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To study the thermal relaxation behavior of the graded medium satisfied the power law, the one-dimensional hyperbolic non-Fourier heat conduction equation of the graded material which satisfied the power law was derived from the Cattaneo-Vernote linear hyperbolic heat transfer equation with the thermal relaxation coefficient and graded exponent induced. The equation was first treated dimensionless. Based on the Laplace transformation, the new heat conduction equation was found to conform to the general form of the Bessel equation called the Lommel equation in the frequency domain, and the Bessel series solution of the temperature field in the frequency domain was obtained. With the asymptotic expansion of the Bessel series, the simplified expression of the temperature field in the frequency domain containing trigonometric function was obtained. The inverse Laplace transformation of the temperature field in the frequency domain was employed to get the first analytical solution of the temperature field in the time domain. Besides the first analytical solution, the new heat conduction equation in the frequency domain was simplified to the Euler equation, and the second kind of analytical solution was obtained by the pole residue method. The second analytical solution exhibits similar fluctuation attenuation and diffusion features, and both the waveform and response time are sensitive to the relaxation time coefficient. However, the second kind of analytical solution differs from the first kind of solution in terms of waveform elements which are highly related to the graded structure. The accuracy of the analytical result is verified by numerical calculation. Taking Mo-ZrC graded composite as an example, the thermal relaxation behavior of graded material satisfied power law under the first kind of temperature boundary and temperature pulse loading are discussed in detail. The temperature field shows both fluctuation attenuation and conduction characteristics. With the increase of the thermal relaxation coefficient, the response time and temperature wave amplitude increase, the unit waveform develops from a trapezoidal wave to a rectangular wave, and the oscillation approaching to the boundary shows an obvious bias.
To study the thermal relaxation behavior of the graded medium satisfied the power law, the one-dimensional hyperbolic non-Fourier heat conduction equation of the graded material which satisfied the power law was derived from the Cattaneo-Vernote linear hyperbolic heat transfer equation with the thermal relaxation coefficient and graded exponent induced. The equation was first treated dimensionless. Based on the Laplace transformation, the new heat conduction equation was found to conform to the general form of the Bessel equation called the Lommel equation in the frequency domain, and the Bessel series solution of the temperature field in the frequency domain was obtained. With the asymptotic expansion of the Bessel series, the simplified expression of the temperature field in the frequency domain containing trigonometric function was obtained. The inverse Laplace transformation of the temperature field in the frequency domain was employed to get the first analytical solution of the temperature field in the time domain. Besides the first analytical solution, the new heat conduction equation in the frequency domain was simplified to the Euler equation, and the second kind of analytical solution was obtained by the pole residue method. The second analytical solution exhibits similar fluctuation attenuation and diffusion features, and both the waveform and response time are sensitive to the relaxation time coefficient. However, the second kind of analytical solution differs from the first kind of solution in terms of waveform elements which are highly related to the graded structure. The accuracy of the analytical result is verified by numerical calculation. Taking Mo-ZrC graded composite as an example, the thermal relaxation behavior of graded material satisfied power law under the first kind of temperature boundary and temperature pulse loading are discussed in detail. The temperature field shows both fluctuation attenuation and conduction characteristics. With the increase of the thermal relaxation coefficient, the response time and temperature wave amplitude increase, the unit waveform develops from a trapezoidal wave to a rectangular wave, and the oscillation approaching to the boundary shows an obvious bias.
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The high-speed kinetic energy missile is a significant anti-tank weapon comprising many crucial components known as "loads" in addition to the kinetic energy penetrator. In order to examine the impact of loads on the penetration behavior of the armor-piercing rod in a steel target, two sets of experiments were performed where both loaded and unloaded rods were used to penetrate 603 armored steel plates. Structural failures of the plates were observed under both loaded and unloaded conditions. Subsequently, numerical simulation methods were employed to analyze the penetration characteristics of both loaded and unloaded armor-piercing rods under various conditions, including incident angles of 45° and 60°, and impact velocities ranging from 1300m/s to 1600m/s.. An analysis was conducted to evaluate the effects of loads, incident angles, impact velocities, and load centroid positions on both the penetration depth and deflection angle of the rods. The research findings indicate that the inclusion of loads substantially enhances the oblique penetration depth of the armor-piercing rod while simultaneously reducing the ballistic deflection angle, thereby effectively improving the overall penetration efficiency. Conversely, in the case of positive penetration, the energy consumption caused by the load striking the target plate's surface impedes the armor-piercing rod's ability to penetrate. It is noteworthy that under an impact velocity of 1400m/s and an incident angle of 60°, the inclusion of loads results in a decrease in the critical jump velocity of the armor-piercing rod. Moreover, observations revealed that as the distance between the centroid of the armor-piercing rod and its head surpasses half of the rod's length, there is an increase in penetration depth accompanied by a corresponding decrease in the deflection angle. Specifically, it has been found that an increased distance between the centroid of the armor-piercing rod and its head leads to an improvement in penetration effectiveness. These findings highlight the substantial impact of load position on the penetration effectiveness and offer valuable insights for future design optimization. The research outcomes offer essential support and guidance for the design of high-speed kinetic energy missiles, thereby facilitating the enhancement of their penetration capabilities.
The high-speed kinetic energy missile is a significant anti-tank weapon comprising many crucial components known as "loads" in addition to the kinetic energy penetrator. In order to examine the impact of loads on the penetration behavior of the armor-piercing rod in a steel target, two sets of experiments were performed where both loaded and unloaded rods were used to penetrate 603 armored steel plates. Structural failures of the plates were observed under both loaded and unloaded conditions. Subsequently, numerical simulation methods were employed to analyze the penetration characteristics of both loaded and unloaded armor-piercing rods under various conditions, including incident angles of 45° and 60°, and impact velocities ranging from 1300m/s to 1600m/s.. An analysis was conducted to evaluate the effects of loads, incident angles, impact velocities, and load centroid positions on both the penetration depth and deflection angle of the rods. The research findings indicate that the inclusion of loads substantially enhances the oblique penetration depth of the armor-piercing rod while simultaneously reducing the ballistic deflection angle, thereby effectively improving the overall penetration efficiency. Conversely, in the case of positive penetration, the energy consumption caused by the load striking the target plate's surface impedes the armor-piercing rod's ability to penetrate. It is noteworthy that under an impact velocity of 1400m/s and an incident angle of 60°, the inclusion of loads results in a decrease in the critical jump velocity of the armor-piercing rod. Moreover, observations revealed that as the distance between the centroid of the armor-piercing rod and its head surpasses half of the rod's length, there is an increase in penetration depth accompanied by a corresponding decrease in the deflection angle. Specifically, it has been found that an increased distance between the centroid of the armor-piercing rod and its head leads to an improvement in penetration effectiveness. These findings highlight the substantial impact of load position on the penetration effectiveness and offer valuable insights for future design optimization. The research outcomes offer essential support and guidance for the design of high-speed kinetic energy missiles, thereby facilitating the enhancement of their penetration capabilities.
