grounded in the assumption of plane waves and utilizing the generalized wave impedance theory, conducts a quantitative theoretical analysis of the structural effects caused by the evolution of stress waves during the elastic compression stage of specimens with mismatched rod and specimen areas. The study explores the characteristics and main factors of the deviation between engineering stress-strain curves of specimens during the elastic stage and the actual material stress-strain curves under different conditions. It further reveals the governing rules and mechanisms influencing these deviations.The research indicates that for linearly incident loading waves, when the dimensionless time is a multiple of 0.5, even if other parameters change, the engineering stress-strain values of the specimen correspond approximately to the actual material stress-strain values. Even when there is a significant stress difference at both ends of the specimen, if the variation of stress difference tends to stabilize, the difference between the engineering stress-strain curve of the specimen and the actual material stress-strain curve is relatively small. The study calculates the maximum stress deviation value of the specimen and its corresponding dimensionless time, as well as the trend of the maximum stress deviation value of the specimen within different fluctuation intervals. Moreover, the study investigates the scenario where the incident wave is a bilinear combination wave. The results show that when a bilinear incident wave is present, the two linear intervals can be independently analyzed. Regardless of the combination or the variation of stress difference, only when the stress difference at both ends of the specimen reaches an approximately constant curve, the corresponding engineering stress-strain of the specimen is relatively accurate.This research provides theoretical references for the refined design of SHPB tests and the accurate processing of data.
Quantitative investigation of stress wave effects during the elastic compression stage of Split Hopkinson Pressure Bar (SHPB) tests is fundamental for decoupling accurate material elastic curves. This paper, grounded in the assumption of plane waves and utilizing the generalized wave impedance theory, conducts a quantitative theoretical analysis of the structural effects caused by the evolution of stress waves during the elastic compression stage of specimens with mismatched rod and specimen areas. The study explores the characteristics and main factors of the deviation between engineering stress-strain curves of specimens during the elastic stage and the actual material stress-strain curves under different conditions. It further reveals the governing rules and mechanisms influencing these deviations.The research indicates that for linearly incident loading waves, when the dimensionless time is a multiple of 0.5, even if other parameters change, the engineering stress-strain values of the specimen correspond approximately to the actual material stress-strain values. Even when there is a significant stress difference at both ends of the specimen, if the variation of stress difference tends to stabilize, the difference between the engineering stress-strain curve of the specimen and the actual material stress-strain curve is relatively small. The study calculates the maximum stress deviation value of the specimen and its corresponding dimensionless time, as well as the trend of the maximum stress deviation value of the specimen within different fluctuation intervals. Moreover, the study investigates the scenario where the incident wave is a bilinear combination wave. The results show that when a bilinear incident wave is present, the two linear intervals can be independently analyzed. Regardless of the combination or the variation of stress difference, only when the stress difference at both ends of the specimen reaches an approximately constant curve, the corresponding engineering stress-strain of the specimen is relatively accurate.This research provides theoretical references for the refined design of SHPB tests and the accurate processing of data.
, Available online ,
doi: 10.11883/bzycj-2024-0145
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Abstract:
In order to explore the structural response characteristics of projectile obliquely penetrating granite target, based on the 30 mm ballistic gun platform, the test of projectile obliquely penetrating granite target was carried out, and the damage parameters of projectile structure under non-normal penetration were obtained. On this basis, combined with the numerical simulation method, the deformation and fracture mechanism of the projectile structure of the projectile obliquely penetrating the granite target are studied, and the influence of the initial conditions of penetration on the structural response of the projectile is analyzed. The results show that the projectile is prone to bending and fracture when it is not penetrating the granite target. The asymmetric force on the head and tail of the projectile is the reason for the different response behaviors of the projectile. The different response behaviors of the projectile are determined by the peak value of the angular velocity difference between the head and tail of the projectile. As the yaw increases, the bending degree of the projectile increases linearly, and the projectile breaks when the yaw increases to 8 °. With the increase of the impact angle, the bending degree of the projectile increases first, then decreases and then increases. When the impact angle is 15 °, the bending degree of the projectile is the smallest. When the impact angle reaches 30 °, the projectile breaks. Compared with the impact angle, the impact angle has a more significant effect on the response behavior of the projectile structure. When the yaw and the yaw are combined, the introduction of the yaw will increase the critical fracture positive yaw of the projectile, and the negative yaw will weaken the ability of the projectile to resist bending deformation and fracture. When the impact velocity is higher than 1600 m/s, the impact velocity of the projectile becomes the main controlling factor for the different response behaviors of the projectile.
In order to explore the structural response characteristics of projectile obliquely penetrating granite target, based on the 30 mm ballistic gun platform, the test of projectile obliquely penetrating granite target was carried out, and the damage parameters of projectile structure under non-normal penetration were obtained. On this basis, combined with the numerical simulation method, the deformation and fracture mechanism of the projectile structure of the projectile obliquely penetrating the granite target are studied, and the influence of the initial conditions of penetration on the structural response of the projectile is analyzed. The results show that the projectile is prone to bending and fracture when it is not penetrating the granite target. The asymmetric force on the head and tail of the projectile is the reason for the different response behaviors of the projectile. The different response behaviors of the projectile are determined by the peak value of the angular velocity difference between the head and tail of the projectile. As the yaw increases, the bending degree of the projectile increases linearly, and the projectile breaks when the yaw increases to 8 °. With the increase of the impact angle, the bending degree of the projectile increases first, then decreases and then increases. When the impact angle is 15 °, the bending degree of the projectile is the smallest. When the impact angle reaches 30 °, the projectile breaks. Compared with the impact angle, the impact angle has a more significant effect on the response behavior of the projectile structure. When the yaw and the yaw are combined, the introduction of the yaw will increase the critical fracture positive yaw of the projectile, and the negative yaw will weaken the ability of the projectile to resist bending deformation and fracture. When the impact velocity is higher than 1600 m/s, the impact velocity of the projectile becomes the main controlling factor for the different response behaviors of the projectile.
Experimental study on dynamic mechanical properties of sandstone based on Lagrangian analysis method
, Available online ,
doi: 10.11883/bzycj-2024-0152
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Abstract:
To investigate the dynamic mechanical properties of sandstone in deep strata under impact loads, an improved Hopkinson pressure bar experimental system was established. The traditional Hopkinson pressure bar's transmission rod was replaced with a long rod specimen made of gray sandstone to better simulate deep geological conditions. Point spalling treatment was applied to the specimen, and strain gauges were meticulously affixed at critical measurement points.Dynamic compression experiments were meticulously conducted on the gray sandstone long rod specimen at various loading rates (9.57 m/s, 14.78 m/s, 19.32 m/s, and 27.60 m/s). Utilizing high-speed digital image correlation (DIC) technology, the evolution of displacement and strain fields on the surface of the specimen throughout each test was closely monitored. This advanced technique enabled a detailed exploration of how the gray sandstone responded to near-field impact loading, particularly focusing on its tensile failure characteristics.Employing the Lagrangian analysis method, displacement-time curves for different mass points derived from the DIC analysis of displacement fields were extracted. These curves provided critical data to compute the stress-strain behavior of the gray sandstone material under dynamic loading conditions. The study reveals several key findings: the gray sandstone long rod specimen predominantly exhibits tensile failure, with distinct patterns of fragmentation near the loading end and layer cracking away from it. Moreover, the dynamic compressive strength factor of the gray sandstone long rod specimen shows a notable increase with higher strain rates, indicating a significant strain rate effect. Correspondingly, both stress and strain peaks observe an upward trend at various measurement points with increasing loading rates.Remarkably, under identical loading rates, stress-strain curves of the gray sandstone long rod specimen exhibit a unique phenomenon where curves from measurement points closer to the loading end envelop those from points farther away. This observation underscores the complex nature of dynamic loading responses in geological materials.Overall, this comprehensive investigation provides essential theoretical insights and methodological references for understanding the dynamic behavior of sandstone within deep geological formations under impact loads. The findings offer valuable contributions to engineering practices concerned with the stability and resilience of underground structures subjected to dynamic loading conditions.
To investigate the dynamic mechanical properties of sandstone in deep strata under impact loads, an improved Hopkinson pressure bar experimental system was established. The traditional Hopkinson pressure bar's transmission rod was replaced with a long rod specimen made of gray sandstone to better simulate deep geological conditions. Point spalling treatment was applied to the specimen, and strain gauges were meticulously affixed at critical measurement points.Dynamic compression experiments were meticulously conducted on the gray sandstone long rod specimen at various loading rates (9.57 m/s, 14.78 m/s, 19.32 m/s, and 27.60 m/s). Utilizing high-speed digital image correlation (DIC) technology, the evolution of displacement and strain fields on the surface of the specimen throughout each test was closely monitored. This advanced technique enabled a detailed exploration of how the gray sandstone responded to near-field impact loading, particularly focusing on its tensile failure characteristics.Employing the Lagrangian analysis method, displacement-time curves for different mass points derived from the DIC analysis of displacement fields were extracted. These curves provided critical data to compute the stress-strain behavior of the gray sandstone material under dynamic loading conditions. The study reveals several key findings: the gray sandstone long rod specimen predominantly exhibits tensile failure, with distinct patterns of fragmentation near the loading end and layer cracking away from it. Moreover, the dynamic compressive strength factor of the gray sandstone long rod specimen shows a notable increase with higher strain rates, indicating a significant strain rate effect. Correspondingly, both stress and strain peaks observe an upward trend at various measurement points with increasing loading rates.Remarkably, under identical loading rates, stress-strain curves of the gray sandstone long rod specimen exhibit a unique phenomenon where curves from measurement points closer to the loading end envelop those from points farther away. This observation underscores the complex nature of dynamic loading responses in geological materials.Overall, this comprehensive investigation provides essential theoretical insights and methodological references for understanding the dynamic behavior of sandstone within deep geological formations under impact loads. The findings offer valuable contributions to engineering practices concerned with the stability and resilience of underground structures subjected to dynamic loading conditions.
, Available online ,
doi: 10.11883/bzycj-2024-0097
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Abstract:
Abstract: Concrete materials are widely used in the construction of infrastructure and defense facilities, in order to study the dynamic mechanical properties of high-temperature concrete under different cooling methods, the dynamic mechanical properties of C30 cylindrical concrete samples at different temperatures under different cooling methods were tested by Φ74mm Split Hopkinson Pressure Bar (SHPB), and their mechanical properties under the combined influence of heat, water and force were obtained, and the effects of cooling methods, temperature and striking velocity on the average strain rate were studied, focuses on the analysis of the dynamic stress-strain curve of high-temperature concrete under different cooling methods, as well as the effects of cooling methods, temperature and striking velocity on its crushing morphology, dynamic compressive strength, elastic modulus, peak strain and a range of dynamic effects. The results show that in the static mechanical test, the peak points of the concrete stress-strain curve are shifted down and to the right under the two cooling methods; The average strain rate of concrete specimens is more obviously affected by temperature during water -cooled, and the striking velocity is approximately linear with the average strain rate under different cooling methods; When the temperature reaches 400 °C and above, the color of the sample changes significantly, and cracking, at the same temperature, the water-cooled sample is darker than the air-cooled color, more fine cracks appear, and the aggregate morphological damage is more serious; The dynamic stress-strain curves of concrete under different temperatures and cooling methods maintain their basic shape, and the dynamic compressive strength of concrete under different cooling methods is proportional to the striking velocity and inversely proportional to the heating temperature; The damage coefficient of elastic modulus of concrete under various striking velocity and temperatures when cooled by water is lower than that at air cooling; The peak strain of high-temperature concrete is directly proportional to the heating temperature and inversely proportional to the striking velocity, and the peak strain under water cooling is higher than that under air cooling. The DIF of concrete is proportional to temperature and striking velocity, and the higher the temperature, the more obvious the strain rate effect of concrete; When the temperature is 200°C, the energy consumption coefficient of concrete rebounds.
Abstract: Concrete materials are widely used in the construction of infrastructure and defense facilities, in order to study the dynamic mechanical properties of high-temperature concrete under different cooling methods, the dynamic mechanical properties of C30 cylindrical concrete samples at different temperatures under different cooling methods were tested by Φ74mm Split Hopkinson Pressure Bar (SHPB), and their mechanical properties under the combined influence of heat, water and force were obtained, and the effects of cooling methods, temperature and striking velocity on the average strain rate were studied, focuses on the analysis of the dynamic stress-strain curve of high-temperature concrete under different cooling methods, as well as the effects of cooling methods, temperature and striking velocity on its crushing morphology, dynamic compressive strength, elastic modulus, peak strain and a range of dynamic effects. The results show that in the static mechanical test, the peak points of the concrete stress-strain curve are shifted down and to the right under the two cooling methods; The average strain rate of concrete specimens is more obviously affected by temperature during water -cooled, and the striking velocity is approximately linear with the average strain rate under different cooling methods; When the temperature reaches 400 °C and above, the color of the sample changes significantly, and cracking, at the same temperature, the water-cooled sample is darker than the air-cooled color, more fine cracks appear, and the aggregate morphological damage is more serious; The dynamic stress-strain curves of concrete under different temperatures and cooling methods maintain their basic shape, and the dynamic compressive strength of concrete under different cooling methods is proportional to the striking velocity and inversely proportional to the heating temperature; The damage coefficient of elastic modulus of concrete under various striking velocity and temperatures when cooled by water is lower than that at air cooling; The peak strain of high-temperature concrete is directly proportional to the heating temperature and inversely proportional to the striking velocity, and the peak strain under water cooling is higher than that under air cooling. The DIF of concrete is proportional to temperature and striking velocity, and the higher the temperature, the more obvious the strain rate effect of concrete; When the temperature is 200°C, the energy consumption coefficient of concrete rebounds.
, Available online ,
doi: 10.11883/bzycj-2024-0102
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Abstract:
In order to reduce the great threat of gas explosion to coal mine operators and coal safety mining, the law of explosion overpressure and impact gas velocity attenuation with the propagation distance of different volumes of gas-air mixed gas in roadway was deeply studied. Firstly, based on dimensional analysis and energy similarity law, a dimensionless formula for the attenuation of gas explosion overpressure and impact gas velocity with propagation distance is established, considering the factors affecting the attenuation of gas explosion overpressure and impact gas velocity with propagation distance. Secondly, by regression analysis of the experimental data in large roadway, the attenuation models of overpressure and impact airflow velocity and their relations are obtained. Finally, the attenuation model and relation are verified. The results show that the energy of gas mixture, the amount of gas accumulation, the distance of measuring point, the hydraulic diameter and the cross-sectional area of roadway are the main factors affecting the attenuation of overpressure and impact gas velocity. Both overpressure and impact gas velocity are positively correlated with the accumulation of mixed gas. The greater the initial overpressure and impact gas velocity, the faster the attenuation. The relative errors between the theoretical value and the test value of the attenuation model and the relative errors between the theoretical value and the test value of the relation are controlled at about 10%, and the overall consistency of the data is high, which verifies the reliability of the data, and can describe the law of gas explosion propagation more simply and intuitively, and realize the rapid calculation of overpressure and gas velocity.
In order to reduce the great threat of gas explosion to coal mine operators and coal safety mining, the law of explosion overpressure and impact gas velocity attenuation with the propagation distance of different volumes of gas-air mixed gas in roadway was deeply studied. Firstly, based on dimensional analysis and energy similarity law, a dimensionless formula for the attenuation of gas explosion overpressure and impact gas velocity with propagation distance is established, considering the factors affecting the attenuation of gas explosion overpressure and impact gas velocity with propagation distance. Secondly, by regression analysis of the experimental data in large roadway, the attenuation models of overpressure and impact airflow velocity and their relations are obtained. Finally, the attenuation model and relation are verified. The results show that the energy of gas mixture, the amount of gas accumulation, the distance of measuring point, the hydraulic diameter and the cross-sectional area of roadway are the main factors affecting the attenuation of overpressure and impact gas velocity. Both overpressure and impact gas velocity are positively correlated with the accumulation of mixed gas. The greater the initial overpressure and impact gas velocity, the faster the attenuation. The relative errors between the theoretical value and the test value of the attenuation model and the relative errors between the theoretical value and the test value of the relation are controlled at about 10%, and the overall consistency of the data is high, which verifies the reliability of the data, and can describe the law of gas explosion propagation more simply and intuitively, and realize the rapid calculation of overpressure and gas velocity.
, Available online ,
doi: 10.11883/bzycj-2024-0021
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Abstract:
Terrorist attacks and local wars occur frequently, which makes the risk of buildings subjected to multiple explosions increasing. Most of the existing research focuses on the single explosion scenario, and there are few studies on the damage effect of reinforced concrete structures under multiple explosions. In order to study the damage effect of reinforcement concrete beams under secondary explosion and offset the shortcomings of the existing research, relevant numerical analysis is carried out. The damage parameters of K&C concrete constitutive model are modified firstly. And the ALE method for FSI (fluid-structure interaction) is used to simulate the secondary explosion experiment of reinforced concrete beam with the full restart function of LS-DYNA. The numerical analysis results are well consistent with the test results, verifying the effectiveness of the simulation method and the modified constitutive model. On this basis, the secondary explosion simulation conditions are expanded. The effects of various parameters, including scaled distance, concrete strength, longitudinal reinforcement ratio and transverse reinforcement details, on the damage effect of typical size reinforcement concrete beams under secondary explosion are further analyzed. The results show that due to the compressive membrane action of reinforcement concrete beam, keeping the total equivalent TNT weight of the explosion unchanged, the damage of RC component caused by one single explosion is more serious than the cumulative damage caused by two successive explosions. The concrete strength has a more significant effect on the blast resistance performance of RC beams under secondary explosion, the higher the concrete strength, the smaller the damage degree of the beam under the secondary explosion. Increasing the longitudinal reinforcement ratio has no obvious effect on improving the blast resistance performance of the beam and educing the transverse reinforcement spacing can effectively reduce the shear failure degree of reinforcement concrete beam which makes the blast resistance performance of RC beams under secondary explosion and near explosion improved. The iso-damage curves of reinforcement concrete beams with two different design parameters are further calculated and the corresponding damage degree zoning maps are established. The present results can provide reference for the blast resistance design of reinforcement concrete structures.
, Available online ,
doi: 10.11883/bzycj-2023-0473
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Abstract:
When shock waves propagate in solid mediums, the internal charge carriers migrate to the electrodes under the action of shock waves to form electric potential and output voltage/current - shock induced polarization effect (SIP). The development of SIP effect has challenged the traditional understanding of physical response of solid medium. In this paper, the SIP effects of typical solid mediums such as crystals, metals, ceramics and polymers are systematically reviewed. The SIP test methods developed at present are also summarized, and the characteristics of SIP induced by different loading methods such as drop hammer/pendulum, SHPB, light gas gun and explosive detonation are analyzed. The applications of finite element method, molecular dynamics, peridynamic and phase field analysis in the numerical simulation of SIP of solid mediums are summarized. The macroscopic phenomenology theories of SIP of solid mediums are summarized based on Allison theory, Zhang Yuheng theory, shock flexoelectric theory and shock wave theory, and the microscopic mechanism of
When shock waves propagate in solid mediums, the internal charge carriers migrate to the electrodes under the action of shock waves to form electric potential and output voltage/current - shock induced polarization effect (SIP). The development of SIP effect has challenged the traditional understanding of physical response of solid medium. In this paper, the SIP effects of typical solid mediums such as crystals, metals, ceramics and polymers are systematically reviewed. The SIP test methods developed at present are also summarized, and the characteristics of SIP induced by different loading methods such as drop hammer/pendulum, SHPB, light gas gun and explosive detonation are analyzed. The applications of finite element method, molecular dynamics, peridynamic and phase field analysis in the numerical simulation of SIP of solid mediums are summarized. The macroscopic phenomenology theories of SIP of solid mediums are summarized based on Allison theory, Zhang Yuheng theory, shock flexoelectric theory and shock wave theory, and the microscopic mechanism of
, Available online ,
doi: 10.11883/bzycj-2024-0071
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Abstract:
There are many microcracks and micropores in the rock, which will initiate, propagate, and coalescence under dynamic loading, leading to rock instability and failure. When blasting excavation is carried out, the retained rock mass will be subjected to the dynamic loading generated by cyclic blasting, resulting in cumulative damage, which will lead to the reduction of the rock mass strength, and even failure. In order to simulate this physical process, this study embeds the existing rock dynamic damage constitutive model, which can perfectly describe the rock dynamic damage induced by blasting, into FLAC through secondary development to analyze the cumulative damage of rock mass under cyclic blasting. And then it is adopted to simulate the dynamic response of the rock slope with the locked segment under cyclic blasting. The results show that the slope stability gradually decreases with increasing the number of cyclic blasting after considering the cumulative damage effect of the rock slope. For the rock slope with the locked segment, the damage of the locked segment firstly occurs at both ends, and then propagates to the middle, in which the rock mass shows a progressive failure mode. Because the cumulative damage of the rock slope is considered, the stability factor of the slope will decrease after each blasting. When the cumulative damage is not considered, the stability factor of the slope is basically unchanged. The failure mode of the rock slope with a locked segment under cyclic blasting is the combination of dynamic tensile failure and shear failure caused by rock mass slip. The location of the locked segment in the weak interlayer affects the failure mode and stability of the slope. Therefore, when carrying out similar engineering activities, the cumulative damage effect of rock mass should be considered to avoid engineering accidents.
There are many microcracks and micropores in the rock, which will initiate, propagate, and coalescence under dynamic loading, leading to rock instability and failure. When blasting excavation is carried out, the retained rock mass will be subjected to the dynamic loading generated by cyclic blasting, resulting in cumulative damage, which will lead to the reduction of the rock mass strength, and even failure. In order to simulate this physical process, this study embeds the existing rock dynamic damage constitutive model, which can perfectly describe the rock dynamic damage induced by blasting, into FLAC through secondary development to analyze the cumulative damage of rock mass under cyclic blasting. And then it is adopted to simulate the dynamic response of the rock slope with the locked segment under cyclic blasting. The results show that the slope stability gradually decreases with increasing the number of cyclic blasting after considering the cumulative damage effect of the rock slope. For the rock slope with the locked segment, the damage of the locked segment firstly occurs at both ends, and then propagates to the middle, in which the rock mass shows a progressive failure mode. Because the cumulative damage of the rock slope is considered, the stability factor of the slope will decrease after each blasting. When the cumulative damage is not considered, the stability factor of the slope is basically unchanged. The failure mode of the rock slope with a locked segment under cyclic blasting is the combination of dynamic tensile failure and shear failure caused by rock mass slip. The location of the locked segment in the weak interlayer affects the failure mode and stability of the slope. Therefore, when carrying out similar engineering activities, the cumulative damage effect of rock mass should be considered to avoid engineering accidents.
