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In order to investigate the damage characteristics, dynamic response, and damage mechanism of reinforced concrete square column components subjected to multi-point synergistic explosion of explosives, including a single node on the column body, double nodes on adjacent surfaces, 4 nodes on adjacent surfaces, and 4 nodes completely surrounding the column. Based on the test results, a refined finite element model was established using the explicit dynamic analysis software LS-DYNA to systematically analyze the damage characteristics and stress development time course of the explosive central section. The results show that: under the same total mass of explosives, the number and arrangement of explosive nodes have significant effects on the damage effect on the square column; the multi-point explosion has greater damage effect on the column than the single-point
In order to investigate the damage characteristics, dynamic response, and damage mechanism of reinforced concrete square column components subjected to multi-point synergistic explosion of explosives, including a single node on the column body, double nodes on adjacent surfaces, 4 nodes on adjacent surfaces, and 4 nodes completely surrounding the column. Based on the test results, a refined finite element model was established using the explicit dynamic analysis software LS-DYNA to systematically analyze the damage characteristics and stress development time course of the explosive central section. The results show that: under the same total mass of explosives, the number and arrangement of explosive nodes have significant effects on the damage effect on the square column; the multi-point explosion has greater damage effect on the column than the single-point
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In order to study the anti-blast performance of prestressed concrete (PC) frame structure, the dynamic response of a 3-story 2-span long-span bonded/unbonded PC frame structure under the action of external remote blast loads of different scaled distances was analyzed using the finite element software LS-DYNA. In the different blast conditions, the type of explosion was surface detonation, the explosion distance was 100 m, and the scaled distances were 2~8 m/kg1/3. Explosive loads on the building surface were calculated in accordance with Unified Facilities Criteria 3-340-02. The different types of prestress in the numerical model were realized by controlling the direction of coupling of concrete and prestressing tendons. In order to validate the numerical model, the results of the numerical simulations were compared with the experimental results. The blast resistance mechanism, story drift ratios, structural damage mode, and damage assessment of PC frames were analyzed under blast loads at different scaled distances. The analysis results show that the ground floor of the large-span PC frame is easy to damage under the action of the external remote blast load, and the ground floor columns can be strengthened to improve the overall structural blast resistance. In the PC frame, columns relative to the frame beams are weaker and prone to damage. The PC
In order to study the anti-blast performance of prestressed concrete (PC) frame structure, the dynamic response of a 3-story 2-span long-span bonded/unbonded PC frame structure under the action of external remote blast loads of different scaled distances was analyzed using the finite element software LS-DYNA. In the different blast conditions, the type of explosion was surface detonation, the explosion distance was 100 m, and the scaled distances were 2~8 m/kg1/3. Explosive loads on the building surface were calculated in accordance with Unified Facilities Criteria 3-340-02. The different types of prestress in the numerical model were realized by controlling the direction of coupling of concrete and prestressing tendons. In order to validate the numerical model, the results of the numerical simulations were compared with the experimental results. The blast resistance mechanism, story drift ratios, structural damage mode, and damage assessment of PC frames were analyzed under blast loads at different scaled distances. The analysis results show that the ground floor of the large-span PC frame is easy to damage under the action of the external remote blast load, and the ground floor columns can be strengthened to improve the overall structural blast resistance. In the PC frame, columns relative to the frame beams are weaker and prone to damage. The PC
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The technique of drilling and blasting is widely applied in rock excavation engineering, and its working efficiency is closely related to the structure and geological environment of rock mass. Initial stress has a significant effect on the blast-induced crack propagation behavior and failure characteristics of rock mass, which leads to engineering problems such as over/underbreak in deep rock. In this paper, the blast-induced damage characteristics and fracture mechanism of rock mass under various initial stresses are investigated by combining theoretical model and numerical simulation. The theoretical model of single-hole blasting is established based on elastic mechanics, and the stress distribution around the borehole under static load and the stress evolution characteristics under dynamic load are analyzed, respectively, then the blasting damage mechanism of rock mass under initial stress is revealed. Besides, the parameters of RHT model were determined and adjusted based on a series of empirical formulas and dynamic mechanical tests, and the numerical model was calibrated by the indoor blasting test. Furthermore, the pressure evolution, crack propagation and fractal features are analyzed by the corresponding numerical model, and the rationality of the theoretical model has been demonstrated again. The results showed that the circumferential tensile stress is an important factor affecting the blasting crack propagation, and the rock fragmentation under blasting can be improved by adjusting the distribution of circumferential stress reasonably when the initial stress is large. In practical engineering, the field of geo-stress control should be employed with presplitting technology.
The technique of drilling and blasting is widely applied in rock excavation engineering, and its working efficiency is closely related to the structure and geological environment of rock mass. Initial stress has a significant effect on the blast-induced crack propagation behavior and failure characteristics of rock mass, which leads to engineering problems such as over/underbreak in deep rock. In this paper, the blast-induced damage characteristics and fracture mechanism of rock mass under various initial stresses are investigated by combining theoretical model and numerical simulation. The theoretical model of single-hole blasting is established based on elastic mechanics, and the stress distribution around the borehole under static load and the stress evolution characteristics under dynamic load are analyzed, respectively, then the blasting damage mechanism of rock mass under initial stress is revealed. Besides, the parameters of RHT model were determined and adjusted based on a series of empirical formulas and dynamic mechanical tests, and the numerical model was calibrated by the indoor blasting test. Furthermore, the pressure evolution, crack propagation and fractal features are analyzed by the corresponding numerical model, and the rationality of the theoretical model has been demonstrated again. The results showed that the circumferential tensile stress is an important factor affecting the blasting crack propagation, and the rock fragmentation under blasting can be improved by adjusting the distribution of circumferential stress reasonably when the initial stress is large. In practical engineering, the field of geo-stress control should be employed with presplitting technology.
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The evaluation of failure effect on concrete under explosion is of great significance to both engineering blasting construction and anti-explosion safety of engineering structures. The key is to obtain the characteristics of failure zone of the target. Firstly, main physical processes of underwater contact explosion were analyzed. Loading characteristics of underwater contact explosion were studied with the difference between underwater contact explosion and air contact explosion compared. Then, a calculation method of failure zone in underwater contact explosion considering the crushing effect on target from explosion shock wave and the quasi-static effect on target from detonation products was established. The quasi-static effect was further subdivided into quasi-static compression fracturing and quasi-static tensile fracturing. Finally, the proposed method was verified with finite element numerical simulation and experimental data in literatures. The results show that the expansion of detonation products is inhibited by water compared with air contact explosion. And then the duration of explosion load and the impulse acting on the surrounding medium are increased in underwater contact explosion. Circumferential compression criterion is suggested to calculate cracked zone of concrete subjected to underwater contact explosion. And fracture zone is suggested to divide into dynamic fracturing zone, quasi-static compression fracturing zone and quasi-static tension fracturing zone for calculation. Failure range of mass concrete subjected to underwater contact explosion is well predicted by proposed calculation method. With the same explosive type and water depth, the range of fracture zone is greatly influenced by the tensile strength and compressive strength ratio of concrete. This provides a basis for both blast resistance research of engineering structures and underwater engineering blasting construction.
The evaluation of failure effect on concrete under explosion is of great significance to both engineering blasting construction and anti-explosion safety of engineering structures. The key is to obtain the characteristics of failure zone of the target. Firstly, main physical processes of underwater contact explosion were analyzed. Loading characteristics of underwater contact explosion were studied with the difference between underwater contact explosion and air contact explosion compared. Then, a calculation method of failure zone in underwater contact explosion considering the crushing effect on target from explosion shock wave and the quasi-static effect on target from detonation products was established. The quasi-static effect was further subdivided into quasi-static compression fracturing and quasi-static tensile fracturing. Finally, the proposed method was verified with finite element numerical simulation and experimental data in literatures. The results show that the expansion of detonation products is inhibited by water compared with air contact explosion. And then the duration of explosion load and the impulse acting on the surrounding medium are increased in underwater contact explosion. Circumferential compression criterion is suggested to calculate cracked zone of concrete subjected to underwater contact explosion. And fracture zone is suggested to divide into dynamic fracturing zone, quasi-static compression fracturing zone and quasi-static tension fracturing zone for calculation. Failure range of mass concrete subjected to underwater contact explosion is well predicted by proposed calculation method. With the same explosive type and water depth, the range of fracture zone is greatly influenced by the tensile strength and compressive strength ratio of concrete. This provides a basis for both blast resistance research of engineering structures and underwater engineering blasting construction.
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The research on generation and properties of materials under ultra-high pressure and density constitutes an important part of the extreme physics and hence a field of modern frontier science, especially the magnetically driven high-energy-density physics herein is meaningful and in great need by core technologies. High pulsed power devices with tens MA output current and thousands Tesla magnetic field were developed in past decades, e.g., the Z machine capable of 30 MA and 100 TW on load at the Sandia Nat. Labs, USA; also a record intense magnetic field of 2800 T achieved with a cascade magneto-cumulative generator of MC-1 type at VNIIEF, Russia. It is available now to compress heavy metals up to 1 TPa or to launch thin Al flyer plates to super high speed over 45 km/s using isentropic compression experiments on the Z machine. Although these experiment takes various forms, they have intrinsic unity in physics, which is based on the conservation laws of mechanics and the macroscopic electromagnetic theory. Therefore, it is feasible and necessary to establish a unified numerical simulation platform and determine the mechanical motion of the load configuration and its coupling with various physical fields under extreme experimental conditions by relying on the load current data (or the real data of the drive circuit). The magneto-hydrodynamics multi-physics codes have been successfully developed in US, e.g., the excellent performance codes--ALEGRA series at the Sandia labs. This paper substantively extends the one-dimensional Lagrangian code SSS, which has been extensively validated by shock, detonation and laser radiation effect simulations, into a magneto-hydrodynamics multi-physics one and now renamed as SSS-MHD. The simulation results of various high energy density dynamic experiments with typical significance, such as planar quasi-isentropic ramp wave compression, ultra-high speed solid flyer launch, solid liner implosion, and explosive-driven magnetic flux compression, indicate that their relative deviations of the SSS-MHD simulations from experimental data of America’s Z machine, China’s CQ and CJ series devices, and ALEGRA-1D/2D calculations are generally less than 5%. The SSS-MHD code turns into a powerful platform to simulate experiments of extreme material dynamics (including gases, liquids, metals and compounds) and its practice could be helpful to develop advanced multi-dimensional MHD multi-physics codes.
The research on generation and properties of materials under ultra-high pressure and density constitutes an important part of the extreme physics and hence a field of modern frontier science, especially the magnetically driven high-energy-density physics herein is meaningful and in great need by core technologies. High pulsed power devices with tens MA output current and thousands Tesla magnetic field were developed in past decades, e.g., the Z machine capable of 30 MA and 100 TW on load at the Sandia Nat. Labs, USA; also a record intense magnetic field of 2800 T achieved with a cascade magneto-cumulative generator of MC-1 type at VNIIEF, Russia. It is available now to compress heavy metals up to 1 TPa or to launch thin Al flyer plates to super high speed over 45 km/s using isentropic compression experiments on the Z machine. Although these experiment takes various forms, they have intrinsic unity in physics, which is based on the conservation laws of mechanics and the macroscopic electromagnetic theory. Therefore, it is feasible and necessary to establish a unified numerical simulation platform and determine the mechanical motion of the load configuration and its coupling with various physical fields under extreme experimental conditions by relying on the load current data (or the real data of the drive circuit). The magneto-hydrodynamics multi-physics codes have been successfully developed in US, e.g., the excellent performance codes--ALEGRA series at the Sandia labs. This paper substantively extends the one-dimensional Lagrangian code SSS, which has been extensively validated by shock, detonation and laser radiation effect simulations, into a magneto-hydrodynamics multi-physics one and now renamed as SSS-MHD. The simulation results of various high energy density dynamic experiments with typical significance, such as planar quasi-isentropic ramp wave compression, ultra-high speed solid flyer launch, solid liner implosion, and explosive-driven magnetic flux compression, indicate that their relative deviations of the SSS-MHD simulations from experimental data of America’s Z machine, China’s CQ and CJ series devices, and ALEGRA-1D/2D calculations are generally less than 5%. The SSS-MHD code turns into a powerful platform to simulate experiments of extreme material dynamics (including gases, liquids, metals and compounds) and its practice could be helpful to develop advanced multi-dimensional MHD multi-physics codes.
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Near-field underwater explosion produces complex loading patterns, and complex boundary conditions make the damage patterns of structures under near-field underwater explosion more difficult to predict. Thus, investigation on the evolution of underwater explosion bubbles and the damage effects on clamped square plates with the coupling of multi-boundary (free surface, elastoplastic plates and sediment boundary) was conducted using the Coupled Eulerian-Lagrangian (CEL) method. Firstly, to verify the accuracy of the finite element method, underwater explosion tests were performed 10 cm under the bottom of the clamped square plates in different dimensions (the side length of the plates were 0.46, 0.92 and 1.61 times the maximum bubble diameter) using 2.5gTNT. Then, the damage mechanism of clamped square plate was analyzed by combining the test and finite element results. Finally, a series of numerical simulations reveal that with the increase of plate dimension and stand-off distance, bubbles show three different evolution modes: collapse, downward jet and upward jet; With the increase of plate dimension, the effects of stand-off distance on the final deformation of plate center decreases. The sediment boundary can alleviate the bubble shrinkage, make the bubble firstly collapse from the middle to form jets in the opposite direction and reduce the displacement and strain of the clamped square plates. The sediment boundary has no effects when the bubbles collapse in advance.
Near-field underwater explosion produces complex loading patterns, and complex boundary conditions make the damage patterns of structures under near-field underwater explosion more difficult to predict. Thus, investigation on the evolution of underwater explosion bubbles and the damage effects on clamped square plates with the coupling of multi-boundary (free surface, elastoplastic plates and sediment boundary) was conducted using the Coupled Eulerian-Lagrangian (CEL) method. Firstly, to verify the accuracy of the finite element method, underwater explosion tests were performed 10 cm under the bottom of the clamped square plates in different dimensions (the side length of the plates were 0.46, 0.92 and 1.61 times the maximum bubble diameter) using 2.5gTNT. Then, the damage mechanism of clamped square plate was analyzed by combining the test and finite element results. Finally, a series of numerical simulations reveal that with the increase of plate dimension and stand-off distance, bubbles show three different evolution modes: collapse, downward jet and upward jet; With the increase of plate dimension, the effects of stand-off distance on the final deformation of plate center decreases. The sediment boundary can alleviate the bubble shrinkage, make the bubble firstly collapse from the middle to form jets in the opposite direction and reduce the displacement and strain of the clamped square plates. The sediment boundary has no effects when the bubbles collapse in advance.
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To investigate the motion evolution process and load action characteristics of a vehicle with airbags falling into water, based on the VOF (Volume of Fluid) multiphase flow model and the k-ω SST turbulence model, the numerical simulation of the inclined falling water impact process of a vehicle with airbags was conducted. The applicability and accuracy of the numerical method were verified by comparing the water entry cavity shape and falling displacement obtained from numerical calculations during the horizontal cylinder’s water entry process with experimental results. The motion evolution process and load action characteristics of a vehicle with airbags during the inclined falling into water process were analyzed. The results show that the process of the vehicle falling into the water is divided into two stages: the impact into the water stage and the heave attenuation stage. Among them, the tail attack of the vehicle, the airbags attack, and the airbags acceleration deployment process all form local peak impact acceleration, and the acceleration peak caused by the airbag acceleration deployment attacking the water body is the highest. The impact force of the airbags will cause a significant tensile peak in the design connecting rod between the airbags and the vehicle during the process of airbag impact entering the water. The collapse load of the water entry cavity will cause local pressure fluctuations of the vehicle, greatly affecting the changes in the vehicle’s water entry attitude. In general, the airbag device can provide good buffering protection for the vehicle falling into water, and the calculated impact response data of the vehicle with airbags can provide a reference for the design of the vehicle's buffer recovery device.
To investigate the motion evolution process and load action characteristics of a vehicle with airbags falling into water, based on the VOF (Volume of Fluid) multiphase flow model and the k-ω SST turbulence model, the numerical simulation of the inclined falling water impact process of a vehicle with airbags was conducted. The applicability and accuracy of the numerical method were verified by comparing the water entry cavity shape and falling displacement obtained from numerical calculations during the horizontal cylinder’s water entry process with experimental results. The motion evolution process and load action characteristics of a vehicle with airbags during the inclined falling into water process were analyzed. The results show that the process of the vehicle falling into the water is divided into two stages: the impact into the water stage and the heave attenuation stage. Among them, the tail attack of the vehicle, the airbags attack, and the airbags acceleration deployment process all form local peak impact acceleration, and the acceleration peak caused by the airbag acceleration deployment attacking the water body is the highest. The impact force of the airbags will cause a significant tensile peak in the design connecting rod between the airbags and the vehicle during the process of airbag impact entering the water. The collapse load of the water entry cavity will cause local pressure fluctuations of the vehicle, greatly affecting the changes in the vehicle’s water entry attitude. In general, the airbag device can provide good buffering protection for the vehicle falling into water, and the calculated impact response data of the vehicle with airbags can provide a reference for the design of the vehicle's buffer recovery device.