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Ammunition warheads are typically cylindrical charges that detonated at moving stage. Accurately calculating the blast wave power field and the blast loadings acting on the structure of cylindrical charges air moving explosion is the prerequisite for predicting the explosive power of warheads, evaluating the target damage effect, and protection design. The peak overpressure and maximal impulse of the incident and reflected blast waves of the cylindrical charges air moving explosion were numerically simulated. Firstly, a three-stage finite element analysis method for cylindrical charges air moving explosion was proposed based on the AUTODYN finite element analysis program, and the reliability of the method was verified by comparing the simulated and test data of existing charges air static and moving explosion tests. Then, on the basis of considering factors such as charge moving velocity, length to diameter ratio, scaled distance, azimuth angle, and rigid reflection, numerical simulations were conducted for 200 sets of scenarios of the cylindrical charges air moving explosion. The distribution characteristics of the moving explosion blast wave field, incident and reflected blast wave loadings were quantitatively analyzed. The influence for blast wave field and blast wave loadings of charge moving velocity and length to diameter ratio was also discussed. Furthermore, for the typical scenarios of cylindrical charges air moving explosion in free field and reflected field where cylindrical charges were perpendicular to the target surface air moving explosion, the engineering calculation models for the peak overpressure and maximal impulse of the incident and reflected blast waves of cylindrical charges air moving explosion were proposed. Finally, through carrying out numerical simulations of 40 sets of scenarios for the moving explosions of two simplified cylindrical TNT charges of prototype warheads (23 kg and 280 kg), and comparing data of engineering calculation models and simulations, the applicability of the proposed calculation model of the blast wave loadings of the cylindrical charges air moving explosion was validated.
Ammunition warheads are typically cylindrical charges that detonated at moving stage. Accurately calculating the blast wave power field and the blast loadings acting on the structure of cylindrical charges air moving explosion is the prerequisite for predicting the explosive power of warheads, evaluating the target damage effect, and protection design. The peak overpressure and maximal impulse of the incident and reflected blast waves of the cylindrical charges air moving explosion were numerically simulated. Firstly, a three-stage finite element analysis method for cylindrical charges air moving explosion was proposed based on the AUTODYN finite element analysis program, and the reliability of the method was verified by comparing the simulated and test data of existing charges air static and moving explosion tests. Then, on the basis of considering factors such as charge moving velocity, length to diameter ratio, scaled distance, azimuth angle, and rigid reflection, numerical simulations were conducted for 200 sets of scenarios of the cylindrical charges air moving explosion. The distribution characteristics of the moving explosion blast wave field, incident and reflected blast wave loadings were quantitatively analyzed. The influence for blast wave field and blast wave loadings of charge moving velocity and length to diameter ratio was also discussed. Furthermore, for the typical scenarios of cylindrical charges air moving explosion in free field and reflected field where cylindrical charges were perpendicular to the target surface air moving explosion, the engineering calculation models for the peak overpressure and maximal impulse of the incident and reflected blast waves of cylindrical charges air moving explosion were proposed. Finally, through carrying out numerical simulations of 40 sets of scenarios for the moving explosions of two simplified cylindrical TNT charges of prototype warheads (23 kg and 280 kg), and comparing data of engineering calculation models and simulations, the applicability of the proposed calculation model of the blast wave loadings of the cylindrical charges air moving explosion was validated.
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Heterogeneous media is very common in nature. Due to the complex internal structure, the heterogeneous compressive shear coupled stress field is inside heterogeneous media, which leads to the mutual influence of compression waves and shear waves. The study of wave mechanics behavior and description of heterogeneity in heterogeneous media is of great significance and full of challenges. This article established a general constitutive relationship that reflected the compression shear coupling characteristics of heterogeneous materials, proposed coupling coefficients to describe material heterogeneity, combined momentum conservation law to establish a generalized wave equation, and provided a general method for solving the generalized wave equation. As an example, Expressions for the three characteristic wave velocities of compression shear coupling under the first-order compression shear coupling constitutive relationship were provided, and the finite difference method was employed to obtain the propagation process of coupled compression waves and shear waves. The effects of four heterogeneous coupling coefficients on stress state, coupled wave velocity, and wave propagation process were studied. The positive and negative values, as well as the combination of coupling parameters, reflected the structural characteristics of heterogeneous media and also determined the properties of compression shear coupling waves. For heterogeneous media with high-pressure effects, shear dilation effects, and shear weakening effects, the coupled compression wave velocity was lower than the elastic compression wave velocity corresponding to uniform media, and the coupled shear wave velocity was higher than the elastic shear wave velocity. The effect of shear on compression delayed the propagation of compressive stress, while compression promoted the propagation of shear. Coupled compression wave velocity was the result of the competition between the coupling effect of shear on compression and the volume compaction effect. Coupled shear wave velocity was the competition between the coupling effect of compression on shear and the shear weakening effect caused by continuous distortion of the medium. These mechanisms could be achieved through different combinations of compression shear coupling parameters. The true triaxial experimental testing system was used to measure the longitudinal wave velocity of granite, model materials made of mortar, and materials made of cement mortar with coarse aggregates under different compressive and shear stresses. The results indicated that for heterogeneous media, the longitudinal wave velocity decreased with the increase of static water pressure and equivalent shear stress, and the shear expansion effect and shear weakening effect dominated. The experimental results and theoretical results had the same trend. The conclusion of this study was expected to provide a physical mechanism explanation for the phenomenon of the variation of wave velocity with stress state in heterogeneous materials.