, Available online ,
doi: 10.11883/bzycj-2023-0342
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Abstract:
The warhead of conventional weapons is usually composed of a cylindrical charge and a metal case, in which the metal case can affect the attenuation law of peak stress induced by explosion. Therefore, it is important for the blast-resistant design to clarify the attenuation law of stress waves in CF120 concrete induced by cylindrical cased charge explosion. Based on the Kong-Fang concrete material model and the Multi-material Arbitrary Lagrangian Eulerian (MM-ALE) algorithm available in the LS-DYNA, the attenuation law of stress waves in concrete subjected to cylindrical cased charge explosion was numerically investigated in this paper. Firstly, the numerical algorithm and material model parameters were validated against two sets of cylindrical charge explosion tests. Then a series of fully enclosed and partially buried cylindrical charge explosion numerical models were established, in which different aspect ratios, shell thicknesses, and charge buried depths were considered as to analyze the influence of charge shape and shell thickness on stress waves in concrete. Finally, an empirical formula for peak stress of compression wave in concrete induced by cylindrical cased charge explosion was presented based on curve-fitting the numerical data. Numerical results demonstrated that the larger the aspect ratio, the higher the peak stress in the near region, while the opposite law holds for the far region. Besides, increasing the shell thickness will make the peak stress higher, but there is a threshold. The influence of charge shape, shell thickness, and charge buried depth on the peak stress can be quantified by defining the length-diameter ratio, thickness-diameter ratio, and coupling factor of peak stress. The empirical formula for peak stress of compression wave in concrete was demonstrated valid for varied aspect ratio, shell thickness, and charge buried depth, which can provide a reliable reference for blast-resistant design to estimate the peak stress induced by cylindrical cased charge explosion.
The warhead of conventional weapons is usually composed of a cylindrical charge and a metal case, in which the metal case can affect the attenuation law of peak stress induced by explosion. Therefore, it is important for the blast-resistant design to clarify the attenuation law of stress waves in CF120 concrete induced by cylindrical cased charge explosion. Based on the Kong-Fang concrete material model and the Multi-material Arbitrary Lagrangian Eulerian (MM-ALE) algorithm available in the LS-DYNA, the attenuation law of stress waves in concrete subjected to cylindrical cased charge explosion was numerically investigated in this paper. Firstly, the numerical algorithm and material model parameters were validated against two sets of cylindrical charge explosion tests. Then a series of fully enclosed and partially buried cylindrical charge explosion numerical models were established, in which different aspect ratios, shell thicknesses, and charge buried depths were considered as to analyze the influence of charge shape and shell thickness on stress waves in concrete. Finally, an empirical formula for peak stress of compression wave in concrete induced by cylindrical cased charge explosion was presented based on curve-fitting the numerical data. Numerical results demonstrated that the larger the aspect ratio, the higher the peak stress in the near region, while the opposite law holds for the far region. Besides, increasing the shell thickness will make the peak stress higher, but there is a threshold. The influence of charge shape, shell thickness, and charge buried depth on the peak stress can be quantified by defining the length-diameter ratio, thickness-diameter ratio, and coupling factor of peak stress. The empirical formula for peak stress of compression wave in concrete was demonstrated valid for varied aspect ratio, shell thickness, and charge buried depth, which can provide a reliable reference for blast-resistant design to estimate the peak stress induced by cylindrical cased charge explosion.
, Available online ,
doi: 10.11883/bzycj-2023-0296
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Abstract:
The dynamic mechanical behavior of a metallic hierarchical corrugated sandwich beam with a hierarchical design under foam projectile impact was studied. After verifying the reliability of the numerical method, the dynamic deformation evolution, quantitative deflection results, deformation failure modes, and energy absorption characteristics of the metallic hierarchical corrugated sandwich beam were analyzed using Abaqus-Explicit simulation results under different projectile momentum levels. The results show that the degree of crushing of the secondary corrugated core on the impact side and the first-order corrugated core of the hierarchical sandwich beam is always greater than that of the rear sandwich's secondary corrugated core. The final mid-span deflection of the rear face of the hierarchical corrugated sandwich beam is always smaller than the corresponding deflection value of the equivalent mass single-level empty corrugated sandwich beam, demonstrating the superior impact protection performance of the hierarchical sandwich beam. This enhancement mechanism is mainly attributed to the increased energy absorption of the added cellular cores, which protects the rear face sheet. Besides, the plastic longitudinal stretching strength of the hierarchical sandwich beam remains almost unchanged, while the plastic bending strength increases due to the increase in the total thickness of the beam structure, thereby enlarging the plastic yield surface of the sandwich structure.
The dynamic mechanical behavior of a metallic hierarchical corrugated sandwich beam with a hierarchical design under foam projectile impact was studied. After verifying the reliability of the numerical method, the dynamic deformation evolution, quantitative deflection results, deformation failure modes, and energy absorption characteristics of the metallic hierarchical corrugated sandwich beam were analyzed using Abaqus-Explicit simulation results under different projectile momentum levels. The results show that the degree of crushing of the secondary corrugated core on the impact side and the first-order corrugated core of the hierarchical sandwich beam is always greater than that of the rear sandwich's secondary corrugated core. The final mid-span deflection of the rear face of the hierarchical corrugated sandwich beam is always smaller than the corresponding deflection value of the equivalent mass single-level empty corrugated sandwich beam, demonstrating the superior impact protection performance of the hierarchical sandwich beam. This enhancement mechanism is mainly attributed to the increased energy absorption of the added cellular cores, which protects the rear face sheet. Besides, the plastic longitudinal stretching strength of the hierarchical sandwich beam remains almost unchanged, while the plastic bending strength increases due to the increase in the total thickness of the beam structure, thereby enlarging the plastic yield surface of the sandwich structure.
, Available online ,
doi: 10.11883/bzycj-2023-0460
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Abstract:
To address the issue of peak load reduction for impact loads in engineering technology, this study investigates the energy absorption characteristics of axial series energy absorbing tubes through a combination of numerical simulation and experimentation. Firstly, the Johnson-Cook dynamic constitutive parameters of the material 06Cr18Ni11Ti GB/T1220-2007 of energy absorbing tubes are established and evaluated based on high-speed tensile tests which indicates 06Cr18Ni11Ti has obvious strain rate hardening effect. Subsequently, numerical simulation and high-speed impact tests are conducted to examine the energy absorption characteristics of energy absorption tubes, with an evaluation of consistency between numerical simulation and test results. The numerical simulation is based on the time-step ABAQUS/Explicit finite element simulation platform. The high speed impact test system uses the high pressure gas inside the air actuated piston cylinder as the power source, which can accelerate the mass block to a speed of 30m/s. Finally, the energy absorption evaluation indexes between the axial series configuration and the single configuration of the energy absorption tube were compared and analyzed by numerical simulation. The analysis demonstrates that deformation mode, load curve, and energy absorption evaluation indexes from both numerical simulations and impact tests exhibit good agreement. The accuracy of material performance parameters confirms the effectiveness of simulation prediction methods while validating reasonability and reliability of high-speed impact test schemes. Compared to axial series configurations with identical structural parameters, single-tube configurations display asymmetric and unstable twist deformations during compression processes. Single-tube configurations experience a 13% reduction in effective compression stroke along with a 33.4% increase in peak load, 15% increase in instantaneous impact load, 13% increase in average compression force, as well as a 17.7% increase in peak-to-average load ratio. Consequently, axial series configurations prove to be more ideal energy absorbing structures. This study can provide a reliable reference for the performance prediction and engineering design and development of energy absorbing components.
To address the issue of peak load reduction for impact loads in engineering technology, this study investigates the energy absorption characteristics of axial series energy absorbing tubes through a combination of numerical simulation and experimentation. Firstly, the Johnson-Cook dynamic constitutive parameters of the material 06Cr18Ni11Ti GB/T1220-2007 of energy absorbing tubes are established and evaluated based on high-speed tensile tests which indicates 06Cr18Ni11Ti has obvious strain rate hardening effect. Subsequently, numerical simulation and high-speed impact tests are conducted to examine the energy absorption characteristics of energy absorption tubes, with an evaluation of consistency between numerical simulation and test results. The numerical simulation is based on the time-step ABAQUS/Explicit finite element simulation platform. The high speed impact test system uses the high pressure gas inside the air actuated piston cylinder as the power source, which can accelerate the mass block to a speed of 30m/s. Finally, the energy absorption evaluation indexes between the axial series configuration and the single configuration of the energy absorption tube were compared and analyzed by numerical simulation. The analysis demonstrates that deformation mode, load curve, and energy absorption evaluation indexes from both numerical simulations and impact tests exhibit good agreement. The accuracy of material performance parameters confirms the effectiveness of simulation prediction methods while validating reasonability and reliability of high-speed impact test schemes. Compared to axial series configurations with identical structural parameters, single-tube configurations display asymmetric and unstable twist deformations during compression processes. Single-tube configurations experience a 13% reduction in effective compression stroke along with a 33.4% increase in peak load, 15% increase in instantaneous impact load, 13% increase in average compression force, as well as a 17.7% increase in peak-to-average load ratio. Consequently, axial series configurations prove to be more ideal energy absorbing structures. This study can provide a reliable reference for the performance prediction and engineering design and development of energy absorbing components.
, Available online ,
doi: 10.11883/bzycj-2022-0309
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Abstract:
In order to predict the critical penetration speed of high-strength steel projectiles penetrating concrete targets at high speed, the experimental and theoretical analysis of the gram-scale G50 ogive nose long-rod projectiles penetrating C40 concrete targets at a speed of 1010-1660m/s was carried out, and the conclusion was as follows: (1) The critical penetration speed of the rigid body of the G50 ogive nose long rod projectile is about 1320-1520m/s; (2) The theoretical model of the critical penetration velocity of the rigid body is established, the experimental results in this paper and in the literature are in good agreement with the calculation results; (3)The penetration depth model
In order to predict the critical penetration speed of high-strength steel projectiles penetrating concrete targets at high speed, the experimental and theoretical analysis of the gram-scale G50 ogive nose long-rod projectiles penetrating C40 concrete targets at a speed of 1010-1660m/s was carried out, and the conclusion was as follows: (1) The critical penetration speed of the rigid body of the G50 ogive nose long rod projectile is about 1320-1520m/s; (2) The theoretical model of the critical penetration velocity of the rigid body is established, the experimental results in this paper and in the literature are in good agreement with the calculation results; (3)The penetration depth model
, Available online ,
doi: 10.11883/bzycj-2022-0310
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Abstract:
In order to study the influence of projectile material parameters (mainly strength, toughness, etc.) on the penetration depth of hypervelocity penetrating concrete targets, experiments of 93W tungsten alloy column-shaped projectiles with different material properties penetrating into concrete targets at 2.3~3.6km/s were carried out. The experimental data of the penetration depth and residual projectile length of different projectiles were obtained. Combined with the experimental results and numerical simulation in the literature, the influence of material parameters on the penetration depth and the length of the residual projectile at different impact velocities were analyzed. The conclusions obtained are as follows: (1) If the toughness of the projectile material increases and the strength does not change, the characteristic parameters of the residual projectile do not change significantly, and the penetration depth does not change significantly, and no significant change in the velocity of the corresponding maximum penetration depth was found. (2) If the strength of the projectile material is increased and the toughness is constant, the ability of the projectile to resist erosion can be enhanced, the residual length of the projectile was increased, and the critical transition speed was increased, thereby increasing the rigid penetration depth and total penetration depth. At the same time, the velocity corresponding to the maximum value of the projectile penetration depth was increased.
In order to study the influence of projectile material parameters (mainly strength, toughness, etc.) on the penetration depth of hypervelocity penetrating concrete targets, experiments of 93W tungsten alloy column-shaped projectiles with different material properties penetrating into concrete targets at 2.3~3.6km/s were carried out. The experimental data of the penetration depth and residual projectile length of different projectiles were obtained. Combined with the experimental results and numerical simulation in the literature, the influence of material parameters on the penetration depth and the length of the residual projectile at different impact velocities were analyzed. The conclusions obtained are as follows: (1) If the toughness of the projectile material increases and the strength does not change, the characteristic parameters of the residual projectile do not change significantly, and the penetration depth does not change significantly, and no significant change in the velocity of the corresponding maximum penetration depth was found. (2) If the strength of the projectile material is increased and the toughness is constant, the ability of the projectile to resist erosion can be enhanced, the residual length of the projectile was increased, and the critical transition speed was increased, thereby increasing the rigid penetration depth and total penetration depth. At the same time, the velocity corresponding to the maximum value of the projectile penetration depth was increased.
, Available online ,
doi: 10.11883/bzycj-2023-0343
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Abstract:
Facing the challenges of accurate and effective prediction under extreme loads, machine learning has gradually demonstrated its potential to replace traditional methods. Existing approaches primarily focus on predicting the peak overpressure or impulse of explosive shock waves, with limited research on predicting the reflected overpressure time history. Load-time history prediction encompasses not only the peak overpressure but also embraces various multi-dimensional information including duration, waveform, and impulse, thereby offering a more comprehensive depiction of the dynamic temporal and spatial characteristics of shock waves. To address this issue, a prediction model for bridge surface reflected overpressure time history is proposed, targeting a planar shock wave diffracting around a bridge section. This model is based on Principal Component Analysis (PCA) and Backpropagation Neural Network (BPNN) algorithm with multi-task learning. A loss function considering the impact of peak overpressure and maximum impulse is introduced to fully consider the potential correlations between different modes after PCA dimension reduction. This enables the
Facing the challenges of accurate and effective prediction under extreme loads, machine learning has gradually demonstrated its potential to replace traditional methods. Existing approaches primarily focus on predicting the peak overpressure or impulse of explosive shock waves, with limited research on predicting the reflected overpressure time history. Load-time history prediction encompasses not only the peak overpressure but also embraces various multi-dimensional information including duration, waveform, and impulse, thereby offering a more comprehensive depiction of the dynamic temporal and spatial characteristics of shock waves. To address this issue, a prediction model for bridge surface reflected overpressure time history is proposed, targeting a planar shock wave diffracting around a bridge section. This model is based on Principal Component Analysis (PCA) and Backpropagation Neural Network (BPNN) algorithm with multi-task learning. A loss function considering the impact of peak overpressure and maximum impulse is introduced to fully consider the potential correlations between different modes after PCA dimension reduction. This enables the
, Available online ,
doi: 10.11883/bzycj-2023-0395
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Abstract:
Propellers serve as pivotal components within ship propulsion systems, directly influencing a vessel's performance through their stability and efficiency. Current research on the resilience of propulsion shafts often simplifies propellers to homogenous discs, neglecting their structural intricacies. This approach fails to accurately capture the transient damage features of propellers under the effects of underwater explosion. Therefore, this paper takes into consideration the propeller's structural characteristics. By initially employing wet modal analysis, the study determines that solid modeling outperforms shell modeling. It investigates the response and damage characteristics of propeller surfaces under the influence of far-field shockwaves while considering the propeller's structural attributes. The paper also analyzes the transient damage characteristics of propellers in conjunction with the hydrodynamic cavitation state generated during high-speed propeller rotation. The research findings demonstrate that at attack angles of 0 degrees and 90 degrees, surface loads on the propeller due to shockwave incidence are higher, but they exhibit an upper limit that correlates with the propeller's structural features. When accounting for the hydrodynamic cavitation state, stress levels on the blades remain consistently uniform. The primary plastic damage zone on the blades is near the root, showcasing both local and complete plastic deformation modes. This paper delves into the damage and cavitation characteristics of propellers under far-field explosions, and its results offer valuable insights for protecting propulsion shafts and propellers against shock impacts.
Propellers serve as pivotal components within ship propulsion systems, directly influencing a vessel's performance through their stability and efficiency. Current research on the resilience of propulsion shafts often simplifies propellers to homogenous discs, neglecting their structural intricacies. This approach fails to accurately capture the transient damage features of propellers under the effects of underwater explosion. Therefore, this paper takes into consideration the propeller's structural characteristics. By initially employing wet modal analysis, the study determines that solid modeling outperforms shell modeling. It investigates the response and damage characteristics of propeller surfaces under the influence of far-field shockwaves while considering the propeller's structural attributes. The paper also analyzes the transient damage characteristics of propellers in conjunction with the hydrodynamic cavitation state generated during high-speed propeller rotation. The research findings demonstrate that at attack angles of 0 degrees and 90 degrees, surface loads on the propeller due to shockwave incidence are higher, but they exhibit an upper limit that correlates with the propeller's structural features. When accounting for the hydrodynamic cavitation state, stress levels on the blades remain consistently uniform. The primary plastic damage zone on the blades is near the root, showcasing both local and complete plastic deformation modes. This paper delves into the damage and cavitation characteristics of propellers under far-field explosions, and its results offer valuable insights for protecting propulsion shafts and propellers against shock impacts.
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Abstract:
To enhance the service safety of nodular cast iron structures such as the spent nuclear fuel storage and transportation vessel under low temperature and dynamic loads, the mode I dynamic fracture toughness of nodular cast iron was experimentally investigated at ambient and cryogenic temperatures (20℃, -40℃, -60℃ and -80℃) using an improved split Hopkinson pressure bar technique. The ductile-brittle transition behavior of the material was specially investigated. The crack initiation time of the specimen was determined by the strain gauge method. The dynamic stress intensity factor (DSIF) at the crack tip and the mode I dynamic fracture toughness (DFT) of the material were determined by the experimental-numerical method. The results show that under the same impact velocity, the DFT and fracture initiation time of nodular cast iron decrease significantly with the decrease in temperature. Through quantitative analysis of the microscopic fracture morphologies, it is revealed that there is a failure mechanism transition at different temperatures. As the temperature decreases, the number of dimples on the fracture surface decreases, while the river patterns as well as cleavage steps increase, which indicates that the ductility of the material is weakened but the brittleness is enhanced at low temperatures. This ductile-brittle transition phenomenon is consistent with the tendency of the measured toughness of the material.
To enhance the service safety of nodular cast iron structures such as the spent nuclear fuel storage and transportation vessel under low temperature and dynamic loads, the mode I dynamic fracture toughness of nodular cast iron was experimentally investigated at ambient and cryogenic temperatures (20℃, -40℃, -60℃ and -80℃) using an improved split Hopkinson pressure bar technique. The ductile-brittle transition behavior of the material was specially investigated. The crack initiation time of the specimen was determined by the strain gauge method. The dynamic stress intensity factor (DSIF) at the crack tip and the mode I dynamic fracture toughness (DFT) of the material were determined by the experimental-numerical method. The results show that under the same impact velocity, the DFT and fracture initiation time of nodular cast iron decrease significantly with the decrease in temperature. Through quantitative analysis of the microscopic fracture morphologies, it is revealed that there is a failure mechanism transition at different temperatures. As the temperature decreases, the number of dimples on the fracture surface decreases, while the river patterns as well as cleavage steps increase, which indicates that the ductility of the material is weakened but the brittleness is enhanced at low temperatures. This ductile-brittle transition phenomenon is consistent with the tendency of the measured toughness of the material.
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Abstract:
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, Available online ,
doi: 10.11883/bzycj-2023-0418
Abstract:
Hydrogen is crucial in the global shift towards clean energy and is gaining significance in the energy industry, while its high flammability and explosive hazard make its safety a research hotspot. It is crucial to thoroughly investigate and assess the safety of hydrogen as it progresses toward commercialization in the energy sector. This article reviews the latest advancements in hydrogen explosion suppression conducted by researchers around the world, aiming at offering a scientific foundation and technical approach to efficiently manage and reduce the damaging impacts of hydrogen explosion incidents. The article focuses on the study of hydrogen explosion suppression materials and their suppression mechanisms, so as to provide scientific understanding and technical support for the safe application of hydrogen. Firstly, it systematically introduces the research progress in hydrogen explosion suppression by discussing four significant categories, i.e., gas, liquid, solid, and multiphase composite explosion suppression materials. By comparing and analyzing the effects, key performance parameters, and the variation rules of these materials, the current research status and effectiveness of various explosion suppression materials are sorted out, helping to deepen the understanding of the explosion suppression effects of these materials. Secondly, focusing on the suppression mechanism, the research delves into the vital role of explosion suppression materials in suppressing hydrogen explosions. Starting from three dimensions, i.e., physical suppression, chemical suppression, and physicochemical comprehensive suppression, it elucidates the mechanisms of action of explosion suppression materials in the suppression process, contributing to a deeper understanding of the role of explosion suppression materials in suppressing or mitigating hydrogen explosions. Finally, the article looks forward to the future development directions of hydrogen explosion suppression materials, especially emphasizing the importance of further studies on the high-efficiency explosion suppression materials and the challenges faced in practical applications. This review is aimed to provide scientific reference and inspiration for the research, development, and application of new hydrogen explosion suppression materials.
Hydrogen is crucial in the global shift towards clean energy and is gaining significance in the energy industry, while its high flammability and explosive hazard make its safety a research hotspot. It is crucial to thoroughly investigate and assess the safety of hydrogen as it progresses toward commercialization in the energy sector. This article reviews the latest advancements in hydrogen explosion suppression conducted by researchers around the world, aiming at offering a scientific foundation and technical approach to efficiently manage and reduce the damaging impacts of hydrogen explosion incidents. The article focuses on the study of hydrogen explosion suppression materials and their suppression mechanisms, so as to provide scientific understanding and technical support for the safe application of hydrogen. Firstly, it systematically introduces the research progress in hydrogen explosion suppression by discussing four significant categories, i.e., gas, liquid, solid, and multiphase composite explosion suppression materials. By comparing and analyzing the effects, key performance parameters, and the variation rules of these materials, the current research status and effectiveness of various explosion suppression materials are sorted out, helping to deepen the understanding of the explosion suppression effects of these materials. Secondly, focusing on the suppression mechanism, the research delves into the vital role of explosion suppression materials in suppressing hydrogen explosions. Starting from three dimensions, i.e., physical suppression, chemical suppression, and physicochemical comprehensive suppression, it elucidates the mechanisms of action of explosion suppression materials in the suppression process, contributing to a deeper understanding of the role of explosion suppression materials in suppressing or mitigating hydrogen explosions. Finally, the article looks forward to the future development directions of hydrogen explosion suppression materials, especially emphasizing the importance of further studies on the high-efficiency explosion suppression materials and the challenges faced in practical applications. This review is aimed to provide scientific reference and inspiration for the research, development, and application of new hydrogen explosion suppression materials.
, Available online ,
doi: 10.11883/bzycj-2024-0083
Abstract:
Reinforced concrete slabs, as the main load-bearing components in the structure of construction projects, are very likely to suffer serious damage in explosive accidents, while polyurea elastomers, with their better anti-blast and anti-impact properties, have been widely used in the field of protective engineering. It is well known that the mechanical properties and deformation mechanisms of thin slabs in the range from 100 mm to 250 mm and thick concrete slabs above 250 mm are not the same, and the thickness of reinforced concrete substrates studied so far is generally concentrated in the range from 100 mm to 250 mm, and there are relatively few studies on thick slabs of polyurea-coated reinforced concrete with a slab thickness of 250 mm or more. In order to study the anti-blast performance of the polyurea/reinforced concrete thick slab composite structure, firstly, the contact explosion tests were carried out on the polyurea/reinforced concrete thick slab composite structure with different charges, while the overall and local damage characteristics were analyzed. Secondly, numerical simulations were carried out using LS-DYNA finite element simulation software to verify the correctness of the numerical model by comparing with the experimental results. Based on LS-DYNA finite element simulations, the damage process of polyurea/reinforced concrete thick plate composite structure and the evolution of shock wave inside the polyurea/reinforced concrete thick plate were investigated, which revealed the anti-blast mechanism of the polyurea coating, and further analyzed the damage mode and damage characteristics of the polyurea/reinforced concrete thick plate composite structure. The test and finite element results showed that the polyurea/steel-reinforced concrete composite structure exhibited six damage modes under the contact explosion load (i.e., crate; spall; spall and bulge; threshold spall, bulging deformation of the polyurea coating; severe spall, serious bulging deformation of the polyurea coating; perforation). The investigation also demonstrated that the backside polyurea-coated reinforced concrete thick slabs effectively improved the anti-blast performance of the composite structure. The results of the study can provide a basis and reference for the design of blast resistance of polyurea/reinforced concrete thick slab composite structures.