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Based on high-speed photography technology, an experiment study on water-entry of oblique projectile constrained by ice hole was conducted. Digital image processing technology was employed to extract the experimental data. The water-entry process of oblique projectile was analyzed under both ice-free and ice hole constraint environment, and the water-entry process is divided into three stages: cavity expansion stage, cavity closure stage and cavity collapse stage. Additionally, a series water-entry experiments were also conducted with different initial velocities of projectiles under the same ice hole constraint, allowing for the establishment of a relationship between initial velocity and ice hole constraint. Results show that during the cavity expansion stage, the free surface under the ice-hole constraint does not form a bulge, and the splashing on the water-away side of the projectile is suppressed by the ice hole and is more dispersed. The ice-hole constraint leads to the obstruction of cavity expansion and the appearance of bending on the left side of the cavity near the free surface, the maximum diameter of cavity decreases. In the cavity closure stage, the closure time of the cavity is advanced under the constraint of the ice hole. The reflected flow impacts the right side of cavity
Based on high-speed photography technology, an experiment study on water-entry of oblique projectile constrained by ice hole was conducted. Digital image processing technology was employed to extract the experimental data. The water-entry process of oblique projectile was analyzed under both ice-free and ice hole constraint environment, and the water-entry process is divided into three stages: cavity expansion stage, cavity closure stage and cavity collapse stage. Additionally, a series water-entry experiments were also conducted with different initial velocities of projectiles under the same ice hole constraint, allowing for the establishment of a relationship between initial velocity and ice hole constraint. Results show that during the cavity expansion stage, the free surface under the ice-hole constraint does not form a bulge, and the splashing on the water-away side of the projectile is suppressed by the ice hole and is more dispersed. The ice-hole constraint leads to the obstruction of cavity expansion and the appearance of bending on the left side of the cavity near the free surface, the maximum diameter of cavity decreases. In the cavity closure stage, the closure time of the cavity is advanced under the constraint of the ice hole. The reflected flow impacts the right side of cavity
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In order to reveal the influence law of graphite ore with different bedding angles under impact load, impact experiments on graphite ore samples with different bedding angles (0°, 45°and 90°) were conducted by using a 50 mm diameter split Hopkinson pressure bar (SHPB) test device, with the combined use of high-speed photography and electron microscopy scan. The dynamic mechanical properties and impact failure modes were investigated during the dynamic fracture process. The results show that most of the minerals in graphite ore are arranged in an allotriomorphic granular orientation within an irregular contact boundary. There is a high content of muscovite and quartz, associated with graphite and enriched along the bedding planes. The bedding angles have a deterioration effect on samples, and the 45° bedding angle has the strongest deterioration effect. The energy dissipation characteristics show a U-shaped trend with the increase of bedding angle, which is similar to the strength characteristics. At the same strain rate, the average particle size of the broken samples is strongly correlated with the energy dissipation density. The average particle size of 0° bedding angle is the smallest, with the largest energy dissipation density. On the contrary, the average particle size is the largest when the bedding angle is 45° , with the smallest energy dissipation density. When the graphite flake is subjected to external forces, it is not only break from the inside, but also is torn by associated minerals. The destruction form can be summarized as the evolution of tensile failure-shear failure-tensile splitting failure. The relevant characteristic results obtained from the experiments show that the damage degree of the graphite flakes is mainly controlled by the magnitude and direction of the impact load. Tensile failure can reduce the internal fracture of graphite flakes, and a low strain rate can reduce the production of rock powder. Therefore, the destructive effect of blasting impact load on graphite flakes can be reduced by adjusting the propagation direction of shock wave, reducing the peak stress and increasing the failure area of ore tensile stress.
In order to reveal the influence law of graphite ore with different bedding angles under impact load, impact experiments on graphite ore samples with different bedding angles (0°, 45°and 90°) were conducted by using a 50 mm diameter split Hopkinson pressure bar (SHPB) test device, with the combined use of high-speed photography and electron microscopy scan. The dynamic mechanical properties and impact failure modes were investigated during the dynamic fracture process. The results show that most of the minerals in graphite ore are arranged in an allotriomorphic granular orientation within an irregular contact boundary. There is a high content of muscovite and quartz, associated with graphite and enriched along the bedding planes. The bedding angles have a deterioration effect on samples, and the 45° bedding angle has the strongest deterioration effect. The energy dissipation characteristics show a U-shaped trend with the increase of bedding angle, which is similar to the strength characteristics. At the same strain rate, the average particle size of the broken samples is strongly correlated with the energy dissipation density. The average particle size of 0° bedding angle is the smallest, with the largest energy dissipation density. On the contrary, the average particle size is the largest when the bedding angle is 45° , with the smallest energy dissipation density. When the graphite flake is subjected to external forces, it is not only break from the inside, but also is torn by associated minerals. The destruction form can be summarized as the evolution of tensile failure-shear failure-tensile splitting failure. The relevant characteristic results obtained from the experiments show that the damage degree of the graphite flakes is mainly controlled by the magnitude and direction of the impact load. Tensile failure can reduce the internal fracture of graphite flakes, and a low strain rate can reduce the production of rock powder. Therefore, the destructive effect of blasting impact load on graphite flakes can be reduced by adjusting the propagation direction of shock wave, reducing the peak stress and increasing the failure area of ore tensile stress.
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A laminated binary charge with equal thickness for each layer was prepared by two kinds of 3, 4-dinitrofurazanfuroxan (DNTF) based explosives with detonation velocity difference of 1.85mm/μs, one of which has a very high detonation velocity and the other has an extremely high detonation heat. The
A laminated binary charge with equal thickness for each layer was prepared by two kinds of 3, 4-dinitrofurazanfuroxan (DNTF) based explosives with detonation velocity difference of 1.85mm/μs, one of which has a very high detonation velocity and the other has an extremely high detonation heat. The
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In frigid regions, the construction of sluice pier structures within river systems is confronted with considerable challenges arising from the presence of severe ice loads and ice-induced vibrations. The collision process between ice and sluice piers is further complicated by the intricate hydrodynamic effects exerted by water. The arbitrary Lagrangian-Eulerian (ALE) fluid-structure interaction (FSI) method is employed in this research to meticulously account for the fluid forces acting upon both the ice and sluice pier surfaces. A comprehensive coupled model encompassing the interactions among water, ice, and sluice piers is established to thoroughly investisluice the mechanical characteristics associated with ice-sluice pier collisions under highly unpredictable conditions. Corresponding ice-concrete collision tests are meticulously designed and conducted, revealing an exemplary concurrence between the simulated impact forces and the values obtained from experimental observations. Upon analyzing the fluid-structure interaction and hydrodynamic effects, the present study demonstrates that the water-ice-sluice pier coupled model adeptly captures the fluid characteristics inherent to water. During the approach of an ice mass towards a sluice pier, the initial hydrodynamic effects initiated by the water medium effectively augment the kinetic energy possessed by the ice. As the ice forcefully interacts with the sluice pier, the water medium swiftly generates a transient high-pressure field, thereby establishing a phenomenon colloquially referred to
In frigid regions, the construction of sluice pier structures within river systems is confronted with considerable challenges arising from the presence of severe ice loads and ice-induced vibrations. The collision process between ice and sluice piers is further complicated by the intricate hydrodynamic effects exerted by water. The arbitrary Lagrangian-Eulerian (ALE) fluid-structure interaction (FSI) method is employed in this research to meticulously account for the fluid forces acting upon both the ice and sluice pier surfaces. A comprehensive coupled model encompassing the interactions among water, ice, and sluice piers is established to thoroughly investisluice the mechanical characteristics associated with ice-sluice pier collisions under highly unpredictable conditions. Corresponding ice-concrete collision tests are meticulously designed and conducted, revealing an exemplary concurrence between the simulated impact forces and the values obtained from experimental observations. Upon analyzing the fluid-structure interaction and hydrodynamic effects, the present study demonstrates that the water-ice-sluice pier coupled model adeptly captures the fluid characteristics inherent to water. During the approach of an ice mass towards a sluice pier, the initial hydrodynamic effects initiated by the water medium effectively augment the kinetic energy possessed by the ice. As the ice forcefully interacts with the sluice pier, the water medium swiftly generates a transient high-pressure field, thereby establishing a phenomenon colloquially referred to
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A Split Hopkinson pressure bar (SHPB) device was used to study the dynamic mechanical properties and deformation and failure characteristics of the combined rock mass with different sandwich materials, using sandstone and granite as the soft and hard rock matrix. The Discrete lattice spring method (DLSM) was used to further investigate the crack propagation, the reaction and transmission at the interlayer interface and the energy distribution characteristics of rock mass under different interlayer materials. The results show that the growth factor of rock mass dynamic strength increases with the increase of rock mass dynamic compressive strength, showing an obvious dynamic compressive strength dependence. The rock mass with different interlayer materials has obvious nonlinear section in the initial loading stage, and the closed pores and cracks in the sandstone of non-interlayer rock have the longest nonlinear section in the initial stress stage. With the increase of the strength of interlayer material, the obstacle ability of interlayer to crack propagation and development of rock mass is gradually weak, and the energy consumption of rock mass crack and failure is gradually reduced. The failure of the intercalated rock mass starts at the cementation surface of the intercalated rock mass. With the increase of the strength of the intercalated material, the failure of the soft rock near the cementation surface is gradually intensified, while the hard rock has no obvious failure. The rock mass with interlayer has a good clipping effect. With the decrease of the strength of interlayer material, the peak stress value of both ends gradually increases and decreases. With the decrease of the strength of the interlayer material, the energy absorption density of the interlayer rock mass increases in a short time, and the stability becomes worse, and it is easy to be destroyed.
A Split Hopkinson pressure bar (SHPB) device was used to study the dynamic mechanical properties and deformation and failure characteristics of the combined rock mass with different sandwich materials, using sandstone and granite as the soft and hard rock matrix. The Discrete lattice spring method (DLSM) was used to further investigate the crack propagation, the reaction and transmission at the interlayer interface and the energy distribution characteristics of rock mass under different interlayer materials. The results show that the growth factor of rock mass dynamic strength increases with the increase of rock mass dynamic compressive strength, showing an obvious dynamic compressive strength dependence. The rock mass with different interlayer materials has obvious nonlinear section in the initial loading stage, and the closed pores and cracks in the sandstone of non-interlayer rock have the longest nonlinear section in the initial stress stage. With the increase of the strength of interlayer material, the obstacle ability of interlayer to crack propagation and development of rock mass is gradually weak, and the energy consumption of rock mass crack and failure is gradually reduced. The failure of the intercalated rock mass starts at the cementation surface of the intercalated rock mass. With the increase of the strength of the intercalated material, the failure of the soft rock near the cementation surface is gradually intensified, while the hard rock has no obvious failure. The rock mass with interlayer has a good clipping effect. With the decrease of the strength of interlayer material, the peak stress value of both ends gradually increases and decreases. With the decrease of the strength of the interlayer material, the energy absorption density of the interlayer rock mass increases in a short time, and the stability becomes worse, and it is easy to be destroyed.
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doi: 10.11883/bzycj-2023-0039
Abstract:
By employing the mode approximation method for rigid-plastic structural dynamic behavior and numerical simulation, a dynamic response analysis was conducted on circular-section concrete-filled steel tubular (CFST) structures subjected to lateral impact loadings. The mechanical model of CFST structure was equivalently represented as a rigid-plastic foundation beam model according to its plastic behavior. Under linear velocity field assumption and the geometric similarity, the equivalently initial velocity for mode approximation of the structure was derived and compared with the existing experimental data. Analytical solution for plastic lateral deformation at mid-span of the CFST with two fixed ends by rigid-plastic mode approximation method was provided, yielding non-dimensional geometric and physical parameters that influenced the ultimate lateral plastic deformation. A numerical model of the CFST structure under lateral impact was established using ABAQUS/Explicit. The theoretical and numerical predictions were both compared with existing experimental global deformations. Dimensional analysis and numerical modeling were combined to analyze the geometric and physical parameters, as well as the initial impact impulse, which influence the plastic deformation of the CFST structure. The results demonstrate a good agreement between the theoretical, numerical results, and experimental data, confirming that the plastic deformations of the structure align with the assumed distribution of plastic hinges. For geometric variables, the ratio of length to diameter and ratio of thickness to diameter exert a significant influence on the final lateral deformation. The relative width of the indenter can alter the deformation shape of the structure. The physical parameters of the steel tube and core concrete have less impact on the deflection at mid-span compared to the geometric variables. The final lateral deformation of the CFST structure exhibits a quadratic correlation with the initial impact impulse. Finally, the applicable range of all the theoretical analysis variables is given according to the corresponding parameter analysis. The proposed mode solutions for rigid-plastic response provide a reliable prediction of the plastic deformation behavior of CFST structures under lateral impact loadings.
By employing the mode approximation method for rigid-plastic structural dynamic behavior and numerical simulation, a dynamic response analysis was conducted on circular-section concrete-filled steel tubular (CFST) structures subjected to lateral impact loadings. The mechanical model of CFST structure was equivalently represented as a rigid-plastic foundation beam model according to its plastic behavior. Under linear velocity field assumption and the geometric similarity, the equivalently initial velocity for mode approximation of the structure was derived and compared with the existing experimental data. Analytical solution for plastic lateral deformation at mid-span of the CFST with two fixed ends by rigid-plastic mode approximation method was provided, yielding non-dimensional geometric and physical parameters that influenced the ultimate lateral plastic deformation. A numerical model of the CFST structure under lateral impact was established using ABAQUS/Explicit. The theoretical and numerical predictions were both compared with existing experimental global deformations. Dimensional analysis and numerical modeling were combined to analyze the geometric and physical parameters, as well as the initial impact impulse, which influence the plastic deformation of the CFST structure. The results demonstrate a good agreement between the theoretical, numerical results, and experimental data, confirming that the plastic deformations of the structure align with the assumed distribution of plastic hinges. For geometric variables, the ratio of length to diameter and ratio of thickness to diameter exert a significant influence on the final lateral deformation. The relative width of the indenter can alter the deformation shape of the structure. The physical parameters of the steel tube and core concrete have less impact on the deflection at mid-span compared to the geometric variables. The final lateral deformation of the CFST structure exhibits a quadratic correlation with the initial impact impulse. Finally, the applicable range of all the theoretical analysis variables is given according to the corresponding parameter analysis. The proposed mode solutions for rigid-plastic response provide a reliable prediction of the plastic deformation behavior of CFST structures under lateral impact loadings.
Study on design and calculation method of double-skin steel-concrete shield based on energy approach
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The calculation method of double-skin steel-concrete shield based on the energy method was discussed. Under the premise of a rigid projectile, the main structures that affect the energy dissipation of projectile penetration are front and rear steel plates, internal concrete, tied bars and distribution layer. In this paper, the energy consumption of steel plate in elastic state, plastic state and plastic film state was analyzed. Based on the principle of minimum energy consumption and dimensionless analysis, the energy consumption states of the rear steel plate under different materials and structural dimensions were inversely deduced. Combined with the strength limit condition of concrete, the formula for calculating the comprehensive energy consumption of the rear steel plate considering the plastic deformation and the penetration failure mode was proposed, and the analytical expression for the minimum critical thickness of the rear steel plate was established. The calculation results indicate that the comprehensive energy consumption of the sheet steel plate can reach 4~5 times that of only considering the penetration effect. In view of the restraint effect of steel plates on both sides of concrete, the current relatively mature formula of concrete penetration energy consumption was modified. Based on the principle of energy conservation, a six-step method for designing double-skin steel-concrete shield was proposed, and the formula for calculating the critical penetration velocity of the projectile was given. The theoretical results were compared with the existing test data. It indicates that the calculation formulas in this paper are in good agreement with the test results and can provide a scientific method for the design of double-skin steel-concrete shield. The main principle of six-step method is to give full play to the plastic deformation energy consumption of the rear steel plate and the anti-penetration energy consumption of the front steel plate. This method is beneficial to reduce the thickness of the double-skin steel-concrete shield and improve the protection effect.
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As the most widely used construction material, concrete is common in military and civil transportation infrastructures. During its services life, concrete may bear dynamic loads such as high-speed penetration, blast and impact of vehicle, ship, rockfall and so on. On the mesoscale, concrete is three-phase material composed of mortar, coarse aggregates and interface transition zone (ITZ). The concrete 3D mesoscale model was established to analyze the crack generation and development, damage evolution, dynamic strength and its influencing factors of concrete. Firstly, randomly distributed convex polyhedron aggregates of random shapes and sizes were modeled based on the conventional “take-and-place” method, and improvement and control of volume fraction (up to 50%) were realized through aggregate drop simulation and reduction. Then, aggregates and mortar were meshed with tetrahedral elements to display their actual physical shapes. Besides, ITZ is represented by interface cohesive contact to improve computational efficiency. Furthermore, SHPB simulations of different coarse aggregates sizes are conducted and the accuracy of model, parameter determination method and simulation methods were proved by comparing test and simulated bar strain-time history, dynamic stress-strain curves and failure patterns of specimens. Finally, influences of the aggregate size (4~8mm, 10~14mm and 22~26mm), volume fraction (20%, 30% and 40%) and type (limestone, granite and basalt) on concrete dynamic compressive strength under the strain rate within 30~100s-1 were analyzed. It shows that the dynamic compressive strength of concrete increases first and then decreases with the increase of aggregate size; the dynamic compressive strength of concrete increases with the increase of volume fraction and strength of aggregates.
As the most widely used construction material, concrete is common in military and civil transportation infrastructures. During its services life, concrete may bear dynamic loads such as high-speed penetration, blast and impact of vehicle, ship, rockfall and so on. On the mesoscale, concrete is three-phase material composed of mortar, coarse aggregates and interface transition zone (ITZ). The concrete 3D mesoscale model was established to analyze the crack generation and development, damage evolution, dynamic strength and its influencing factors of concrete. Firstly, randomly distributed convex polyhedron aggregates of random shapes and sizes were modeled based on the conventional “take-and-place” method, and improvement and control of volume fraction (up to 50%) were realized through aggregate drop simulation and reduction. Then, aggregates and mortar were meshed with tetrahedral elements to display their actual physical shapes. Besides, ITZ is represented by interface cohesive contact to improve computational efficiency. Furthermore, SHPB simulations of different coarse aggregates sizes are conducted and the accuracy of model, parameter determination method and simulation methods were proved by comparing test and simulated bar strain-time history, dynamic stress-strain curves and failure patterns of specimens. Finally, influences of the aggregate size (4~8mm, 10~14mm and 22~26mm), volume fraction (20%, 30% and 40%) and type (limestone, granite and basalt) on concrete dynamic compressive strength under the strain rate within 30~100s-1 were analyzed. It shows that the dynamic compressive strength of concrete increases first and then decreases with the increase of aggregate size; the dynamic compressive strength of concrete increases with the increase of volume fraction and strength of aggregates.
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In order to investigate the effect of the pores per inch (PPI) of copper foam and hydrogen volume fractions (φ) on the explosive characteristics of premixed syngas-air, a copper foams with PPI of 15, 25 and 40 respectively was employed in a closed pipe (100 × 100 × 1000 mm) and its distance to the ignition end is 500 mm. Correspondingly, the premixed syngas-air flame propagates in duct without copper foam was compared. The premixed syngas-air mixtures with equivalence ratio of 1 but over a wide range of hydrogen volume fractions (from 10% to 90%) were tested. Detailed flame evolution process was visualized by a high-speed camera and the overpressure was recorded by pressure transducer. The results indicated that the copper foam has a significant impact on flame propagation and overpressure-time histories of premixed syngas-air explosion. The flame structure, flame tip velocity and overpressure obtained before the flame approaches the copper foam are determined by the formation process of “tulip” flame. And they are only related to the fuel component, not the copper foam. The PPI and j affect not only the time of “tulip” flame formation, but also affect the appearance of distorted “tulip” flame. The copper foam could lead to the segmentation of flame front and translate the flame front from laminar to turbulence, resulting in the flame acceleration. This phenomenon becomes more evident with the decreasing of PPI. The growth of overpressure recorded in premixed syngas-air explosion was closely related to the flame structure evolution. The presence of copper foam can increases the flame tip speed and overpressure significantly. For the case with a smaller PPI, both the maximum flame tip speed, growth of overpressure and maximum overpressure of premixed syngas-air increase with the φ. The research results have important engineering value and reference significance for the risk prevention and explosion control of syngas-air in practical applications.