Heterogeneous media is very common in nature. Due to the complex internal structure, the heterogeneous compressive shear coupled stress field is inside heterogeneous media, which leads to the mutual influence of compression waves and shear waves. The study of wave mechanics behavior and description of heterogeneity in heterogeneous media is of great significance and full of challenges. This article established a general constitutive relationship that reflected the compression shear coupling characteristics of heterogeneous materials, proposed coupling coefficients to describe material heterogeneity, combined momentum conservation law to establish a generalized wave equation, and provided a general method for solving the generalized wave equation. As an example, Expressions for the three characteristic wave velocities of compression shear coupling under the first-order compression shear coupling constitutive relationship were provided, and the finite difference method was employed to obtain the propagation process of coupled compression waves and shear waves. The effects of four heterogeneous coupling coefficients on stress state, coupled wave velocity, and wave propagation process were studied. The positive and negative values, as well as the combination of coupling parameters, reflected the structural characteristics of heterogeneous media and also determined the properties of compression shear coupling waves. For heterogeneous media with high-pressure effects, shear dilation effects, and shear weakening effects, the coupled compression wave velocity was lower than the elastic compression wave velocity corresponding to uniform media, and the coupled shear wave velocity was higher than the elastic shear wave velocity. The effect of shear on compression delayed the propagation of compressive stress, while compression promoted the propagation of shear. Coupled compression wave velocity was the result of the competition between the coupling effect of shear on compression and the volume compaction effect. Coupled shear wave velocity was the competition between the coupling effect of compression on shear and the shear weakening effect caused by continuous distortion of the medium. These mechanisms could be achieved through different combinations of compression shear coupling parameters. The true triaxial experimental testing system was used to measure the longitudinal wave velocity of granite, model materials made of mortar, and materials made of cement mortar with coarse aggregates under different compressive and shear stresses. The results indicated that for heterogeneous media, the longitudinal wave velocity decreased with the increase of static water pressure and equivalent shear stress, and the shear expansion effect and shear weakening effect dominated. The experimental results and theoretical results had the same trend. The conclusion of this study was expected to provide a physical mechanism explanation for the phenomenon of the variation of wave velocity with stress state in heterogeneous materials.
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To investigate the influence of typical metal powders on the shock wave effect and thermal damage performance of fuel air explosive (FAE), the explosion characteristics, flame structure and temperature distribution characteristics of epoxypropane (PO) with different types and contents of metal powders were studied using a 20 L spherical liquid explosion test system. The temperature field of explosion flame was reconstructed by the colorimetric temperature measurement method with a high-speed camera, which was based on the gray-body radiation theory and a self-written python code. The tungsten lamp was used to calibrate the measuring accuracy of the temperature mapping system, and the fitting relationship between the temperatures and the gray values of the high-speed images was derived to obtain the conversion coefficient. The experimental results show that the optimal mass concentration of pure PO was 780 g·m-3, both the maximum explosion overpressure (?Pmax) and maximum explosion pressure rise rate ((dP/dt)max) reached the maximum, ?Pmax=0.799 MPa and (dP/dt)max=52.438 MPa·s-1, respectively. The maximum explosion overpressure, maximum explosion pressure rise rate and maximum average temperature of PO added with Al, Ti and Mg powders are increasing with the increase of mass ratios (I), and the trend of maximum pressure rise time is opposite. The variation rules of maximum explosion overpressure and maximum average temperature are consistent: Al/PO > Mg/PO > Ti/PO. When I=40%, the maximum explosion overpressure value of the three solid-liquid mixed fuels increases by 12.00%, 8.41% and 11.54%, respectively, compared with pure PO. In addition, the variation rules of maximum explosion pressure rise rate and the combustion rate are consistent: Al/PO > Mg/PO > Ti/PO. When I=40%, the the maximum explosion pressure rise rate value of the three solid-liquid mixed fuels increases by 41.91%, 39.60% and 45.29%, respectively, compared with the pure PO. The results indicate that different high-energy metal powders have varied advantages in improving the explosion performance of PO, metal powders should be reasonably selected as energetic additives according to the damage performance index in the formulation design of FAE.
To investigate the influence of typical metal powders on the shock wave effect and thermal damage performance of fuel air explosive (FAE), the explosion characteristics, flame structure and temperature distribution characteristics of epoxypropane (PO) with different types and contents of metal powders were studied using a 20 L spherical liquid explosion test system. The temperature field of explosion flame was reconstructed by the colorimetric temperature measurement method with a high-speed camera, which was based on the gray-body radiation theory and a self-written python code. The tungsten lamp was used to calibrate the measuring accuracy of the temperature mapping system, and the fitting relationship between the temperatures and the gray values of the high-speed images was derived to obtain the conversion coefficient. The experimental results show that the optimal mass concentration of pure PO was 780 g·m-3, both the maximum explosion overpressure (?Pmax) and maximum explosion pressure rise rate ((dP/dt)max) reached the maximum, ?Pmax=0.799 MPa and (dP/dt)max=52.438 MPa·s-1, respectively. The maximum explosion overpressure, maximum explosion pressure rise rate and maximum average temperature of PO added with Al, Ti and Mg powders are increasing with the increase of mass ratios (I), and the trend of maximum pressure rise time is opposite. The variation rules of maximum explosion overpressure and maximum average temperature are consistent: Al/PO > Mg/PO > Ti/PO. When I=40%, the maximum explosion overpressure value of the three solid-liquid mixed fuels increases by 12.00%, 8.41% and 11.54%, respectively, compared with pure PO. In addition, the variation rules of maximum explosion pressure rise rate and the combustion rate are consistent: Al/PO > Mg/PO > Ti/PO. When I=40%, the the maximum explosion pressure rise rate value of the three solid-liquid mixed fuels increases by 41.91%, 39.60% and 45.29%, respectively, compared with the pure PO. The results indicate that different high-energy metal powders have varied advantages in improving the explosion performance of PO, metal powders should be reasonably selected as energetic additives according to the damage performance index in the formulation design of FAE.