Reinforced concrete slabs, as the main load-bearing components in the structure of construction projects, are very likely to suffer serious damage in explosive accidents, while polyurea elastomers, with their better anti-blast and anti-impact properties, have been widely used in the field of protective engineering. It is well known that the mechanical properties and deformation mechanisms of thin slabs in the range from 100 mm to 250 mm and thick concrete slabs above 250 mm are not the same, and the thickness of reinforced concrete substrates studied so far is generally concentrated in the range from 100 mm to 250 mm, and there are relatively few studies on thick slabs of polyurea-coated reinforced concrete with a slab thickness of 250 mm or more. In order to study the anti-blast performance of the polyurea/reinforced concrete thick slab composite structure, firstly, the contact explosion tests were carried out on the polyurea/reinforced concrete thick slab composite structure with different charges, while the overall and local damage characteristics were analyzed. Secondly, numerical simulations were carried out using LS-DYNA finite element simulation software to verify the correctness of the numerical model by comparing with the experimental results. Based on LS-DYNA finite element simulations, the damage process of polyurea/reinforced concrete thick plate composite structure and the evolution of shock wave inside the polyurea/reinforced concrete thick plate were investigated, which revealed the anti-blast mechanism of the polyurea coating, and further analyzed the damage mode and damage characteristics of the polyurea/reinforced concrete thick plate composite structure. The test and finite element results showed that the polyurea/steel-reinforced concrete composite structure exhibited six damage modes under the contact explosion load (i.e., crate; spall; spall and bulge; threshold spall, bulging deformation of the polyurea coating; severe spall, serious bulging deformation of the polyurea coating; perforation). The investigation also demonstrated that the backside polyurea-coated reinforced concrete thick slabs effectively improved the anti-blast performance of the composite structure. The results of the study can provide a basis and reference for the design of blast resistance of polyurea/reinforced concrete thick slab composite structures.
, Available online ,
doi: 10.11883/bzycj-2024-0053
Abstract:
Damage assessment of building structures plays an important role in military operations and engineering protection design. However, there is a lack of high-efficiency and validated damage assessment methods due to the complexity, variety, and large size of building structures. Therefore, a structural damage assessment method was proposed based on the high-precision numerical simulation analysis, in which the blast loadings, as well as the damage degrees of members, rooms, and building structures, were comprehensively considered. Firstly, the typical explosion tests and collapse accidents of reinforced concrete (RC) structures and masonry walls were numerically reproduced to verify the reliability of the numerical simulation approach for masonry-infilled RC frame structures. Subsequently, the blast-resistant analysis of a typical three-story masonry-infilled RC frame structure was conducted under internal explosions of different charge weights (25−200kg TNT), including the propagation of blast waves, structural damage, and scattering of infilled walls. Besides, the proposed high-efficiency assessment method exhibited four key characteristics: (1) the concept of mirror explosion source and the non-linear shock addition rules were combined to predict the internal blast loadings in central and adjacent rooms; (2) the damage degrees of structural and non-structural members, i.e., beams, slabs, columns, and infilled walls, were determined by the equivalent single degree of freedom method; (3) the importance factor of members was considered and weighted to evaluate the damage degree of the room; (4) the influence of usage and location of each room on the damage degree of the building structure was considered. Finally, the proposed assessment method was employed to predict the aforementioned explosion scenarios. It derives that the RC frame structures exhibit slight, moderate, and severe damage under the explosions of 25, 100, and 200 kg TNT, respectively. The predicted damage degrees are identical to the simulation results, while the calculation time is reduced by over 99%. Therefore, the proposed method possesses reliability and timeliness in damage assessment of building structures.
Damage assessment of building structures plays an important role in military operations and engineering protection design. However, there is a lack of high-efficiency and validated damage assessment methods due to the complexity, variety, and large size of building structures. Therefore, a structural damage assessment method was proposed based on the high-precision numerical simulation analysis, in which the blast loadings, as well as the damage degrees of members, rooms, and building structures, were comprehensively considered. Firstly, the typical explosion tests and collapse accidents of reinforced concrete (RC) structures and masonry walls were numerically reproduced to verify the reliability of the numerical simulation approach for masonry-infilled RC frame structures. Subsequently, the blast-resistant analysis of a typical three-story masonry-infilled RC frame structure was conducted under internal explosions of different charge weights (25−200kg TNT), including the propagation of blast waves, structural damage, and scattering of infilled walls. Besides, the proposed high-efficiency assessment method exhibited four key characteristics: (1) the concept of mirror explosion source and the non-linear shock addition rules were combined to predict the internal blast loadings in central and adjacent rooms; (2) the damage degrees of structural and non-structural members, i.e., beams, slabs, columns, and infilled walls, were determined by the equivalent single degree of freedom method; (3) the importance factor of members was considered and weighted to evaluate the damage degree of the room; (4) the influence of usage and location of each room on the damage degree of the building structure was considered. Finally, the proposed assessment method was employed to predict the aforementioned explosion scenarios. It derives that the RC frame structures exhibit slight, moderate, and severe damage under the explosions of 25, 100, and 200 kg TNT, respectively. The predicted damage degrees are identical to the simulation results, while the calculation time is reduced by over 99%. Therefore, the proposed method possesses reliability and timeliness in damage assessment of building structures.
, Available online ,
doi: 10.11883/bzycj-2024-0061
Abstract:
Due to the high compressive/tensile strengths and fracture toughness, ultra-high performance concrete (UHPC) has great application potential in protective structures against the attack of earth penetrating weapons. Accurately evaluating the damage and failure and establishing reliable design methods of UHPC shields against the combination of penetration and explosion of warheads can provide a helpful reference for protective structure design and resistance improvement. In this study, combined tests of 105 mm-caliber projectile penetration test and 5 kg TNT explosion test on semi-infinite UHPC target were conducted first. The detailed test data of the projectile and target under penetration and the combined effect of penetration and explosion were recorded. Then, a finite element model of UHPC under penetration and explosion was established. By conducting the numerical simulations of the above-conducted test and the existing prefabricated hole charge explosion test on the finite UHPC slab, as well as comprehensively comparing the destroy depth and cracking dimension of the target, the reliability of the established finite element model and the corresponding analysis approach in predicting the damage and failure of UHPC shield against the combination of penetration and explosion of warheads were validated. Finally, the perforation limit and scabbing limit of the UHPC shield under the combination of penetration and explosion of three typical prototype warheads, i.e., SDB, WDU-43/B, and BLU-109/B, were determined and compared with those of normal strength concrete shield. The results show that, the perforation limit and scabbing limit of the UHPC shield against the above three warheads are in ranges of 1.30−2.60 m and 1.70−5.00 m, respectively. The corresponding critical perforation and scabbing coefficients are in the ranges of 1.81−2.17 and 2.46−4.17, respectively. Compared with the normal strength concrete shield, the cracking diameter of the UHPC shield is reduced by 34.4%−42.4%. The perforation limit and scabbing limit are reduced by 7.1%−31.6% and 39.7%−52.8%, respectively. The present work can provide an analysis method and reference for the resistance evaluation and design of the UHPC shield.
Due to the high compressive/tensile strengths and fracture toughness, ultra-high performance concrete (UHPC) has great application potential in protective structures against the attack of earth penetrating weapons. Accurately evaluating the damage and failure and establishing reliable design methods of UHPC shields against the combination of penetration and explosion of warheads can provide a helpful reference for protective structure design and resistance improvement. In this study, combined tests of 105 mm-caliber projectile penetration test and 5 kg TNT explosion test on semi-infinite UHPC target were conducted first. The detailed test data of the projectile and target under penetration and the combined effect of penetration and explosion were recorded. Then, a finite element model of UHPC under penetration and explosion was established. By conducting the numerical simulations of the above-conducted test and the existing prefabricated hole charge explosion test on the finite UHPC slab, as well as comprehensively comparing the destroy depth and cracking dimension of the target, the reliability of the established finite element model and the corresponding analysis approach in predicting the damage and failure of UHPC shield against the combination of penetration and explosion of warheads were validated. Finally, the perforation limit and scabbing limit of the UHPC shield under the combination of penetration and explosion of three typical prototype warheads, i.e., SDB, WDU-43/B, and BLU-109/B, were determined and compared with those of normal strength concrete shield. The results show that, the perforation limit and scabbing limit of the UHPC shield against the above three warheads are in ranges of 1.30−2.60 m and 1.70−5.00 m, respectively. The corresponding critical perforation and scabbing coefficients are in the ranges of 1.81−2.17 and 2.46−4.17, respectively. Compared with the normal strength concrete shield, the cracking diameter of the UHPC shield is reduced by 34.4%−42.4%. The perforation limit and scabbing limit are reduced by 7.1%−31.6% and 39.7%−52.8%, respectively. The present work can provide an analysis method and reference for the resistance evaluation and design of the UHPC shield.
, Available online ,
doi: 10.11883/bzycj-2024-0070
Abstract:
Silicone rubber has been widely used as a typical sandwich-structure or cushion-structure material in various high pressure loading environments. Under pressure loading of up to tens of GPa, silicone rubber may undergo shock decomposition reaction, and the decomposition products contain gas-solid mixture. Numerical simulation without the shock decomposition of silicone rubber can’t interpret some complex physical phenomena observed in detonation driven experiment. In order to illustrate the shock decomposition effect of silicone rubber, a simple shock decomposition model for silicone rubber is proposed based on the existing physical knowledge. By using the simple shock decomposition model for silicone rubber, the simulations of the experiment setup of detonation driven silicone rubber foam are carried out, and the simulated free surface velocities are compared with the experiments. The results show that the shock decomposition of silicone rubber can reasonably interpret the two grotesque phenomena observed in the experiment. During the shock decomposition process, the first incident pressure of silicone rubber would relax around the critical shock decomposition pressure for a period of time. As a result, the free surface velocity of steel plate exhibits a platform as observed in the experiment during the first take-off process. The compressibility of gas phase products of silicone rubber after shock decomposition is much higher than the solid/fluid materials, so more energy in the first incident wave is consumed to compress gas products to do work, leading to energy attenuation and peak pressure reduction when the first incident wave propagates to the outer surface of steel plate. Consequently, the peak value of the first take-off free surface velocity of steel plate decreases. Insight into the dynamic behavior of silicone rubber at high pressures is particularly valuable for predicting their response to extreme conditions, and it contributes to a deeper understanding of such experimental phenomena and to the proposal of a more refined shock decomposition model for silicone rubber.
Silicone rubber has been widely used as a typical sandwich-structure or cushion-structure material in various high pressure loading environments. Under pressure loading of up to tens of GPa, silicone rubber may undergo shock decomposition reaction, and the decomposition products contain gas-solid mixture. Numerical simulation without the shock decomposition of silicone rubber can’t interpret some complex physical phenomena observed in detonation driven experiment. In order to illustrate the shock decomposition effect of silicone rubber, a simple shock decomposition model for silicone rubber is proposed based on the existing physical knowledge. By using the simple shock decomposition model for silicone rubber, the simulations of the experiment setup of detonation driven silicone rubber foam are carried out, and the simulated free surface velocities are compared with the experiments. The results show that the shock decomposition of silicone rubber can reasonably interpret the two grotesque phenomena observed in the experiment. During the shock decomposition process, the first incident pressure of silicone rubber would relax around the critical shock decomposition pressure for a period of time. As a result, the free surface velocity of steel plate exhibits a platform as observed in the experiment during the first take-off process. The compressibility of gas phase products of silicone rubber after shock decomposition is much higher than the solid/fluid materials, so more energy in the first incident wave is consumed to compress gas products to do work, leading to energy attenuation and peak pressure reduction when the first incident wave propagates to the outer surface of steel plate. Consequently, the peak value of the first take-off free surface velocity of steel plate decreases. Insight into the dynamic behavior of silicone rubber at high pressures is particularly valuable for predicting their response to extreme conditions, and it contributes to a deeper understanding of such experimental phenomena and to the proposal of a more refined shock decomposition model for silicone rubber.
, Available online ,
doi: 10.11883/bzycj-2023-0452
Abstract:
To predict precisely the lower explosion limit of thermal runaway products of lithium iron phosphate batteries, thermal runaway tests of lithium iron phosphate batteries were carried out in a closed pressure vessel. The experiments were carried out at 25 ℃ and 0.1 MPa, and the method was used to analyze the thermal runaway gas production. The vent gas species composition of lithium iron phosphate batteries was analyzed by gas chromatography and mass spectrometry. Combined with the thermal runaway characteristics of the battery and gas chromatography-mass spectrometry (GC-MS) technology, the gas composition of thermal runaway products of lithium iron phosphate batteries was calculated. It was assumed that the thermal runway products released from the relief valve to the first injection were all dimethyl carbonate (DMC), and the secondary injection gas was the mixed gas generated by the internal chemical reaction, which is mainly composed of H2, CO2, CO, CH4, and C2H4. A prediction model of the lower explosion limit of thermal runaway products was established based on the energy conservation equation and adiabatic flame temperature. The prediction methods of lower explosion limit of multicomponent gases based on adiabatic flame temperature, Le Chatelier law method, and Jones method were verified, and the influence of electrolyte vapor on the lower explosion limit of thermal runaway production was also investigated. The results show that the smallest deviation of the lower explosion limit calculated by the Le Chatelier law method at normal temperature and pressure was 1.14%, and the largest deviation of the lower explosion limit calculated by the adiabatic flame temperature method was 10.02%. Within the range of 60%~100% SOC, the lower explosion limit of the discharge gas increases first and then decreases. When the electrolyte vapor is considered in the thermal runaway products, the lower explosion limit of thermal runaway products of lithium iron phosphate batteries with 60% SOC is only 3.93%, which is 22.49% lower than that of the thermal runaway gas without considering the electrolyte vapor. Actually, the electrolyte vapor is contained in the thermal runaway products of lithium iron phosphate batteries. These results indicate that the addition of electrolyte vapor increases the explosion risk of thermal runaway production of lithium iron phosphate batteries.
To predict precisely the lower explosion limit of thermal runaway products of lithium iron phosphate batteries, thermal runaway tests of lithium iron phosphate batteries were carried out in a closed pressure vessel. The experiments were carried out at 25 ℃ and 0.1 MPa, and the method was used to analyze the thermal runaway gas production. The vent gas species composition of lithium iron phosphate batteries was analyzed by gas chromatography and mass spectrometry. Combined with the thermal runaway characteristics of the battery and gas chromatography-mass spectrometry (GC-MS) technology, the gas composition of thermal runaway products of lithium iron phosphate batteries was calculated. It was assumed that the thermal runway products released from the relief valve to the first injection were all dimethyl carbonate (DMC), and the secondary injection gas was the mixed gas generated by the internal chemical reaction, which is mainly composed of H2, CO2, CO, CH4, and C2H4. A prediction model of the lower explosion limit of thermal runaway products was established based on the energy conservation equation and adiabatic flame temperature. The prediction methods of lower explosion limit of multicomponent gases based on adiabatic flame temperature, Le Chatelier law method, and Jones method were verified, and the influence of electrolyte vapor on the lower explosion limit of thermal runaway production was also investigated. The results show that the smallest deviation of the lower explosion limit calculated by the Le Chatelier law method at normal temperature and pressure was 1.14%, and the largest deviation of the lower explosion limit calculated by the adiabatic flame temperature method was 10.02%. Within the range of 60%~100% SOC, the lower explosion limit of the discharge gas increases first and then decreases. When the electrolyte vapor is considered in the thermal runaway products, the lower explosion limit of thermal runaway products of lithium iron phosphate batteries with 60% SOC is only 3.93%, which is 22.49% lower than that of the thermal runaway gas without considering the electrolyte vapor. Actually, the electrolyte vapor is contained in the thermal runaway products of lithium iron phosphate batteries. These results indicate that the addition of electrolyte vapor increases the explosion risk of thermal runaway production of lithium iron phosphate batteries.
, Available online ,
doi: 10.11883/bzycj-2024-0063
Abstract:
Reactive fragments are composed of multifunctional impact reactive structural materials. After reactive fragments penetrate the front target of warhead, the debris cloud generated by the sufficient reaction of reactive material will damage the medium behind the target in the form of kinetic energy-chemical energy coupling damage. Ballistic impact experiments and finite element simulations were conducted to investigate the impact damage effect of reactive fragments on cased charge. Based on the criteria for failure levels of cased charge characterized by equivalent fragments initial velocity and equivalent gurney velocity, the ratio of the equivalent gurney velocity under abnormal detonation conditions to gurney velocity or the ratio of the equivalent fragments initial velocity under abnormal detonation conditions to the fragments initial velocity is used to measure the reaction violence of the cased charge. Equivalent gurney velocity of cased charge under impact of inert fragments and reactive fragments, response duration of cased charge, the damage of the authentication target, and the peak pressure of explosive layer are compared. The influence of energy release characteristics of reactive fragments on the failure of cased charge is also analyzed. The results show that explosive detonate under the impact of inert fragments, while explosive deflagrate or explode under the impact of reactive fragments. The steel verification target only presents significant circular pit during explosive detonation. The explosive detonation process captured by high-speed photography is on the microsecond scale, while the explosive explosion or deflagration process is on the millisecond scale. Under the penetration of six reactive fragments, the corresponding ratio of equivalent gurney velocity to gurney velocity ranges from 0.014 to 0.233, which is far below the ratio of equivalent gurney velocity to gurney velocity under the condition of inert fragments penetrating cased charges. By using AUTODYN, the peak pressure at the observation point on the axis of the cased charge during detonation failure under the penetration of inert fragments ranges from 17.3 to 34.5 GPa, while the peak pressure of cased charge during deflagration failure under the penetration of reactive fragments ranges from 1.04 to 3.62 GPa, which is far below the critical detonation pressure. Based on the ratio of the equivalent gurney velocity to gurney velocity, the peak pressure of explosive and superimposed effect of kinetic energy and chemical energy of reactive fragments, the idea that it is difficult to detonate cased charge under the penetration of reactive fragments is proposed.
Reactive fragments are composed of multifunctional impact reactive structural materials. After reactive fragments penetrate the front target of warhead, the debris cloud generated by the sufficient reaction of reactive material will damage the medium behind the target in the form of kinetic energy-chemical energy coupling damage. Ballistic impact experiments and finite element simulations were conducted to investigate the impact damage effect of reactive fragments on cased charge. Based on the criteria for failure levels of cased charge characterized by equivalent fragments initial velocity and equivalent gurney velocity, the ratio of the equivalent gurney velocity under abnormal detonation conditions to gurney velocity or the ratio of the equivalent fragments initial velocity under abnormal detonation conditions to the fragments initial velocity is used to measure the reaction violence of the cased charge. Equivalent gurney velocity of cased charge under impact of inert fragments and reactive fragments, response duration of cased charge, the damage of the authentication target, and the peak pressure of explosive layer are compared. The influence of energy release characteristics of reactive fragments on the failure of cased charge is also analyzed. The results show that explosive detonate under the impact of inert fragments, while explosive deflagrate or explode under the impact of reactive fragments. The steel verification target only presents significant circular pit during explosive detonation. The explosive detonation process captured by high-speed photography is on the microsecond scale, while the explosive explosion or deflagration process is on the millisecond scale. Under the penetration of six reactive fragments, the corresponding ratio of equivalent gurney velocity to gurney velocity ranges from 0.014 to 0.233, which is far below the ratio of equivalent gurney velocity to gurney velocity under the condition of inert fragments penetrating cased charges. By using AUTODYN, the peak pressure at the observation point on the axis of the cased charge during detonation failure under the penetration of inert fragments ranges from 17.3 to 34.5 GPa, while the peak pressure of cased charge during deflagration failure under the penetration of reactive fragments ranges from 1.04 to 3.62 GPa, which is far below the critical detonation pressure. Based on the ratio of the equivalent gurney velocity to gurney velocity, the peak pressure of explosive and superimposed effect of kinetic energy and chemical energy of reactive fragments, the idea that it is difficult to detonate cased charge under the penetration of reactive fragments is proposed.
, Available online ,
doi: 10.11883/bzycj-2023-0199
Abstract:
As a typical characteristic of fireball phenomena, thermal radiation plays an important role in damage assessments. Up to now, many studies of thermal radiation using theoretical, numerical, and experimental methods have been carried out and empirical formulas in forms of yield or density are constructed to feature the extremal characteristic of fireball thermal radiation. However, due to the combined action of radiation free path (RFP) and fireball characteristic length (FCL) it is difficult to identify these formula’s application scope and further theoretical studies are needed to take the scale effect (SE) into account. By radiation heat conduction approximation model under optical thickness assumption, scale effect similarity parameter (SESP) is theoretically derived and its scope of application is further verified by high-precision numerical method. The numerical code is developed within a framework of Euler method and adaptive mesh refinement method is employed to improve the precision in the radiation front. The results of theoretical analysis show that SESP is consistent with existed conclusions regarding the thermal radiation of fireball at different altitudes, and it can be applied to the analysis of laboratory scale fireball. Meanwhile, numerical results also show that both scale effects at different altitudes and laboratory scale can be characterized by SESP.
As a typical characteristic of fireball phenomena, thermal radiation plays an important role in damage assessments. Up to now, many studies of thermal radiation using theoretical, numerical, and experimental methods have been carried out and empirical formulas in forms of yield or density are constructed to feature the extremal characteristic of fireball thermal radiation. However, due to the combined action of radiation free path (RFP) and fireball characteristic length (FCL) it is difficult to identify these formula’s application scope and further theoretical studies are needed to take the scale effect (SE) into account. By radiation heat conduction approximation model under optical thickness assumption, scale effect similarity parameter (SESP) is theoretically derived and its scope of application is further verified by high-precision numerical method. The numerical code is developed within a framework of Euler method and adaptive mesh refinement method is employed to improve the precision in the radiation front. The results of theoretical analysis show that SESP is consistent with existed conclusions regarding the thermal radiation of fireball at different altitudes, and it can be applied to the analysis of laboratory scale fireball. Meanwhile, numerical results also show that both scale effects at different altitudes and laboratory scale can be characterized by SESP.