In order to investigate the effect of the pores per inch (PPI) of copper foam and hydrogen volume fractions (φ) on the explosive characteristics of premixed syngas-air, a copper foams with PPI of 15, 25 and 40 respectively was employed in a closed pipe (100 × 100 × 1000 mm) and its distance to the ignition end is 500 mm. Correspondingly, the premixed syngas-air flame propagates in duct without copper foam was compared. The premixed syngas-air mixtures with equivalence ratio of 1 but over a wide range of hydrogen volume fractions (from 10% to 90%) were tested. Detailed flame evolution process was visualized by a high-speed camera and the overpressure was recorded by pressure transducer. The results indicated that the copper foam has a significant impact on flame propagation and overpressure-time histories of premixed syngas-air explosion. The flame structure, flame tip velocity and overpressure obtained before the flame approaches the copper foam are determined by the formation process of “tulip” flame. And they are only related to the fuel component, not the copper foam. The PPI and j affect not only the time of “tulip” flame formation, but also affect the appearance of distorted “tulip” flame. The copper foam could lead to the segmentation of flame front and translate the flame front from laminar to turbulence, resulting in the flame acceleration. This phenomenon becomes more evident with the decreasing of PPI. The growth of overpressure recorded in premixed syngas-air explosion was closely related to the flame structure evolution. The presence of copper foam can increases the flame tip speed and overpressure significantly. For the case with a smaller PPI, both the maximum flame tip speed, growth of overpressure and maximum overpressure of premixed syngas-air increase with the φ. The research results have important engineering value and reference significance for the risk prevention and explosion control of syngas-air in practical applications.
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In order to study the containment properties of aero-engine casing made of ZL114A(ZAlSi7Mg1A) aluminum alloy under the impact of blade fragments at different temperatures, the material models describing the large deformation and failure behavior of ZL114A aluminum alloy under a large range of temperatures were established. Firstly, quasi-static tensile tests at various temperatures and dynamic compression tests were conducted in the universal testing machine and the SHPB (Split Hopkinson Pressure Bar), respectively. Based on the force-displacement data obtained in tensile tests, the finite element code and optimization algorithm were used to reversely identify the material hardening parameters at temperatures of 25°C~375°C. In this process, the accuracy of two hardening laws, Ludwik and Hockett/Sherby, describing the plastic flow behavior of ZL114A aluminum alloy under large deformation were compared. Subsequently, combined with the dynamic behavior relation of ZL114A aluminum alloy at strain rates of 1310s-1~5964s-1, a modified empirical constitutive model incorporating plastic strain, temperature, and strain rate was established, based on the Hockett/Sherby hardening law and Cowper-Symonds model. Further, the tests of notch tension, notch compression and shear were carried out, and the parallel finite element models were numerically calculated. The limitation of failure parameters related to failure criterion by the theoretical formula was analyzed, and the failure parameters are obtained by combining experiment and finite element method. Johnson-Cook failure criterion in branch form was used to describe the relationship between failure strain and stress triaxiality of ZL114A aluminum alloy. Considering the influence of temperature and strain rate, the failure criterion describing the failure behavior of ZL114A aluminum alloy was obtained. Finally, the validity of the fracture criterion and its parameters were verified by the ZL114A aluminum alloy flat plate penetration tests and the numerical simulations at various temperatures. The results show ZL114A aluminum alloy has obvious characteristics of strain hardening, temperature softening, and high strain rate strengthening. The Hockett/Sherby hardening law with stress saturation characteristics more accurately describes the stress flow behavior of ZL114A aluminum alloy than that of Ludwik under large deformation. The modified constitutive relation effectively describes the stress flow behavior of ZL114A aluminum alloy to a certain degree under large strain, wide temperature, and high strain rate. At the same time, the fracture criterion in branch form has good applicability to predict the impact failure behavior of flat plates at different temperatures.
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Ultra High Performance Concrete (UHPC) is a new type of protective material with both ultra-high strength and ultra-high toughness can be adopted as an ideal material in the impact resistant design of structures. In this paper, the impact resistance of 160MPa UHPC was investigated experimentally by conducting the high-speed projectile penetration tests which launched by the 30mm-diameter, smooth-bore powder gun at the striking velocities 216 m/s and 350 m/s. The test results show that with the increase of projectile velocity, the penetration depth and crater diameter increase obviously. The MAT_RHT is implemented into finite element package LS-DYNA for UHPC. In order to verify the accuracy of the material model, split Hopkinson pressure bar (SHPB) testing results are used to validate 3D finite element material model. With the validated numerical model of UHPC, Numerical studies are conducted to simulate the projectile penetration process into UHPC targets with the assistance of a computer program LS-DYNA. The numerical results in terms of the depth of penetration and crater diameter are compared with the experimental results. In addition, parametric studies are conducted to investigate effects of UHPC compressive strength, projectile mass, projectile striking velocity, projectile diameter and projectile caliber-radius-head (CRH) ratio on the depth of penetration of UHPC targets. Moreover, an empirical formula to predict the depth of penetration is derived according to the simulated data.
Ultra High Performance Concrete (UHPC) is a new type of protective material with both ultra-high strength and ultra-high toughness can be adopted as an ideal material in the impact resistant design of structures. In this paper, the impact resistance of 160MPa UHPC was investigated experimentally by conducting the high-speed projectile penetration tests which launched by the 30mm-diameter, smooth-bore powder gun at the striking velocities 216 m/s and 350 m/s. The test results show that with the increase of projectile velocity, the penetration depth and crater diameter increase obviously. The MAT_RHT is implemented into finite element package LS-DYNA for UHPC. In order to verify the accuracy of the material model, split Hopkinson pressure bar (SHPB) testing results are used to validate 3D finite element material model. With the validated numerical model of UHPC, Numerical studies are conducted to simulate the projectile penetration process into UHPC targets with the assistance of a computer program LS-DYNA. The numerical results in terms of the depth of penetration and crater diameter are compared with the experimental results. In addition, parametric studies are conducted to investigate effects of UHPC compressive strength, projectile mass, projectile striking velocity, projectile diameter and projectile caliber-radius-head (CRH) ratio on the depth of penetration of UHPC targets. Moreover, an empirical formula to predict the depth of penetration is derived according to the simulated data.
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Damage elements such as high-speed shaped charge projectile and strong discontinuous shock wave are generated during the process of the shaped charge associated with the underwater explosion. The theory of the action time sequence of the shaped charge projectile and the shock wave should be improved because their action time is close. Therefore, it is of great significance to investigate the action time sequence of different loads and their damage into ship structures. First, the basic form of acceleration and velocity equations are deduced in the formation process of the shaped charge projectile, based on contact explosion theory and Newton's second law. Subsequently, based on the Eulerian control equations, numerical models of air and water explosions of shaped charges are established. The evolution of pressure at the interaction of the charge and the liner is obtained. The acceleration and velocity equations of the shaped charge projectile are given quantitatively in this manuscript as a result. Besides, the obtained theoretical formulation can be utilized to solve the problem of the action time sequence of the shaped charge projectile and direct shock wave. In order to verify the reliability of this theoretical formulation, the case that the air cavity length is five times of the charge radius is conducted. The numerical results are in general agreement with those of the theoretical derivation. The results show that when the length of the air cavity is five times of the charge radius and the stand-off distance is larger than three times of the charge radius, the shock wave precedes the shaped charge projectile. The basic form of theoretical formulas is presented for the acceleration and velocity of the shaped charge projectile. Besides, the idea of solving the action time sequence problem of these two loads, which provides a theoretical basis for analyzing the action time sequence of underwater explosives.
Damage elements such as high-speed shaped charge projectile and strong discontinuous shock wave are generated during the process of the shaped charge associated with the underwater explosion. The theory of the action time sequence of the shaped charge projectile and the shock wave should be improved because their action time is close. Therefore, it is of great significance to investigate the action time sequence of different loads and their damage into ship structures. First, the basic form of acceleration and velocity equations are deduced in the formation process of the shaped charge projectile, based on contact explosion theory and Newton's second law. Subsequently, based on the Eulerian control equations, numerical models of air and water explosions of shaped charges are established. The evolution of pressure at the interaction of the charge and the liner is obtained. The acceleration and velocity equations of the shaped charge projectile are given quantitatively in this manuscript as a result. Besides, the obtained theoretical formulation can be utilized to solve the problem of the action time sequence of the shaped charge projectile and direct shock wave. In order to verify the reliability of this theoretical formulation, the case that the air cavity length is five times of the charge radius is conducted. The numerical results are in general agreement with those of the theoretical derivation. The results show that when the length of the air cavity is five times of the charge radius and the stand-off distance is larger than three times of the charge radius, the shock wave precedes the shaped charge projectile. The basic form of theoretical formulas is presented for the acceleration and velocity of the shaped charge projectile. Besides, the idea of solving the action time sequence problem of these two loads, which provides a theoretical basis for analyzing the action time sequence of underwater explosives.
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Under the threat of terrorism attacks and military strikes, building columns of the perimeter frames are likely to suffer near-field near-ground explosion. To rapidly assess the dynamic responses and failure modes of the building columns under such blast scenarios, in this paper numerical simulation method is employed to investigate the distribution pattern of the shock waves on the front face of building columns under near-field near-ground blast scenarios, and a corresponding simplified blast load model is proposed. To this end, firstly, the existing experimental data of overpressure and impulse are selected to validate the numerical model for blast load. Then, a typical numerical model under near-field near-ground blast scenarios is established to study the effects of the scaled distance and scaled height of the spherical charges on the characteristic values of the shock waves acting at the building columns. Finally, formulae for the maximum reflected impulse and the representative value of the positive overpressure duration are derived based on regression analysis, and the blast load at each location of the column front face is represented by an equivalent triangular load model. The results indicate that when the scaled height of the charge is less than 0.3 m/kg1/3, the distribution of the maximum reflected impulse along the column length can be represented as a trilinear model and a bilinear model for the scaled distance of 0.4 m/kg1/3-0.6 m/kg1/3 and 0.6 m/kg1/3-1.4 m/kg1/3, respectively. Moreover, under a given scaled distance and a scaled height, with increasing the charge weight, the peak reflected overpressure remains constant but the maximum reflected impulse is proportional to the cubic root of the charge weight at the locations with the identical scaled height of the column.
Under the threat of terrorism attacks and military strikes, building columns of the perimeter frames are likely to suffer near-field near-ground explosion. To rapidly assess the dynamic responses and failure modes of the building columns under such blast scenarios, in this paper numerical simulation method is employed to investigate the distribution pattern of the shock waves on the front face of building columns under near-field near-ground blast scenarios, and a corresponding simplified blast load model is proposed. To this end, firstly, the existing experimental data of overpressure and impulse are selected to validate the numerical model for blast load. Then, a typical numerical model under near-field near-ground blast scenarios is established to study the effects of the scaled distance and scaled height of the spherical charges on the characteristic values of the shock waves acting at the building columns. Finally, formulae for the maximum reflected impulse and the representative value of the positive overpressure duration are derived based on regression analysis, and the blast load at each location of the column front face is represented by an equivalent triangular load model. The results indicate that when the scaled height of the charge is less than 0.3 m/kg1/3, the distribution of the maximum reflected impulse along the column length can be represented as a trilinear model and a bilinear model for the scaled distance of 0.4 m/kg1/3-0.6 m/kg1/3 and 0.6 m/kg1/3-1.4 m/kg1/3, respectively. Moreover, under a given scaled distance and a scaled height, with increasing the charge weight, the peak reflected overpressure remains constant but the maximum reflected impulse is proportional to the cubic root of the charge weight at the locations with the identical scaled height of the column.
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doi: 10.11883/bzycj-2023-0108
Abstract:
To examine the mitigation characterisitics of blast wave in water mist, a comprehensive series of blast experiments were carried out utilizing a blast-driven shock tube with a 4 m length and 180 mm square inner cross-section. The blast wave was generated by detonating trinitrotoluene charges with masses of 7, 10 and 13 g within the shock tube. Five pressure gauges were installed to measure blast wave pressure within the spray region. In order to create varying water mist properties, a spray system was employed, which covered a distance of 3 m within the experimental setup. Droplet size and distribution were measured using a laser light scattering analyzer. The mitigation effect of water mist with two distinct properties on blast overpressure and impulse was evaluated. Results indicated that the pressure in the spray region raised in two stages. The first stage corresponded to the pressure associated with the transmitted shock wave, while the second stage was attributed to the secondary atomization and relaxation processes of the droplets. The longer the spray region traversed by the blast wave, the greater the mitigation effect on peak overpressure and impulse. Increased shock wave intensity diminished the mitigation effect of water mist on blast loads. Specifically, when water mist with a Sauter mean diameter of 136.04 μm and a volume fraction of 1.72×10−3 was employed, peak pressure values experienced a reduction ranging from 34.2% to 60.9%, while impulse values were reduced by 9% to 54%. On the other hand, when water mist with a Sauter mean diameter of 255.34 μm and a volume fraction of 3.43×10−3 was used, peak pressure values witnessed a reduction ranging from 48.4% to 78.6%, and impulse values were reduced by 14% to 66%. The mitigation coefficient of peak overpressure decreased linearly with increased scaled exchange surface area between blast wave and droplets.
To examine the mitigation characterisitics of blast wave in water mist, a comprehensive series of blast experiments were carried out utilizing a blast-driven shock tube with a 4 m length and 180 mm square inner cross-section. The blast wave was generated by detonating trinitrotoluene charges with masses of 7, 10 and 13 g within the shock tube. Five pressure gauges were installed to measure blast wave pressure within the spray region. In order to create varying water mist properties, a spray system was employed, which covered a distance of 3 m within the experimental setup. Droplet size and distribution were measured using a laser light scattering analyzer. The mitigation effect of water mist with two distinct properties on blast overpressure and impulse was evaluated. Results indicated that the pressure in the spray region raised in two stages. The first stage corresponded to the pressure associated with the transmitted shock wave, while the second stage was attributed to the secondary atomization and relaxation processes of the droplets. The longer the spray region traversed by the blast wave, the greater the mitigation effect on peak overpressure and impulse. Increased shock wave intensity diminished the mitigation effect of water mist on blast loads. Specifically, when water mist with a Sauter mean diameter of 136.04 μm and a volume fraction of 1.72×10−3 was employed, peak pressure values experienced a reduction ranging from 34.2% to 60.9%, while impulse values were reduced by 9% to 54%. On the other hand, when water mist with a Sauter mean diameter of 255.34 μm and a volume fraction of 3.43×10−3 was used, peak pressure values witnessed a reduction ranging from 48.4% to 78.6%, and impulse values were reduced by 14% to 66%. The mitigation coefficient of peak overpressure decreased linearly with increased scaled exchange surface area between blast wave and droplets.
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doi: 10.11883/bzycj-2023-0084
Abstract:
In order to further explore the energy absorption characteristics of the foamed metal with the explosion-facing surface structure different from that of its base subjected to gas explosion, based on the previous experiments carried on the energy absorption characteristics of serrated structural materials, mixed methane-air explosion energy absorption tests were conducted by using the self-built gas explosion pipe network experimental platform. Three kinds of different corrugated foamed metals were chosen as the explosion-proof materials and their explosion-facing surfaces took on full convex, full concave and continuous concave/convex, respectively. The variations of the corresponding typical physical quantities with time and space were measured and analyzed including explosion shock wave overpressure, flame propagation velocity and flame temperature. Results are shown as follows. (1) The foamed metals with corrugated structures can reduce explosion overpressure more effectively than the ones with the serrated structure and plane structure, and the foamed metals with fully convex and continuous concave-convex corrugated structures can decrease the explosion shock wave overpressure faster than the ones with the serrated and full-concave structures. Additionally, the foamed metals with the serrated structures can slow the flame propagation velocity down slightly faster than the ones with the corrugated and plane structures. And the foamed metals with the corrugated structures can weaken the flame temperature more strongly than the ones with the serrated and plane structures. (2) The quenching parameters of the corrugated foam metals whose explosion-facing surfaces taking on full convex, full concave and continuous concave/convex are 5.338, 4.340 and 6.090 MPa·°C, respectively, which are lower than that of the one with the serrated explosion-facing surface 17.680 MPa·°C, and far lower than the safety value 390 MPa·°C, indicating that the foamed metals with the corrugated explosion-facing surface have better explosion-proof capabilities. (3) The energy absorption performances of the foamed metals with the corrugated explosion-facing surfaces are stronger than those of the ones with the serrated explosion-facing surfaces, and are obviously stronger than that of the one with the plane explosion-facing surface. In addition, the foamed metals with the corrugated explosion-facing surfaces can still keep intact after the experiments, displaying that their material strengths are higher than those of the ones with the serrated structures.
In order to further explore the energy absorption characteristics of the foamed metal with the explosion-facing surface structure different from that of its base subjected to gas explosion, based on the previous experiments carried on the energy absorption characteristics of serrated structural materials, mixed methane-air explosion energy absorption tests were conducted by using the self-built gas explosion pipe network experimental platform. Three kinds of different corrugated foamed metals were chosen as the explosion-proof materials and their explosion-facing surfaces took on full convex, full concave and continuous concave/convex, respectively. The variations of the corresponding typical physical quantities with time and space were measured and analyzed including explosion shock wave overpressure, flame propagation velocity and flame temperature. Results are shown as follows. (1) The foamed metals with corrugated structures can reduce explosion overpressure more effectively than the ones with the serrated structure and plane structure, and the foamed metals with fully convex and continuous concave-convex corrugated structures can decrease the explosion shock wave overpressure faster than the ones with the serrated and full-concave structures. Additionally, the foamed metals with the serrated structures can slow the flame propagation velocity down slightly faster than the ones with the corrugated and plane structures. And the foamed metals with the corrugated structures can weaken the flame temperature more strongly than the ones with the serrated and plane structures. (2) The quenching parameters of the corrugated foam metals whose explosion-facing surfaces taking on full convex, full concave and continuous concave/convex are 5.338, 4.340 and 6.090 MPa·°C, respectively, which are lower than that of the one with the serrated explosion-facing surface 17.680 MPa·°C, and far lower than the safety value 390 MPa·°C, indicating that the foamed metals with the corrugated explosion-facing surface have better explosion-proof capabilities. (3) The energy absorption performances of the foamed metals with the corrugated explosion-facing surfaces are stronger than those of the ones with the serrated explosion-facing surfaces, and are obviously stronger than that of the one with the plane explosion-facing surface. In addition, the foamed metals with the corrugated explosion-facing surfaces can still keep intact after the experiments, displaying that their material strengths are higher than those of the ones with the serrated structures.