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The wave propagation and pressure distribution during the interaction between long duration blast waves and structures are important foundations for the large scale explosion protection design and safety assessment. In order to understand the interaction mechanism between long duration blast waves and cylindrical shells, as well as the distribution law of the surface load on the cylindrical shells under their action, the overpressure history on the cylindrical structure surface were obtained through the 150ms long duration blast wave shock tube experiment, and the shock wave evolution and the pressure load distribution were investigated numerically using the large eddy simulation and hybrid WENO - TCD (Weighted Essentially Non-Oscillatory–Tuned Centered Difference) method. The results show that the overpressure load of the calculation results is in good agreement with the experimental results, and the overpressure load on the cylindrical shell appears a clear angle and height correlation. The pressure on the back shell is higher than that on the side surface or even comparable to the blast on the facing surface, which exhibit different pressure attenuation modes from the traditional short duration blast wave propagation. The sudden expansion on the side surface is the main reason for the initial oscillation of pressure, and has a lower pressure than that at the windward and leeward sides. On the other hand, a series of diffracted shock waves collides and reflects on the symmetry plane of the shell leeward, as well as the stationary and superimposed effects of the series of decelerating shock waves near the 135° phase, which are the main mechanisms that cause the overall increase of the pressure load on the cylindrical shell. In addition, the formation and evolution of wake vortex structures on the leeward side due to the boundary effects is a key factor leading to differences in the load distribution along the height direction. The above analysis methods and related results lay the foundation for the subsequent study of load distribution models for typical structural components under long duration blast waves.
The wave propagation and pressure distribution during the interaction between long duration blast waves and structures are important foundations for the large scale explosion protection design and safety assessment. In order to understand the interaction mechanism between long duration blast waves and cylindrical shells, as well as the distribution law of the surface load on the cylindrical shells under their action, the overpressure history on the cylindrical structure surface were obtained through the 150ms long duration blast wave shock tube experiment, and the shock wave evolution and the pressure load distribution were investigated numerically using the large eddy simulation and hybrid WENO - TCD (Weighted Essentially Non-Oscillatory–Tuned Centered Difference) method. The results show that the overpressure load of the calculation results is in good agreement with the experimental results, and the overpressure load on the cylindrical shell appears a clear angle and height correlation. The pressure on the back shell is higher than that on the side surface or even comparable to the blast on the facing surface, which exhibit different pressure attenuation modes from the traditional short duration blast wave propagation. The sudden expansion on the side surface is the main reason for the initial oscillation of pressure, and has a lower pressure than that at the windward and leeward sides. On the other hand, a series of diffracted shock waves collides and reflects on the symmetry plane of the shell leeward, as well as the stationary and superimposed effects of the series of decelerating shock waves near the 135° phase, which are the main mechanisms that cause the overall increase of the pressure load on the cylindrical shell. In addition, the formation and evolution of wake vortex structures on the leeward side due to the boundary effects is a key factor leading to differences in the load distribution along the height direction. The above analysis methods and related results lay the foundation for the subsequent study of load distribution models for typical structural components under long duration blast waves.
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A kind of microporous modified coal gangue (MCG) with rough surface and large specific surface area was obtained by roasting, acid-alkali excitation and physical grinding of industrial solid waste coal gangue (CG) as raw material. Using MCG as matrix, a new flame retardant sodium alginate (SA) was combined with MCG by mechanochemical technology (MCT) to prepare an efficient, environmentally friendly and economical modified coal gangue-sodium alginate (MCG-SA) powder explosion suppressor. The three powders were characterized by thermogravimetric analysis, SEM analysis and XRD analysis to determine their thermal decomposition characteristics, micro-morphology and crystal phase composition. Through the SEM analysis, it can be clearly observed that the powder is irregularly stacked with particles, has many micro-pore cracks, rough surface, and weakened agglomeration effect. The XRD analysis shows that there are characteristic peaks of SA and MCG in the composite powder, which proves that the combination of the two is successful. It is not difficult to see from the thermogravimetric analysis that the composite powder has both the thermogravimetric characteristics of MCG and SA, and the mass loss of thermal decomposition is as high as 67.02%, which has excellent heat absorption performance. On the basis of the self-built test platform, the effects of MCG, SA and their composite powders on the explosion pressure and flame propagation speed of methane-air premixed gas under different compounding ratios and adding masses were investigated. The results show that MCG, SA and MCG-SA powders have good anti-explosion effect, and the anti-explosion ability of composite powders is better than that of single powders. Among them, the composite powder with mass of 250 mg and SA mass fraction of 50% has the most significant synergistic inhibition effect on 9.5% methane/air explosion, and the maximum explosion pressure and maximum flame propagation velocity are reduced by 36.72% and 68.93%, respectively. The arrival time of the maximum explosion pressure and the maximum flame propagation speed is extended by 243.36% and 171.33%, respectively. The mechanism of explosion suppression of composite powder is mainly reflected in barrier effect, heat absorption, adsorption and consumption of free radicals. This research has certain research significance and reference value in the field of industrial environmental protection and gas explosion protection.
A kind of microporous modified coal gangue (MCG) with rough surface and large specific surface area was obtained by roasting, acid-alkali excitation and physical grinding of industrial solid waste coal gangue (CG) as raw material. Using MCG as matrix, a new flame retardant sodium alginate (SA) was combined with MCG by mechanochemical technology (MCT) to prepare an efficient, environmentally friendly and economical modified coal gangue-sodium alginate (MCG-SA) powder explosion suppressor. The three powders were characterized by thermogravimetric analysis, SEM analysis and XRD analysis to determine their thermal decomposition characteristics, micro-morphology and crystal phase composition. Through the SEM analysis, it can be clearly observed that the powder is irregularly stacked with particles, has many micro-pore cracks, rough surface, and weakened agglomeration effect. The XRD analysis shows that there are characteristic peaks of SA and MCG in the composite powder, which proves that the combination of the two is successful. It is not difficult to see from the thermogravimetric analysis that the composite powder has both the thermogravimetric characteristics of MCG and SA, and the mass loss of thermal decomposition is as high as 67.02%, which has excellent heat absorption performance. On the basis of the self-built test platform, the effects of MCG, SA and their composite powders on the explosion pressure and flame propagation speed of methane-air premixed gas under different compounding ratios and adding masses were investigated. The results show that MCG, SA and MCG-SA powders have good anti-explosion effect, and the anti-explosion ability of composite powders is better than that of single powders. Among them, the composite powder with mass of 250 mg and SA mass fraction of 50% has the most significant synergistic inhibition effect on 9.5% methane/air explosion, and the maximum explosion pressure and maximum flame propagation velocity are reduced by 36.72% and 68.93%, respectively. The arrival time of the maximum explosion pressure and the maximum flame propagation speed is extended by 243.36% and 171.33%, respectively. The mechanism of explosion suppression of composite powder is mainly reflected in barrier effect, heat absorption, adsorption and consumption of free radicals. This research has certain research significance and reference value in the field of industrial environmental protection and gas explosion protection.