, Available online ,
doi: 10.11883/bzycj-2023-0208
Abstract:
In order to solve the problem of high-performance lightweight bulletproof inserts being protected by the penetration of light weapon killing element, this paper carried out penetration experiments on ultra-high molecular weight polyethylene (UHMWPE) laminated sheet, analysed the deformation and failure characteristics of the UHMWPE sheet after penetration and compared the damage morphology of light weapon killing element. A numerical model of UHMWPE laminate against the penetration of light weapon killers was established by using the finite element software LS-DYNA, and the validity of the numerical model was verified by the experimental results of the damage morphology of the target plate, the depth of the depression and the deformation of the warhead. On this basis, the failure mode of UHMWPE thin plate subjected to oblique penetration by the projectile is investigated by numerical methods, and the influence of the incidence angle on the ricochet phenomenon and the damage morphology of UHMWPE thin plate under the penetration of three kinds of light weapon killing elements is revealed. The results show that the ricochet angles of 7.62 mm×25 mm steel-core bullets and 7.62 mm×39 mm ordinary bullets (steel-core) obliquely penetrating UHMWPE plates are located in the range of 45°–50°; 7.62 mm×25 mm lead-core bullets can be completely ricocheted out when the angle of incidence is greater than 70°, and the rest of the bullets are in the form of broken shrapnel splinters, and the destruction of the bullet body has an effect on the ricochet condition; the oblique penetration bullets produce a large area and a large number of damage patterns at a smaller angle of incidence; the oblique penetration bullets produce a larger area and a larger number of damage patterns in the UHMWPE plates. When the angle of incidence is small, the oblique penetration bullet will produce a larger area and a certain depth of the crater, the next bullet will be easier to penetrate the crater weakness of the fibre plate, the oblique penetration effect on the thin plate by the secondary penetration of the negative impact, the angle of incidence is larger, the bullet will be more complete ricochet and has a high residual velocity, which will produce a secondary killing of personnel. The research results can be used for UHMWPE thin plate for lightweight military bulletproof insert design to provide reference.
In order to solve the problem of high-performance lightweight bulletproof inserts being protected by the penetration of light weapon killing element, this paper carried out penetration experiments on ultra-high molecular weight polyethylene (UHMWPE) laminated sheet, analysed the deformation and failure characteristics of the UHMWPE sheet after penetration and compared the damage morphology of light weapon killing element. A numerical model of UHMWPE laminate against the penetration of light weapon killers was established by using the finite element software LS-DYNA, and the validity of the numerical model was verified by the experimental results of the damage morphology of the target plate, the depth of the depression and the deformation of the warhead. On this basis, the failure mode of UHMWPE thin plate subjected to oblique penetration by the projectile is investigated by numerical methods, and the influence of the incidence angle on the ricochet phenomenon and the damage morphology of UHMWPE thin plate under the penetration of three kinds of light weapon killing elements is revealed. The results show that the ricochet angles of 7.62 mm×25 mm steel-core bullets and 7.62 mm×39 mm ordinary bullets (steel-core) obliquely penetrating UHMWPE plates are located in the range of 45°–50°; 7.62 mm×25 mm lead-core bullets can be completely ricocheted out when the angle of incidence is greater than 70°, and the rest of the bullets are in the form of broken shrapnel splinters, and the destruction of the bullet body has an effect on the ricochet condition; the oblique penetration bullets produce a large area and a large number of damage patterns at a smaller angle of incidence; the oblique penetration bullets produce a larger area and a larger number of damage patterns in the UHMWPE plates. When the angle of incidence is small, the oblique penetration bullet will produce a larger area and a certain depth of the crater, the next bullet will be easier to penetrate the crater weakness of the fibre plate, the oblique penetration effect on the thin plate by the secondary penetration of the negative impact, the angle of incidence is larger, the bullet will be more complete ricochet and has a high residual velocity, which will produce a secondary killing of personnel. The research results can be used for UHMWPE thin plate for lightweight military bulletproof insert design to provide reference.
, Available online ,
doi: 10.11883/bzycj-2024-0082
Abstract:
When X-rays generated by high-altitude nuclear detonation irradiates on the shell structure of missile, blow-off impulse (BOI) and thermal shock waves generated may produce dynamic response and damage on it. The existing three one-dimensional theoretical models, Whitener, BBAY, and MBBAY, can only provide approximate BOI values and accurate results of peak pressure and other information are inaccessible. Solving this problem requires numerical calculations based on real physical laws. The numerical simulation program TSHOCK3D for X-ray thermal excitation wave is used to calculate the BOI and peak pressure to make a comparative analysis. An aluminum plate with a length and width of 0.4 centimeters and a thickness of 0.1 centimeters is set as the target for X-ray radiation. The range of the working conditions is 0.1−3.0 keV for the Planck's blackbody temperatures and radiant energy flux are in the range of 220−400 J/cm2. The results indicate that the TSHOCK3D can give the results effectively and reliably. The simulation results are consistent with the theoretical models mentioned above. The BOI and peak pressure are approximately linear with the energy flux, while the maximum value exist for different blackbody temperatures.
When X-rays generated by high-altitude nuclear detonation irradiates on the shell structure of missile, blow-off impulse (BOI) and thermal shock waves generated may produce dynamic response and damage on it. The existing three one-dimensional theoretical models, Whitener, BBAY, and MBBAY, can only provide approximate BOI values and accurate results of peak pressure and other information are inaccessible. Solving this problem requires numerical calculations based on real physical laws. The numerical simulation program TSHOCK3D for X-ray thermal excitation wave is used to calculate the BOI and peak pressure to make a comparative analysis. An aluminum plate with a length and width of 0.4 centimeters and a thickness of 0.1 centimeters is set as the target for X-ray radiation. The range of the working conditions is 0.1−3.0 keV for the Planck's blackbody temperatures and radiant energy flux are in the range of 220−400 J/cm2. The results indicate that the TSHOCK3D can give the results effectively and reliably. The simulation results are consistent with the theoretical models mentioned above. The BOI and peak pressure are approximately linear with the energy flux, while the maximum value exist for different blackbody temperatures.
, Available online ,
doi: 10.11883/bzycj-2023-0368
Abstract:
Shape memory alloys undergo phase transformation under strong impact loads, and the phase transformation has a significant impact on the dynamic mechanical response of their structural components. Based on the phase transformation critical criterion considering both hydrostatic pressure and deviatoric stress effects, an incremental constitutive model of phase transformation is derived. The analytical expression of characteristic wave speed under complex stress state is obtained based on the generalized characteristic theory. The characteristic wave speed is not only related to the mechanical parameters of the material itself (such as the tension-compression asymmetry and the modulus of the mixed phase), but also related to the stress state of the material. For TiNi alloys with volume expansion due to phase transformation, the increase of tensile-compressive asymmetry coefficient will increase the wave speed of slow waves, while having almost no effect on fast waves. At the short axis of the phase transformation ellipse (α = 90°), the wave speed of slow waves is the lowest and decreases significantly with the increase of the dimensionless modulus of the mixed phase. When the dimensionless modulus of the mixed phase increases from 2 to 5, the wave speed decreases by 36.2%, while the wave speed of fast waves reaches the maximum value c0, which is independent of the modulus of the mixed phase; at the long axis of the phase transformation ellipse (α = 180°), the speed of slow waves reaches the maximum value, and the wave speed of fast waves reaches the minimum value c2.
Shape memory alloys undergo phase transformation under strong impact loads, and the phase transformation has a significant impact on the dynamic mechanical response of their structural components. Based on the phase transformation critical criterion considering both hydrostatic pressure and deviatoric stress effects, an incremental constitutive model of phase transformation is derived. The analytical expression of characteristic wave speed under complex stress state is obtained based on the generalized characteristic theory. The characteristic wave speed is not only related to the mechanical parameters of the material itself (such as the tension-compression asymmetry and the modulus of the mixed phase), but also related to the stress state of the material. For TiNi alloys with volume expansion due to phase transformation, the increase of tensile-compressive asymmetry coefficient will increase the wave speed of slow waves, while having almost no effect on fast waves. At the short axis of the phase transformation ellipse (α = 90°), the wave speed of slow waves is the lowest and decreases significantly with the increase of the dimensionless modulus of the mixed phase. When the dimensionless modulus of the mixed phase increases from 2 to 5, the wave speed decreases by 36.2%, while the wave speed of fast waves reaches the maximum value c0, which is independent of the modulus of the mixed phase; at the long axis of the phase transformation ellipse (α = 180°), the speed of slow waves reaches the maximum value, and the wave speed of fast waves reaches the minimum value c2.
, Available online ,
doi: 10.11883/bzycj-2024-0074
Abstract:
The annular shaped charges serve as the precursor of a tandem warhead, prized for its ability to create large diameter perforation in targets. In an effort to enhance the penetration capacity of the annular shaped charge jet and mitigate the impact of the inner casing on subsequent sections induced by a reversed penetrator, a novel approach was taken to implement the investigation. Four different combinations of inner and outer casing materials based on steel and aluminum alloy were explored. It was found that when the inner casing was made of aluminum alloy, the average penetration depth in the rear target was 36.13% lower than that when the inner casing was made of steel. Selecting an inner casing of aluminum alloy and an outer casing of steel, the effects of tip offset, liner thickness, and standoff distance on the formation and penetration characteristics of the annular jet were further investigated. The results show that the jet formed by the non-eccentric liner exhibits radial offset, negatively influencing its penetration capability. However, by offsetting the liner tip to the outer side by 0.05d (where d represents the radial thickness of the annular shaped charge), both the forming and penetration performances of the jet are significantly improved. In addition, as the liner thickness increases, the velocity of the jet tip gradually decreases. Notably, the annular jet formed by an eccentric conical liner with a thickness of 0.045d exhibits superior penetration performance. Furthermore, the standoff distance emerges as a critical factor influencing the penetration capability of the annular jet. Optimal performance is achieved at a standoff distance of 1.12d. Under the same scenario, jet penetration tests were implemented. The difference between the radius of the penetration tunnel from numerical and experimental study lies within 12%. Subsequently, the reliability of the numerical simulation model and the conclusions are verified.
The annular shaped charges serve as the precursor of a tandem warhead, prized for its ability to create large diameter perforation in targets. In an effort to enhance the penetration capacity of the annular shaped charge jet and mitigate the impact of the inner casing on subsequent sections induced by a reversed penetrator, a novel approach was taken to implement the investigation. Four different combinations of inner and outer casing materials based on steel and aluminum alloy were explored. It was found that when the inner casing was made of aluminum alloy, the average penetration depth in the rear target was 36.13% lower than that when the inner casing was made of steel. Selecting an inner casing of aluminum alloy and an outer casing of steel, the effects of tip offset, liner thickness, and standoff distance on the formation and penetration characteristics of the annular jet were further investigated. The results show that the jet formed by the non-eccentric liner exhibits radial offset, negatively influencing its penetration capability. However, by offsetting the liner tip to the outer side by 0.05d (where d represents the radial thickness of the annular shaped charge), both the forming and penetration performances of the jet are significantly improved. In addition, as the liner thickness increases, the velocity of the jet tip gradually decreases. Notably, the annular jet formed by an eccentric conical liner with a thickness of 0.045d exhibits superior penetration performance. Furthermore, the standoff distance emerges as a critical factor influencing the penetration capability of the annular jet. Optimal performance is achieved at a standoff distance of 1.12d. Under the same scenario, jet penetration tests were implemented. The difference between the radius of the penetration tunnel from numerical and experimental study lies within 12%. Subsequently, the reliability of the numerical simulation model and the conclusions are verified.
, Available online ,
doi: 10.11883/bzycj-2024-0007
Abstract:
The propagation characteristics of waves are the basis for studying the dynamic behavior of materials, and the theoretical study of waves in continuous media at the macro scale has been well developed. With the widespread application of materials and structures at the micro and nano scales, the study of wave propagation characteristics at the lattice scale is receiving increasing attention. In this article, the Tersoff potential interaction between lattices is applied to study the wave propagation characteristics in single-crystal and polycrystalline systems. Firstly, in the case of micro-vibration, the propagation of lattice waves in a single-crystal system is studied based on three potential energy functions between lattices: linear interaction, Tersoff potential, and Tersoff potential with defects. The dispersion relationship in the lattice and the expression of lattice wave velocity are obtained. Secondly, taking carbon lattice and silicon lattice as examples, the finite difference method is applied to study the wave propagation process in the single-crystal system under three potential energies. The differences in lattice motion under compressive and tensile impacts are compared, and the influence of incident velocity on the displacement peak and force peak is discussed, which reveals the difference in wave propagation between single-crystal systems and continuous media. Finally, taking diamond and silicon carbide as examples, molecular dynamics simulations are used to study the wave propagation characteristics in polycrystalline systems, and the differences in atomic motion at different spatial positions are discussed. The results indicate that the lattice structure in polycrystalline systems is more complex, and the wave propagation characteristics in polycrystalline systems are different from those in single-crystal systems. The existence of defects has a significant impact on the propagation law of waves, which is more prominent in polycrystalline systems. This study has good reference significance for the study of material dynamics performance at the micro and nano scales.
The propagation characteristics of waves are the basis for studying the dynamic behavior of materials, and the theoretical study of waves in continuous media at the macro scale has been well developed. With the widespread application of materials and structures at the micro and nano scales, the study of wave propagation characteristics at the lattice scale is receiving increasing attention. In this article, the Tersoff potential interaction between lattices is applied to study the wave propagation characteristics in single-crystal and polycrystalline systems. Firstly, in the case of micro-vibration, the propagation of lattice waves in a single-crystal system is studied based on three potential energy functions between lattices: linear interaction, Tersoff potential, and Tersoff potential with defects. The dispersion relationship in the lattice and the expression of lattice wave velocity are obtained. Secondly, taking carbon lattice and silicon lattice as examples, the finite difference method is applied to study the wave propagation process in the single-crystal system under three potential energies. The differences in lattice motion under compressive and tensile impacts are compared, and the influence of incident velocity on the displacement peak and force peak is discussed, which reveals the difference in wave propagation between single-crystal systems and continuous media. Finally, taking diamond and silicon carbide as examples, molecular dynamics simulations are used to study the wave propagation characteristics in polycrystalline systems, and the differences in atomic motion at different spatial positions are discussed. The results indicate that the lattice structure in polycrystalline systems is more complex, and the wave propagation characteristics in polycrystalline systems are different from those in single-crystal systems. The existence of defects has a significant impact on the propagation law of waves, which is more prominent in polycrystalline systems. This study has good reference significance for the study of material dynamics performance at the micro and nano scales.
, Available online ,
doi: 10.11883/bzycj-2023-0195
Abstract:
Based on the basic principles of electromagnetic induction, an impact device is proposed that generates high-amplitude and long-pulse acceleration loads driven by electromagnetic forces. The impact device goes to make up for the shortcomings of the current stage of ground impact test technology. The disadvantages of the current stage of ground impact test technology include mainly time-consuming, high cost, low repeatability and controllability, and it is difficult to continuously improve the pulse width of acceleration load. Acceleration impact tests were performed using an electromagnetic Hopkinson bar, and the working process of the device from the generation of electromagnetic force to its transformation into impact load was analyzed. In the acceleration impact test, the stress on the bar was obtained by strain gauges and the acceleration loads at the end of the bar were obtained by acceleration transducers. A plurality of test results without loss of repeatability. The classical one-dimensional stress wave theory for predicting the relationship between acceleration and stress in slender bars is developed. Comparative analysis against experimental data are presented to demonstrate the effectiveness of the present approach. The electromagnetic Hopkinson bar acceleration impact test was numerically simulated using COMSOL finite element software, and the simulation results showed good consistency with the experimental results, indicating that the numerical model could simulate this kind of impact test more accurately and verifying the accuracy of the numerical model. Based on this finite element model, an impact device that generates high-amplitude, long-pulse acceleration is proposed, and numerical simulations of the device are carried out at different voltages and capacitances. The simulation results show that the device is able to generate the required acceleration. The acceleration amplitude increases with increasing capacitance voltage and the acceleration pulse width increases with increasing capacitance value. By regulating the values of the circuit parameters, the device can generate acceleration loads with different amplitudes and pulse widths.
Based on the basic principles of electromagnetic induction, an impact device is proposed that generates high-amplitude and long-pulse acceleration loads driven by electromagnetic forces. The impact device goes to make up for the shortcomings of the current stage of ground impact test technology. The disadvantages of the current stage of ground impact test technology include mainly time-consuming, high cost, low repeatability and controllability, and it is difficult to continuously improve the pulse width of acceleration load. Acceleration impact tests were performed using an electromagnetic Hopkinson bar, and the working process of the device from the generation of electromagnetic force to its transformation into impact load was analyzed. In the acceleration impact test, the stress on the bar was obtained by strain gauges and the acceleration loads at the end of the bar were obtained by acceleration transducers. A plurality of test results without loss of repeatability. The classical one-dimensional stress wave theory for predicting the relationship between acceleration and stress in slender bars is developed. Comparative analysis against experimental data are presented to demonstrate the effectiveness of the present approach. The electromagnetic Hopkinson bar acceleration impact test was numerically simulated using COMSOL finite element software, and the simulation results showed good consistency with the experimental results, indicating that the numerical model could simulate this kind of impact test more accurately and verifying the accuracy of the numerical model. Based on this finite element model, an impact device that generates high-amplitude, long-pulse acceleration is proposed, and numerical simulations of the device are carried out at different voltages and capacitances. The simulation results show that the device is able to generate the required acceleration. The acceleration amplitude increases with increasing capacitance voltage and the acceleration pulse width increases with increasing capacitance value. By regulating the values of the circuit parameters, the device can generate acceleration loads with different amplitudes and pulse widths.
, Available online ,
doi: 10.11883/bzycj-2023-0455
Abstract:
Explosive welding production in a vacuum explosion containment vessel can not only restrict the shock wave and noise generated by explosive explosion in a certain space range, but also effectively improve the quality of explosive welding products. Meanwhile, it also alleviates the problems of unstable product quality and rainy season shutdown caused by the influence of weather and climate during explosive welding production, which is an invention that can promote the development of the explosive processing industry. In order to develop a super large vacuum explosion containment vessel for explosive welding, it is necessary to explore the internal blast load and dynamic response of vacuum explosion containment vessel with sand covered for explosive welding. In order to meet the requirements of the experiment, a 0.55 m3 small cylindrical vacuum explosion containment vessel with the cap covered by a certain thickness of sand was designed, and a series of vacuum explosion experiments were carried out in it. At the same time, using the AUTODYN finite element analysis program, the numerical simulation analysis of the corresponding experimental groups is carried out. The evolution of shock wave inside the container, the distribution of blast load, the dynamic response of the structure, and the mechanism of sand covering on the end of the container on the damping of the plate structure are explored in depth. By analyzing the results of experiment and numerical simulation, it is concluded that the peak value of the second impulse of the time-history curve of the blast load in the explosion containment vessel is obviously higher than that of the first impulse, and the superposition and reflection of the shock wave always occur in the inner wall of the cover. With the decrease of vacuum degree inside the container, the peak value of the blast load is weakened obviously. According to the time-history curves of blast load and dynamic strain calculated by the numerical simulation, the dynamic response of the container cover is divided into four development phases: step-up phase, impulse follower phase, inertial lag phase and static pressure stabilization phase. With the decrease of vacuum degree, the amplitude of dynamic response is weakened obviously. With the increase of the thickness of sand cover, the dynamic response of explosion vessel is gradually weakened. Ultimately, it is concluded that reducing the environmental pressure inside the vessel and increasing the thickness of the sand covered on the cap of the container can be used as an effective method to reduce the forced vibration of the explosion containment vessel. The conclusions of the study are useful for the structural design of super large vacuum explosion containment vessels.
Explosive welding production in a vacuum explosion containment vessel can not only restrict the shock wave and noise generated by explosive explosion in a certain space range, but also effectively improve the quality of explosive welding products. Meanwhile, it also alleviates the problems of unstable product quality and rainy season shutdown caused by the influence of weather and climate during explosive welding production, which is an invention that can promote the development of the explosive processing industry. In order to develop a super large vacuum explosion containment vessel for explosive welding, it is necessary to explore the internal blast load and dynamic response of vacuum explosion containment vessel with sand covered for explosive welding. In order to meet the requirements of the experiment, a 0.55 m3 small cylindrical vacuum explosion containment vessel with the cap covered by a certain thickness of sand was designed, and a series of vacuum explosion experiments were carried out in it. At the same time, using the AUTODYN finite element analysis program, the numerical simulation analysis of the corresponding experimental groups is carried out. The evolution of shock wave inside the container, the distribution of blast load, the dynamic response of the structure, and the mechanism of sand covering on the end of the container on the damping of the plate structure are explored in depth. By analyzing the results of experiment and numerical simulation, it is concluded that the peak value of the second impulse of the time-history curve of the blast load in the explosion containment vessel is obviously higher than that of the first impulse, and the superposition and reflection of the shock wave always occur in the inner wall of the cover. With the decrease of vacuum degree inside the container, the peak value of the blast load is weakened obviously. According to the time-history curves of blast load and dynamic strain calculated by the numerical simulation, the dynamic response of the container cover is divided into four development phases: step-up phase, impulse follower phase, inertial lag phase and static pressure stabilization phase. With the decrease of vacuum degree, the amplitude of dynamic response is weakened obviously. With the increase of the thickness of sand cover, the dynamic response of explosion vessel is gradually weakened. Ultimately, it is concluded that reducing the environmental pressure inside the vessel and increasing the thickness of the sand covered on the cap of the container can be used as an effective method to reduce the forced vibration of the explosion containment vessel. The conclusions of the study are useful for the structural design of super large vacuum explosion containment vessels.
, Available online ,
doi: 10.11883/bzycj-2023-0433
Abstract:
In order to deal with the difficulty of measuring the transmitted wave in the backfilling SHPB (split Hopkinson pressure bar) test, rock bars are used to instead of steel bar as the incident bar and transmitted bar for improving the pendulum hammer driven SHPB system. The wave impedance matching formula and viscoelastic wave propagation in SHPB test is proposed. Based on the study of stress wave propagation in rock bar systems, the viscosity attenuation coefficients of stress wave propagation in the incident and transmitted rock bars and the reflection and transmission attenuation coefficient of the rock bar-backfilling body are defined. Based on the Kelvin-Voigt model, the effects of rock bar density and wave velocity on the transmitted wave measured of the filling body in the SHPB tests were simulated and analyzed by using a one-dimensional wave propagation analysis procedure. The relationship between the wave impedance matching coefficient and the reflection and transmission attenuation coefficient of the rock bar-backfilling body were obtained. According to the characteristics of field backfilling, the wave impedance matching coefficient and the reflection and transmission attenuation coefficient, four long rock bars were selected to modify the pendulum hammer driven SHPB system. The viscosity coefficient of the rock bar was measured and stresses and strains on the interfaces of rock bar and backfilling body were calculated by using the one-dimensional wave propagation analysis procedure. The stress waveform characteristics and signal-to-noise ratio of the transmitted waves were analyzed. The matching degree of four kinds of rock bars and backfilling wave impedance from good to poor is obtained, which is green sandstone, granite, marble and basalt. The dynamic impacting experiment on the filling body was conducted and the stress balance in the sample was verified. The pendulum hammer driven SHPB system with green sandstone incident bar and transmission bar is established, which provides support for the dynamic mechanical characteristics of the backfilling.