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doi: 10.11883/bzycj-2022-0562
Abstract:
To investigate the synergistic effect of N2 and combined porous media to suppress gas explosion, the experiments were carried out in an independently designed explosion pipe. The nitrogen curtain was 0.9 m away from the ignition location. The combined porous media used in the experiments consist of a combination of iron-nickel foam with pore densities of 10, 20, 30 and 40 ppi, as well as a combination of iron-nickel foam with 10 ppi and copper foam with 20 and 40 ppi. The results show that nitrogen curtains cause intact flames to propagate forward in a fragmented manner, diluting the concentration of combustible gases upstream of the porous medium and slowing down the flame propagation speed. The porous medium, on the other hand, effectively absorbs the precursor shock wave and disrupts the positive feedback mechanism, leading to further weakening of the flame propagation speed towards the porous medium and enhancing the quenching performance of the medium. The porous media with high pore density as the second layer of the combined porous media, can block the nitrogen from escaping upstream of the porous media, significantly reducing the concentration of combustible gases upstream, the flame propagation speed then decreases rapidly, and the slowed down flame is more easily quenched by the combined porous media. When the pore density of the second layer increases, the first overpressure peak remains largely unchanged, while the second overpressure peak rises sharply, which increases the risk of explosion. The combination of iron-nickel foam in the first layer and copper foam in the second layer significantly reduces the intensity of the flame when it reaches the porous media and lowers the overpressure peak, while the high strength of iron-nickel foam in front of the copper foam prevents the low strength copper foam from deforming and causing quenching failure. The combination with the best explosion suppression effect is the pore density 10 ppi of iron-nickel foam metal and 40 ppi of copper foam to form a combination of porous media.
To investigate the synergistic effect of N2 and combined porous media to suppress gas explosion, the experiments were carried out in an independently designed explosion pipe. The nitrogen curtain was 0.9 m away from the ignition location. The combined porous media used in the experiments consist of a combination of iron-nickel foam with pore densities of 10, 20, 30 and 40 ppi, as well as a combination of iron-nickel foam with 10 ppi and copper foam with 20 and 40 ppi. The results show that nitrogen curtains cause intact flames to propagate forward in a fragmented manner, diluting the concentration of combustible gases upstream of the porous medium and slowing down the flame propagation speed. The porous medium, on the other hand, effectively absorbs the precursor shock wave and disrupts the positive feedback mechanism, leading to further weakening of the flame propagation speed towards the porous medium and enhancing the quenching performance of the medium. The porous media with high pore density as the second layer of the combined porous media, can block the nitrogen from escaping upstream of the porous media, significantly reducing the concentration of combustible gases upstream, the flame propagation speed then decreases rapidly, and the slowed down flame is more easily quenched by the combined porous media. When the pore density of the second layer increases, the first overpressure peak remains largely unchanged, while the second overpressure peak rises sharply, which increases the risk of explosion. The combination of iron-nickel foam in the first layer and copper foam in the second layer significantly reduces the intensity of the flame when it reaches the porous media and lowers the overpressure peak, while the high strength of iron-nickel foam in front of the copper foam prevents the low strength copper foam from deforming and causing quenching failure. The combination with the best explosion suppression effect is the pore density 10 ppi of iron-nickel foam metal and 40 ppi of copper foam to form a combination of porous media.
, Available online ,
doi: 10.11883/bzycj-2022-0335
Abstract:
FRP-concrete-steel double skin tubular columns (FRP-DSTCs) consist of an outer FRP tube and an inner steel tube, with the space between them infilled by concrete. This type of members has been applied in bridge piers, and the impact resistance is an important index for its utilization. Therefore, based on the previous test, the finite element analysis (FEA) models considering the coupling of axial and impact loads are established using ABAQUS software and verified by comparing the simulation and test results. In the model, the static implicit and dynamic explicit analysis are coupled by using “Restart” and “Import” commands. In addition, the strain rate effect of the steel and concrete are considered. Firstly, the mechanism of impact resistance under coupling axial and impact loads is analyzed. Then, the influence of thickness and fiber orientations of FRP, axial-load ratio, impact velocity, hollow ratio, diameter-to-thickness ratio of the steel tube and material strengths on the impact resistance are investigated. Finally, the formula used to predict the dynamic increase factor of the plateau impact force under coupling axial and impact loads is suggested. Results indicate that the deformation pattern of FRP-DSTCs mainly presents flexural deformation, and the plastic deformation of concrete is the main energy dissipation mechanism of such members. The outer FRP can significantly improve the lateral impact resistance of the specimen, and increasing the number of FRP layers leads to enhanced impact resistance. In addition, the axial load has an obvious effect on the impact resistance, and the effect is negative when the axial load ratio exceeds 0.7. The diameter-to-thickness ratio of steel tube presents marginal effects on the impact resistance. The proposed formula that considers the hollow ratio, strengths of concrete and inner steel tube, thickness of FRP, axial load ratio and impact velocity can reasonably predict the impact bearing capacity of FRP-DSTCs.
FRP-concrete-steel double skin tubular columns (FRP-DSTCs) consist of an outer FRP tube and an inner steel tube, with the space between them infilled by concrete. This type of members has been applied in bridge piers, and the impact resistance is an important index for its utilization. Therefore, based on the previous test, the finite element analysis (FEA) models considering the coupling of axial and impact loads are established using ABAQUS software and verified by comparing the simulation and test results. In the model, the static implicit and dynamic explicit analysis are coupled by using “Restart” and “Import” commands. In addition, the strain rate effect of the steel and concrete are considered. Firstly, the mechanism of impact resistance under coupling axial and impact loads is analyzed. Then, the influence of thickness and fiber orientations of FRP, axial-load ratio, impact velocity, hollow ratio, diameter-to-thickness ratio of the steel tube and material strengths on the impact resistance are investigated. Finally, the formula used to predict the dynamic increase factor of the plateau impact force under coupling axial and impact loads is suggested. Results indicate that the deformation pattern of FRP-DSTCs mainly presents flexural deformation, and the plastic deformation of concrete is the main energy dissipation mechanism of such members. The outer FRP can significantly improve the lateral impact resistance of the specimen, and increasing the number of FRP layers leads to enhanced impact resistance. In addition, the axial load has an obvious effect on the impact resistance, and the effect is negative when the axial load ratio exceeds 0.7. The diameter-to-thickness ratio of steel tube presents marginal effects on the impact resistance. The proposed formula that considers the hollow ratio, strengths of concrete and inner steel tube, thickness of FRP, axial load ratio and impact velocity can reasonably predict the impact bearing capacity of FRP-DSTCs.
, Available online ,
doi: 10.11883/bzycj-2022-0486
Abstract:
Under irradiation conditions, a large number of micro-defects such as helium bubbles are produced in some materials, and the size and number density of helium bubbles increase with the increase of irradiation years. The variation of helium bubble distribution not only affects the physical and mechanical properties of the material itself, but also directly affects the distribution characteristics of fracture particle size in the later stage of spallation damage evolution. The evolution process of spallation damage in ductile materials generally includes nucleation, growth and confluence of pores. However, due to the inhibition of existing pores on new nucleation pores, when the initial number density of pores reaches a certain critical value, the calculation of spallation damage can not consider the influence of new nucleation. Based on the characteristics of early damage evolution, a formula for calculating this critical value is given, and based on this formula, the calculation method of spallation damage of plutonium materials irradiated by helium bubbles is further discussed. Then, in order to solve the problem of the difference between the initial damage parameters of the damage model and the real initial damage of the material, we give a method to determine the damage parameters in the VG (void growth) model. Finally, this problem is analyzed qualitatively by using the experimental results of spallation of conventional aluminum materials containing helium bubbles. The analysis results show that, for the calculation of spallation damage of irradiated materials containing helium bubbles, when the helium bubble size changes little and the helium bubble concentration is lower than the critical helium bubble concentration given in this paper, it is necessary to consider the comprehensive influence of initial helium bubbles and new holes; On the contrary, a simple spallation damage model can be adopted, and the nucleation of holes does not need to be calculated.
Under irradiation conditions, a large number of micro-defects such as helium bubbles are produced in some materials, and the size and number density of helium bubbles increase with the increase of irradiation years. The variation of helium bubble distribution not only affects the physical and mechanical properties of the material itself, but also directly affects the distribution characteristics of fracture particle size in the later stage of spallation damage evolution. The evolution process of spallation damage in ductile materials generally includes nucleation, growth and confluence of pores. However, due to the inhibition of existing pores on new nucleation pores, when the initial number density of pores reaches a certain critical value, the calculation of spallation damage can not consider the influence of new nucleation. Based on the characteristics of early damage evolution, a formula for calculating this critical value is given, and based on this formula, the calculation method of spallation damage of plutonium materials irradiated by helium bubbles is further discussed. Then, in order to solve the problem of the difference between the initial damage parameters of the damage model and the real initial damage of the material, we give a method to determine the damage parameters in the VG (void growth) model. Finally, this problem is analyzed qualitatively by using the experimental results of spallation of conventional aluminum materials containing helium bubbles. The analysis results show that, for the calculation of spallation damage of irradiated materials containing helium bubbles, when the helium bubble size changes little and the helium bubble concentration is lower than the critical helium bubble concentration given in this paper, it is necessary to consider the comprehensive influence of initial helium bubbles and new holes; On the contrary, a simple spallation damage model can be adopted, and the nucleation of holes does not need to be calculated.
, Available online ,
doi: 10.11883/bzycj-2023-0153
Abstract:
In order to study the response law of a metal target plate under the simultaneous initiation of two charges and to construct a calculation model for the deformation and deflection of the target plate under the action of dual explosion source shock waves, the dynamic response of the metal plate under the action of double explosion sources was studied through dimensional analysis. Based on the numerical simulation calculation results using the finite element software, the influence of the charge quality, charge spacing, and vertical distance from the charge to the target plate of the double explosion source on the maximum deflection of the 45 steel target plate was summarized. The results show that the maximum deflection of the target plate increases linearly with the charge mass, decreases linearly with the charge spacing and decreases exponentially with the vertical distance from the charge to the target plate. The functional relationship between different parameters and the maximum deformation deflection of the target plate was fitted. This study can to some extent achieve rapid calculation of the explosion effect of charges with different distributions.
In order to study the response law of a metal target plate under the simultaneous initiation of two charges and to construct a calculation model for the deformation and deflection of the target plate under the action of dual explosion source shock waves, the dynamic response of the metal plate under the action of double explosion sources was studied through dimensional analysis. Based on the numerical simulation calculation results using the finite element software, the influence of the charge quality, charge spacing, and vertical distance from the charge to the target plate of the double explosion source on the maximum deflection of the 45 steel target plate was summarized. The results show that the maximum deflection of the target plate increases linearly with the charge mass, decreases linearly with the charge spacing and decreases exponentially with the vertical distance from the charge to the target plate. The functional relationship between different parameters and the maximum deformation deflection of the target plate was fitted. This study can to some extent achieve rapid calculation of the explosion effect of charges with different distributions.
, Available online ,
doi: 10.11883/bzycj-2022-0375
Abstract:
In view of the hot problem of reducing the harm of explosive terrorist attacks in public security field, the research on explosion-proof structures is urgent. Polyurethane foam has the advantages of being lightweight, has excellent mechanical properties, and can avoid secondary debris damage. It has a good application prospect in the new explosive disposal equipment. Based on the research background of explosion hazard reduction, the mechanism and effectiveness of shock wave weakening of polyurethane foam and polyurethane-based composite barriers need to be investigated. The microstructure and mechanical properties of porous polyurethane were tested firstly. It was to obtain the basic parameters and contribute to construct the simulation model of the samples with different densities (100 ~ 300 kg/m3). A directional flow field device was set up to impact the polyurethane plate and the feasibility of the corresponding numerical model was analyzed to study its protective performance against the plane shock wave. On this basis, the weakening effect of the polyurethane-water annular composite barrier under internal explosive loading was analyzed numerically by using the verified numerical model. The design premise was that the total volume of barriers was equal, and the shockwave weakening performances of PU/Water, pure Water and Water/PU barriers were compared. The influence of polyurethane density on shock wave weakening performance was analyzed. The results show that the existence of a barrier forces the shock wave to reflect, diffract, transmit and interact with each other. Compared with a pure Water barrier, the PU/Water barrier can effectively reduce shock wave peak (up to 13.3%) when the total mass decreases by 32%. This is mainly because of the lower impedance of the inner polyurethane foam, which can reduce the strength of the shock wave reflected back from the barrier wall. Under current simulation conditions, it is more effective for the protection of corresponding barrier when the density of PU is 200 kg/m3 in the PU/Water barrier.
In view of the hot problem of reducing the harm of explosive terrorist attacks in public security field, the research on explosion-proof structures is urgent. Polyurethane foam has the advantages of being lightweight, has excellent mechanical properties, and can avoid secondary debris damage. It has a good application prospect in the new explosive disposal equipment. Based on the research background of explosion hazard reduction, the mechanism and effectiveness of shock wave weakening of polyurethane foam and polyurethane-based composite barriers need to be investigated. The microstructure and mechanical properties of porous polyurethane were tested firstly. It was to obtain the basic parameters and contribute to construct the simulation model of the samples with different densities (100 ~ 300 kg/m3). A directional flow field device was set up to impact the polyurethane plate and the feasibility of the corresponding numerical model was analyzed to study its protective performance against the plane shock wave. On this basis, the weakening effect of the polyurethane-water annular composite barrier under internal explosive loading was analyzed numerically by using the verified numerical model. The design premise was that the total volume of barriers was equal, and the shockwave weakening performances of PU/Water, pure Water and Water/PU barriers were compared. The influence of polyurethane density on shock wave weakening performance was analyzed. The results show that the existence of a barrier forces the shock wave to reflect, diffract, transmit and interact with each other. Compared with a pure Water barrier, the PU/Water barrier can effectively reduce shock wave peak (up to 13.3%) when the total mass decreases by 32%. This is mainly because of the lower impedance of the inner polyurethane foam, which can reduce the strength of the shock wave reflected back from the barrier wall. Under current simulation conditions, it is more effective for the protection of corresponding barrier when the density of PU is 200 kg/m3 in the PU/Water barrier.
, Available online ,
doi: 10.11883/bzycj-2022-0509
Abstract:
To study the cavity development characteristics and motion characteristics of the trans-media vehicle with tail-skirt during the process of oblique water entry at high speed, a high-speed water-entry experiment platform was built, and an experimental model with inertial measurement unit system was designed. The experimental study was carried out on the trans-media vehicle model with tail-skirt when the water entry angle was 20° and the water entry velocity was in the range from 30m/s to 130m/s. The high-speed camera was used to record the cavity during water entry, and the inertial measurement unit was used to measure the motion parameters of the vehicle and the pressure inside the cavity. The cavity development characteristics, the motion characteristics and the changing law of the pressure inside the cavity during the high-speed oblique water entry were obtained. The experimental results show that the planning motion characteristics is formed during the water entry process of the trans-media vehicle with tail-skirt, and the bending deformation of the cavity occurs. With the increase of the water entry velocity, the upward deflection trend of the water entry trajectory becomes more obvious. The peak axial load of the vehicle entering water takes a long time, so load reduction should be considered in the process of crossing media. The peak normal load gradually drops to about 0 after entering the water 1.5 times the length of the vehicle. During the high-speed water entry process, the upper surface of the trans-media vehicle is always wrapped in the cavity. The pressure inside the cavity decreases first and then increases with the formation and development of the cavity. The minimum pressure changes linearly with the water entry velocity, and the formation time is basically the same.
To study the cavity development characteristics and motion characteristics of the trans-media vehicle with tail-skirt during the process of oblique water entry at high speed, a high-speed water-entry experiment platform was built, and an experimental model with inertial measurement unit system was designed. The experimental study was carried out on the trans-media vehicle model with tail-skirt when the water entry angle was 20° and the water entry velocity was in the range from 30m/s to 130m/s. The high-speed camera was used to record the cavity during water entry, and the inertial measurement unit was used to measure the motion parameters of the vehicle and the pressure inside the cavity. The cavity development characteristics, the motion characteristics and the changing law of the pressure inside the cavity during the high-speed oblique water entry were obtained. The experimental results show that the planning motion characteristics is formed during the water entry process of the trans-media vehicle with tail-skirt, and the bending deformation of the cavity occurs. With the increase of the water entry velocity, the upward deflection trend of the water entry trajectory becomes more obvious. The peak axial load of the vehicle entering water takes a long time, so load reduction should be considered in the process of crossing media. The peak normal load gradually drops to about 0 after entering the water 1.5 times the length of the vehicle. During the high-speed water entry process, the upper surface of the trans-media vehicle is always wrapped in the cavity. The pressure inside the cavity decreases first and then increases with the formation and development of the cavity. The minimum pressure changes linearly with the water entry velocity, and the formation time is basically the same.