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Integrated with a high-speed oblique water entry test of a large caliber conical nose projectile, the deflection behavior of the projectile obliquely entering water is studied based on the Arbitrary-Lagrange-Euler (ALE) fluid structure coupling method. Firstly, the variation of contact force mode as well as load characteristics of the projectile in the condition of water entry at 500m/s is analyzed, and the corresponding mechanism is discussed. In addition, the influence of water entry angle on the deflection behavior of projectile is also investigated. Related analysis demonstrated that the projectile will deflect upward due to the effect of pitch moment, and the deflection velocity increases first and then decreases gradually during the entry process. The variation trend of deflection degree is different within different entry angle range: When the entry angle is less than 15°, the projectile usually jumps out of the water; When the entry angle locates in the range of 30°-60°, the deflection trend of projectile is almost the same, i.e., the projectile rotates from the initial tilted state to the horizontal state and further the vertical state, and finally the projectile moves downward with its nose opposite the initial water entry direction; When the entry angle increases to 75°, the projectile cannot continue to rotate to a vertical state after it rotates to a horizontal, instead it moves downward in a tilted state with its nose facing upward. Moreover, the penetration depth of the projectile increases with the increase of entry angle, and it almost shows an exponential relationship.
Integrated with a high-speed oblique water entry test of a large caliber conical nose projectile, the deflection behavior of the projectile obliquely entering water is studied based on the Arbitrary-Lagrange-Euler (ALE) fluid structure coupling method. Firstly, the variation of contact force mode as well as load characteristics of the projectile in the condition of water entry at 500m/s is analyzed, and the corresponding mechanism is discussed. In addition, the influence of water entry angle on the deflection behavior of projectile is also investigated. Related analysis demonstrated that the projectile will deflect upward due to the effect of pitch moment, and the deflection velocity increases first and then decreases gradually during the entry process. The variation trend of deflection degree is different within different entry angle range: When the entry angle is less than 15°, the projectile usually jumps out of the water; When the entry angle locates in the range of 30°-60°, the deflection trend of projectile is almost the same, i.e., the projectile rotates from the initial tilted state to the horizontal state and further the vertical state, and finally the projectile moves downward with its nose opposite the initial water entry direction; When the entry angle increases to 75°, the projectile cannot continue to rotate to a vertical state after it rotates to a horizontal, instead it moves downward in a tilted state with its nose facing upward. Moreover, the penetration depth of the projectile increases with the increase of entry angle, and it almost shows an exponential relationship.
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Understanding the role of temperature rise in dynamic shear is of great significant, for it helps us to predict accurately the dynamic failure of materials and structures. In order to obtain the temperature rise and the distribution of temperature in the shear zone of TC11 titanium alloy, dynamic shear tests were conducted on the “flat-hat” shaped specimens of TC11 titanium alloy by using the split Hopkinson pressure bar. The evolution of temperature rise in the shear zone with time was obtained which based the high speed infrared InSb detecting technology. Theoretical analysis of the distribution of temperature rise in the shear zone with time and sapce is carried out by solving the one dimensional thermal conduction euqation. The initiation and propagation of shear band and the relative distribution of temperature fields in the shear zone are obtained by FEM simulation analysis. It was found from the experimental resuts that the TC11 titanium alloy behaves brittlely under dynamic shearing. The fracture morphologies demonstrate that significatn temperature rise occurs during dynamic shearing. The temperature rise test results demonstrate that the maximal temperature rise in the shear zone achieves 430℃. Furthermore, the loading rate plays insignificant effect on the temperature rise in the shear zone. The temperature rise in the shear zone is highly-localized, the significant temperature rise distributes several micro-meters around the center of the shear zone, and the significant temperature rise maintains several tens of micro-seconds. The results of the theoretical analysis and FEM simulation demonstrate that the maximal temperature rise can achieve 751℃, and the distribution laws of the temperature are consistent with the experimental results. It was found from the experimental and FEM simulation results that the maximum temperature rise occurs at the time of failing of material, indicating that the temperature rise in the shear zone results from the highly localized shear deformation.
Understanding the role of temperature rise in dynamic shear is of great significant, for it helps us to predict accurately the dynamic failure of materials and structures. In order to obtain the temperature rise and the distribution of temperature in the shear zone of TC11 titanium alloy, dynamic shear tests were conducted on the “flat-hat” shaped specimens of TC11 titanium alloy by using the split Hopkinson pressure bar. The evolution of temperature rise in the shear zone with time was obtained which based the high speed infrared InSb detecting technology. Theoretical analysis of the distribution of temperature rise in the shear zone with time and sapce is carried out by solving the one dimensional thermal conduction euqation. The initiation and propagation of shear band and the relative distribution of temperature fields in the shear zone are obtained by FEM simulation analysis. It was found from the experimental resuts that the TC11 titanium alloy behaves brittlely under dynamic shearing. The fracture morphologies demonstrate that significatn temperature rise occurs during dynamic shearing. The temperature rise test results demonstrate that the maximal temperature rise in the shear zone achieves 430℃. Furthermore, the loading rate plays insignificant effect on the temperature rise in the shear zone. The temperature rise in the shear zone is highly-localized, the significant temperature rise distributes several micro-meters around the center of the shear zone, and the significant temperature rise maintains several tens of micro-seconds. The results of the theoretical analysis and FEM simulation demonstrate that the maximal temperature rise can achieve 751℃, and the distribution laws of the temperature are consistent with the experimental results. It was found from the experimental and FEM simulation results that the maximum temperature rise occurs at the time of failing of material, indicating that the temperature rise in the shear zone results from the highly localized shear deformation.