In order to deal with the difficulty of measuring the transmitted wave in the backfilling SHPB (split Hopkinson pressure bar) test, rock bars are used to instead of steel bar as the incident bar and transmitted bar for improving the pendulum hammer driven SHPB system. The wave impedance matching formula and viscoelastic wave propagation in SHPB test is proposed. Based on the study of stress wave propagation in rock bar systems, the viscosity attenuation coefficients of stress wave propagation in the incident and transmitted rock bars and the reflection and transmission attenuation coefficient of the rock bar-backfilling body are defined. Based on the Kelvin-Voigt model, the effects of rock bar density and wave velocity on the transmitted wave measured of the filling body in the SHPB tests were simulated and analyzed by using a one-dimensional wave propagation analysis procedure. The relationship between the wave impedance matching coefficient and the reflection and transmission attenuation coefficient of the rock bar-backfilling body were obtained. According to the characteristics of field backfilling, the wave impedance matching coefficient and the reflection and transmission attenuation coefficient, four long rock bars were selected to modify the pendulum hammer driven SHPB system. The viscosity coefficient of the rock bar was measured and stresses and strains on the interfaces of rock bar and backfilling body were calculated by using the one-dimensional wave propagation analysis procedure. The stress waveform characteristics and signal-to-noise ratio of the transmitted waves were analyzed. The matching degree of four kinds of rock bars and backfilling wave impedance from good to poor is obtained, which is green sandstone, granite, marble and basalt. The dynamic impacting experiment on the filling body was conducted and the stress balance in the sample was verified. The pendulum hammer driven SHPB system with green sandstone incident bar and transmission bar is established, which provides support for the dynamic mechanical characteristics of the backfilling.
, Available online ,
doi: 10.11883/bzycj-2024-0077
Abstract:
In order to study the anti-explosion ability of reinforced masonry wall and the reinforcement performance of polyurea on the wall, LS-DYNA software was used to numerically simulate the dynamic response of unreinforced masonry wall, reinforced masonry wall, and masonry wall strengthened with polyurea respectively. The anti-gas explosion performance of different walls under gas explosion load with peak value of 5, 10, 20 and 30 kPa was obtained. The reinforcing effect of vertical reinforcement in ash joint and polyurea were compared and analyzed. The results show that: (1) The anti-gas explosion capability of the unreinforced wall is relatively weak, which generally causes irreparable damage under the load of 20 kPa and collapses under the load of 30 kPa. (2) The explosion resistance of the masonry wall can be enhanced by the vertical displacement of rebar in the ash joint and the spraying of polyurea on the wall surface. Under the load of 20 kPa, the peak displacement at mid-span of each reinforced wall is smaller than that of the unreinforced wall, and the damage is lighter, which is repairable. Among them, the anti-explosion effect of double-sided spraying polyurea on unreinforced wall surface is the best, and there is no collapse damage under the load of 30 kPa. The reinforcing effect of vertical reinforcement in ash joint and polyurea spraying on the back surface are the second. (3) The three groups of reinforced walls with polyurea can all withstand 30 kPa gas explosion load. Cracks occur in the middle of the wall strengthened by spraying on the explosive side, fragments splash, the mid-span peak displacement is the largest. Local damage occurs at both ends of the wall strengthened by back side and double-sided spraying, and the walls are basically complete, and the mid-span peak displacement of the wall strengthened by double-side spraying is the smallest. It is shown that spraying polyurea on both sides on the basis of vertical reinforcement in ash joint has the best explosion resistance effect, and can also bear greater gas explosion load. The research results can provide reference for the reinforcement of reinforced masonry wall against gas explosion.
In order to study the anti-explosion ability of reinforced masonry wall and the reinforcement performance of polyurea on the wall, LS-DYNA software was used to numerically simulate the dynamic response of unreinforced masonry wall, reinforced masonry wall, and masonry wall strengthened with polyurea respectively. The anti-gas explosion performance of different walls under gas explosion load with peak value of 5, 10, 20 and 30 kPa was obtained. The reinforcing effect of vertical reinforcement in ash joint and polyurea were compared and analyzed. The results show that: (1) The anti-gas explosion capability of the unreinforced wall is relatively weak, which generally causes irreparable damage under the load of 20 kPa and collapses under the load of 30 kPa. (2) The explosion resistance of the masonry wall can be enhanced by the vertical displacement of rebar in the ash joint and the spraying of polyurea on the wall surface. Under the load of 20 kPa, the peak displacement at mid-span of each reinforced wall is smaller than that of the unreinforced wall, and the damage is lighter, which is repairable. Among them, the anti-explosion effect of double-sided spraying polyurea on unreinforced wall surface is the best, and there is no collapse damage under the load of 30 kPa. The reinforcing effect of vertical reinforcement in ash joint and polyurea spraying on the back surface are the second. (3) The three groups of reinforced walls with polyurea can all withstand 30 kPa gas explosion load. Cracks occur in the middle of the wall strengthened by spraying on the explosive side, fragments splash, the mid-span peak displacement is the largest. Local damage occurs at both ends of the wall strengthened by back side and double-sided spraying, and the walls are basically complete, and the mid-span peak displacement of the wall strengthened by double-side spraying is the smallest. It is shown that spraying polyurea on both sides on the basis of vertical reinforcement in ash joint has the best explosion resistance effect, and can also bear greater gas explosion load. The research results can provide reference for the reinforcement of reinforced masonry wall against gas explosion.
, Available online ,
doi: 10.11883/bzycj-2024-0036
Abstract:
X-ray diffraction test was used to analyze the changes in the mineral composition of the granite before and after filling with water to study the effects of saturated water and initial damage degree on macroscopic and microscopic failure characteristics of granite under impact load. The Hopkinson device was used to carry out dynamic mechanical tests on the granite samples under different states to analyze the dynamic mechanical properties of the granite and the block size characteristics under different states. In addition, some of the granite fragments after impact were selected for electron microscope scanning test to analyze the fracture failure characteristics. The fractal dimension was used to analyze the fragmentation degree of the granite fragments after impact and the scanning images of the fracture under electron microscopy. The influence of the image magnification selected during electron microscope scanning on the fractal dimension is discussed. The micro-cracking mechanism of granite induced by saturated water under impact load is briefly analyzed. The results show that the mineral composition of the saturated granite changes compared with the natural granite. The proportions of hornblende, albite, microcline, and quartz in the saturated granite decrease, while the proportion of kaolinite increases significantly. With the increase of initial damage, the dynamic peak stress of granite gradually decreases while the fragmentation degree and the fractal dimension of the block increase gradually, and the influence of initial damage on the fractal dimension of the block is greater than that of saturated water. With the increase of initial damage, more micro-cracks and debris appear in the fracture image, and the fractal dimension of the fracture image increases gradually. In a certain range, the fractal dimension of electron microscope scanning images increases with the increase of image magnification, but when the image exceeds a certain multiple, the fractal dimension will decrease. The research results can provide some theoretical and engineering references for the failure and instability mechanism analysis of disturbed water-saturated granite with initial damage in geotechnical engineering.
X-ray diffraction test was used to analyze the changes in the mineral composition of the granite before and after filling with water to study the effects of saturated water and initial damage degree on macroscopic and microscopic failure characteristics of granite under impact load. The Hopkinson device was used to carry out dynamic mechanical tests on the granite samples under different states to analyze the dynamic mechanical properties of the granite and the block size characteristics under different states. In addition, some of the granite fragments after impact were selected for electron microscope scanning test to analyze the fracture failure characteristics. The fractal dimension was used to analyze the fragmentation degree of the granite fragments after impact and the scanning images of the fracture under electron microscopy. The influence of the image magnification selected during electron microscope scanning on the fractal dimension is discussed. The micro-cracking mechanism of granite induced by saturated water under impact load is briefly analyzed. The results show that the mineral composition of the saturated granite changes compared with the natural granite. The proportions of hornblende, albite, microcline, and quartz in the saturated granite decrease, while the proportion of kaolinite increases significantly. With the increase of initial damage, the dynamic peak stress of granite gradually decreases while the fragmentation degree and the fractal dimension of the block increase gradually, and the influence of initial damage on the fractal dimension of the block is greater than that of saturated water. With the increase of initial damage, more micro-cracks and debris appear in the fracture image, and the fractal dimension of the fracture image increases gradually. In a certain range, the fractal dimension of electron microscope scanning images increases with the increase of image magnification, but when the image exceeds a certain multiple, the fractal dimension will decrease. The research results can provide some theoretical and engineering references for the failure and instability mechanism analysis of disturbed water-saturated granite with initial damage in geotechnical engineering.
, Available online ,
doi: 10.11883/bzycj-2023-0472
Abstract:
It is of great scientific significance and application value to study the anti-penetration performance of continuous fiber-reinforced high-porosity composites. First, the ballistic penetration experiments of 20 mm thick continuous fiber-reinforced high-porosity composites were carried out by using two-stage light gas gun firing Q235 steel projectiles of diameter 4.5 mm. Based on the analysis of the initial and final velocities of bullet penetration, the ballistic limit of the material is obtained. By observing the damage patterns of the target plate, these patterns are divided into three types from low to high according to the initial velocity of the projectiles: back-crack type, back-burst type and penetrated type. The anti-penetration performance of this composite material is compared with other materials by specific energy absorption, showing that the anti-penetration performance of the composite against low-speed penetration up to 600 m/s is better than those of steel, aluminum, Kevlar and glass fiber composite. Then, an orthogonal anisotropic continuum damage constitutive model is proposed for the continuous fiber-reinforced high-porosity composites. This constitutive model is written as a subroutine and embedded in the finite element software by secondary development. On this basis, the finite element simulations of ballistic penetrations of continuous fiber reinforced high-porosity composites are conducted. The validity of the constitutive and finite element models is verified by comparing the final velocity, ballistic limit and damage range of the back surface obtained from experiment and simulation. Furthermore, the damage mechanism of the penetration process is analyzed by observing the shape of the bullet hole, stress distribution and damage distribution obtained from the finite element simulation. The results show that the formation of the bullet hole during the penetration of spherical projectile is caused by shear damage, the debonding of fiber and matrix is caused by the combined action of compression and shear, the delamination damage of the target plate is caused by the tension wave created by the reflection of compression wave, and the fiber breakage belongs to tension damage. Besides, the kinetic energy, internal energy and their proportion to the kinetic energy change of the bullet are compared with the initial velocity. It is pointed out that most of the kinetic energy of the projectile is transformed into the kinetic energy of the fragment of target plates and the plastic deformation energy of the projectile. The research results provide a reference for the multifunctional integration of these composite materials in heat protection, penetration protection and load bearing.
It is of great scientific significance and application value to study the anti-penetration performance of continuous fiber-reinforced high-porosity composites. First, the ballistic penetration experiments of 20 mm thick continuous fiber-reinforced high-porosity composites were carried out by using two-stage light gas gun firing Q235 steel projectiles of diameter 4.5 mm. Based on the analysis of the initial and final velocities of bullet penetration, the ballistic limit of the material is obtained. By observing the damage patterns of the target plate, these patterns are divided into three types from low to high according to the initial velocity of the projectiles: back-crack type, back-burst type and penetrated type. The anti-penetration performance of this composite material is compared with other materials by specific energy absorption, showing that the anti-penetration performance of the composite against low-speed penetration up to 600 m/s is better than those of steel, aluminum, Kevlar and glass fiber composite. Then, an orthogonal anisotropic continuum damage constitutive model is proposed for the continuous fiber-reinforced high-porosity composites. This constitutive model is written as a subroutine and embedded in the finite element software by secondary development. On this basis, the finite element simulations of ballistic penetrations of continuous fiber reinforced high-porosity composites are conducted. The validity of the constitutive and finite element models is verified by comparing the final velocity, ballistic limit and damage range of the back surface obtained from experiment and simulation. Furthermore, the damage mechanism of the penetration process is analyzed by observing the shape of the bullet hole, stress distribution and damage distribution obtained from the finite element simulation. The results show that the formation of the bullet hole during the penetration of spherical projectile is caused by shear damage, the debonding of fiber and matrix is caused by the combined action of compression and shear, the delamination damage of the target plate is caused by the tension wave created by the reflection of compression wave, and the fiber breakage belongs to tension damage. Besides, the kinetic energy, internal energy and their proportion to the kinetic energy change of the bullet are compared with the initial velocity. It is pointed out that most of the kinetic energy of the projectile is transformed into the kinetic energy of the fragment of target plates and the plastic deformation energy of the projectile. The research results provide a reference for the multifunctional integration of these composite materials in heat protection, penetration protection and load bearing.
, Available online ,
doi: 10.11883/bzycj-2024-0045
Abstract:
Cellular projectiles are widely used in the impact tests of protective structures, but the actual loads of cellular projectiles acting on the tested sandwich structures are still unclear. To explore the coupling response process between the uniform/graded cellular projectile and the foam sandwich beam and the loading effect of cellular projectiles, theoretical analysis, numerical simulations, and impact tests were carried out. The foam sandwich beam was equivalent to a monolithic beam to simplify the analysis. Based on the shock wave model of the cellular projectile and the equivalent response model of the foam sandwich beam, a coupling analysis model of the cellular projectile impacting the foam sandwich beam was developed, and its governing equations were presented and solved numerically by Runge-Kutta method. Meso-finite element simulations of a uniform/graded cellular projectile impacting a foam sandwich beam were carried out based on the 3D Voronoi technique. Impact tests were performed on the test platform of cellular projectiles, and the velocity response of the cellular projectiles and the foam sandwich beams was obtained by using a high-speed camera and a digital image processing technique. It is found that the coupling analysis model can accurately predict the velocity history curves of the cellular projectile and the foam sandwich beam and the impact pressure of the cellular projectile. Subjected to cellular projectiles with the same initial momentum but different density distribution or initial velocity, foam sandwich beams with the same configuration present different mechanical response processes, which demonstrates that the impact of cellular projectiles cannot be simply equivalent to impulse loading, and the coupling effect between the projectile and the sandwich beam cannot be ignored. Compared with uniform cellular projectiles, the impact pressure waveform of the graded cellular projectile is sharper and shows stronger nonlinearity during its attenuation. This study clarifies the loading effect of cellular projectiles on foam sandwich beams and lays a theoretical foundation for the optimal design of cellular projectiles simulating blast loads.
Cellular projectiles are widely used in the impact tests of protective structures, but the actual loads of cellular projectiles acting on the tested sandwich structures are still unclear. To explore the coupling response process between the uniform/graded cellular projectile and the foam sandwich beam and the loading effect of cellular projectiles, theoretical analysis, numerical simulations, and impact tests were carried out. The foam sandwich beam was equivalent to a monolithic beam to simplify the analysis. Based on the shock wave model of the cellular projectile and the equivalent response model of the foam sandwich beam, a coupling analysis model of the cellular projectile impacting the foam sandwich beam was developed, and its governing equations were presented and solved numerically by Runge-Kutta method. Meso-finite element simulations of a uniform/graded cellular projectile impacting a foam sandwich beam were carried out based on the 3D Voronoi technique. Impact tests were performed on the test platform of cellular projectiles, and the velocity response of the cellular projectiles and the foam sandwich beams was obtained by using a high-speed camera and a digital image processing technique. It is found that the coupling analysis model can accurately predict the velocity history curves of the cellular projectile and the foam sandwich beam and the impact pressure of the cellular projectile. Subjected to cellular projectiles with the same initial momentum but different density distribution or initial velocity, foam sandwich beams with the same configuration present different mechanical response processes, which demonstrates that the impact of cellular projectiles cannot be simply equivalent to impulse loading, and the coupling effect between the projectile and the sandwich beam cannot be ignored. Compared with uniform cellular projectiles, the impact pressure waveform of the graded cellular projectile is sharper and shows stronger nonlinearity during its attenuation. This study clarifies the loading effect of cellular projectiles on foam sandwich beams and lays a theoretical foundation for the optimal design of cellular projectiles simulating blast loads.
, Available online ,
doi: 10.11883/bzycj-2023-0404
Abstract:
To study the explosion process of carbon-iron nanomaterials synthesized by gaseous detonation, the effects of different molar ratios of hydrogen-oxygen (2∶1, 3∶1, 4∶1) on the peak value time-history curve of detonation parameters (detonation velocity, detonation temperature, and detonation pressure) and the morphology of carbon-iron nanomaterials were studied by combination of hydrogen-oxygen experiments and numerical simulations. The explosion experiments used hydrogen and oxygen with a purity of 99.999% in a closed detonation tube. The precursor was ferrocene with a purity of 99%. A high-speed camera was used to observe in the middle of the tube. After the experiments, the samples were collected and characterized by transmission electron microscopy. The numerical simulation used ICEM software for modeling and meshing and then used FLUENT software to verify the rationality of the mesh size, and then performed simulation calculations after confirming the optimal mesh size. The results indicate that hydrogen-oxygen explosion inside a detonation tube involves two processes: the propagation of detonation waves and the attenuation of combustion waves, and the hydrogen-oxygen molar ratio has a significant impact on the peak time history curves of detonation velocity, detonation temperature, and detonation pressure. With the increase of the molar ratio of hydrogen to oxygen, the detonation velocity, detonation temperature, detonation pressure, and attenuation rate of the detonation wave all decrease. The molar ratio of hydrogen to oxygen affects the morphology growth of carbon-iron nanomaterials by influencing the propagation and attenuation of detonation waves. At zero oxygen balance, the sample consists of carbon-coated iron nanoparticles. As the hydrogen-oxygen molar ratio increases, the number of carbon nanotubes in the sample gradually increases. Adjusting the molar ratio of hydrogen to oxygen can achieve control over the propagation and attenuation process of detonation waves, and also achieve the goal of controlling the preparation of carbon iron nanomaterials with specific morphologies through gaseous detonation.
To study the explosion process of carbon-iron nanomaterials synthesized by gaseous detonation, the effects of different molar ratios of hydrogen-oxygen (2∶1, 3∶1, 4∶1) on the peak value time-history curve of detonation parameters (detonation velocity, detonation temperature, and detonation pressure) and the morphology of carbon-iron nanomaterials were studied by combination of hydrogen-oxygen experiments and numerical simulations. The explosion experiments used hydrogen and oxygen with a purity of 99.999% in a closed detonation tube. The precursor was ferrocene with a purity of 99%. A high-speed camera was used to observe in the middle of the tube. After the experiments, the samples were collected and characterized by transmission electron microscopy. The numerical simulation used ICEM software for modeling and meshing and then used FLUENT software to verify the rationality of the mesh size, and then performed simulation calculations after confirming the optimal mesh size. The results indicate that hydrogen-oxygen explosion inside a detonation tube involves two processes: the propagation of detonation waves and the attenuation of combustion waves, and the hydrogen-oxygen molar ratio has a significant impact on the peak time history curves of detonation velocity, detonation temperature, and detonation pressure. With the increase of the molar ratio of hydrogen to oxygen, the detonation velocity, detonation temperature, detonation pressure, and attenuation rate of the detonation wave all decrease. The molar ratio of hydrogen to oxygen affects the morphology growth of carbon-iron nanomaterials by influencing the propagation and attenuation of detonation waves. At zero oxygen balance, the sample consists of carbon-coated iron nanoparticles. As the hydrogen-oxygen molar ratio increases, the number of carbon nanotubes in the sample gradually increases. Adjusting the molar ratio of hydrogen to oxygen can achieve control over the propagation and attenuation process of detonation waves, and also achieve the goal of controlling the preparation of carbon iron nanomaterials with specific morphologies through gaseous detonation.
, Available online ,
doi: 10.11883/bzycj-2-23-0466
Abstract:
Coral concrete is a material with severely asymmetric tensile and compressive strengths. Therefore, studying the dynamic tensile mechanical properties of coral concrete is of great significance for island reef protective engineering. To investigate the dynamic tensile mechanical properties of carbon fiber (CF) and stainless steel fiber (SSF) reinforced coral sand cement mortar under impact loading, dynamic splitting tests were conducted using a 100 mm diameter split Hopkinson pressure bar (SHPB) device. Comparative analysis was carried out on the dynamic tensile strength and energy dissipation patterns of coral sand cement mortars with different fiber contents at various strain rates. In the SHPB tests, cement mortar specimens with different fiber contents were prepared: no fiber, 1.5% CF, 1.5% CF with 0.5% SSF, 1.5% CF with 1.0% SSF, and 1.5% CF with 1.5% SSF. The specimens were subjected to four impact speeds: 3.45, 4.86, 6.54, and 7.34 m/s. This allowed for impact-splitting tests conducted at different strain-rate ranges. In addition, SEM (Scanning Electron Microscope) tests were performed to reveal the action mechanism of the hybrid fibers. The results indicate that the static and dynamic tensile strengths of CF and SSF-reinforced coral sand cement mortar samples are significantly improved, with a maximum dynamic tensile strength increase rate of 66.03%. At the same strain rate, the dynamic tensile strength of the samples positively correlates with the fiber content, while the fragmentation degree negatively correlates with the fiber content. The fiber bridging effect effectively suppresses the development of cracks in the samples. Under the same fiber content, the dynamic increase factor increases significantly with the increase of strain rate, with a maximum increase factor of 2.44, demonstrating a clear tensile strain rate effect. The fragmentation degree and dissipated energy of coral sand cement mortar samples positively correlate with the strain rate, and samples with higher fiber dosages require more energy to dissipate during failure.
Coral concrete is a material with severely asymmetric tensile and compressive strengths. Therefore, studying the dynamic tensile mechanical properties of coral concrete is of great significance for island reef protective engineering. To investigate the dynamic tensile mechanical properties of carbon fiber (CF) and stainless steel fiber (SSF) reinforced coral sand cement mortar under impact loading, dynamic splitting tests were conducted using a 100 mm diameter split Hopkinson pressure bar (SHPB) device. Comparative analysis was carried out on the dynamic tensile strength and energy dissipation patterns of coral sand cement mortars with different fiber contents at various strain rates. In the SHPB tests, cement mortar specimens with different fiber contents were prepared: no fiber, 1.5% CF, 1.5% CF with 0.5% SSF, 1.5% CF with 1.0% SSF, and 1.5% CF with 1.5% SSF. The specimens were subjected to four impact speeds: 3.45, 4.86, 6.54, and 7.34 m/s. This allowed for impact-splitting tests conducted at different strain-rate ranges. In addition, SEM (Scanning Electron Microscope) tests were performed to reveal the action mechanism of the hybrid fibers. The results indicate that the static and dynamic tensile strengths of CF and SSF-reinforced coral sand cement mortar samples are significantly improved, with a maximum dynamic tensile strength increase rate of 66.03%. At the same strain rate, the dynamic tensile strength of the samples positively correlates with the fiber content, while the fragmentation degree negatively correlates with the fiber content. The fiber bridging effect effectively suppresses the development of cracks in the samples. Under the same fiber content, the dynamic increase factor increases significantly with the increase of strain rate, with a maximum increase factor of 2.44, demonstrating a clear tensile strain rate effect. The fragmentation degree and dissipated energy of coral sand cement mortar samples positively correlate with the strain rate, and samples with higher fiber dosages require more energy to dissipate during failure.