, Available online ,
doi: 10.11883/bzycj-2023-0061
Abstract:
In this experiment, finite size red sandstone containing pre-existing single crack was taken as the research object. The ratio of length to width of the samples was set about 0.65. The inclination angle of the precrack includes 0°, 30°, 45°, 60° and 90°. A split Hopkinson pressure bar was used for impact test, and a high-speed camera was used to record the crack propagation. The dynamic loads were applied along the width of the samples. Velocities of striker in impact tests were set as 6 m/s, 8 m/s and 10 m/s by adjusting the pressure of the air gun. Acquisition frequency of the high-speed camera was set as 75000 fps. The characteristics of crack propagation, dynamic compressive strength and dynamic elastic modulus of the samples were obtained. The fractal theory was used to describe the fragmentation characteristics of the samples. The relationship between dynamic mechanical properties, fragmentation characteristics and crack propagation under medium strain rate was discussed. The findings show that when the strain rate is high, more far-field cracks and separation cracks appear in the sample. In the range of medium strain rate, the failure mode and the number of cracks change differently with strain rate compared with the experimental results of low strain rate. The strain rate and the angle of pre-existing crack have a great influence on the crack propagation and failure mode of the samples. The crack propagation of the samples with different pre-existing crack is different. With the increase of strain rate, the failure mode of the sample becomes more complex, gradually evolving from critical failure with a tensile crack to complex failure mainly with X-type shear crack. When the angle of the pre-existing crack is fixed, the dynamic compressive strength and dynamic elastic modulus of the samples show obvious strain rate effect, and the pre-existing crack with different angles have significant influence on the strain rate sensitivity of the samples. With the increase of pre-existing crack angle, the variation of dynamic compressive strength, dynamic elastic modulus and fractal dimension of the samples show a certain similarity. In all types of samples, the dynamic compressive strength, dynamic elastic modulus and fractal dimension of the sample containing cracks with the inclination angle at 45° are the smallest. With the increase of strain rate, distribution of fragments becomes more dispersed. The higher the strain rate, the more significant the effect of the pre-existing crack on the fracture degree and fractal dimension of the samples.
In this experiment, finite size red sandstone containing pre-existing single crack was taken as the research object. The ratio of length to width of the samples was set about 0.65. The inclination angle of the precrack includes 0°, 30°, 45°, 60° and 90°. A split Hopkinson pressure bar was used for impact test, and a high-speed camera was used to record the crack propagation. The dynamic loads were applied along the width of the samples. Velocities of striker in impact tests were set as 6 m/s, 8 m/s and 10 m/s by adjusting the pressure of the air gun. Acquisition frequency of the high-speed camera was set as 75000 fps. The characteristics of crack propagation, dynamic compressive strength and dynamic elastic modulus of the samples were obtained. The fractal theory was used to describe the fragmentation characteristics of the samples. The relationship between dynamic mechanical properties, fragmentation characteristics and crack propagation under medium strain rate was discussed. The findings show that when the strain rate is high, more far-field cracks and separation cracks appear in the sample. In the range of medium strain rate, the failure mode and the number of cracks change differently with strain rate compared with the experimental results of low strain rate. The strain rate and the angle of pre-existing crack have a great influence on the crack propagation and failure mode of the samples. The crack propagation of the samples with different pre-existing crack is different. With the increase of strain rate, the failure mode of the sample becomes more complex, gradually evolving from critical failure with a tensile crack to complex failure mainly with X-type shear crack. When the angle of the pre-existing crack is fixed, the dynamic compressive strength and dynamic elastic modulus of the samples show obvious strain rate effect, and the pre-existing crack with different angles have significant influence on the strain rate sensitivity of the samples. With the increase of pre-existing crack angle, the variation of dynamic compressive strength, dynamic elastic modulus and fractal dimension of the samples show a certain similarity. In all types of samples, the dynamic compressive strength, dynamic elastic modulus and fractal dimension of the sample containing cracks with the inclination angle at 45° are the smallest. With the increase of strain rate, distribution of fragments becomes more dispersed. The higher the strain rate, the more significant the effect of the pre-existing crack on the fracture degree and fractal dimension of the samples.
, Available online ,
doi: 10.11883.bzycj-2023-0130
Abstract:
The impact resistance of T300 carbon fiber blades was studied through experiments and numerical simulations. The deformation damage pattern and the effect of the number of fiber layers on the impact resistance of the blade are studied. The impact experiment was conducted on the carbon fiber blades of different layers. Based on the macro-level continuum damage mechanics theory and the Hashin failure criterion, a vectorized user-material subroutine was written for the carbon fiber material, and the smooth particle hydrodynamics algorithm was used to simulate the gelatin projectiles. Numerical simulations of bird impact on the composite blades with different layers were carried out in ABAQUS/Explicit. The blade deformation process, bird flow state, and impact duration time of the experiments agree well with the numerical results. In the initial impact stage, the blade specimens have large deformations, and the deformation modes of the three carbon fiber blades with different layers are similar to each other. However, in the impact attenuation and constant flow stages, the deflection and fracture of different layers of carbon fiber blades are quite different. The damage mode of the 6-layer carbon fiber blade is complete fractures at the blade root and top, the damage mode of the 8-layer carbon fiber blade is root fracture, and there is no obvious macroscopic visible damage in the 10-layer carbon fiber blade. Under the gelatin projectile impact loading, the blade deformation mode is mainly coupled with the bending and torsional deformation process, and the bending deformation dominates the damage and failure process. Experimental results show that the damage pattern of carbon fiber blades is mainly classified as (1) edge damage at the root, (2) complete fracture at the root, and (3) complete fracture at the root and top edge. The impact resistance of carbon fiber is greatly influenced by the number of layers. The mechanism analysis of gelatin projectile impact on carbon fiber blades through experiments and numerical simulations can provide a reference for the engineering design and application of carbon fiber blades.
The impact resistance of T300 carbon fiber blades was studied through experiments and numerical simulations. The deformation damage pattern and the effect of the number of fiber layers on the impact resistance of the blade are studied. The impact experiment was conducted on the carbon fiber blades of different layers. Based on the macro-level continuum damage mechanics theory and the Hashin failure criterion, a vectorized user-material subroutine was written for the carbon fiber material, and the smooth particle hydrodynamics algorithm was used to simulate the gelatin projectiles. Numerical simulations of bird impact on the composite blades with different layers were carried out in ABAQUS/Explicit. The blade deformation process, bird flow state, and impact duration time of the experiments agree well with the numerical results. In the initial impact stage, the blade specimens have large deformations, and the deformation modes of the three carbon fiber blades with different layers are similar to each other. However, in the impact attenuation and constant flow stages, the deflection and fracture of different layers of carbon fiber blades are quite different. The damage mode of the 6-layer carbon fiber blade is complete fractures at the blade root and top, the damage mode of the 8-layer carbon fiber blade is root fracture, and there is no obvious macroscopic visible damage in the 10-layer carbon fiber blade. Under the gelatin projectile impact loading, the blade deformation mode is mainly coupled with the bending and torsional deformation process, and the bending deformation dominates the damage and failure process. Experimental results show that the damage pattern of carbon fiber blades is mainly classified as (1) edge damage at the root, (2) complete fracture at the root, and (3) complete fracture at the root and top edge. The impact resistance of carbon fiber is greatly influenced by the number of layers. The mechanism analysis of gelatin projectile impact on carbon fiber blades through experiments and numerical simulations can provide a reference for the engineering design and application of carbon fiber blades.
, Available online ,
doi: 10.11883/bzycj/2022-0520
Abstract:
High porosity structures with negative Poisson’s ratio often experience severe stress fluctuations and significant peak stresses during energy absorption, which can easily cause local damage to the honeycomb structure and affect continuous energy absorption. In order to reduce the occurrence of local damage, an anti-symmetric arc-shaped cell element is designed based on the traditional negative Poisson’s ratio honeycomb cell element, and 2 new anti-symmetric negative Poisson’s ratio arc-shaped honeycomb structures are obtained through different array directions. Through 0.0025 m/s (quasi-static) compression test and 10 m/s (low speed), 50 m/s (medium speed) and 100 m/s (high speed) finite element simulation, the effect of velocity gradient on the overall deformation pattern, horizontal strain distribution of different layers, deformation mechanism, and impact resistance of the new anti-symmetric arc-shaped honeycomb structure model are revealed. The research results show that unlike the large number of local densification areas that appear in traditional negative Poisson’s ratio honeycomb models, the local densification bands in the new anti-symmetric negative Poisson’s ratio arc-shaped honeycomb structure are significantly reduced. The deformation areas composed of multiple layers of cells in the structure participate in deformation at the same time, showing a very stable deformation pattern as a whole. This is closely related to the increase in maximum horizontal strain and the enhancement of impact resistance of the new honeycomb structure. Especially under the medium-speed loading, the impact resistance of the new anti-symmetric arc-shaped honeycomb model is significantly enhanced, and the impact load efficiency reaches 78%, which is much higher than the 43% impact load efficiency of the traditional honeycomb model; in addition, the anti-symmetric arc-shaped honeycomb structure cells also drive the cell walls between adjacent cells to bend upwards to resist bending moments, further increasing the maximum horizontal strain. Under low-speed loading, the maximum horizontal strain of the two types of new anti-symmetric arc-shaped honeycomb models increases by 100% and 36%, respectively. Under medium-speed loading, it increases by 39% for both types.
High porosity structures with negative Poisson’s ratio often experience severe stress fluctuations and significant peak stresses during energy absorption, which can easily cause local damage to the honeycomb structure and affect continuous energy absorption. In order to reduce the occurrence of local damage, an anti-symmetric arc-shaped cell element is designed based on the traditional negative Poisson’s ratio honeycomb cell element, and 2 new anti-symmetric negative Poisson’s ratio arc-shaped honeycomb structures are obtained through different array directions. Through 0.0025 m/s (quasi-static) compression test and 10 m/s (low speed), 50 m/s (medium speed) and 100 m/s (high speed) finite element simulation, the effect of velocity gradient on the overall deformation pattern, horizontal strain distribution of different layers, deformation mechanism, and impact resistance of the new anti-symmetric arc-shaped honeycomb structure model are revealed. The research results show that unlike the large number of local densification areas that appear in traditional negative Poisson’s ratio honeycomb models, the local densification bands in the new anti-symmetric negative Poisson’s ratio arc-shaped honeycomb structure are significantly reduced. The deformation areas composed of multiple layers of cells in the structure participate in deformation at the same time, showing a very stable deformation pattern as a whole. This is closely related to the increase in maximum horizontal strain and the enhancement of impact resistance of the new honeycomb structure. Especially under the medium-speed loading, the impact resistance of the new anti-symmetric arc-shaped honeycomb model is significantly enhanced, and the impact load efficiency reaches 78%, which is much higher than the 43% impact load efficiency of the traditional honeycomb model; in addition, the anti-symmetric arc-shaped honeycomb structure cells also drive the cell walls between adjacent cells to bend upwards to resist bending moments, further increasing the maximum horizontal strain. Under low-speed loading, the maximum horizontal strain of the two types of new anti-symmetric arc-shaped honeycomb models increases by 100% and 36%, respectively. Under medium-speed loading, it increases by 39% for both types.
, Available online ,
doi: 10.11883/bzycj-2022-0199
Abstract:
Transparent material has been widely used in the field of special protection, in order to avoid common brittle transparent material damage failure of secondary injury, often use a variety of transparent materials preparation of transparent laminated structure to play a variety of materials, the advantages of shock resistance for structure as a whole but for different materials, the effects of lack of quick and easy design guidance, Artificial neural network has a good applicability to the nonlinear problems of multi-material structures and provides a new idea for structural design. In this paper, we study for alumina ceramic layer thickness, silica inorganic glass and polycarbonate organic glass as an energy absorption layer, through the transparent laminated structure of polyurethane cementation in the mechanical response of high-speed impact, this paper adopted level light gas gun to the impact experiment of sample, sample showing a ceramic layer bending failure destruction of led and the impact compression failure led two failure mode, The dynamic crack propagation process was recorded by high-speed camera. Subsequently, the finite element software, Abaqus was used to simulate the projectile impact at 120, 150 and 180 m/s for transparent sandwich structures with multiple layersʼ thickness ratio. For ceramic materials, a subroutine based on JH-2 constitutive model was introduced, and the process of crack propagation and debris splashing was simulated in combination with element removal method. The simulation results were in good agreement with the experiment. Finally, BP neural network algorithm is employed to forecast the impact point peak bending, monolayer and multilayer neural network model calculation takes 1 minute respectively and three minutes on average, the mean relative errors were 7.6% and 3.2% respectively, and the model computation time and precision meet the requirements, compared with the traditional time-consuming hours of finite element calculation, save a lot of time, It can provide guidance and help to the design and development of transparent sandwich structures.
Transparent material has been widely used in the field of special protection, in order to avoid common brittle transparent material damage failure of secondary injury, often use a variety of transparent materials preparation of transparent laminated structure to play a variety of materials, the advantages of shock resistance for structure as a whole but for different materials, the effects of lack of quick and easy design guidance, Artificial neural network has a good applicability to the nonlinear problems of multi-material structures and provides a new idea for structural design. In this paper, we study for alumina ceramic layer thickness, silica inorganic glass and polycarbonate organic glass as an energy absorption layer, through the transparent laminated structure of polyurethane cementation in the mechanical response of high-speed impact, this paper adopted level light gas gun to the impact experiment of sample, sample showing a ceramic layer bending failure destruction of led and the impact compression failure led two failure mode, The dynamic crack propagation process was recorded by high-speed camera. Subsequently, the finite element software, Abaqus was used to simulate the projectile impact at 120, 150 and 180 m/s for transparent sandwich structures with multiple layersʼ thickness ratio. For ceramic materials, a subroutine based on JH-2 constitutive model was introduced, and the process of crack propagation and debris splashing was simulated in combination with element removal method. The simulation results were in good agreement with the experiment. Finally, BP neural network algorithm is employed to forecast the impact point peak bending, monolayer and multilayer neural network model calculation takes 1 minute respectively and three minutes on average, the mean relative errors were 7.6% and 3.2% respectively, and the model computation time and precision meet the requirements, compared with the traditional time-consuming hours of finite element calculation, save a lot of time, It can provide guidance and help to the design and development of transparent sandwich structures.
, Available online ,
doi: 10.11883/bzycj-2023-0172
Abstract:
In order to in-depth understand the dynamic fracture behaviors of metal materials under complex loading, based on the finite element simulation, two types of Mach stem loading experiments were designed and carried out to investigate the dynamic fragmentation of oxygen-free high-conducting copper (OFHC Cu) under complex loading. In the experiments, a powder gun was used to impact the Mach lens and a laser particle-velocity interferometer was applied to measure the free surface velocity. And dynamic loadings with the peak pressures of 95.75 and 32.38 GPa, respectively, were achieved. Stable Mach stem loading was successfully generated, and the Mach stem-related features were consistent with the simulated ones. At the same time, two different near-surface fracture behaviors in the OFHC Cu were observed, namely the micro-spallation under high pressure and the triangular-wave spallation under low pressure, with the cracked area distributed in a convex shape. These findings have certain value for further understanding the dynamic fracture behaviors of metal materials and can provide new experimental methods for understanding material failure under various complex loading conditions.
In order to in-depth understand the dynamic fracture behaviors of metal materials under complex loading, based on the finite element simulation, two types of Mach stem loading experiments were designed and carried out to investigate the dynamic fragmentation of oxygen-free high-conducting copper (OFHC Cu) under complex loading. In the experiments, a powder gun was used to impact the Mach lens and a laser particle-velocity interferometer was applied to measure the free surface velocity. And dynamic loadings with the peak pressures of 95.75 and 32.38 GPa, respectively, were achieved. Stable Mach stem loading was successfully generated, and the Mach stem-related features were consistent with the simulated ones. At the same time, two different near-surface fracture behaviors in the OFHC Cu were observed, namely the micro-spallation under high pressure and the triangular-wave spallation under low pressure, with the cracked area distributed in a convex shape. These findings have certain value for further understanding the dynamic fracture behaviors of metal materials and can provide new experimental methods for understanding material failure under various complex loading conditions.
, Available online ,
doi: 10.11883/bzycj-2023-0065
Abstract:
The identification of stress threshold for crack propagation of rock under compressive loading is an important issue for understanding the progressive damage process and analyzing the macroscopic damage mechanism of rocks. In order to accurately identify the stress threshold of brittle hard rock under quasi-static and dynamic compressive loads, uniaxial and dynamic compression tests were carried out for three kinds of rock specimens (including marble, coarse granite and fine granite) by using the INSTRON 1346 and the split Hopkinson pressure bar (SHPB) systems. Two deformation parameters were introduced in the paper, including crack axial strain and crack radial area strain. According to the slope difference of the crack radial area strain curves at the failure point, the three kinds of rocks were classified into type Ι (marble) and type Ⅱ (coarse granite and fine granite) rocks. The testing results indicate that the crack axial strain curves and crack axial strain stiffness curves can be used to accurately identify the crack stability propagation stress σsd, crack instability propagation stress σusd and the crack connectivity stress σct under quasi-static compressive loading for type Ι and type Ⅱ rocks respectively. It is proved that the stress thresholds of type I and type II rocks can be identified only by using the axial strain data. The method based on crack axial strain is extended to identify the stress threshold of rock under dynamic impact loading. It solves the problem to identify the stress threshold of rock specimens under dynamic compressive loading. Different from the stress threshold of rock under quasi static loading, it is found that the ratio of the crack stability propagation stress to the peak strength of the rock decreases under dynamic loading. The crack instability propagation stress and the crack connectivity stress coincide with each other, and the ratio to the peak strength also decreases. When the specimen is failed under dynamic loading, it usually generates more penetrating cracks and more fragments than that under quasi-static loading.
The identification of stress threshold for crack propagation of rock under compressive loading is an important issue for understanding the progressive damage process and analyzing the macroscopic damage mechanism of rocks. In order to accurately identify the stress threshold of brittle hard rock under quasi-static and dynamic compressive loads, uniaxial and dynamic compression tests were carried out for three kinds of rock specimens (including marble, coarse granite and fine granite) by using the INSTRON 1346 and the split Hopkinson pressure bar (SHPB) systems. Two deformation parameters were introduced in the paper, including crack axial strain and crack radial area strain. According to the slope difference of the crack radial area strain curves at the failure point, the three kinds of rocks were classified into type Ι (marble) and type Ⅱ (coarse granite and fine granite) rocks. The testing results indicate that the crack axial strain curves and crack axial strain stiffness curves can be used to accurately identify the crack stability propagation stress σsd, crack instability propagation stress σusd and the crack connectivity stress σct under quasi-static compressive loading for type Ι and type Ⅱ rocks respectively. It is proved that the stress thresholds of type I and type II rocks can be identified only by using the axial strain data. The method based on crack axial strain is extended to identify the stress threshold of rock under dynamic impact loading. It solves the problem to identify the stress threshold of rock specimens under dynamic compressive loading. Different from the stress threshold of rock under quasi static loading, it is found that the ratio of the crack stability propagation stress to the peak strength of the rock decreases under dynamic loading. The crack instability propagation stress and the crack connectivity stress coincide with each other, and the ratio to the peak strength also decreases. When the specimen is failed under dynamic loading, it usually generates more penetrating cracks and more fragments than that under quasi-static loading.