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Abstract:
In order to investigate the dynamic compression behavior of carbon nanotubes reinforced concrete under impact load, the impact compression tests were carried out by using a split Hopkinson pressure bar (SHPB) test device with a diameter of 100 mm. Then, based on this, the evolution laws of dynamic compressive strength, compression deformation, and energy dissipation characteristics of concrete under different impact velocities and carbon nanotubes contents were compared and analyzed. The impact velocities of SHPB test were around 6.8 m·s-1, 7.8 m·s-1, 8.8 m·s-1, 9.8 m·s-1, and 10.8 m·s-1, respectively. The contents of carbon nanotubes in concrete (as a percentage of cement mass) were 0% (i.e. ordinary concrete, as a control group), 0.10%, 0.20%, 0.30%, and 0.40%, respectively. The experimental results show that the dynamic strength characteristics of carbon nanotubes reinforced concrete have significant loading rate sensitivity. The dynamic compressive strength and dynamic strength increase factor show a linear positive correlation with impact velocity. When the loading level is the same, the dynamic compressive strength increases first and then decreases slightly with the increase of carbon nanotubes content, and the growth rate can reach 23.7% compared to ordinary concrete. The variation characteristics of ultimate strain and impact toughness of carbon nanotubes reinforced concrete are similar, which gradually increase with the increase of impact velocity, and have a certain impact velocity strengthening effect, but there is no obvious linear relationship with impact velocity. Toughness is a comprehensive reflection of material strength and deformation. Therefore, at the same loading level, when the content of carbon nanotubes is 0.30%, the impact toughness of concrete is relatively maximum, which is about 10% higher than that of ordinary concrete. The appropriate addition of carbon nanotubes can effectively enhance the integrity and compactness of the internal structure of concrete, thereby improving its dynamic mechanical properties and energy dissipation characteristics.
In order to investigate the dynamic compression behavior of carbon nanotubes reinforced concrete under impact load, the impact compression tests were carried out by using a split Hopkinson pressure bar (SHPB) test device with a diameter of 100 mm. Then, based on this, the evolution laws of dynamic compressive strength, compression deformation, and energy dissipation characteristics of concrete under different impact velocities and carbon nanotubes contents were compared and analyzed. The impact velocities of SHPB test were around 6.8 m·s-1, 7.8 m·s-1, 8.8 m·s-1, 9.8 m·s-1, and 10.8 m·s-1, respectively. The contents of carbon nanotubes in concrete (as a percentage of cement mass) were 0% (i.e. ordinary concrete, as a control group), 0.10%, 0.20%, 0.30%, and 0.40%, respectively. The experimental results show that the dynamic strength characteristics of carbon nanotubes reinforced concrete have significant loading rate sensitivity. The dynamic compressive strength and dynamic strength increase factor show a linear positive correlation with impact velocity. When the loading level is the same, the dynamic compressive strength increases first and then decreases slightly with the increase of carbon nanotubes content, and the growth rate can reach 23.7% compared to ordinary concrete. The variation characteristics of ultimate strain and impact toughness of carbon nanotubes reinforced concrete are similar, which gradually increase with the increase of impact velocity, and have a certain impact velocity strengthening effect, but there is no obvious linear relationship with impact velocity. Toughness is a comprehensive reflection of material strength and deformation. Therefore, at the same loading level, when the content of carbon nanotubes is 0.30%, the impact toughness of concrete is relatively maximum, which is about 10% higher than that of ordinary concrete. The appropriate addition of carbon nanotubes can effectively enhance the integrity and compactness of the internal structure of concrete, thereby improving its dynamic mechanical properties and energy dissipation characteristics.
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Abstract:
Cuttlefish bone is a biomineralized shell produced inside the cuttlefish that enables deep and shallow floating by adjusting the gas-liquid ratio. Its light-weight and high rigidity make it well adapted to the deep-sea environment, making it a typical porous material with high specific stiffness. Therefore, cuttlebone is often designed as a biomimetic porous material for its high porosity and high stiffness mechanical properties. However, the mechanical behavior of cuttlebone under dynamic load is still unclear, which is extremely unfavorable for the dynamic design of cuttlebone. This research delved into an extensive exploration of cuttlebone's mechanical behavior under compressions with different loading strain rates using Instron material testing machine and split Hopkinson pressure bar experimental device. Under quasi-static loading conditions, the compression stress-strain curves of cuttlebone were obtained and exhibited three typical stages, namely linear elastic stage, long plateau stage and densification stage. The specific energy absorption of cuttlebone calculated from the stress-strain curve were illustrated and the result shows that cuttlebone has a better energy absorption capability compared with other common bionic structures and porous materials. Under dynamic loading scenarios with using of split Hopkinson pressure bar, the dynamic stress strain curves of cuttlebone were obtained at approximately loading strain rates of 400-530 s-1. Both the dynamic initial crushing stress and the plateau stress of cuttlebone exhibited a pronounced escalation with increasing loading strain rates, indicating the cuttlebone structure is strongly sensitive to the loading strain rate. Furthermore, the mechanical attributes of cuttlebone with respect to different growth directions during quasi-static compression tests were investigated. As the growth direction increases, a discernible decline in both stiffness and energy absorption performance within the cuttlebone structure was observed, thus revealing the anisotropy of the compression behavior of cuttlefish bone. These insights not only deepen the understanding of cuttlebone's mechanical behavior but also offer valuable knowledge that can inform biomimetic and bioinspired engineering designs for a range of applications.
Cuttlefish bone is a biomineralized shell produced inside the cuttlefish that enables deep and shallow floating by adjusting the gas-liquid ratio. Its light-weight and high rigidity make it well adapted to the deep-sea environment, making it a typical porous material with high specific stiffness. Therefore, cuttlebone is often designed as a biomimetic porous material for its high porosity and high stiffness mechanical properties. However, the mechanical behavior of cuttlebone under dynamic load is still unclear, which is extremely unfavorable for the dynamic design of cuttlebone. This research delved into an extensive exploration of cuttlebone's mechanical behavior under compressions with different loading strain rates using Instron material testing machine and split Hopkinson pressure bar experimental device. Under quasi-static loading conditions, the compression stress-strain curves of cuttlebone were obtained and exhibited three typical stages, namely linear elastic stage, long plateau stage and densification stage. The specific energy absorption of cuttlebone calculated from the stress-strain curve were illustrated and the result shows that cuttlebone has a better energy absorption capability compared with other common bionic structures and porous materials. Under dynamic loading scenarios with using of split Hopkinson pressure bar, the dynamic stress strain curves of cuttlebone were obtained at approximately loading strain rates of 400-530 s-1. Both the dynamic initial crushing stress and the plateau stress of cuttlebone exhibited a pronounced escalation with increasing loading strain rates, indicating the cuttlebone structure is strongly sensitive to the loading strain rate. Furthermore, the mechanical attributes of cuttlebone with respect to different growth directions during quasi-static compression tests were investigated. As the growth direction increases, a discernible decline in both stiffness and energy absorption performance within the cuttlebone structure was observed, thus revealing the anisotropy of the compression behavior of cuttlefish bone. These insights not only deepen the understanding of cuttlebone's mechanical behavior but also offer valuable knowledge that can inform biomimetic and bioinspired engineering designs for a range of applications.