, Available online ,
doi: 10.11883/bzycj-2023-0459
Abstract:
The layered protective structure composed of bursting layer, distribution layer and structure layer is usually used to resist the penetration and blast waves induced by advanced earth penetrating weapons (EPWs). The defect of traditional layered protective structure with medium/coarse sand as the distribution layer is that it is difficult to reliably control the load on the structure layer. To solve this issue, an alternative approach is presented by replacing the material of distribution layer from the frequently-used medium/coarse sand to foam concrete. To investigate the blast resistance of layered protective structure sandwiched by foam concrete (named composite protective structure), the blast test on the layered composite target composed of CF120 concrete (a fiber reinforced high-strength concrete) bursting layer, C5 foam concrete distribution layer and C40 reinforced concrete structure layer was firstly conducted in the present study, in which the damage and failure in the layered composite target and blast waves at specific locations were the major concern and were accurately recorded. Then based on the concrete material model established by Kong and Fang and the Smoothed Particle Galerkin (SPG) algorithm available in the LS-DYNA, a corresponding numerical model was developed and validated against test data. Using the validated numerical model, the propagation and attenuation of blast waves and damage and failure in the composite protective structure induced by cylindrical charge explosion are discussed in detail. It is found that the blast resistance mechanism of the composite protective structure is attributed to the extreme wave impedance mismatch between the bursting layer and the foam concrete layer, which greatly reduces the propagation of blast waves into the foam concrete layer, leading to a transformation of more blast energy to the bursting layer, so that the blast load and energy on the structure layer can be greatly reduced. The research results can provide important reference for the design of protective structure against EPWs.
The layered protective structure composed of bursting layer, distribution layer and structure layer is usually used to resist the penetration and blast waves induced by advanced earth penetrating weapons (EPWs). The defect of traditional layered protective structure with medium/coarse sand as the distribution layer is that it is difficult to reliably control the load on the structure layer. To solve this issue, an alternative approach is presented by replacing the material of distribution layer from the frequently-used medium/coarse sand to foam concrete. To investigate the blast resistance of layered protective structure sandwiched by foam concrete (named composite protective structure), the blast test on the layered composite target composed of CF120 concrete (a fiber reinforced high-strength concrete) bursting layer, C5 foam concrete distribution layer and C40 reinforced concrete structure layer was firstly conducted in the present study, in which the damage and failure in the layered composite target and blast waves at specific locations were the major concern and were accurately recorded. Then based on the concrete material model established by Kong and Fang and the Smoothed Particle Galerkin (SPG) algorithm available in the LS-DYNA, a corresponding numerical model was developed and validated against test data. Using the validated numerical model, the propagation and attenuation of blast waves and damage and failure in the composite protective structure induced by cylindrical charge explosion are discussed in detail. It is found that the blast resistance mechanism of the composite protective structure is attributed to the extreme wave impedance mismatch between the bursting layer and the foam concrete layer, which greatly reduces the propagation of blast waves into the foam concrete layer, leading to a transformation of more blast energy to the bursting layer, so that the blast load and energy on the structure layer can be greatly reduced. The research results can provide important reference for the design of protective structure against EPWs.
, Available online ,
doi: 10.11883/bzycj-2024-0041
Abstract:
To investigate the velocity distribution characteristics of elliptical section warhead (ECSW) fragments under different initiation modes, a numerical simulation model was established for five ECSWs with different shape ratios. Numerical simulations were conducted to investigate the velocity distribution and energy output characteristics of fragments from ECSW under five different initiation modes: central single-point initiation, dual-point initiation at the midpoint of the minor (or major) axis, four-point initiation at the midpoint of the major and minor axes, as well as surface-initiated detonation. The research findings suggest that the maximum radial velocity of fragments follows a consistent logarithmic growth pattern in the radial direction across various initiation modes, increasing from the major axis to the minor axis direction. With an increase in the shape ratio, the difference in fragment velocities between the major and minor axis directions gradually decreases. However, the maximum velocity profiles of fragments from elliptical section warheads exhibit noticeable differences in average velocities under different initiation modes. Surface-initiated detonation produces the highest average radial velocity, whereas single-point initiation leads to the lowest. As the number of initiation points increases, the overall average fragment velocity on the maximum velocity profile gradually rises. In the axial direction, the influence of rarefaction waves leads to the maximum fragment velocities occurring near the 1/4 position from the non-initiating end at different azimuthal angles. Initiation points along the minor axis enhance the fragment velocity in the major axis direction near the initiating end compared to initiating points along the major axis. However, there are no significant variations in the axial velocity distribution of fragments in the minor axis direction. The different initiation modes have negligible effects on the energy output characteristics of elliptical section charges. Approximately 27% of the charge energy is converted into shell kinetic energy, while 50% is dissipated through casing fracture deformation and air shock wave propagation.
To investigate the velocity distribution characteristics of elliptical section warhead (ECSW) fragments under different initiation modes, a numerical simulation model was established for five ECSWs with different shape ratios. Numerical simulations were conducted to investigate the velocity distribution and energy output characteristics of fragments from ECSW under five different initiation modes: central single-point initiation, dual-point initiation at the midpoint of the minor (or major) axis, four-point initiation at the midpoint of the major and minor axes, as well as surface-initiated detonation. The research findings suggest that the maximum radial velocity of fragments follows a consistent logarithmic growth pattern in the radial direction across various initiation modes, increasing from the major axis to the minor axis direction. With an increase in the shape ratio, the difference in fragment velocities between the major and minor axis directions gradually decreases. However, the maximum velocity profiles of fragments from elliptical section warheads exhibit noticeable differences in average velocities under different initiation modes. Surface-initiated detonation produces the highest average radial velocity, whereas single-point initiation leads to the lowest. As the number of initiation points increases, the overall average fragment velocity on the maximum velocity profile gradually rises. In the axial direction, the influence of rarefaction waves leads to the maximum fragment velocities occurring near the 1/4 position from the non-initiating end at different azimuthal angles. Initiation points along the minor axis enhance the fragment velocity in the major axis direction near the initiating end compared to initiating points along the major axis. However, there are no significant variations in the axial velocity distribution of fragments in the minor axis direction. The different initiation modes have negligible effects on the energy output characteristics of elliptical section charges. Approximately 27% of the charge energy is converted into shell kinetic energy, while 50% is dissipated through casing fracture deformation and air shock wave propagation.
, Available online ,
doi: 10.11883/bzycj-2023-0465
Abstract:
To investigate the influence of typical metal powders on the shock wave effect and thermal damage performance of fuel air explosive (FAE), the explosion characteristics, flame structure and temperature distribution characteristics of epoxypropane (PO) with different types and contents of metal powders were experimentally studied using a 20 L spherical liquid explosion test system. The temperature field of explosion flame was reconstructed by the colorimetric temperature measurement method with a high-speed camera, which is based on the gray-body radiation theory and a self-written python code. The tungsten lamp was used to calibrate the measuring accuracy of the temperature mapping system, and the fitting relationship between the temperatures and the gray values of the high-speed images is derived to obtain the conversion coefficient. The experimental results show that the optimal mass concentration of pure PO was 780 g/m3, both the explosion overpressure (∆pmax) and the explosion pressure rise rate ((dp/dt)max) reached the maximum, ∆pmax=0.799 MPa and (dp/dt)max=52.438 MPa/s, respectively. The maximum explosion overpressure, maximum explosion pressure rise rate and maximum average temperature of PO added with Al, Ti and Mg powders all increase with the increase of mass ratios (I), while the trend of maximum pressure rise time is opposite. The variation rules of the maximum explosion overpressure and maximum average temperature are consistent, the order of their values is: Al/PO, Mg/PO, Ti/PO. When I=40%, the maximum explosion overpressure value of the three solid-liquid mixed fuels increases by 12.00%, 8.41% and 11.54%, respectively, compared with pure PO. In addition, the variation rules of the maximum explosion pressure rise rate and the combustion rate are consistent, the order of their values is: Al/PO, Mg/PO, Ti/PO. When I=40%, the maximum explosion pressure rise rate value of the three solid-liquid mixed fuels increases by 41.91%, 39.60% and 45.29%, respectively, compared with the pure PO. The results indicate that different high-energy metal powders have varied advantages in improving the explosion performance of PO, so metal powders should be appropriately selected as energetic additives according to the damage performance index in the formulation design of FAE.
To investigate the influence of typical metal powders on the shock wave effect and thermal damage performance of fuel air explosive (FAE), the explosion characteristics, flame structure and temperature distribution characteristics of epoxypropane (PO) with different types and contents of metal powders were experimentally studied using a 20 L spherical liquid explosion test system. The temperature field of explosion flame was reconstructed by the colorimetric temperature measurement method with a high-speed camera, which is based on the gray-body radiation theory and a self-written python code. The tungsten lamp was used to calibrate the measuring accuracy of the temperature mapping system, and the fitting relationship between the temperatures and the gray values of the high-speed images is derived to obtain the conversion coefficient. The experimental results show that the optimal mass concentration of pure PO was 780 g/m3, both the explosion overpressure (∆pmax) and the explosion pressure rise rate ((dp/dt)max) reached the maximum, ∆pmax=0.799 MPa and (dp/dt)max=52.438 MPa/s, respectively. The maximum explosion overpressure, maximum explosion pressure rise rate and maximum average temperature of PO added with Al, Ti and Mg powders all increase with the increase of mass ratios (I), while the trend of maximum pressure rise time is opposite. The variation rules of the maximum explosion overpressure and maximum average temperature are consistent, the order of their values is: Al/PO, Mg/PO, Ti/PO. When I=40%, the maximum explosion overpressure value of the three solid-liquid mixed fuels increases by 12.00%, 8.41% and 11.54%, respectively, compared with pure PO. In addition, the variation rules of the maximum explosion pressure rise rate and the combustion rate are consistent, the order of their values is: Al/PO, Mg/PO, Ti/PO. When I=40%, the maximum explosion pressure rise rate value of the three solid-liquid mixed fuels increases by 41.91%, 39.60% and 45.29%, respectively, compared with the pure PO. The results indicate that different high-energy metal powders have varied advantages in improving the explosion performance of PO, so metal powders should be appropriately selected as energetic additives according to the damage performance index in the formulation design of FAE.
, Available online ,
doi: 10.11883/bzycj-2023-0438
Abstract:
Heterogeneous media is very common in nature. Due to the complex internal structure, the heterogeneous compressive shear coupled stress field is inside heterogeneous media, which leads to the mutual influence of compression waves and shear waves. The study of wave mechanics behavior and description of heterogeneity in heterogeneous media is of great significance and full of challenges. This article established a general constitutive relationship that reflected the compression shear coupling characteristics of heterogeneous materials, proposed coupling coefficients to describe material heterogeneity, combined momentum conservation law to establish a generalized wave equation, and provided a general method for solving the generalized wave equation. As an example, expressions for the three characteristic wave velocities of compression shear coupling under the first-order compression shear coupling constitutive relationship were provided, and the finite difference method was employed to obtain the propagation process of coupled compression waves and shear waves. The effects of four heterogeneous coupling coefficients on stress state, coupled wave velocity, and wave propagation process were studied. The positive and negative values, as well as the combination of coupling parameters, reflected the structural characteristics of heterogeneous media and also determined the properties of compression shear coupling waves. For heterogeneous media with high-pressure effects, shear dilation effects, and shear weakening effects, the coupled compression wave velocity was lower than the elastic compression wave velocity corresponding to uniform media, and the coupled shear wave velocity was higher than the elastic shear wave velocity. The effect of shear on compression delayed the propagation of compressive stress, while compression promoted the propagation of shear. Coupled compression wave velocity was the result of the competition between the coupling effect of shear on compression and the volume compaction effect. Coupled shear wave velocity was the competition between the coupling effect of compression on shear and the shear weakening effect caused by continuous distortion of the medium. These mechanisms could be achieved through different combinations of compression shear coupling parameters. The true triaxial experimental testing system was used to measure the longitudinal wave velocity of granite, model materials made of mortar, and materials made of cement mortar with coarse aggregates under different compressive and shear stresses. The results indicated that for heterogeneous media, the longitudinal wave velocity decreased with the increase of static water pressure and equivalent shear stress, and the shear expansion effect and shear weakening effect dominated. The experimental results and theoretical results had the same trend. The conclusion of this study was expected to provide a physical mechanism explanation for the phenomenon of the variation of wave velocity with stress state in heterogeneous materials.
Heterogeneous media is very common in nature. Due to the complex internal structure, the heterogeneous compressive shear coupled stress field is inside heterogeneous media, which leads to the mutual influence of compression waves and shear waves. The study of wave mechanics behavior and description of heterogeneity in heterogeneous media is of great significance and full of challenges. This article established a general constitutive relationship that reflected the compression shear coupling characteristics of heterogeneous materials, proposed coupling coefficients to describe material heterogeneity, combined momentum conservation law to establish a generalized wave equation, and provided a general method for solving the generalized wave equation. As an example, expressions for the three characteristic wave velocities of compression shear coupling under the first-order compression shear coupling constitutive relationship were provided, and the finite difference method was employed to obtain the propagation process of coupled compression waves and shear waves. The effects of four heterogeneous coupling coefficients on stress state, coupled wave velocity, and wave propagation process were studied. The positive and negative values, as well as the combination of coupling parameters, reflected the structural characteristics of heterogeneous media and also determined the properties of compression shear coupling waves. For heterogeneous media with high-pressure effects, shear dilation effects, and shear weakening effects, the coupled compression wave velocity was lower than the elastic compression wave velocity corresponding to uniform media, and the coupled shear wave velocity was higher than the elastic shear wave velocity. The effect of shear on compression delayed the propagation of compressive stress, while compression promoted the propagation of shear. Coupled compression wave velocity was the result of the competition between the coupling effect of shear on compression and the volume compaction effect. Coupled shear wave velocity was the competition between the coupling effect of compression on shear and the shear weakening effect caused by continuous distortion of the medium. These mechanisms could be achieved through different combinations of compression shear coupling parameters. The true triaxial experimental testing system was used to measure the longitudinal wave velocity of granite, model materials made of mortar, and materials made of cement mortar with coarse aggregates under different compressive and shear stresses. The results indicated that for heterogeneous media, the longitudinal wave velocity decreased with the increase of static water pressure and equivalent shear stress, and the shear expansion effect and shear weakening effect dominated. The experimental results and theoretical results had the same trend. The conclusion of this study was expected to provide a physical mechanism explanation for the phenomenon of the variation of wave velocity with stress state in heterogeneous materials.
, Available online ,
doi: 10.11883/bzycj-2023-0252
Abstract:
A numerical simulation study is carried out on the overall battle damage circumstances of structures and the residual behavior of fragments after the typical parts of aircraft are attacked by high-speed fragments. An adaptive FEM-SPH coupling simulation method is established by using LS-DYNA software and combining the advantages of Finite Element Method (FEM) and Smoothed Particle Hydrodynamics (SPH). Using this coupling simulation method, the computational model of two typical parts of the aircraft is set up, and the accurate simulation of the core position is realized by a local refinement method of hexahedral FEM grids. Experiments were carried out to verify the numerical model. A series of high-velocity impact (HVI) battle damage simulations are carried out. The debris cloud and crater appearance formed after fragment impacting on structure at high speed under different working conditions are compared, while the residual velocity and mass of the fragment are analyzed. The critical ricochet angles of the fragment on the skin are also determined. The major conclusions are given below. The calculation results of the adaptive FEM-SPH coupling algorithm are in good agreement with the experimental results, and it can simulate fragment HVI damage effectively and precisely. The distribution shape of debris cloud becomes narrow and long with the increase of fragment incident velocity, and the incidence angle can change the shape orientation of debris cloud and crater on the structure. The variation trends of height and spread velocity of debris cloud with incident velocity or angle are basically consistent and linear. The velocity reduction of the fragment does not change with the incident velocity, and the mass reduction is positively correlated with it, both of which are negatively correlated with the incidence angle. The critical ricochet angle of fragment varies almost linearly with the incident velocity. The research results can provide a reference for the damage prediction and rapid maintenance of aircraft after air combat.
A numerical simulation study is carried out on the overall battle damage circumstances of structures and the residual behavior of fragments after the typical parts of aircraft are attacked by high-speed fragments. An adaptive FEM-SPH coupling simulation method is established by using LS-DYNA software and combining the advantages of Finite Element Method (FEM) and Smoothed Particle Hydrodynamics (SPH). Using this coupling simulation method, the computational model of two typical parts of the aircraft is set up, and the accurate simulation of the core position is realized by a local refinement method of hexahedral FEM grids. Experiments were carried out to verify the numerical model. A series of high-velocity impact (HVI) battle damage simulations are carried out. The debris cloud and crater appearance formed after fragment impacting on structure at high speed under different working conditions are compared, while the residual velocity and mass of the fragment are analyzed. The critical ricochet angles of the fragment on the skin are also determined. The major conclusions are given below. The calculation results of the adaptive FEM-SPH coupling algorithm are in good agreement with the experimental results, and it can simulate fragment HVI damage effectively and precisely. The distribution shape of debris cloud becomes narrow and long with the increase of fragment incident velocity, and the incidence angle can change the shape orientation of debris cloud and crater on the structure. The variation trends of height and spread velocity of debris cloud with incident velocity or angle are basically consistent and linear. The velocity reduction of the fragment does not change with the incident velocity, and the mass reduction is positively correlated with it, both of which are negatively correlated with the incidence angle. The critical ricochet angle of fragment varies almost linearly with the incident velocity. The research results can provide a reference for the damage prediction and rapid maintenance of aircraft after air combat.
, Available online ,
doi: 10.11883/bzycj-2023-0440
Abstract:
There is a lack of reliable calculation theory for the transmission and reflection pressures of shock waves at the water-soil interface. Using the mass conservation equation, momentum conservation equation, and the equations of state of water and soil, the Hugoniot relationship and p-u curve of the propagation of shock waves in water and soil medium are derived, and then the transmission and reflection pressures of the shock wave at the water-soil interface can be analyzed theoretically. Two-dimensional numerical models of the free field in water and water-soil layered medium field are established, in which the water and soil parameters are consistent with those in the three-phase medium saturated soil model used in the theoretical derivation. The calculation results show that the theoretical and numerical solutions of the water-soil interface transmission and reflection pressures are highly consistent. When using 80 g TNT explosives and exploding at 0.1–0.9 m from the water-soil interface (proportional burst distance of 0.232–2.089 m/kg1/3), the error of the theoretical and numerical solutions for transmission and reflection pressures is less than 7%, and the coefficient of the reflection pressure is in the range of 1.6–1.8 according to the analytical solution of the reflection pressure and the ratio of the incident pressure in the water. When exploding at 0.5 m from the water-soil interface and the gas content of the saturated soil varies in the range of 0–10%, the transmission and reflection pressures are 63.8–70.0 MPa, and the reflection pressure coefficients are in the range of 1.55–1.70 at this time. The calculation method for the shock wave transmission and reflection pressure at the water-soil interface has a clear physical meaning and high precision and can provide a theoretical basis for the soil damage assessment of engineering structures in submerged soil caused by underwater explosions.
There is a lack of reliable calculation theory for the transmission and reflection pressures of shock waves at the water-soil interface. Using the mass conservation equation, momentum conservation equation, and the equations of state of water and soil, the Hugoniot relationship and p-u curve of the propagation of shock waves in water and soil medium are derived, and then the transmission and reflection pressures of the shock wave at the water-soil interface can be analyzed theoretically. Two-dimensional numerical models of the free field in water and water-soil layered medium field are established, in which the water and soil parameters are consistent with those in the three-phase medium saturated soil model used in the theoretical derivation. The calculation results show that the theoretical and numerical solutions of the water-soil interface transmission and reflection pressures are highly consistent. When using 80 g TNT explosives and exploding at 0.1–0.9 m from the water-soil interface (proportional burst distance of 0.232–2.089 m/kg1/3), the error of the theoretical and numerical solutions for transmission and reflection pressures is less than 7%, and the coefficient of the reflection pressure is in the range of 1.6–1.8 according to the analytical solution of the reflection pressure and the ratio of the incident pressure in the water. When exploding at 0.5 m from the water-soil interface and the gas content of the saturated soil varies in the range of 0–10%, the transmission and reflection pressures are 63.8–70.0 MPa, and the reflection pressure coefficients are in the range of 1.55–1.70 at this time. The calculation method for the shock wave transmission and reflection pressure at the water-soil interface has a clear physical meaning and high precision and can provide a theoretical basis for the soil damage assessment of engineering structures in submerged soil caused by underwater explosions.
, Available online ,
doi: 10.11883/bzycj-2023-0424
Abstract:
In order to investigate the dynamic compression behavior of carbon nanotubes reinforced concrete under impact loading, the impact compression tests were carried out by using a split Hopkinson pressure bar (SHPB) test device with a diameter of 100 mm. The impact velocities in the SHPB tests were about 6.8, 7.8, 8.8, 9.8 and 10.8 m/s, respectively. The contents of carbon nanotubes in concrete (as a percentage of cement mass) were 0% (i.e. ordinary concrete, as a baseline of comparison), 0.10%, 0.20%, 0.30% and 0.40%, respectively. Then, based on the test results, the evolution laws of dynamic compressive strength, compression deformation, and energy dissipation characteristics of concrete under different impact velocities and carbon nanotubes contents were compared and analyzed. The experimental results show that the dynamic strength characteristics of carbon nanotubes reinforced concrete have significant loading rate sensitivity. The dynamic compressive strength and dynamic enhancement factor show linear positive correlations with impact velocity. When the loading level remains the same, the dynamic compressive strength increases first and then decreases slightly with the increase of carbon nanotubes content, and the growth rate can reach 23.7% compared to ordinary concrete. The variation characteristics of ultimate strain and impact toughness of carbon nanotubes reinforced concrete are similar, which gradually increase with the increase of impact velocity, and have a certain impact velocity strengthening effect, but there is no obvious linear relationship with the impact velocity. Toughness is a comprehensive reflection of material strength and deformation. Therefore, at the same loading level, when the content of carbon nanotubes was 0.30%, the impact toughness of concrete achieved a relative maximum, being about 10% higher than that of ordinary concrete. The appropriate addition of carbon nanotubes can effectively enhance the integrity and compactness of the internal structure of concrete, thereby improving its dynamic mechanical properties and energy dissipation performance.
In order to investigate the dynamic compression behavior of carbon nanotubes reinforced concrete under impact loading, the impact compression tests were carried out by using a split Hopkinson pressure bar (SHPB) test device with a diameter of 100 mm. The impact velocities in the SHPB tests were about 6.8, 7.8, 8.8, 9.8 and 10.8 m/s, respectively. The contents of carbon nanotubes in concrete (as a percentage of cement mass) were 0% (i.e. ordinary concrete, as a baseline of comparison), 0.10%, 0.20%, 0.30% and 0.40%, respectively. Then, based on the test results, the evolution laws of dynamic compressive strength, compression deformation, and energy dissipation characteristics of concrete under different impact velocities and carbon nanotubes contents were compared and analyzed. The experimental results show that the dynamic strength characteristics of carbon nanotubes reinforced concrete have significant loading rate sensitivity. The dynamic compressive strength and dynamic enhancement factor show linear positive correlations with impact velocity. When the loading level remains the same, the dynamic compressive strength increases first and then decreases slightly with the increase of carbon nanotubes content, and the growth rate can reach 23.7% compared to ordinary concrete. The variation characteristics of ultimate strain and impact toughness of carbon nanotubes reinforced concrete are similar, which gradually increase with the increase of impact velocity, and have a certain impact velocity strengthening effect, but there is no obvious linear relationship with the impact velocity. Toughness is a comprehensive reflection of material strength and deformation. Therefore, at the same loading level, when the content of carbon nanotubes was 0.30%, the impact toughness of concrete achieved a relative maximum, being about 10% higher than that of ordinary concrete. The appropriate addition of carbon nanotubes can effectively enhance the integrity and compactness of the internal structure of concrete, thereby improving its dynamic mechanical properties and energy dissipation performance.