, Available online ,
doi: 10.11883/bzycj-2023-0047
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Abstract:
In order to study the design thickness of foam concrete distribution layer under blast load, the numerical model of one-dimensional blast wave propagation in foam concrete was established based on the LS-DYNA software, which was verified by comparing with the corresponding experimental data, and then the propagation and attenuation of blast wave in the foam concrete bars with semi-infinite and finite thicknesses were analyzed in detail based on the simplified stress-strain curve of foam concrete. The numerical results demonstrated that the triangular-shaped blast load will be attenuated into a trapezoidal-shaped load with the same amplitude as the yield strength of foam concrete when its thickness is enough, while the so-called load enhancement effect will occur at the fixed end due to the action of the stronger reflected wave when its thickness is small. Based on the compaction of foam concrete, the foam concrete with sufficient length can be divided into five regions, i.e., the compaction zone 1, the plateau zone 1, the elastic zone, the plateau zone 2 and the compaction zone 2, where the range of the elastic zone is gradually shortened as the pole length decreases. To avoid the load enhancement effect and minimize the load on the protected structures, the minimum thickness of distribution layer of foam concrete was defined, which is corresponding to that when the elastic area and two plateau area are disappeared. The sensitivity analysis of blast load and density of foam concrete on the minimum thickness of foam concrete found that for the blast load concerned, the minimum thickness increased with the peak and duration time of blast load , but was less affected by the rise time of blast load. Furthermore, the minimum thickness of low-density foam concrete is larger than that of high-density foam concrete under a same blast load. Based on the numerical results, a formula for minimum thickness was proposed.
In order to study the design thickness of foam concrete distribution layer under blast load, the numerical model of one-dimensional blast wave propagation in foam concrete was established based on the LS-DYNA software, which was verified by comparing with the corresponding experimental data, and then the propagation and attenuation of blast wave in the foam concrete bars with semi-infinite and finite thicknesses were analyzed in detail based on the simplified stress-strain curve of foam concrete. The numerical results demonstrated that the triangular-shaped blast load will be attenuated into a trapezoidal-shaped load with the same amplitude as the yield strength of foam concrete when its thickness is enough, while the so-called load enhancement effect will occur at the fixed end due to the action of the stronger reflected wave when its thickness is small. Based on the compaction of foam concrete, the foam concrete with sufficient length can be divided into five regions, i.e., the compaction zone 1, the plateau zone 1, the elastic zone, the plateau zone 2 and the compaction zone 2, where the range of the elastic zone is gradually shortened as the pole length decreases. To avoid the load enhancement effect and minimize the load on the protected structures, the minimum thickness of distribution layer of foam concrete was defined, which is corresponding to that when the elastic area and two plateau area are disappeared. The sensitivity analysis of blast load and density of foam concrete on the minimum thickness of foam concrete found that for the blast load concerned, the minimum thickness increased with the peak and duration time of blast load , but was less affected by the rise time of blast load. Furthermore, the minimum thickness of low-density foam concrete is larger than that of high-density foam concrete under a same blast load. Based on the numerical results, a formula for minimum thickness was proposed.
, Available online ,
doi: 10.11883/bzycj-2022-556
Abstract:
With the further development of ocean engineering, the dynamic response of calcareous sand sites under strong dynamic loading warrants broad attention. In order to investigate the crater characteristics of calcareous sand sites under explosion impact, both the filed experiments and numerical simulations were conducted. Firstly, a series of field explosion tests were conducted on calcareous sand sites, with varying equivalent sizes and burial depths. The longitudinal and transverse diameter, as well as the depth of craters were measured for each case. Secondly, a new numerical algorithm (FEM-SPH) coupling the finite element model (FEM) and the smoothed particle hydrodynamics (SPH) was used to simulate the formation process of explosion craters. Furthermore, the crater dimensions of the simulation results were compared with test results to validate the accuracy of the FEM-SPH model. Thanks to the advantage of the FEM-SPH in simulating large deformations, the crater formation process of ground contact explosions and buried explosions agreed well with the experimental results. The experiment research showed the crater size resulting from buried explosions is larger in calcareous sand compared to siliceous sand. The phenomenon was mainly attributed to the higher porosity and lower interparticle bonding strength of calcareous sand. With the validated FEM-SPH model, parametric analyses, including soil parameters and shapes of charges, were detailed discussed. Under the same equivalent, the influence of soil parameters on the size of the crater was about 6%, while the change in shape of the charge caused a significant influence on the shape and size of the craters. Finally, with the cubic charge, the carter fitted formulas were derived according to the FEM-SPH numerical results in calcareous sand sites. The formulas can predict the dimensions of ground contact explosions and buried explosions within different equivalent charge weight ranges (0 —500 kg). The above research results provided a useful reference for the blast-resistant protection design and emergency reinforcement of calcareous sand foundation.
With the further development of ocean engineering, the dynamic response of calcareous sand sites under strong dynamic loading warrants broad attention. In order to investigate the crater characteristics of calcareous sand sites under explosion impact, both the filed experiments and numerical simulations were conducted. Firstly, a series of field explosion tests were conducted on calcareous sand sites, with varying equivalent sizes and burial depths. The longitudinal and transverse diameter, as well as the depth of craters were measured for each case. Secondly, a new numerical algorithm (FEM-SPH) coupling the finite element model (FEM) and the smoothed particle hydrodynamics (SPH) was used to simulate the formation process of explosion craters. Furthermore, the crater dimensions of the simulation results were compared with test results to validate the accuracy of the FEM-SPH model. Thanks to the advantage of the FEM-SPH in simulating large deformations, the crater formation process of ground contact explosions and buried explosions agreed well with the experimental results. The experiment research showed the crater size resulting from buried explosions is larger in calcareous sand compared to siliceous sand. The phenomenon was mainly attributed to the higher porosity and lower interparticle bonding strength of calcareous sand. With the validated FEM-SPH model, parametric analyses, including soil parameters and shapes of charges, were detailed discussed. Under the same equivalent, the influence of soil parameters on the size of the crater was about 6%, while the change in shape of the charge caused a significant influence on the shape and size of the craters. Finally, with the cubic charge, the carter fitted formulas were derived according to the FEM-SPH numerical results in calcareous sand sites. The formulas can predict the dimensions of ground contact explosions and buried explosions within different equivalent charge weight ranges (0 —500 kg). The above research results provided a useful reference for the blast-resistant protection design and emergency reinforcement of calcareous sand foundation.
, Available online ,
doi: 10.11883/bzycj-2023-0030
Abstract:
Chapman-Jouguet theory is a powerful tool to predict the states of physical quantities at the rear of the shock front. However uncertain factors and their influence on system response quantity are neglected in the model of previous research. Actually, the reliability and predictability of numerical simulation will be greatly influenced by these uncertainties. To begin with, uncertainties of modeling and simulation of detonation process was discussed based on the detonation mechanism. Initial density and detonation velocity of PBX-9502 were assumed to satisfy the logarithmic normal distribution. The probability density function (PDF) of initial density and detonation velocity was derived from Anderson-Darling hypothesis test and parameter estimation combined with real experimental data. Beta distribution was utilized to cope with empirical parameters which have none physical meaning at all, with shaping parameters and supporting set are given according to the engineer’s experience. Rosenblatt transformation was used to transform the dependent and non-Gaussian random variables into independent standard Gaussian random variables. Furthermore, nonintrusive polynomial chaos (PC) method was used to study high dimensional uncertainty propagation of detonation waves. Specifically, as to one variable PC, orthogonal polynomials were derived through Gram-Schmidt algorithm in Gauss-Hilbert space, Gauss integral formula with 6 quadrature points was used to compute coefficients of PC. Full tensor product of quadratures and weights was applied in PC of multivariate. PDF and corresponding Gaussian statistics such as expectation, standard deviation and confidence interval of quantity of interest (QoI) are obtained from the multivariate polynomial chaos. The result shows that the variation of detonation pressure is large and the range of confidential interval is wide. It coincides with Professor Chengwei Sun’s conclusion that ‘The discreteness of detonation pressure is large in experimental measurement’. The experimental data falls into the confidential interval of QoIs, then the reliability and robustness of the modeling is enhanced. And the methodology can be extended to the detonation system with much more complex equation of state.
Chapman-Jouguet theory is a powerful tool to predict the states of physical quantities at the rear of the shock front. However uncertain factors and their influence on system response quantity are neglected in the model of previous research. Actually, the reliability and predictability of numerical simulation will be greatly influenced by these uncertainties. To begin with, uncertainties of modeling and simulation of detonation process was discussed based on the detonation mechanism. Initial density and detonation velocity of PBX-9502 were assumed to satisfy the logarithmic normal distribution. The probability density function (PDF) of initial density and detonation velocity was derived from Anderson-Darling hypothesis test and parameter estimation combined with real experimental data. Beta distribution was utilized to cope with empirical parameters which have none physical meaning at all, with shaping parameters and supporting set are given according to the engineer’s experience. Rosenblatt transformation was used to transform the dependent and non-Gaussian random variables into independent standard Gaussian random variables. Furthermore, nonintrusive polynomial chaos (PC) method was used to study high dimensional uncertainty propagation of detonation waves. Specifically, as to one variable PC, orthogonal polynomials were derived through Gram-Schmidt algorithm in Gauss-Hilbert space, Gauss integral formula with 6 quadrature points was used to compute coefficients of PC. Full tensor product of quadratures and weights was applied in PC of multivariate. PDF and corresponding Gaussian statistics such as expectation, standard deviation and confidence interval of quantity of interest (QoI) are obtained from the multivariate polynomial chaos. The result shows that the variation of detonation pressure is large and the range of confidential interval is wide. It coincides with Professor Chengwei Sun’s conclusion that ‘The discreteness of detonation pressure is large in experimental measurement’. The experimental data falls into the confidential interval of QoIs, then the reliability and robustness of the modeling is enhanced. And the methodology can be extended to the detonation system with much more complex equation of state.
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2023, 43(9): 091400.
doi: 10.11883/bzycj-2023-0240
Abstract:
2023, 43(9): 091401.
doi: 10.11883/bzycj-2023-0189
Abstract:
Disordered alloy is a new kind of reactive material, which breaks through the design concept of traditional alloy and exhibits excellent mechanical properties, impact energy release characteristics and adiabatic shear sensitivity, showing good application prospects in high temperature, high pressure, high strain rates and other application environments. Analyzing the impact energy release characteristics of reactive disordered alloy has an important guiding role for its development in the military field and can provide the basis for the design and application of warheads for ammunition. In this paper, the impact energy release characteristics of reactive disordered alloys are introduced from four aspects, including the energy release phenomenon of chemical reaction, the energy release law induced by impacting, the energy release mechanism and the regulation of the energy release behaviors. The chemical reaction showing energy release phenomenon in static and dynamic mechanical experiments is described. The relationship between impact velocities and the energy release overpressures or the efficiency of energy release of reactive disordered alloys is obtained. The effect between impact velocities and crushing degree of the reactive disordered alloys or characteristics of the target on the energy release mechanism is discussed. At the same time, the regulation effects of preparation process and the kinds of element on energy release effect of disordered alloy materials are summarized. This kind of alloy own good impact energy release characteristics, presented an ideal energetic structural material. Furthermore, the research progress of reactive disordered alloys applied to warheads in military area is summarized from three directions, including fragment, armor-piercing core and shaped charge liner. The macro and micro penetration behavior and mechanism of warheads of reactive disordered alloys are analyzed under high-speed loading conditions. Via the design of the structure, the good penetration and damage performance benefit from the self-sharpening and energy release characteristics of the material. Finally, the further development trend and demands of reactive disordered alloy are prospected.
Disordered alloy is a new kind of reactive material, which breaks through the design concept of traditional alloy and exhibits excellent mechanical properties, impact energy release characteristics and adiabatic shear sensitivity, showing good application prospects in high temperature, high pressure, high strain rates and other application environments. Analyzing the impact energy release characteristics of reactive disordered alloy has an important guiding role for its development in the military field and can provide the basis for the design and application of warheads for ammunition. In this paper, the impact energy release characteristics of reactive disordered alloys are introduced from four aspects, including the energy release phenomenon of chemical reaction, the energy release law induced by impacting, the energy release mechanism and the regulation of the energy release behaviors. The chemical reaction showing energy release phenomenon in static and dynamic mechanical experiments is described. The relationship between impact velocities and the energy release overpressures or the efficiency of energy release of reactive disordered alloys is obtained. The effect between impact velocities and crushing degree of the reactive disordered alloys or characteristics of the target on the energy release mechanism is discussed. At the same time, the regulation effects of preparation process and the kinds of element on energy release effect of disordered alloy materials are summarized. This kind of alloy own good impact energy release characteristics, presented an ideal energetic structural material. Furthermore, the research progress of reactive disordered alloys applied to warheads in military area is summarized from three directions, including fragment, armor-piercing core and shaped charge liner. The macro and micro penetration behavior and mechanism of warheads of reactive disordered alloys are analyzed under high-speed loading conditions. Via the design of the structure, the good penetration and damage performance benefit from the self-sharpening and energy release characteristics of the material. Finally, the further development trend and demands of reactive disordered alloy are prospected.
2023, 43(9): 091402.
doi: 10.11883/bzycj-2022-0512
Abstract:
In order to study the cratering stage in the dynamic penetration process of projectiles into the concrete targets, the cratering stage is further divided into two phases according to the damage of the projectile during penetration. Combined with the shape function of projectile head, streamline field of the Z model and normal expansion theory (NET), an analytical and calculation model of penetration resistance during the cratering stage is established, which considers the influence of concrete ejection process. Reliability of penetration resistance model during the cratering stage is then verified by test data taken from published papers. The advantages of the present model compared with the existing classical model are analyzed, while the influences of initial impact velocity of projectile, the caliber-radius-head and uniaxial compressive strength of concrete on the dynamic process during the cratering stage are analyzed. With the increase of the initial impact velocity of projectile, the diameter and depth of the ejection region gradually increase, the time of the ejection region to reach the maximum size is gradually shortened, and the time of the dynamic process during the cratering stage is also shortened. With the increase of the caliber-radius-head of the projectile, the diameter and depth of the ejection region gradually decrease, the time of the ejection region to reach the maximum size gradually increases, and the time of the dynamic process during the cratering stage increases, too. With the increase of uniaxial compressive strength of concrete, the diameter and depth of the ejection region are gradually reduced, the time of the ejection region to reach the maximum size is gradually shortened, and the time of the dynamic process during the cratering stage is also shortened. The velocity has the greatest influence on the dynamic process during the cratering stage of the projectile penetration into the concrete target, followed by the caliber-radius-head of the projectile and uniaxial compressive strength of concrete.
In order to study the cratering stage in the dynamic penetration process of projectiles into the concrete targets, the cratering stage is further divided into two phases according to the damage of the projectile during penetration. Combined with the shape function of projectile head, streamline field of the Z model and normal expansion theory (NET), an analytical and calculation model of penetration resistance during the cratering stage is established, which considers the influence of concrete ejection process. Reliability of penetration resistance model during the cratering stage is then verified by test data taken from published papers. The advantages of the present model compared with the existing classical model are analyzed, while the influences of initial impact velocity of projectile, the caliber-radius-head and uniaxial compressive strength of concrete on the dynamic process during the cratering stage are analyzed. With the increase of the initial impact velocity of projectile, the diameter and depth of the ejection region gradually increase, the time of the ejection region to reach the maximum size is gradually shortened, and the time of the dynamic process during the cratering stage is also shortened. With the increase of the caliber-radius-head of the projectile, the diameter and depth of the ejection region gradually decrease, the time of the ejection region to reach the maximum size gradually increases, and the time of the dynamic process during the cratering stage increases, too. With the increase of uniaxial compressive strength of concrete, the diameter and depth of the ejection region are gradually reduced, the time of the ejection region to reach the maximum size is gradually shortened, and the time of the dynamic process during the cratering stage is also shortened. The velocity has the greatest influence on the dynamic process during the cratering stage of the projectile penetration into the concrete target, followed by the caliber-radius-head of the projectile and uniaxial compressive strength of concrete.
2023, 43(9): 091403.
doi: 10.11883/bzycj-2022-0511
Abstract:
Aiming at the urgent demand for theoretical research and engineering application of deep super hard targets in the field of damage and protection, the response zone and boundary conditions during the cavity expansding process are optimized in this paper based on the improved Ottosen yield condition. The entire process of cavity expansion is solved, the changes in the response zone of concrete with different strengths are analyzed. According to the relationship between cavity boundary stress and cavity expansion velocity, a calculation model of projectile penetration depth is established, and the penetration depth of projectile penetration into concrete with different strengths are calculated. The mechanism of the influence of target strength on penetration depth is also analyzed. The results show that the elastic and plastic cracking zone of high-strength concrete is larger and the compacted zone is smaller, indicating that high-strength concrete is more brittle and compact. And the addition of plastic cracking zone can better reflect the phenomenon of concrete with different strengths in penetration. By comparing with the experimental data, it can be seen that the cavity expansion theory established in this paper has good applicability for normal concrete and high-strength concrete. The relationship between radial stress and cavity boundary velocity and the penetration depth also can be accurately calculated by this theory. With the increase of concrete strength, the difference in the cavity boundary stress of the concrete becomes smaller, resulting in a smaller increase in the penetration depth of the projectile as the velocity increases, and the penetration depth of the projectile decreases and gradually tends to a certain value at the same speed.
Aiming at the urgent demand for theoretical research and engineering application of deep super hard targets in the field of damage and protection, the response zone and boundary conditions during the cavity expansding process are optimized in this paper based on the improved Ottosen yield condition. The entire process of cavity expansion is solved, the changes in the response zone of concrete with different strengths are analyzed. According to the relationship between cavity boundary stress and cavity expansion velocity, a calculation model of projectile penetration depth is established, and the penetration depth of projectile penetration into concrete with different strengths are calculated. The mechanism of the influence of target strength on penetration depth is also analyzed. The results show that the elastic and plastic cracking zone of high-strength concrete is larger and the compacted zone is smaller, indicating that high-strength concrete is more brittle and compact. And the addition of plastic cracking zone can better reflect the phenomenon of concrete with different strengths in penetration. By comparing with the experimental data, it can be seen that the cavity expansion theory established in this paper has good applicability for normal concrete and high-strength concrete. The relationship between radial stress and cavity boundary velocity and the penetration depth also can be accurately calculated by this theory. With the increase of concrete strength, the difference in the cavity boundary stress of the concrete becomes smaller, resulting in a smaller increase in the penetration depth of the projectile as the velocity increases, and the penetration depth of the projectile decreases and gradually tends to a certain value at the same speed.