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Abstract:
Accurately predicting the blast loadings on building structures is the foundation for evaluating the ammunition damage efficiency, analyzing structural dynamic response and damage/failure, as well as the corresponding blast-resistant design and retrofit. The existing specifications and studies mainly focus on the scenarios that the spherical charges ignited at the central point and explosion in free air, while the studies of the blast loadings of cylindrical charges air explosion, especially the reflected overpressure acting on the structure, are relatively limited. The existing blast loading calculation formula for spherical charge cannot be applied for cylindrical charge attributed to the parametric influences such as scaled distance Z, length-to-diameter ratio L/D, ignition method, azimuth angle, incident angle and relative location of reflected plane. To explore the incident and reflected blast loadings of cylindrical charges air explosion, firstly, three shots of explosion test of the single-end ignited cylindrical TNT charge was conducted. The corresponding numerical simulations were conducted based on the finite element program AUTODYN, and the applicability of the adopted finite element analysis method was verified by comparing with the experimental incident and reflected overpressure-time histories of spherical and cylindrical charges air explosion of tests, as well as the peak incident overpressure-scaled distance relationship of UFC 3-340-02 specification of spherical charges air explosion. Furthermore, the numerical simulations of more than 1000 sets of cylindrical charges air explosion scenarios considering the scaled distance, length-to-diameter ratio, ignition method, azimuth angle and rigid reflection were carried out based on validated finite element analysis method. The distribution characteristics of peak overpressure, maximal impulse of the incident blast wave and the corresponding shape factors were examined and discussed. The judging criteria and determination methods for the critical scaled distance of peak overpressure and maximal impulse were proposed by data fitting, and the variation law of the reflected peak overpressure and the rigid reflection coefficient were revealed. Finally, a calculation method for the incident (0.3≤Z≤15 m/kg1/3) and reflected (1≤Z≤5 m/kg1/3) blast loadings of cylindrical charges (0.25:1≤L/D≤10:1) air explosion was proposed and experimentally verified by 360 sets data.
Accurately predicting the blast loadings on building structures is the foundation for evaluating the ammunition damage efficiency, analyzing structural dynamic response and damage/failure, as well as the corresponding blast-resistant design and retrofit. The existing specifications and studies mainly focus on the scenarios that the spherical charges ignited at the central point and explosion in free air, while the studies of the blast loadings of cylindrical charges air explosion, especially the reflected overpressure acting on the structure, are relatively limited. The existing blast loading calculation formula for spherical charge cannot be applied for cylindrical charge attributed to the parametric influences such as scaled distance Z, length-to-diameter ratio L/D, ignition method, azimuth angle, incident angle and relative location of reflected plane. To explore the incident and reflected blast loadings of cylindrical charges air explosion, firstly, three shots of explosion test of the single-end ignited cylindrical TNT charge was conducted. The corresponding numerical simulations were conducted based on the finite element program AUTODYN, and the applicability of the adopted finite element analysis method was verified by comparing with the experimental incident and reflected overpressure-time histories of spherical and cylindrical charges air explosion of tests, as well as the peak incident overpressure-scaled distance relationship of UFC 3-340-02 specification of spherical charges air explosion. Furthermore, the numerical simulations of more than 1000 sets of cylindrical charges air explosion scenarios considering the scaled distance, length-to-diameter ratio, ignition method, azimuth angle and rigid reflection were carried out based on validated finite element analysis method. The distribution characteristics of peak overpressure, maximal impulse of the incident blast wave and the corresponding shape factors were examined and discussed. The judging criteria and determination methods for the critical scaled distance of peak overpressure and maximal impulse were proposed by data fitting, and the variation law of the reflected peak overpressure and the rigid reflection coefficient were revealed. Finally, a calculation method for the incident (0.3≤Z≤15 m/kg1/3) and reflected (1≤Z≤5 m/kg1/3) blast loadings of cylindrical charges (0.25:1≤L/D≤10:1) air explosion was proposed and experimentally verified by 360 sets data.
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Abstract:
In order to compare and analyze the characteristic and mechanism of damaging on 45 steel target plate penetrated by the WF/Zr-MG and 93W rod, a penetration experiment under hypervelocity impact was carried out. The analysis of penetration was performed at both macro and micro levels, in which the macroscopic quantitative characterization quantity was studied by equivalent diameter of reamer, and the microscopic morphology, phase transition and hardness characteristics of the target plate were obtained by scanning electron microscopy, optical microscope, X-ray diffraction and microhardness tester.The experimental results indicate that the WF/Zr-MG rod completely penetrated the target plate, while the 93W rod remained in the target plate. The armor-piercing capacity of WF/Zr-MG rod is higher than that of 93W rod with equivalent reaming diameter of 16.7 mm and 18.4 mm respectively, and the former is 10.18% lower than the latter. From the microscopic perspective, the aspect ratios of the fine grain layer after penetrated by the WF/Zr-MG rod and the 93W rod are 4.5 and 7.3, respectively. In addition, the width of the high-hardness layer are 10.2 mm and 8.9 mm, with peak hardness of HV=249 and HV=287. The wider high-hardness layer observed in the former case can be attributed to the continuous burning of the Zr-based amorphous alloy during the penetration process, resulting in a larger temperature affected zone and consequently a greater area of hardness enhancement. On the other hand, in the latter case, the strength of the target plate during penetration is significantly higher due to the buckling and backflow of the WF/Zr-MG rod, while the 93W alloy core exhibits a "mushroom head" phenomenon. This reduces extrusion deformation on the target plate, thereby weakening the effect of grain elongation, reducing the increase in hardness peak value, and minimizing energy loss per unit length of the target plate. Ultimately, it enhances the armor-piercing capability of the WF/Zr-MG rod.