, Available online ,
doi: 10.11883/bzycj-2023-0380
Abstract:
The stress-strain data obtained from split Hopkinson pressure bar (SHPB) tests include both strain rate effects and structural effects, where the structural effects result in non-uniform stress in the elastic phase of the stress-strain curve. The elastic phase is a critical focus of study for materials like concrete with low sound velocity or certain metals under high strain rate loading conditions. In this paper, we focus on one-dimensional rod systems and employ one-dimensional elastic incremental wave theory to derive analytical expressions for stress-strain curves and Young’s modulus under one-dimensional stress wave conditions with linear incident waves. We investigate the effects and mechanisms of stress difference and velocity difference at both ends of the specimen on the accuracy of stress-strain curves and Young’s modulus. Furthermore, we provide a method for determining stress-strain curves and tangent Young’s modulus during the elastic phase for arbitrary incident waveforms. We analyze the influence of the incident wave slope and shape characteristics on the stress uniformity in specimens and stress-strain curves. We establish the inherent relationship between stress uniformity and experimental stress-strain curves, and clarify the relative accuracy and applicability conditions of tangent modulus and secant modulus. The results indicate that stress uniformity is a key factor affecting the accuracy of stress-strain curves and Young’s modulus. However, the accuracy of Young’s modulus is not solely dependent on the change in stress difference at both ends of the specimen; it is also related to the factors such as the incident wave slope, shape characteristics, and the elastic segment range of the specimen. An increase in the linear wave slope leads to a greater difference between the tangent modulus and the secant modulus from the actual values. For larger slopes, the accuracy of the secant modulus is higher than that of the tangent modulus. When the incident wave shape is considered as a reference, curves with low initial slopes, such as sine waves, have higher accuracy for the tangent modulus compared to the secant modulus, whereas curves with high initial slopes show the opposite trend. For concrete specimens, we verify the influence of incident wave slope on Young’s modulus and evaluate the maximum incident wave slopes for concrete specimens to reach accurate values, which are 0.128 MPa/μs for the tangent modulus and 0.319 MPa/μs for the secant modulus.
The stress-strain data obtained from split Hopkinson pressure bar (SHPB) tests include both strain rate effects and structural effects, where the structural effects result in non-uniform stress in the elastic phase of the stress-strain curve. The elastic phase is a critical focus of study for materials like concrete with low sound velocity or certain metals under high strain rate loading conditions. In this paper, we focus on one-dimensional rod systems and employ one-dimensional elastic incremental wave theory to derive analytical expressions for stress-strain curves and Young’s modulus under one-dimensional stress wave conditions with linear incident waves. We investigate the effects and mechanisms of stress difference and velocity difference at both ends of the specimen on the accuracy of stress-strain curves and Young’s modulus. Furthermore, we provide a method for determining stress-strain curves and tangent Young’s modulus during the elastic phase for arbitrary incident waveforms. We analyze the influence of the incident wave slope and shape characteristics on the stress uniformity in specimens and stress-strain curves. We establish the inherent relationship between stress uniformity and experimental stress-strain curves, and clarify the relative accuracy and applicability conditions of tangent modulus and secant modulus. The results indicate that stress uniformity is a key factor affecting the accuracy of stress-strain curves and Young’s modulus. However, the accuracy of Young’s modulus is not solely dependent on the change in stress difference at both ends of the specimen; it is also related to the factors such as the incident wave slope, shape characteristics, and the elastic segment range of the specimen. An increase in the linear wave slope leads to a greater difference between the tangent modulus and the secant modulus from the actual values. For larger slopes, the accuracy of the secant modulus is higher than that of the tangent modulus. When the incident wave shape is considered as a reference, curves with low initial slopes, such as sine waves, have higher accuracy for the tangent modulus compared to the secant modulus, whereas curves with high initial slopes show the opposite trend. For concrete specimens, we verify the influence of incident wave slope on Young’s modulus and evaluate the maximum incident wave slopes for concrete specimens to reach accurate values, which are 0.128 MPa/μs for the tangent modulus and 0.319 MPa/μs for the secant modulus.
, Available online ,
doi: 10.11883/bzycj-2023-0365
Abstract:
Solid mediums, like rocks, concretes, shells and porous materials, etc., has the characteristics of microscopic discontinuity and macroscopic continuity. It is of great significance for material design, safety protection and other fields to reveal the influence of the meso-discontinuity on the dynamic response of the material. In this paper, based on the generalized Taylor’s formula under fractional definition, the governing equation of 1-D wave propagation in discontinuous medium is derived. Equivalent fractional order is introduced and the simplified form of the governing equation is presented for easily calculating. By using the finite difference method, the numerical solution of the governing equation is obtained. The influence of equivalent fractional order on wave propagation are analyzed. By the time domain analysis, the smaller the equivalent fractional order, the greater the degree of attenuation of the calculated waveform. By the frequency domain analysis, both high frequency wave and low frequency wave exhibit attenuation, and the attenuation of high frequency wave is higher than that of low frequency wave, which makes the pulse duration of the wave being larger. It is obvious that the equivalent fractional order has a certain relationship with the spatial structure of discontinuous medium. Based on the structural characteristics of some meso-discontinuous medium, e.g., porous materials and rocks, a randomly distributed pores model is established by using ABAQUS to verify the reliability of the governing equation and study the wave propagation of meso-discontinuous medium. The effects of porosity, material properties and input waves on wave propagation are analyzed. The degree of wave attenuation is positively related to the porosity of the medium, and negatively related to the wave velocity and the pulse duration of input wave. However, the equivalent fractional order is only related to the porosity and pore distribution of the discontinuous medium. When the spatial structure of the discontinuous medium remains unchanged, the corresponding equivalent fractional order does not change with the material property and the pulse duration of the input wave. By the randomly distributed pores model with various porosities, it is found that the equivalent fractional order decreases with the increase of porosity. Under the same porosity, the heterogeneity of pore distribution will result in different waveforms, while with the increase of porosity, this difference becomes more obvious, but the corresponding equivalent fractional order only has little difference. The statistical relation between equivalent fractional order and porosity is approximately linear when the pore distribution is almost the same. Compared with the randomly distributed pores medium, the statistical relation between equivalent fractional order and porosity of discontinuous medium with uniform distribution of different porosity shifts upward, indicating that the attenuation effect of random structure on wave is higher than that of uniform structure. This paper provides a new approach to investigate wave propagation in meso-discontinuous medium such as porous materials, rocks, shells, etc. It can be used as a basis to evaluate the dynamic response of discontinuous medium.
Solid mediums, like rocks, concretes, shells and porous materials, etc., has the characteristics of microscopic discontinuity and macroscopic continuity. It is of great significance for material design, safety protection and other fields to reveal the influence of the meso-discontinuity on the dynamic response of the material. In this paper, based on the generalized Taylor’s formula under fractional definition, the governing equation of 1-D wave propagation in discontinuous medium is derived. Equivalent fractional order is introduced and the simplified form of the governing equation is presented for easily calculating. By using the finite difference method, the numerical solution of the governing equation is obtained. The influence of equivalent fractional order on wave propagation are analyzed. By the time domain analysis, the smaller the equivalent fractional order, the greater the degree of attenuation of the calculated waveform. By the frequency domain analysis, both high frequency wave and low frequency wave exhibit attenuation, and the attenuation of high frequency wave is higher than that of low frequency wave, which makes the pulse duration of the wave being larger. It is obvious that the equivalent fractional order has a certain relationship with the spatial structure of discontinuous medium. Based on the structural characteristics of some meso-discontinuous medium, e.g., porous materials and rocks, a randomly distributed pores model is established by using ABAQUS to verify the reliability of the governing equation and study the wave propagation of meso-discontinuous medium. The effects of porosity, material properties and input waves on wave propagation are analyzed. The degree of wave attenuation is positively related to the porosity of the medium, and negatively related to the wave velocity and the pulse duration of input wave. However, the equivalent fractional order is only related to the porosity and pore distribution of the discontinuous medium. When the spatial structure of the discontinuous medium remains unchanged, the corresponding equivalent fractional order does not change with the material property and the pulse duration of the input wave. By the randomly distributed pores model with various porosities, it is found that the equivalent fractional order decreases with the increase of porosity. Under the same porosity, the heterogeneity of pore distribution will result in different waveforms, while with the increase of porosity, this difference becomes more obvious, but the corresponding equivalent fractional order only has little difference. The statistical relation between equivalent fractional order and porosity is approximately linear when the pore distribution is almost the same. Compared with the randomly distributed pores medium, the statistical relation between equivalent fractional order and porosity of discontinuous medium with uniform distribution of different porosity shifts upward, indicating that the attenuation effect of random structure on wave is higher than that of uniform structure. This paper provides a new approach to investigate wave propagation in meso-discontinuous medium such as porous materials, rocks, shells, etc. It can be used as a basis to evaluate the dynamic response of discontinuous medium.
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2024, 44(8): 081401.
doi: 10.11883/bzycj-2024-0233
Abstract:
2024, 44(8): 081402.
doi: 10.11883/bzycj-2024-0000
Abstract:
2024, 44(8): 081411.
doi: 10.11883/bzycj-2024-0086
Abstract:
Cellular materials are structures with a large number of internal cavities and cells, which have the properties of lightweight and high specific energy absorption, and they are widely used in the collision/explosion protection, such as aerospace, transportation, and human protection. Introducing a gradient design to cellular materials helps the materials to meet the protection requirements in different scenarios and conditions with the properties of orderly dissipation of energy and manipulation of loads. A review of research advances in the dynamic analysis and design on mechanical behavior of graded cellular materials is presented. Three cases of the applications of graded cellular materials/structures, i.e., impact resistance, blast resistance, and blast-mimicking loading, are elaborated. Firstly, graded cellular materials are briefly described from various aspects, such as natural vs. artificial, layered vs. continuous, strength gradient vs. density gradient, and conventional manufacturing vs. additive manufacturing. The studies of the deformation characteristics, shock wave models, and protective properties of graded cellular materials under dynamic loading are then reviewed systematically. A competitive mechanism of density/strength gradients and inertial effects exists in graded cellular materials to synergistically modulate collapse deformation modes. According to the stress-strain curve characteristics of cellular materials, choosing the appropriate constitutive model could increase the characterization accuracy for its dynamic mechanical behavior. Secondly, the shock wave models are used as a mechanical tool to guide the design of graded cellular materials/structures. Some strategies are elaborated, such as the backward design of graded cellular materials for impact resistance, the design of several types of anti-blast sandwich structures, and the design of blast-load simulators with the projectile-beam coupling effect being taken into account. The optimal protection effect or precise load control had been realized efficiently, which provides a theoretical basis and technical support for the protection design and rapid evaluation of impact/explosion resistance structures. Finally, for the applications in the scenarios of extreme environmental loading, large energy impacts, and strong nonlinear load manipulation, the investigations of graded cellular materials are full of challenges and expectation.
Cellular materials are structures with a large number of internal cavities and cells, which have the properties of lightweight and high specific energy absorption, and they are widely used in the collision/explosion protection, such as aerospace, transportation, and human protection. Introducing a gradient design to cellular materials helps the materials to meet the protection requirements in different scenarios and conditions with the properties of orderly dissipation of energy and manipulation of loads. A review of research advances in the dynamic analysis and design on mechanical behavior of graded cellular materials is presented. Three cases of the applications of graded cellular materials/structures, i.e., impact resistance, blast resistance, and blast-mimicking loading, are elaborated. Firstly, graded cellular materials are briefly described from various aspects, such as natural vs. artificial, layered vs. continuous, strength gradient vs. density gradient, and conventional manufacturing vs. additive manufacturing. The studies of the deformation characteristics, shock wave models, and protective properties of graded cellular materials under dynamic loading are then reviewed systematically. A competitive mechanism of density/strength gradients and inertial effects exists in graded cellular materials to synergistically modulate collapse deformation modes. According to the stress-strain curve characteristics of cellular materials, choosing the appropriate constitutive model could increase the characterization accuracy for its dynamic mechanical behavior. Secondly, the shock wave models are used as a mechanical tool to guide the design of graded cellular materials/structures. Some strategies are elaborated, such as the backward design of graded cellular materials for impact resistance, the design of several types of anti-blast sandwich structures, and the design of blast-load simulators with the projectile-beam coupling effect being taken into account. The optimal protection effect or precise load control had been realized efficiently, which provides a theoretical basis and technical support for the protection design and rapid evaluation of impact/explosion resistance structures. Finally, for the applications in the scenarios of extreme environmental loading, large energy impacts, and strong nonlinear load manipulation, the investigations of graded cellular materials are full of challenges and expectation.
2024, 44(8): 081421.
doi: 10.11883/bzycj-2023-0437
Abstract:
To study the thermal relaxation behavior of graded media that satisfies the power law, a one-dimensional hyperbolic non-Fourier heat conduction equation of the graded material which satisfies the power law was derived from the Cattaneo-Vernotte linear hyperbolic heat transfer equation with the thermal relaxation coefficient and graded exponent induced. The equation was first treated dimensionless. Based on the Laplace transformation, the new heat conduction equation was found to conform to the general form of the Bessel equation called the Lommel equation in the frequency domain, and the Bessel series solution of the temperature field in the frequency domain was obtained. With the asymptotic expansion of the Bessel series, a simplified expression of the temperature field in the frequency domain containing trigonometric function was obtained. The inverse Laplace transformation of the temperature field in the frequency domain was employed to get the first analytical solution of the temperature field in the time domain. Besides the first analytical solution, the new heat conduction equation in the frequency domain was simplified to the Euler equation, and the second kind of analytical solution was obtained by the pole residue method. The second analytical solution exhibits similar fluctuation attenuation and diffusion features, and both the waveform and response time are sensitive to the relaxation time coefficient. However, the second kind of analytical solution differs from the first kind of solution in terms of waveform elements which are highly related to the graded structure. The accuracy of the analytical result is verified by numerical calculation. Taking Mo-ZrC graded composite as an example, the thermal relaxation behavior of graded material that satisfies power law under the first kind of temperature boundary and temperature pulse loading are discussed in detail. The temperature field shows both fluctuation attenuation and conduction characteristics. With the increase of the thermal relaxation coefficient, the response time and temperature wave amplitude increase, the unit waveform develops from a trapezoidal wave to a rectangular wave, and the oscillation approaching the boundary shows an obvious bias.
To study the thermal relaxation behavior of graded media that satisfies the power law, a one-dimensional hyperbolic non-Fourier heat conduction equation of the graded material which satisfies the power law was derived from the Cattaneo-Vernotte linear hyperbolic heat transfer equation with the thermal relaxation coefficient and graded exponent induced. The equation was first treated dimensionless. Based on the Laplace transformation, the new heat conduction equation was found to conform to the general form of the Bessel equation called the Lommel equation in the frequency domain, and the Bessel series solution of the temperature field in the frequency domain was obtained. With the asymptotic expansion of the Bessel series, a simplified expression of the temperature field in the frequency domain containing trigonometric function was obtained. The inverse Laplace transformation of the temperature field in the frequency domain was employed to get the first analytical solution of the temperature field in the time domain. Besides the first analytical solution, the new heat conduction equation in the frequency domain was simplified to the Euler equation, and the second kind of analytical solution was obtained by the pole residue method. The second analytical solution exhibits similar fluctuation attenuation and diffusion features, and both the waveform and response time are sensitive to the relaxation time coefficient. However, the second kind of analytical solution differs from the first kind of solution in terms of waveform elements which are highly related to the graded structure. The accuracy of the analytical result is verified by numerical calculation. Taking Mo-ZrC graded composite as an example, the thermal relaxation behavior of graded material that satisfies power law under the first kind of temperature boundary and temperature pulse loading are discussed in detail. The temperature field shows both fluctuation attenuation and conduction characteristics. With the increase of the thermal relaxation coefficient, the response time and temperature wave amplitude increase, the unit waveform develops from a trapezoidal wave to a rectangular wave, and the oscillation approaching the boundary shows an obvious bias.
2024, 44(8): 081422.
doi: 10.11883/bzycj-2023-0469
Abstract:
The diffusion behavior of shear instability control under dynamic load is the inducement for the development of local large deformation and the deterioration of macroscopic mechanical properties of rock. Firstly, the energy function of the unstable interface was established; and then based on the generalized variational principle, the interface disturbance analysis was carried out, while the first and second-order variances of the function were taken into consideration. Thus the governing equation of dynamic instability of the interface under shear load was established. Based on the discriminant equation, the influence of shear force and dynamic effect on the angle of the unstable interface is obtained. The results show that the angle of the shear deformation zone increases to a certain extent with the increase of external shear force. With the increase of the local dynamic coefficient, that is, the increase of the local inertial force, the shear band angle decreases obviously. By solving the diffusion equation with the edge displacement, the analytical expression of displacement was obtained, showing that the displacement increases gradually with the increase of loading time. To verify the reliability of the theoretical model and further study the deformation behavior of interface instability and its influence on wave propagation, the evolution of the fine and microscopic morphology of the contact surface during dynamic shear was described by combining with the SHPB rod-beam experiment technique, and an evaluation method for the influence of the evolution of surface contact parameters on mechanical parameters during interface instability was proposed. The numerical analysis model was established, and its result shows that interface instability is the leading condition of local shear failure slip. With the increase of interface thickness and shear force, the local displacement increases. The interfacial shear diffusion behavior greatly reduces the amplitude and changes the frequency of the transmitted wave. This study provides a good theoretical reference for the study of localization deformation and dynamic strength of rocks.
The diffusion behavior of shear instability control under dynamic load is the inducement for the development of local large deformation and the deterioration of macroscopic mechanical properties of rock. Firstly, the energy function of the unstable interface was established; and then based on the generalized variational principle, the interface disturbance analysis was carried out, while the first and second-order variances of the function were taken into consideration. Thus the governing equation of dynamic instability of the interface under shear load was established. Based on the discriminant equation, the influence of shear force and dynamic effect on the angle of the unstable interface is obtained. The results show that the angle of the shear deformation zone increases to a certain extent with the increase of external shear force. With the increase of the local dynamic coefficient, that is, the increase of the local inertial force, the shear band angle decreases obviously. By solving the diffusion equation with the edge displacement, the analytical expression of displacement was obtained, showing that the displacement increases gradually with the increase of loading time. To verify the reliability of the theoretical model and further study the deformation behavior of interface instability and its influence on wave propagation, the evolution of the fine and microscopic morphology of the contact surface during dynamic shear was described by combining with the SHPB rod-beam experiment technique, and an evaluation method for the influence of the evolution of surface contact parameters on mechanical parameters during interface instability was proposed. The numerical analysis model was established, and its result shows that interface instability is the leading condition of local shear failure slip. With the increase of interface thickness and shear force, the local displacement increases. The interfacial shear diffusion behavior greatly reduces the amplitude and changes the frequency of the transmitted wave. This study provides a good theoretical reference for the study of localization deformation and dynamic strength of rocks.
2024, 44(8): 081423.
doi: 10.11883/bzycj-2023-0454
Abstract:
The scattering of seismic waves by shallow-buried underground structures has significant theoretical value in the engineering field. However, previous studies have mainly focused on the case of plane waves or the case of complete bonding between lining and surrounding rock, with little consideration of the effects of source distance and non-complete bonding between lining and surrounding rock. In order to deepen the understanding of the influence of source distance and non-complete bonding on seismic wave scattering, the series solution of the dynamic response of shallow-buried circular non-complete bonded tunnels under the loading of anti-plane line source was derived based on the displacement discontinuity model, wave function expansion method, Graf formula and mirror method. The accuracy of the obtained solution was verified by the relationship between the residuals of the inner and outer boundary conditions of the lining and the number of truncated terms in the series solution. By systematically analyzing the parameters of this series solution, the influence of factors such as the contact stiffness between lining and surrounding rock, lining modulus, lining thickness, tunnel depth and source distance on the displacement and circumferential shear stress on the inner surface of the lining was discussed. The results show that the contact stiffness between lining and surrounding rock has a significant influence on the dynamic response of the tunnel, especially in cases with relatively low contact stiffness, where the amplitude of the dynamic response of the tunnel can be very large. Increasing the lining modulus reduces the displacement but increases the circumferential shear stress. Increasing the lining thickness can simultaneously reduce the displacement and circumferential shear stress. As the tunnel depth increases, the maximum displacement and circumferential shear stress on the inner surface of the lining shifts towards the apex of the tunnel. Increasing the horizontal distance between the line source and the tunnel increases the relative amplitude of the tunnel's back wave side.
The scattering of seismic waves by shallow-buried underground structures has significant theoretical value in the engineering field. However, previous studies have mainly focused on the case of plane waves or the case of complete bonding between lining and surrounding rock, with little consideration of the effects of source distance and non-complete bonding between lining and surrounding rock. In order to deepen the understanding of the influence of source distance and non-complete bonding on seismic wave scattering, the series solution of the dynamic response of shallow-buried circular non-complete bonded tunnels under the loading of anti-plane line source was derived based on the displacement discontinuity model, wave function expansion method, Graf formula and mirror method. The accuracy of the obtained solution was verified by the relationship between the residuals of the inner and outer boundary conditions of the lining and the number of truncated terms in the series solution. By systematically analyzing the parameters of this series solution, the influence of factors such as the contact stiffness between lining and surrounding rock, lining modulus, lining thickness, tunnel depth and source distance on the displacement and circumferential shear stress on the inner surface of the lining was discussed. The results show that the contact stiffness between lining and surrounding rock has a significant influence on the dynamic response of the tunnel, especially in cases with relatively low contact stiffness, where the amplitude of the dynamic response of the tunnel can be very large. Increasing the lining modulus reduces the displacement but increases the circumferential shear stress. Increasing the lining thickness can simultaneously reduce the displacement and circumferential shear stress. As the tunnel depth increases, the maximum displacement and circumferential shear stress on the inner surface of the lining shifts towards the apex of the tunnel. Increasing the horizontal distance between the line source and the tunnel increases the relative amplitude of the tunnel's back wave side.
2024, 44(8): 081431.
doi: 10.11883/bzycj-2024-0004
Abstract:
A 1D SPH (smoothed particle hydrodynamics) and approximate HLLC (Harten-Lax-van Leer-contact) Riemann solver coupled method for elastic-perfectly plastic model is proposed through elastic and plastic wave analysis. In SPH simulations, each particle pair in the supporting domain generates a Riemann problem, whose solutions are substituted into governing equations. The philosophy of HLLC approximate Riemann solver is to divide the procedure into three steps: assume the whole state in elastic deformation and compute Riemann problem, and then reconstruct flux under von Mises yielding conditions and compute the final HLLC Riemann solution with reconstructed fluxes. We compare the new SPH-HLLC method with the traditional SPH method in several numerical tests, which show that this method can effectively simulate collision and reflected rarefaction waves between the materials, and it can profoundly suppress oscillations of pressure and deviatoric stress at contact interface between different materials, which the traditional SPH method finds difficult to realize. Moreover, the new SPH-HLLC scheme shows better energy performance than the traditional SPH method in 2D test case where initial kinetic energy is successfully transformed into internal energy with new SPH-HLLC scheme while total energy significantly decreases with time using the traditional SPH method.