2023, 43(9): 091404.
doi: 10.11883/bzycj-2023-0068
Abstract:
Earth penetration weapon (EPW) is commonly used to attack the underground target. However, the ballistic trajectory deflection, which is essentially caused by the deflection of the penetrator, commonly decreases the penetration efficiency of the penetrator. Thus, both the deflection angle and depth of penetration (DOP) of the projectile demand rapid and precise predictions. Based on the differential-areal-force-law (DAFL) approach, an analytical contact-resistant pressure is applied on the projectile surface in simulation. It represents the resistant force of the target and considers the free-surface effects of all surfaces of a finite concrete target. The simulation model is verified by comparing with the test results of the DOP and rotation angle of projectiles in open references. The influence of structural deformation upon the deflection of the penetrator is investigated by comparing the dynamics and movement of rigid and deformable projectiles. It indicates that the structural deformation drives the deformable projectile to deflect, which changes the total moment and instant angular velocity of the projectile. Under the same impact conditions, the rotation angle of the deformable projectile is usually larger than that of the rigid projectile. With the aspect ratio of projectile and impact velocity of the projectile decreasing, and the oblique angle of the projectile increasing, the rotation angle of the rigid projectile increases. However, for the deformable projectile, with the aspect ratio and oblique angle of the projectile increasing and the thickness of the projectile decreasing, the rotation angle of projectile increases. The rotation angle of deformable projectile does not monotonously increase with the impact velocity of the projectile increasing. It should be analyzed according to its actual structural deformation. When the impact velocity is less than or equal to 800 m/s and the oblique angle of the projectile is larger than or equal to 20°, the higher the impact velocity, the larger the oblique angle and the aspect ratio, the thinner the thickness of the projectile, the structural deformation contributes larger deflection of the projectile. In this way, to promote the accuracy and reasonability of simulation, it is suggested that the projectile should be deformable when the deformation and dynamics of the projectile are demanded for non-ideal penetration of a penetrator.
Earth penetration weapon (EPW) is commonly used to attack the underground target. However, the ballistic trajectory deflection, which is essentially caused by the deflection of the penetrator, commonly decreases the penetration efficiency of the penetrator. Thus, both the deflection angle and depth of penetration (DOP) of the projectile demand rapid and precise predictions. Based on the differential-areal-force-law (DAFL) approach, an analytical contact-resistant pressure is applied on the projectile surface in simulation. It represents the resistant force of the target and considers the free-surface effects of all surfaces of a finite concrete target. The simulation model is verified by comparing with the test results of the DOP and rotation angle of projectiles in open references. The influence of structural deformation upon the deflection of the penetrator is investigated by comparing the dynamics and movement of rigid and deformable projectiles. It indicates that the structural deformation drives the deformable projectile to deflect, which changes the total moment and instant angular velocity of the projectile. Under the same impact conditions, the rotation angle of the deformable projectile is usually larger than that of the rigid projectile. With the aspect ratio of projectile and impact velocity of the projectile decreasing, and the oblique angle of the projectile increasing, the rotation angle of the rigid projectile increases. However, for the deformable projectile, with the aspect ratio and oblique angle of the projectile increasing and the thickness of the projectile decreasing, the rotation angle of projectile increases. The rotation angle of deformable projectile does not monotonously increase with the impact velocity of the projectile increasing. It should be analyzed according to its actual structural deformation. When the impact velocity is less than or equal to 800 m/s and the oblique angle of the projectile is larger than or equal to 20°, the higher the impact velocity, the larger the oblique angle and the aspect ratio, the thinner the thickness of the projectile, the structural deformation contributes larger deflection of the projectile. In this way, to promote the accuracy and reasonability of simulation, it is suggested that the projectile should be deformable when the deformation and dynamics of the projectile are demanded for non-ideal penetration of a penetrator.
2023, 43(9): 091405.
doi: 10.11883/bzycj-2022-0513
Abstract:
It is a developing trend of protection engineering to use high resistance materials such as ultra-high performance concrete to construct bullet-shielding structures. The phenomenon of projectile body rebound was found in the tests of projectile body penetrating ultra-high performance concrete. The projectile rebound effect is very important in the study of engineering protection, weapon damage and warhead design. In order to study the rebound velocity of projectile body after penetration and its influencing factors, the stress of projectile body from penetration to rebound was analyzed. Based on the expression of penetration resistance given by the cavity expansion theory, a one-dimensional elastic bar potential energy model was established from the perspective of the accumulation of deformation energy by penetration resistance, and a one-dimensional stress wave model was established from the perspective of stress wave generated by penetration resistance. The analytical solutions of the rebound velocity were derived from the two models respectively, and the physical quantities affecting the rebound velocity were analyzed. Through numerical simulation, the rebound phenomenon of the projectile body after penetrating the ultra-high performance concrete is reproduced, and the numerical results of the rebound velocity agree well with the two analytical solutions. Through numerical calculation of the same penetration model with different material parameters, the relationship between the rebound velocity and the material parameters in the analytical solution is verified, and the reliability of the theoretical model is proved. The results show that the projectile body accumulates deformation potential energy due to penetration resistance, and the projectile body bounces back due to the release of deformation potential energy after penetration. The initial rebound velocity is independent of the target velocity, proportional to the target material, yield strength and warhead shape coefficient, and inversely proportional to the elastic modulus and density of the projectile body. The results can preliminarily predict the rebound velocity and provide a reference for the design of ultra-high performance concrete protective structure and warhead.
It is a developing trend of protection engineering to use high resistance materials such as ultra-high performance concrete to construct bullet-shielding structures. The phenomenon of projectile body rebound was found in the tests of projectile body penetrating ultra-high performance concrete. The projectile rebound effect is very important in the study of engineering protection, weapon damage and warhead design. In order to study the rebound velocity of projectile body after penetration and its influencing factors, the stress of projectile body from penetration to rebound was analyzed. Based on the expression of penetration resistance given by the cavity expansion theory, a one-dimensional elastic bar potential energy model was established from the perspective of the accumulation of deformation energy by penetration resistance, and a one-dimensional stress wave model was established from the perspective of stress wave generated by penetration resistance. The analytical solutions of the rebound velocity were derived from the two models respectively, and the physical quantities affecting the rebound velocity were analyzed. Through numerical simulation, the rebound phenomenon of the projectile body after penetrating the ultra-high performance concrete is reproduced, and the numerical results of the rebound velocity agree well with the two analytical solutions. Through numerical calculation of the same penetration model with different material parameters, the relationship between the rebound velocity and the material parameters in the analytical solution is verified, and the reliability of the theoretical model is proved. The results show that the projectile body accumulates deformation potential energy due to penetration resistance, and the projectile body bounces back due to the release of deformation potential energy after penetration. The initial rebound velocity is independent of the target velocity, proportional to the target material, yield strength and warhead shape coefficient, and inversely proportional to the elastic modulus and density of the projectile body. The results can preliminarily predict the rebound velocity and provide a reference for the design of ultra-high performance concrete protective structure and warhead.
2023, 43(9): 091406.
doi: 10.11883/bzycj-2023-0074
Abstract:
With the development of the hypersonic weapon system, the non-circular cross-section projectile with more space utilization has attracted extensive attention. The high-velocity penetration mechanism of the non-circular cross-section projectile is a crucial issue that must be solved. Based on the truncated conical head structure of a typical anti-ship warhead and the elliptical section projectile’s shape, the elliptical section’s resistance characteristics and damage mechanism of thetruncated cone projectile through the metal sheet at high velocity are studied by numerical simulation. The load applied on the projectile is divided into two parts: shear punching resistance and ductile enlargement resistance. Combined with the numerical simulation results, the high-velocity penetration resistance function and the analytical model of residual velocity are proposed, which are suitable for elliptic cross-section flat projectile and ogive projectile. The differential surface force method and rigid body dynamics are used to construct a normal penetration model, and numerical simulation results verify the validity of the theoretical model. The results show that the elliptical cross-section truncated cone projectile penetrating through the metal sheet can be divided into the head penetration stage under load and the body penetration stage without load. In the head invasion stage, the failure mode of the thin sheet due to project penetration is decomposed into the shear plugging caused by the truncated cone platform and the ductility enlargement of the curved surface of the head. Under high-velocity impact, the damage to the sheet caused by elliptic ogive projectile/blunt projectile is different from that caused by low-velocity impact. When the ogive projectile penetrates through the sheet, ductile enlargement failure occurs. When the sheet is impacted by blunt projectile at high velocity, the coupled failure mode of shear punching and ductile enlargement takes place. The resistance of the elliptical cross-section projectile is the same as that of the circular cross-section projectile with the same cross-sectional area. The difference is that the asymmetric structure of the elliptical cross-section projectile leads to non-uniform load distribution.
With the development of the hypersonic weapon system, the non-circular cross-section projectile with more space utilization has attracted extensive attention. The high-velocity penetration mechanism of the non-circular cross-section projectile is a crucial issue that must be solved. Based on the truncated conical head structure of a typical anti-ship warhead and the elliptical section projectile’s shape, the elliptical section’s resistance characteristics and damage mechanism of thetruncated cone projectile through the metal sheet at high velocity are studied by numerical simulation. The load applied on the projectile is divided into two parts: shear punching resistance and ductile enlargement resistance. Combined with the numerical simulation results, the high-velocity penetration resistance function and the analytical model of residual velocity are proposed, which are suitable for elliptic cross-section flat projectile and ogive projectile. The differential surface force method and rigid body dynamics are used to construct a normal penetration model, and numerical simulation results verify the validity of the theoretical model. The results show that the elliptical cross-section truncated cone projectile penetrating through the metal sheet can be divided into the head penetration stage under load and the body penetration stage without load. In the head invasion stage, the failure mode of the thin sheet due to project penetration is decomposed into the shear plugging caused by the truncated cone platform and the ductility enlargement of the curved surface of the head. Under high-velocity impact, the damage to the sheet caused by elliptic ogive projectile/blunt projectile is different from that caused by low-velocity impact. When the ogive projectile penetrates through the sheet, ductile enlargement failure occurs. When the sheet is impacted by blunt projectile at high velocity, the coupled failure mode of shear punching and ductile enlargement takes place. The resistance of the elliptical cross-section projectile is the same as that of the circular cross-section projectile with the same cross-sectional area. The difference is that the asymmetric structure of the elliptical cross-section projectile leads to non-uniform load distribution.
2023, 43(9): 091407.
doi: 10.11883/bzycj-2022-0571
Abstract:
In order to deeply investigate the trajectory deflection characteristics of a warhead during the non-normal penetration into the multi-layer spaced target, the trajectories under different impact attitudes are analyzed with combined numerical simulation and theoretical analysis, in which finite element method (FEM) simulations on the penetration process under various impact conditions are conducted systemically, and the deformation and failure morphologies of warhead and target as well as the interaction characteristics between them are discussed in detail. Besides some feature parameters, lateral contact force and angular moment, are introduced in the theoretical analysis. Furthermore, the influence rules of oblique angle and attacking angle on the trajectory deflection characteristics are investigated in detail. Related results indicate that during the non-normal penetration into multi-layer spaced target, the warhead behaves as small staged axial velocity decay combined with obvious lateral trajectory deflection, and the trajectory deflection is mainly derived from the lateral contact force as well as the corresponding angular moment, and the lateral contact force mainly makes its effect during three periods, i.e., when the nose, shoulder and tail of warhead pass through the target, respectively. The oblique angle mainly affects the degree of external load asymmetry exerting on the warhead with increase of the oblique angle, the downward lateral contact force as well as the corresponding angular moment exerting on the warhead all increase, thus the trajectory deflection becomes more severe. Comparatively, the attacking angle determines two factors, one is the radial velocity of warhead at the time when its nose passes through the target, and another is the contact position between the warhead and target when the warhead tail passes through the target. These two factors determine the trajectory simultaneously, so different attacking angles make the lateral contact force and the corresponding angular moment differing from each other during the process of the warhead tail passing through the first target, leading to a critical attacking angle at which the evolution trend of trajectory deflection would turn the other way round. Compared to the penetration into a single layer target, a remarkable feature in the penetration of a warhead into the multi-layer spaced target is that the trajectory deflection shows a cumulative effect, and the situation in the penetration into the former target plate significantly affects the interaction condition between the warhead and the latter target plates, and this further results in a coupling effect between the trajectory deflection and the contact force. The present investigation is of good significance in the practical engineering application, e.g., predicting the penetrating ability of a warhead into the multi-layer spaced target, and optimizing the warhead structure and its impact attitude, etc.
In order to deeply investigate the trajectory deflection characteristics of a warhead during the non-normal penetration into the multi-layer spaced target, the trajectories under different impact attitudes are analyzed with combined numerical simulation and theoretical analysis, in which finite element method (FEM) simulations on the penetration process under various impact conditions are conducted systemically, and the deformation and failure morphologies of warhead and target as well as the interaction characteristics between them are discussed in detail. Besides some feature parameters, lateral contact force and angular moment, are introduced in the theoretical analysis. Furthermore, the influence rules of oblique angle and attacking angle on the trajectory deflection characteristics are investigated in detail. Related results indicate that during the non-normal penetration into multi-layer spaced target, the warhead behaves as small staged axial velocity decay combined with obvious lateral trajectory deflection, and the trajectory deflection is mainly derived from the lateral contact force as well as the corresponding angular moment, and the lateral contact force mainly makes its effect during three periods, i.e., when the nose, shoulder and tail of warhead pass through the target, respectively. The oblique angle mainly affects the degree of external load asymmetry exerting on the warhead with increase of the oblique angle, the downward lateral contact force as well as the corresponding angular moment exerting on the warhead all increase, thus the trajectory deflection becomes more severe. Comparatively, the attacking angle determines two factors, one is the radial velocity of warhead at the time when its nose passes through the target, and another is the contact position between the warhead and target when the warhead tail passes through the target. These two factors determine the trajectory simultaneously, so different attacking angles make the lateral contact force and the corresponding angular moment differing from each other during the process of the warhead tail passing through the first target, leading to a critical attacking angle at which the evolution trend of trajectory deflection would turn the other way round. Compared to the penetration into a single layer target, a remarkable feature in the penetration of a warhead into the multi-layer spaced target is that the trajectory deflection shows a cumulative effect, and the situation in the penetration into the former target plate significantly affects the interaction condition between the warhead and the latter target plates, and this further results in a coupling effect between the trajectory deflection and the contact force. The present investigation is of good significance in the practical engineering application, e.g., predicting the penetrating ability of a warhead into the multi-layer spaced target, and optimizing the warhead structure and its impact attitude, etc.
2023, 43(9): 091408.
doi: 10.11883/bzycj-2023-0017
Abstract:
In order to investigate the structural response and failure of projectiles obliquely penetrating into a multi-layered steel plate target, oblique penetration tests were conducted, in which three kinds of projectiles with circular, elliptical, and asymmetric elliptical cross-sections were employed while the ballistic trajectory and structural failure of projectiles were recorded. With the photographs captured by high-speed camera, a pixel measuring method was used to obtain the velocity and attitude deflection angle of projectiles. Based on the test results, the ballistic characteristics, dynamic loads and structural response of projectiles are analyzed by using FEM code ABAQUS/explicit, focusing on the oblique penetration at initial speed of 480 m/s and attack angle within 2°. Then, based on the free-free beam theory and the dynamic loads obtained by numerical simulation, the distributions of axial force, shear force and bending moment within projectiles are calculated, and an analytical method for structural strength and dynamic failure of projectiles is developed. The results show that when the projectile horizontally penetrates a multi-layered steel plate target with positive inclined angle, there exists a critical attack angle. If the attack angle is smaller than this critical value, the projectile will head drop and its trajectory turns downwards; when the attack angle is larger than the critical value, the projectile will be raised and its trajectory turns upwards. In addition, the critical attack angle increases as the thickness of the target plate decreases. For the projectiles with high strength and low ductility, the failure mode is brittle fracture and the distances between the fracture position and the projectile nose is 0.72−0.81 times of its length, which is mainly due to the lateral impact load at the rear part of projectile. Moreover, by means of the dynamic model of the projectile based on the free-free beam theory, the fracture position of projectile during oblique penetration process could be well predicted. Also, among the three types of projectiles with the same length and cross-sectional area, the projectile with asymmetric elliptical cross-section is easier to fracture and the position is even closer to the projectile nose.
In order to investigate the structural response and failure of projectiles obliquely penetrating into a multi-layered steel plate target, oblique penetration tests were conducted, in which three kinds of projectiles with circular, elliptical, and asymmetric elliptical cross-sections were employed while the ballistic trajectory and structural failure of projectiles were recorded. With the photographs captured by high-speed camera, a pixel measuring method was used to obtain the velocity and attitude deflection angle of projectiles. Based on the test results, the ballistic characteristics, dynamic loads and structural response of projectiles are analyzed by using FEM code ABAQUS/explicit, focusing on the oblique penetration at initial speed of 480 m/s and attack angle within 2°. Then, based on the free-free beam theory and the dynamic loads obtained by numerical simulation, the distributions of axial force, shear force and bending moment within projectiles are calculated, and an analytical method for structural strength and dynamic failure of projectiles is developed. The results show that when the projectile horizontally penetrates a multi-layered steel plate target with positive inclined angle, there exists a critical attack angle. If the attack angle is smaller than this critical value, the projectile will head drop and its trajectory turns downwards; when the attack angle is larger than the critical value, the projectile will be raised and its trajectory turns upwards. In addition, the critical attack angle increases as the thickness of the target plate decreases. For the projectiles with high strength and low ductility, the failure mode is brittle fracture and the distances between the fracture position and the projectile nose is 0.72−0.81 times of its length, which is mainly due to the lateral impact load at the rear part of projectile. Moreover, by means of the dynamic model of the projectile based on the free-free beam theory, the fracture position of projectile during oblique penetration process could be well predicted. Also, among the three types of projectiles with the same length and cross-sectional area, the projectile with asymmetric elliptical cross-section is easier to fracture and the position is even closer to the projectile nose.
2023, 43(9): 091409.
doi: 10.11883/bzycj-2023-0132
Abstract:
In order to study the influence of the cross-section shape and caliber radius head on the penetration performance of elliptical cross-section projectiles, the static deep indentation test of the elliptical cross-section conical indenters was carried out, and the force-displacement curves of different cross-section indenter slowly penetrating the material were obtained. Then, by means of a 30-mm-caliber ballistic gun platform, a series of experiments were carried out on 2A12 thick aluminum targets subjected to normal penetration by three kinds of 30CrMnSi2A steel projectiles with different elliptical cross-section shapes in the striking velocity ranging from 400 m/s to 800 m/s. The penetration depth of projectiles and the failure morphology of targets were experimentally obtained. The penetration dynamic model of projectile into thick metal target was established on the basis of the cavity expansion theory and resistance function correction coefficient. The correctness of the theoretical model is validated by the experimental results in this paper, and the influence of the cross-section shape and caliber radius head of the projectile on the penetration performance are systematically analyzed. The results show that the elliptical section indenter with the same cross-sectional area has higher resistance while slowly penetrating into the material. When the major-to-minor axis length ratio of the cross-sectional of indenters increases from 1.00 to 2.00, the material resistance increases by 10.1%. It is found that there is a large difference in the failure morphology of the target under the penetration of circular and elliptical cross-section projectiles, and the shape of the target tunnel area is consistent with the shape of the projectile cross-section. In addition, when the cross-sectional area of the projectile is equivalent and the major-to-minor axis length ratio of each cross-section was constant, the penetration performance of projectile decreases with the increase of the larger the major-to-minor axis length ratio. The penetration performance of projectile with elliptical cross-section decreases with the increase of the major-to-minor axis length ratio and the decrease of the caliber radius head of the projectile.
In order to study the influence of the cross-section shape and caliber radius head on the penetration performance of elliptical cross-section projectiles, the static deep indentation test of the elliptical cross-section conical indenters was carried out, and the force-displacement curves of different cross-section indenter slowly penetrating the material were obtained. Then, by means of a 30-mm-caliber ballistic gun platform, a series of experiments were carried out on 2A12 thick aluminum targets subjected to normal penetration by three kinds of 30CrMnSi2A steel projectiles with different elliptical cross-section shapes in the striking velocity ranging from 400 m/s to 800 m/s. The penetration depth of projectiles and the failure morphology of targets were experimentally obtained. The penetration dynamic model of projectile into thick metal target was established on the basis of the cavity expansion theory and resistance function correction coefficient. The correctness of the theoretical model is validated by the experimental results in this paper, and the influence of the cross-section shape and caliber radius head of the projectile on the penetration performance are systematically analyzed. The results show that the elliptical section indenter with the same cross-sectional area has higher resistance while slowly penetrating into the material. When the major-to-minor axis length ratio of the cross-sectional of indenters increases from 1.00 to 2.00, the material resistance increases by 10.1%. It is found that there is a large difference in the failure morphology of the target under the penetration of circular and elliptical cross-section projectiles, and the shape of the target tunnel area is consistent with the shape of the projectile cross-section. In addition, when the cross-sectional area of the projectile is equivalent and the major-to-minor axis length ratio of each cross-section was constant, the penetration performance of projectile decreases with the increase of the larger the major-to-minor axis length ratio. The penetration performance of projectile with elliptical cross-section decreases with the increase of the major-to-minor axis length ratio and the decrease of the caliber radius head of the projectile.
2023, 43(9): 091410.
doi: 10.11883/bzycj-2023-0016
Abstract:
To study the penetration performance and failure characteristics of ultra-high strength steel targets against high-mass tungsten alloy kinetic projectiles with different impact velocities, a ballistic gun was used to carry out 215 g tungsten alloy kinetic projectiles to impact the ultra-high strength G50 steel and 45 steel targets at velocities in the range of 689−1489 m/s. According to the experimental results, a conic-like crater was observed in the ultra-high strength steel target against a tungsten alloy kinetic projectile, which was different from the column-like crater mode observed in the experiments of 45 steel targets. It was also observed that there were several unique tensile spall cracks on the crater surface and bottom for the ultra-high strength steel. The depth of penetration (DOP) and the crater volume of these two steel targets were further obtained, which showed that the DOP of G50 steel targets is shorter than that of 45 steel at similar penetration velocity, while the corresponding crater volume is greater than that of 45 steel. Based on the interaction mechanism between the projectile and target, the high-mass tungsten alloy kinetic projectiles are considered to undergo local fragmentation under high radial stress during penetration into the G50 steel target, resulting in unloading tensile waves within the target. It is believed the unloading waves within the target lead to the spalling damage of the crater wall, resulting in the fish-scale-like rough walls and spallation cracks. This also explains why the crater volume of G50 steel is greater than that of 45 steel. In addition, the sharpening effect was caused by the local fragmentation of the kinetic projectile head. Therefore, it is considered that this failure mode was mainly caused by both the tensile fracture of the target induced by the local fragmentation of the projectile and the sharpening behavior of the projectile. Numerical simulations of the penetration of high-mass tungsten alloy projectiles into ultra-high strength steel targets were further performed to demonstrate the entire process of deformation, damage, and failure of the target plate and projectile, which further validated the failure mechanism of the targets.
To study the penetration performance and failure characteristics of ultra-high strength steel targets against high-mass tungsten alloy kinetic projectiles with different impact velocities, a ballistic gun was used to carry out 215 g tungsten alloy kinetic projectiles to impact the ultra-high strength G50 steel and 45 steel targets at velocities in the range of 689−1489 m/s. According to the experimental results, a conic-like crater was observed in the ultra-high strength steel target against a tungsten alloy kinetic projectile, which was different from the column-like crater mode observed in the experiments of 45 steel targets. It was also observed that there were several unique tensile spall cracks on the crater surface and bottom for the ultra-high strength steel. The depth of penetration (DOP) and the crater volume of these two steel targets were further obtained, which showed that the DOP of G50 steel targets is shorter than that of 45 steel at similar penetration velocity, while the corresponding crater volume is greater than that of 45 steel. Based on the interaction mechanism between the projectile and target, the high-mass tungsten alloy kinetic projectiles are considered to undergo local fragmentation under high radial stress during penetration into the G50 steel target, resulting in unloading tensile waves within the target. It is believed the unloading waves within the target lead to the spalling damage of the crater wall, resulting in the fish-scale-like rough walls and spallation cracks. This also explains why the crater volume of G50 steel is greater than that of 45 steel. In addition, the sharpening effect was caused by the local fragmentation of the kinetic projectile head. Therefore, it is considered that this failure mode was mainly caused by both the tensile fracture of the target induced by the local fragmentation of the projectile and the sharpening behavior of the projectile. Numerical simulations of the penetration of high-mass tungsten alloy projectiles into ultra-high strength steel targets were further performed to demonstrate the entire process of deformation, damage, and failure of the target plate and projectile, which further validated the failure mechanism of the targets.
2023, 43(9): 091411.
doi: 10.11883/bzycj-2023-0133
Abstract:
Lightweight ceramic composite armor is widely used for its lightweight and high bullet-resistant performance. To improve the bullet-resistant performance of ceramic composite armor, research has been conducted on the lightweight and performance improvement of different backing plates. The optimization of the structural design of lightweight ceramic composite armor is of great significance. Taking boron carbide ceramic as the front bullet-resistant panel, and different combinations of carbon fiber T300, UHMWPE, and Kevlar high-performance fiber boards as its composite backing plates. Using a 12.7 mm armor-piercing incendiary bullet to conduct ballistic impact experiments on ceramic/composite backing plates of different structures, the distribution law of fragment blocks and bullet-resistant performance of ceramic composite armor corresponding to different backing plates were analyzed by recovering shattered bullets and ceramic fragments and performing multi-stage screening and weighing. The study shows that adding a layer of carbon fiber board between the ceramic and fiber backing plates can significantly improve the bullet-resistant stiffness gradient of the composite armor, increase the structural stiffness of the entire bullet-resistant target board, and improve the stress wave propagation form between the bullet and the entire panel, prolonging the time and the effect of the stress wave propagation inside the entire ceramic panel after the formation of the ceramic cone and detachment from the ceramic panel, thereby reducing the tensile fracture caused by tensile waves inside the ceramic panel and prolonging the phenomenon of bullet retention. The Rosin-Rammler distribution model was used to characterize the fragment forms of ceramics and bullets. The results show that replacing half-thickness UHMWPE fiber board and Kevlar fiber board with carbon fiber backing plate respectively increased the half-cone angle of the ceramic panel by 2.05% and 4.20%, and the overall average characteristic size of the fragmentation zone decreased by 16.92% and 42.96% respectively. After adding a carbon fiber with high bending strength as the intermediate transition layer of the composite armor board, the failure mode of the backing plate changed, fully utilizing the high tensile strength of the fiber backing plate, thereby improving the overall bullet-resistant performance of the composite armor.
Lightweight ceramic composite armor is widely used for its lightweight and high bullet-resistant performance. To improve the bullet-resistant performance of ceramic composite armor, research has been conducted on the lightweight and performance improvement of different backing plates. The optimization of the structural design of lightweight ceramic composite armor is of great significance. Taking boron carbide ceramic as the front bullet-resistant panel, and different combinations of carbon fiber T300, UHMWPE, and Kevlar high-performance fiber boards as its composite backing plates. Using a 12.7 mm armor-piercing incendiary bullet to conduct ballistic impact experiments on ceramic/composite backing plates of different structures, the distribution law of fragment blocks and bullet-resistant performance of ceramic composite armor corresponding to different backing plates were analyzed by recovering shattered bullets and ceramic fragments and performing multi-stage screening and weighing. The study shows that adding a layer of carbon fiber board between the ceramic and fiber backing plates can significantly improve the bullet-resistant stiffness gradient of the composite armor, increase the structural stiffness of the entire bullet-resistant target board, and improve the stress wave propagation form between the bullet and the entire panel, prolonging the time and the effect of the stress wave propagation inside the entire ceramic panel after the formation of the ceramic cone and detachment from the ceramic panel, thereby reducing the tensile fracture caused by tensile waves inside the ceramic panel and prolonging the phenomenon of bullet retention. The Rosin-Rammler distribution model was used to characterize the fragment forms of ceramics and bullets. The results show that replacing half-thickness UHMWPE fiber board and Kevlar fiber board with carbon fiber backing plate respectively increased the half-cone angle of the ceramic panel by 2.05% and 4.20%, and the overall average characteristic size of the fragmentation zone decreased by 16.92% and 42.96% respectively. After adding a carbon fiber with high bending strength as the intermediate transition layer of the composite armor board, the failure mode of the backing plate changed, fully utilizing the high tensile strength of the fiber backing plate, thereby improving the overall bullet-resistant performance of the composite armor.
2023, 43(9): 091412.
doi: 10.11883/bzycj-2023-0135
Abstract:
In order to study the mechanism of fragmentation and damage characteristics of elliptical cross-section warhead under internal explosive loading, five types of warheads were designed with the same ratio of charge mass to casing mass but different ratio of minor axis to major axis, and static explosion tests were conducted. The detonation process of the warhead was recorded by high-speed camera, and the destruction capability of the warheads were quantified by measuring the cratering parameters of the witness targets, while the radial velocity distribution of the fragments was obtained by the velocity-measuring targets. The test results show that the radial velocity of the fragments of elliptical cross-section warhead logarithmically increases from the major axis direction to the minor axis direction. There is a significant velocity enhancement compared to circular cross-section warhead, when the ratio of minor to major axis is equal to 0.40, the enhancement reaches to an amazing 83%. The fragments near the major axis are subjected to slip detonation as the dominant driving effect, and the circumferential tensile stress inside the casing leads to tensile cracks on the inner surface of the fragments. At the same time, the tensile cracks disappear gradually as the ratio of minor to major axis increases. In the minor axis direction, the scattered detonation always dominated, and the casing is mainly subjected to radial compressive stresses, thus no tensile crack appears. In addition, due to the influence of rarefaction waves on the end face, the maximum destructive power of the warhead axially occurs at 1/4 of the distance from the non-detonation end. And in the radial direction, the damage power of fragment in the direction of minor axis is significantly greater than that in the major axis direction. Especially when the ratio of minor to major axis is equal to 0.40, the destructive power of the minor axis reaches 1.83 times that of the major axis, but the difference decreases with the increase of minor to major axis ratio.
In order to study the mechanism of fragmentation and damage characteristics of elliptical cross-section warhead under internal explosive loading, five types of warheads were designed with the same ratio of charge mass to casing mass but different ratio of minor axis to major axis, and static explosion tests were conducted. The detonation process of the warhead was recorded by high-speed camera, and the destruction capability of the warheads were quantified by measuring the cratering parameters of the witness targets, while the radial velocity distribution of the fragments was obtained by the velocity-measuring targets. The test results show that the radial velocity of the fragments of elliptical cross-section warhead logarithmically increases from the major axis direction to the minor axis direction. There is a significant velocity enhancement compared to circular cross-section warhead, when the ratio of minor to major axis is equal to 0.40, the enhancement reaches to an amazing 83%. The fragments near the major axis are subjected to slip detonation as the dominant driving effect, and the circumferential tensile stress inside the casing leads to tensile cracks on the inner surface of the fragments. At the same time, the tensile cracks disappear gradually as the ratio of minor to major axis increases. In the minor axis direction, the scattered detonation always dominated, and the casing is mainly subjected to radial compressive stresses, thus no tensile crack appears. In addition, due to the influence of rarefaction waves on the end face, the maximum destructive power of the warhead axially occurs at 1/4 of the distance from the non-detonation end. And in the radial direction, the damage power of fragment in the direction of minor axis is significantly greater than that in the major axis direction. Especially when the ratio of minor to major axis is equal to 0.40, the destructive power of the minor axis reaches 1.83 times that of the major axis, but the difference decreases with the increase of minor to major axis ratio.
2023, 43(9): 091413.
doi: 10.11883/bzycj-2023-0072
Abstract:
In order to deepen the understanding of the dynamic response of cylindrical shell under near-field/contact underwater explosion, small-scale model of cylindrical shell was designed and then optical and electronical tests were conducted to investigate the dynamic response of the model. The physical images of the interaction of shock wave/bubble with cylindrical shell were obtained using a camera with high frequency and high resolution. At the same time, dynamic strain, overpressure and damage mode were obtained. By analyzing the damage morphology of 3D laser scanning and high-speed optical physical images, the physical process of the interaction between shock waves, bubbles, and cylindrical shell structures as well as final damage mode are presented. Through the analysis of dynamic strains, the transformation of tension and compression strains and the division of response stages of the explosion-facing surface and back surface of cylindrical shell structure during loading are revealed. Through the analysis of overpressure loads, the completeness of charge detonation and the influence of structural energy absorption on overpressure under contact explosion loading are clarified. Research results have shown that changes in detonation distance can significantly affect the damage morphology of cylindrical shell structures. Under close range loading, cylindrical shell structures mainly exhibit large plastic deformation, while under contact loading, cylindrical shell structures mainly exhibit tearing failure. The formation and collapse of the cavitation zone on the explosion facing surface of cylindrical shell structures under close range loading cannot be ignored, and the damage effect caused by secondary loading should be further studied. The research results can provide a reference basis for the damage assessment of cylindrical shell structures under near-field/contact underwater explosion.
In order to deepen the understanding of the dynamic response of cylindrical shell under near-field/contact underwater explosion, small-scale model of cylindrical shell was designed and then optical and electronical tests were conducted to investigate the dynamic response of the model. The physical images of the interaction of shock wave/bubble with cylindrical shell were obtained using a camera with high frequency and high resolution. At the same time, dynamic strain, overpressure and damage mode were obtained. By analyzing the damage morphology of 3D laser scanning and high-speed optical physical images, the physical process of the interaction between shock waves, bubbles, and cylindrical shell structures as well as final damage mode are presented. Through the analysis of dynamic strains, the transformation of tension and compression strains and the division of response stages of the explosion-facing surface and back surface of cylindrical shell structure during loading are revealed. Through the analysis of overpressure loads, the completeness of charge detonation and the influence of structural energy absorption on overpressure under contact explosion loading are clarified. Research results have shown that changes in detonation distance can significantly affect the damage morphology of cylindrical shell structures. Under close range loading, cylindrical shell structures mainly exhibit large plastic deformation, while under contact loading, cylindrical shell structures mainly exhibit tearing failure. The formation and collapse of the cavitation zone on the explosion facing surface of cylindrical shell structures under close range loading cannot be ignored, and the damage effect caused by secondary loading should be further studied. The research results can provide a reference basis for the damage assessment of cylindrical shell structures under near-field/contact underwater explosion.
2023, 43(9): 091414.
doi: 10.11883/bzycj/2022-0477
Abstract:
In order to lower the collateral damage of warhead in urban warfare, the new material, polyether ether ketone (PEEK) was used as the warhead shell in this work, by which the fragments could be eliminated while the killing range of shock waves was maintained. The comparison between the warhead using PEEK shell and the one with 2A12 shell and identical shell thickness was conducted, in which the overpressure, specific impulse and fragment velocity were analyzed, the acceleration of fragment was recorded by high-speed camera and the fragments were recovered for further investigation. The results show that the warhead using PEEK shell possessed a 54% lower weight than the one using 2A12 shell and an identical overpressure damage radius. By using PEEK shell, the energy converted into shock wave is more than the case using 2A12 shell, thus the specific impulse is also higher as the proportional distance increasing. Few PEEK fragments were recovered since the tiny PEEK fragments formed under the blast loads were completely burned during the acceleration driven by high temperature detonation products. Therefore, the lethality of warhead using PEEK shell was limited to shock wave and was easily controlled to meet the requirement of low collateral damage in urban warfare.
In order to lower the collateral damage of warhead in urban warfare, the new material, polyether ether ketone (PEEK) was used as the warhead shell in this work, by which the fragments could be eliminated while the killing range of shock waves was maintained. The comparison between the warhead using PEEK shell and the one with 2A12 shell and identical shell thickness was conducted, in which the overpressure, specific impulse and fragment velocity were analyzed, the acceleration of fragment was recorded by high-speed camera and the fragments were recovered for further investigation. The results show that the warhead using PEEK shell possessed a 54% lower weight than the one using 2A12 shell and an identical overpressure damage radius. By using PEEK shell, the energy converted into shock wave is more than the case using 2A12 shell, thus the specific impulse is also higher as the proportional distance increasing. Few PEEK fragments were recovered since the tiny PEEK fragments formed under the blast loads were completely burned during the acceleration driven by high temperature detonation products. Therefore, the lethality of warhead using PEEK shell was limited to shock wave and was easily controlled to meet the requirement of low collateral damage in urban warfare.