A 1D SPH (smoothed particle hydrodynamics) and approximate HLLC (Harten-Lax-van Leer-contact) Riemann solver coupled method for elastic-perfectly plastic model is proposed through elastic and plastic wave analysis. In SPH simulations, each particle pair in the supporting domain generates a Riemann problem, whose solutions are substituted into governing equations. The philosophy of HLLC approximate Riemann solver is to divide the procedure into three steps: assume the whole state in elastic deformation and compute Riemann problem, and then reconstruct flux under von Mises yielding conditions and compute the final HLLC Riemann solution with reconstructed fluxes. We compare the new SPH-HLLC method with the traditional SPH method in several numerical tests, which show that this method can effectively simulate collision and reflected rarefaction waves between the materials, and it can profoundly suppress oscillations of pressure and deviatoric stress at contact interface between different materials, which the traditional SPH method finds difficult to realize. Moreover, the new SPH-HLLC scheme shows better energy performance than the traditional SPH method in 2D test case where initial kinetic energy is successfully transformed into internal energy with new SPH-HLLC scheme while total energy significantly decreases with time using the traditional SPH method.
2024, 44(8): 081432.
doi: 10.11883/bzycj-2024-0026
Abstract:
To investigate the wound effectiveness of cross-medium bullets, gelatin is chosen as a simulated human target. The numerical simulation of the penetration process of the designed 7.62 mm multi-environment bullet into the simulated target is conducted using LS-DYNA software. The motion of the bullet and the changes in the target cavity are analyzed. By utilizing a three-degree-of-freedom rigid body motion model, the theoretical variations of bullet motion are obtained. In the same time, the penetration experiment was carried out by using multi-parameter synchronous measurement techniques. The results show that the numerical simulation agrees well with the experimental observations, effectively reproducing the penetration process and the wound effects of the multi-environment bullet. The theoretical model exhibits small errors compared to the experimental results but accurately predicts the motion characteristics of the bullet in the target. By employing a cavity structure, the stability of the bullet's motion across different media is improved. Compared to the traditional 56-type 7.62 mm rifle bullet, the designed bullet demonstrates longer stable flight time, greater distance, slower velocity decay, smaller deflection angle during tumbling phase, and comparable maximum cavity, permanent cavity, and energy transfer efficiency. It also exhibits a certain killing effect on the target. The research findings enrich the design theory of bullets and provide data support for the optimization design of new lightweight ammunition.
To investigate the wound effectiveness of cross-medium bullets, gelatin is chosen as a simulated human target. The numerical simulation of the penetration process of the designed 7.62 mm multi-environment bullet into the simulated target is conducted using LS-DYNA software. The motion of the bullet and the changes in the target cavity are analyzed. By utilizing a three-degree-of-freedom rigid body motion model, the theoretical variations of bullet motion are obtained. In the same time, the penetration experiment was carried out by using multi-parameter synchronous measurement techniques. The results show that the numerical simulation agrees well with the experimental observations, effectively reproducing the penetration process and the wound effects of the multi-environment bullet. The theoretical model exhibits small errors compared to the experimental results but accurately predicts the motion characteristics of the bullet in the target. By employing a cavity structure, the stability of the bullet's motion across different media is improved. Compared to the traditional 56-type 7.62 mm rifle bullet, the designed bullet demonstrates longer stable flight time, greater distance, slower velocity decay, smaller deflection angle during tumbling phase, and comparable maximum cavity, permanent cavity, and energy transfer efficiency. It also exhibits a certain killing effect on the target. The research findings enrich the design theory of bullets and provide data support for the optimization design of new lightweight ammunition.
2024, 44(8): 081433.
doi: 10.11883/bzycj-2023-0470
Abstract:
The wave propagation and pressure distribution during the interaction between long duration blast waves and structures are important foundations for the large scale explosion protection design and safety assessment. In order to understand the interaction mechanism between long duration blast waves and cylindrical shells, as well as the distribution law of the surface load on the cylindrical shells under their action, the overpressure histories on the cylindrical structure surface were obtained through the 150 ms long duration blast wave shock tube experiment, and the shock wave evolution and the pressure load distribution were investigated numerically using the large eddy simulation and hybrid WENO-TCD (weighted essentially non-oscillatory-tuned centered difference) method. The results show that the overpressure load of the calculation results is in good agreement with the experimental results, and the overpressure load on the cylindrical shell appears a clear angle and height correlation. The pressure on the back shell is higher than that on the side surface or even comparable to the blast on the facing surface, which exhibit different pressure attenuation modes from the traditional short duration blast wave propagation. The sudden expansion on the side surface is the main reason for the initial oscillation of pressure, and has a lower pressure than that at the windward and leeward sides. On the other hand, a series of diffracted shock waves collides and reflects on the symmetry plane of the shell leeward, as well as the stationary and superimposed effects of the series of decelerating shock waves near the 135° phase, which are the main mechanisms that cause the overall increase of the pressure load on the cylindrical shell. In addition, the formation and evolution of wake vortex structures on the leeward side due to the boundary effects is a key factor leading to differences in the load distribution along the height direction. The above analysis methods and related results lay the foundation for the subsequent study of load distribution models for typical structural components under long duration blast waves.
The wave propagation and pressure distribution during the interaction between long duration blast waves and structures are important foundations for the large scale explosion protection design and safety assessment. In order to understand the interaction mechanism between long duration blast waves and cylindrical shells, as well as the distribution law of the surface load on the cylindrical shells under their action, the overpressure histories on the cylindrical structure surface were obtained through the 150 ms long duration blast wave shock tube experiment, and the shock wave evolution and the pressure load distribution were investigated numerically using the large eddy simulation and hybrid WENO-TCD (weighted essentially non-oscillatory-tuned centered difference) method. The results show that the overpressure load of the calculation results is in good agreement with the experimental results, and the overpressure load on the cylindrical shell appears a clear angle and height correlation. The pressure on the back shell is higher than that on the side surface or even comparable to the blast on the facing surface, which exhibit different pressure attenuation modes from the traditional short duration blast wave propagation. The sudden expansion on the side surface is the main reason for the initial oscillation of pressure, and has a lower pressure than that at the windward and leeward sides. On the other hand, a series of diffracted shock waves collides and reflects on the symmetry plane of the shell leeward, as well as the stationary and superimposed effects of the series of decelerating shock waves near the 135° phase, which are the main mechanisms that cause the overall increase of the pressure load on the cylindrical shell. In addition, the formation and evolution of wake vortex structures on the leeward side due to the boundary effects is a key factor leading to differences in the load distribution along the height direction. The above analysis methods and related results lay the foundation for the subsequent study of load distribution models for typical structural components under long duration blast waves.
2024, 44(8): 081441.
doi: 10.11883/bzycj-2023-0389
Abstract:
The reflected and transmitted waves in split Hopkinson pressure bar (SHPB) tests provide crucial information for obtaining the stress-strain relationship of materials. Accurately analyzing the formation process and influencing mechanisms of the reflected and incident waves is a key prerequisite for precise experimental design and accurate data processing. In this paper, the propagation and evolution of one-dimensional elastic-plastic waves in the loading stages of the SHPB test are presented particularly for a sandwich bar system consisting of the incident wave, specimen, and transmitted bar. Based on the theory of elastic-plastic incremental waves and numerical simulation calculations, the propagation of elastic-plastic waves in the specimen, the transmission and reflection of elastic-plastic waves at the two interfaces, and the interaction of the resulting series of transmitted and reflected waves are quantitatively investigated. The research findings are as follows. Firstly, although the design principle of the SHPB apparatus is based on linear elastic wave theory, the elastic-plastic waves, especially the stress waves, have a major influence on the transmission and reflection at the elastic-plastic interface, while the transmission and propagation of purely elastic waves have a relatively minor effect. Secondly, when the loading interval of the incident wave has a certain width, the multiple transmission and reflection of elastic waves at the two interfaces in bar 2 attenuate the reflected wave while further strengthening the transmitted wave. This attenuation causes the peak of the reflected wave for the half-sine wave to occur earlier than at 0.5 nondimensional time. Thirdly, in contrary to the preliminary laws of elastic wave transmission and reflection at interfaces in traditional SHPB analysis, variations in the Young’s modulus and density of the specimen material have little effect on the waveform and peak intensity of the transmitted wave, regardless of whether the incident wave is rectangular, trapezoidal, or half-sine. This investigationprovides a scientific basis for the refined design of SHPB experiments and precise analysis of data.
The reflected and transmitted waves in split Hopkinson pressure bar (SHPB) tests provide crucial information for obtaining the stress-strain relationship of materials. Accurately analyzing the formation process and influencing mechanisms of the reflected and incident waves is a key prerequisite for precise experimental design and accurate data processing. In this paper, the propagation and evolution of one-dimensional elastic-plastic waves in the loading stages of the SHPB test are presented particularly for a sandwich bar system consisting of the incident wave, specimen, and transmitted bar. Based on the theory of elastic-plastic incremental waves and numerical simulation calculations, the propagation of elastic-plastic waves in the specimen, the transmission and reflection of elastic-plastic waves at the two interfaces, and the interaction of the resulting series of transmitted and reflected waves are quantitatively investigated. The research findings are as follows. Firstly, although the design principle of the SHPB apparatus is based on linear elastic wave theory, the elastic-plastic waves, especially the stress waves, have a major influence on the transmission and reflection at the elastic-plastic interface, while the transmission and propagation of purely elastic waves have a relatively minor effect. Secondly, when the loading interval of the incident wave has a certain width, the multiple transmission and reflection of elastic waves at the two interfaces in bar 2 attenuate the reflected wave while further strengthening the transmitted wave. This attenuation causes the peak of the reflected wave for the half-sine wave to occur earlier than at 0.5 nondimensional time. Thirdly, in contrary to the preliminary laws of elastic wave transmission and reflection at interfaces in traditional SHPB analysis, variations in the Young’s modulus and density of the specimen material have little effect on the waveform and peak intensity of the transmitted wave, regardless of whether the incident wave is rectangular, trapezoidal, or half-sine. This investigationprovides a scientific basis for the refined design of SHPB experiments and precise analysis of data.
2024, 44(8): 081442.
doi: 10.11883/bzycj-2023-0392
Abstract:
Compared to the reflection and transmission analysis process during the incident wave loading phase, the incident wave plateau phase lasts longer, and the elastic-plastic propagation and evolution behavior are much more complex. The effects of elastic-plastic wave interactions within the specimen during this phase are very pronounced. Using the elastic-plastic incremental wave theory, combined with numerical simulation, the calculations of elastic-plastic wave’s interactions inside the specimens under rectangular incident wave action and its elastic-plastic transmission and reflection behavior at the two interfaces are carried out. The attenuation characteristics of the reflected waves in the sandwich rod system are investigated. The results show that under strong incident wave action, the specimen internally forms a curve-shaped elastic-plastic interface due to the interactions of elastic-plastic waves. This causes the transmission end to reach the yield state significantly earlier. This elastic-plastic interface propagates towards the reflection end at a speed greater than the elastic sound speed. The attenuation of the reflected wave during the plastic phase is the sum of the increase in generalized wave impedance due to the increase in the specimen’s cross-sectional area and the increase in the number of back-and-forth plastic waves caused by compression. Calculations also show that although the change of the specimen density significantly affects its wave speed and wave impedance, the sum of the attenuations caused by these two factors is close to zero. Hence, the effect of density changes on the transmission and reflection wave plateau phase can be ignored. An increase in the plastic modulus causes the reflection wave plateau to attenuate faster, but the effect of the specimen’s diameter is not monotonous. When it increases from 4 mm to 10 mm, the reflection wave attenuation speed increases, but when it further increases to 12 mm, the attenuation amount decreases. This study has certain reference value for in-depth analysis of split Hopkinson pressure bar test for the transmission waveforms as well as for the detailed test design and data processing.
Compared to the reflection and transmission analysis process during the incident wave loading phase, the incident wave plateau phase lasts longer, and the elastic-plastic propagation and evolution behavior are much more complex. The effects of elastic-plastic wave interactions within the specimen during this phase are very pronounced. Using the elastic-plastic incremental wave theory, combined with numerical simulation, the calculations of elastic-plastic wave’s interactions inside the specimens under rectangular incident wave action and its elastic-plastic transmission and reflection behavior at the two interfaces are carried out. The attenuation characteristics of the reflected waves in the sandwich rod system are investigated. The results show that under strong incident wave action, the specimen internally forms a curve-shaped elastic-plastic interface due to the interactions of elastic-plastic waves. This causes the transmission end to reach the yield state significantly earlier. This elastic-plastic interface propagates towards the reflection end at a speed greater than the elastic sound speed. The attenuation of the reflected wave during the plastic phase is the sum of the increase in generalized wave impedance due to the increase in the specimen’s cross-sectional area and the increase in the number of back-and-forth plastic waves caused by compression. Calculations also show that although the change of the specimen density significantly affects its wave speed and wave impedance, the sum of the attenuations caused by these two factors is close to zero. Hence, the effect of density changes on the transmission and reflection wave plateau phase can be ignored. An increase in the plastic modulus causes the reflection wave plateau to attenuate faster, but the effect of the specimen’s diameter is not monotonous. When it increases from 4 mm to 10 mm, the reflection wave attenuation speed increases, but when it further increases to 12 mm, the attenuation amount decreases. This study has certain reference value for in-depth analysis of split Hopkinson pressure bar test for the transmission waveforms as well as for the detailed test design and data processing.
2024, 44(8): 081443.
doi: 10.11883/bzycj-2023-0449
Abstract:
To study the strength, deformation characteristic and damage mechanism of freeze-thaw treated rock mass under the action of cyclic dynamic disturbance, the cyclic impact tests of freeze-thaw treated red sandstone under two kinds of impact pressure were carried out to investigate the effects of cyclic impact number and freeze-thaw number on stress wave propagation, dynamic stress-strain curve, peak stress, and peak strain. In addition, the calculation method of cumulative damage factor, which can comprehensive consider the effects of cyclic impact and freeze-thaw, is proposed based on the Lemaitre strain equivalence principle. Finally, the microstructure characteristics of red sandstone after freeze-thaw and cyclic impact are analyzed in detail. Results show that red sandstone specimens treated with different freeze-thaw number show tensile failure mode under cyclic impact load. The cyclic impact number that red sandstone specimen can withstand is negatively correlated with freeze-thaw cycle number, and red sandstone specimen after 75 freeze-thaw cycles treatments reaches the failure state after the first impact loading. Moreover, the cyclic impact number mainly affects the jump point, abscissa corresponding to peak point and amplitude of transmitted waves, and the amplitude of reflected waves. While the freeze-thaw number shows a great effect on the jump point, abscissa corresponding to peak point, and amplitude of transmitted waves during the first impact process. The cumulative damage factor of red sandstone specimen exhibits a good negative correlation with the dynamic peak stress. After the combination effects of freeze-thaw and cyclic impact, the cracks inside red sandstone spread along the grain boundary and connect with the pores to form a complex network.
To study the strength, deformation characteristic and damage mechanism of freeze-thaw treated rock mass under the action of cyclic dynamic disturbance, the cyclic impact tests of freeze-thaw treated red sandstone under two kinds of impact pressure were carried out to investigate the effects of cyclic impact number and freeze-thaw number on stress wave propagation, dynamic stress-strain curve, peak stress, and peak strain. In addition, the calculation method of cumulative damage factor, which can comprehensive consider the effects of cyclic impact and freeze-thaw, is proposed based on the Lemaitre strain equivalence principle. Finally, the microstructure characteristics of red sandstone after freeze-thaw and cyclic impact are analyzed in detail. Results show that red sandstone specimens treated with different freeze-thaw number show tensile failure mode under cyclic impact load. The cyclic impact number that red sandstone specimen can withstand is negatively correlated with freeze-thaw cycle number, and red sandstone specimen after 75 freeze-thaw cycles treatments reaches the failure state after the first impact loading. Moreover, the cyclic impact number mainly affects the jump point, abscissa corresponding to peak point and amplitude of transmitted waves, and the amplitude of reflected waves. While the freeze-thaw number shows a great effect on the jump point, abscissa corresponding to peak point, and amplitude of transmitted waves during the first impact process. The cumulative damage factor of red sandstone specimen exhibits a good negative correlation with the dynamic peak stress. After the combination effects of freeze-thaw and cyclic impact, the cracks inside red sandstone spread along the grain boundary and connect with the pores to form a complex network.
2024, 44(8): 081444.
doi: 10.11883/bzycj-2024-0003
Abstract:
In order to study the effects of free surface on underwater explosion shock wave, bubble behavior and water plumes formed by strong coupling between bubble and free surface, a small yield pentaerythritol tetranitrate (PETN) spherical charge near water surface underwater explosion experimental system was designed, five typical conditions of underwater explosion experiments were carried out, and the evolution process of bubble and water plumes, as well as time history of pressure at the gauge were obtained by high-speed camera and pressure sensor respectively. Based on the characteristics of shock waves and bubble time series, their free surface effects were analyzed separately. The shock wave mainly manifests as truncation effects. The interaction between bubble and free surface is manifested as complex bubble evolution and water plume generation and evolution, which were mainly analyzed through high-speed images, appropriately combined with pressure values. The free surface effects of the bubble were further quantitatively analyzed by the horizontal radius of the bubble, the offset displacement of the bubble, and the maximum height of water plume. The results show that with the decrease of the detonation depth , the difference of the surface reflection wave path decreases, and the truncation effect of the free surface on shock wave increases, that is, the time of the positive pressure of shock wave decreases, and the maximum deviation between the measured truncation time difference and the calculated time difference is 6.81%. With the decrease of the scaled detonation depth, the free surface effects increase, and the shapes of bubble and water plumes become more complicated. The bubble evolves from a sphere to an oval shape, even more complex shapes. The water plume gradually changes from a single water spike to a complex form such as a water spike-top splash column, a water spike-vertical jet column-water jet, etc. The change of the horizontal radius of the bubble no longer retain pulsation characteristics from the second pulsation period to the first pulsation period and even to the first bubble expansion stage. The offset displacement of the center of the bubble’s horizontal radius shows a two-stage variation law, and in the early rapidly-increasing stage (0–20 mm), the offset displacements at 4 scaled detonation depths show a linear variation law, and the linear coefficients are close.
In order to study the effects of free surface on underwater explosion shock wave, bubble behavior and water plumes formed by strong coupling between bubble and free surface, a small yield pentaerythritol tetranitrate (PETN) spherical charge near water surface underwater explosion experimental system was designed, five typical conditions of underwater explosion experiments were carried out, and the evolution process of bubble and water plumes, as well as time history of pressure at the gauge were obtained by high-speed camera and pressure sensor respectively. Based on the characteristics of shock waves and bubble time series, their free surface effects were analyzed separately. The shock wave mainly manifests as truncation effects. The interaction between bubble and free surface is manifested as complex bubble evolution and water plume generation and evolution, which were mainly analyzed through high-speed images, appropriately combined with pressure values. The free surface effects of the bubble were further quantitatively analyzed by the horizontal radius of the bubble, the offset displacement of the bubble, and the maximum height of water plume. The results show that with the decrease of the detonation depth , the difference of the surface reflection wave path decreases, and the truncation effect of the free surface on shock wave increases, that is, the time of the positive pressure of shock wave decreases, and the maximum deviation between the measured truncation time difference and the calculated time difference is 6.81%. With the decrease of the scaled detonation depth, the free surface effects increase, and the shapes of bubble and water plumes become more complicated. The bubble evolves from a sphere to an oval shape, even more complex shapes. The water plume gradually changes from a single water spike to a complex form such as a water spike-top splash column, a water spike-vertical jet column-water jet, etc. The change of the horizontal radius of the bubble no longer retain pulsation characteristics from the second pulsation period to the first pulsation period and even to the first bubble expansion stage. The offset displacement of the center of the bubble’s horizontal radius shows a two-stage variation law, and in the early rapidly-increasing stage (0–20 mm), the offset displacements at 4 scaled detonation depths show a linear variation law, and the linear coefficients are close.
2024, 44(8): 081445.
doi: 10.11883/bzycj-2023-0442
Abstract:
Theoretical study on the attenuation law of underwater explosion shock waves plays a crucial role in predicting the underwater explosion power. The attenuation law of underwater explosion shock waves could be analyzed from the shock waves pressure-time curve. The pressure-impulse (p-I) model has usually been used to assess damage on material and structure. In this paper, the pressure-time formula is analytically derived according to the p-I model. To verify the accuracy of the formula, the pressure-time relation curve was obtained by experiments with various explosive charges and distances. The experimental data was fitted in accordance with the theoretical equations of Cole and Орленко, and also with the developed pressure-time formula. The parameters of the formula are thus obtained. The accuracy could be described by the fitting coefficient R-squared (R2) value. The R-squared value of the developed pressure-time formula exceeds 0.988, which is greater than the R-squared values calculated by the equations of Cole and Орленко. In order to further validate the formula, the impulse and energy of underwater explosion shock waves are derived from the developed pressure-time formula, experimental data, and the equations of Cole and Орленко, respectively. Compared with the experimental results, the error of impulse derived from the developed pressure-time remains below 4%, which is 5%−10% lower than the errors of impulse between the experimental results and the equations of Cole and Орленко. The energy of the shock waves is similarly analyzed. Compared with the experimental results, the error of energy derived from the developed pressure-time remains below 1%, approximately the same as the errors of energy between the experimental results and the equations of Cole and Орленко. Compared with the calculation by equations of Cole and Орленко, it is seen that there is better correlation between the developed pressure-time formula and the experimental results. The developed pressure-time formula can be used to calculate the impulse and energy of underwater explosion shock waves.
Theoretical study on the attenuation law of underwater explosion shock waves plays a crucial role in predicting the underwater explosion power. The attenuation law of underwater explosion shock waves could be analyzed from the shock waves pressure-time curve. The pressure-impulse (p-I) model has usually been used to assess damage on material and structure. In this paper, the pressure-time formula is analytically derived according to the p-I model. To verify the accuracy of the formula, the pressure-time relation curve was obtained by experiments with various explosive charges and distances. The experimental data was fitted in accordance with the theoretical equations of Cole and Орленко, and also with the developed pressure-time formula. The parameters of the formula are thus obtained. The accuracy could be described by the fitting coefficient R-squared (R2) value. The R-squared value of the developed pressure-time formula exceeds 0.988, which is greater than the R-squared values calculated by the equations of Cole and Орленко. In order to further validate the formula, the impulse and energy of underwater explosion shock waves are derived from the developed pressure-time formula, experimental data, and the equations of Cole and Орленко, respectively. Compared with the experimental results, the error of impulse derived from the developed pressure-time remains below 4%, which is 5%−10% lower than the errors of impulse between the experimental results and the equations of Cole and Орленко. The energy of the shock waves is similarly analyzed. Compared with the experimental results, the error of energy derived from the developed pressure-time remains below 1%, approximately the same as the errors of energy between the experimental results and the equations of Cole and Орленко. Compared with the calculation by equations of Cole and Орленко, it is seen that there is better correlation between the developed pressure-time formula and the experimental results. The developed pressure-time formula can be used to calculate the impulse and energy of underwater explosion shock waves.
Founded in 1981 monthly
Sponsored byChinese Society of Theoretical and Applied Mechanics
Institude of Fluid Physics, CAEP
Editor-in-ChiefCangli Liu