In order to compare and analyze the characteristic and mechanism of damaging on 45 steel target plate penetrated by the WF/Zr-MG and 93W rod, a penetration experiment under hypervelocity impact was carried out. The analysis of penetration was performed at both macro and micro levels, in which the macroscopic quantitative characterization quantity was studied by equivalent diameter of reamer, and the microscopic morphology, phase transition and hardness characteristics of the target plate were obtained by scanning electron microscopy, optical microscope, X-ray diffraction and microhardness tester.The experimental results indicate that the WF/Zr-MG rod completely penetrated the target plate, while the 93W rod remained in the target plate. The armor-piercing capacity of WF/Zr-MG rod is higher than that of 93W rod with equivalent reaming diameter of 16.7 mm and 18.4 mm respectively, and the former is 10.18% lower than the latter. From the microscopic perspective, the aspect ratios of the fine grain layer after penetrated by the WF/Zr-MG rod and the 93W rod are 4.5 and 7.3, respectively. In addition, the width of the high-hardness layer are 10.2 mm and 8.9 mm, with peak hardness of HV=249 and HV=287. The wider high-hardness layer observed in the former case can be attributed to the continuous burning of the Zr-based amorphous alloy during the penetration process, resulting in a larger temperature affected zone and consequently a greater area of hardness enhancement. On the other hand, in the latter case, the strength of the target plate during penetration is significantly higher due to the buckling and backflow of the WF/Zr-MG rod, while the 93W alloy core exhibits a "mushroom head" phenomenon. This reduces extrusion deformation on the target plate, thereby weakening the effect of grain elongation, reducing the increase in hardness peak value, and minimizing energy loss per unit length of the target plate. Ultimately, it enhances the armor-piercing capability of the WF/Zr-MG rod.
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doi: 10.11883/bzycj-2023-0218
Abstract:
The dynamic tensile spallation damage caused by shock wave reflection on the free surface of target is one of the typical damage modes of materials. The initial microstructure of materials, the strength and strain rate of impact loading, temperature and other factors directly affect the spallation damage evolution process in materials.The change of free surface velocity c of target indirectly reflects the evolution process of spall damage in materials. For the research of physical model of spallation damage, there are few literatures about using suitable spallation damage model to simulate the free surface velocity profile of target under different impact loading waveforms. The relationship between loading waveforms and free surface velocity profile and the evolution process of spallation damage is mainly discussed by means of experiments. Considering that the shear viscosity coefficient and the hardening coefficient are the basic parameters of the material, the calculation method of the initial damage parameters of the damage model is given by analyzing the relationship between the spall strength, the loading strain rate and the initial damage paramer of the damagr model. The initial damage parameter of the damage model is effectively associated with the loading strain rate, and the program automatic calculation of the intial damage parameter under different loading strain ratea is realized. On this basis, not only the free surface velocity profiles of spallation tests of aluminum materials loaded by square wave, triangular wave and Taylor wave can be well simulated, the calculated spall strengths and spall plate thicknesses are also consisten with the tests results. In addition, the relationship between the distribution of initial damage, spall strength and loading strain rate at different positions in the target is further anayzed. So, compared with the existing damage model, the new method not only further improves the existing damage model, but also improves the validity of the calculation results. At the same time, it also provides ideas for improving other spall damage models.
The dynamic tensile spallation damage caused by shock wave reflection on the free surface of target is one of the typical damage modes of materials. The initial microstructure of materials, the strength and strain rate of impact loading, temperature and other factors directly affect the spallation damage evolution process in materials.The change of free surface velocity c of target indirectly reflects the evolution process of spall damage in materials. For the research of physical model of spallation damage, there are few literatures about using suitable spallation damage model to simulate the free surface velocity profile of target under different impact loading waveforms. The relationship between loading waveforms and free surface velocity profile and the evolution process of spallation damage is mainly discussed by means of experiments. Considering that the shear viscosity coefficient and the hardening coefficient are the basic parameters of the material, the calculation method of the initial damage parameters of the damage model is given by analyzing the relationship between the spall strength, the loading strain rate and the initial damage paramer of the damagr model. The initial damage parameter of the damage model is effectively associated with the loading strain rate, and the program automatic calculation of the intial damage parameter under different loading strain ratea is realized. On this basis, not only the free surface velocity profiles of spallation tests of aluminum materials loaded by square wave, triangular wave and Taylor wave can be well simulated, the calculated spall strengths and spall plate thicknesses are also consisten with the tests results. In addition, the relationship between the distribution of initial damage, spall strength and loading strain rate at different positions in the target is further anayzed. So, compared with the existing damage model, the new method not only further improves the existing damage model, but also improves the validity of the calculation results. At the same time, it also provides ideas for improving other spall damage models.
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doi: 10.11883/bzycj-2023-0328
Abstract:
Aircraft fuel tanks, marine liquid tanks, oil liquid storage tanks, and other types of liquid filled structures may be threatened by blast waves, projectile penetration, and other impact loads during the engineering practice. The dynamic response of the liquid filled structure under impact load may be affected by various factors such as the characteristics of the load, the configuration of the structure, and the way of liquid filling. Accordingly, the protection mechanism of the liquid filled structure against various types of shock loads involves the fluid-solid interaction of multiphase media, wave propagation in different media, cavitation of liquid media, dynamic mechanical properties of the structure, and several other scientific issues. In this paper, the dynamic response and protection mechanism of the liquid filled structure under different impact loads are reviewed, the typical forms of the liquid filled structure in the engineering field are summarized, and the dynamic response processes, damage modes, load dissipation processes, energy conversion, and absorption processes of various types of the liquid filled structure under the loads of blast shock wave, projectile penetration and their combined effects are analyzed. Furthermore, the impact dynamic response characteristics of the liquid filled structure under the action of blast shock wave loading, projectile penetration loading, and the combined loads of blast shock wave and high-speed fragmentation group are summarized. The protection mechanisms of the liquid filled structure against various types of impact loads are summarized from the perspectives of attenuating and dissipating loads, and transferring and converting energy. In the end, the research on anti-impact characteristics of the liquid filled structure prospects from the perspectives of dynamic response and protection characteristics of the multi-cell liquid filled structure, mechanisms for destruction of the liquid filled structure by combined loads, efficient numerical computation methods, and dynamic response and protection mechanism of the liquid filled structure made of new materials.
Aircraft fuel tanks, marine liquid tanks, oil liquid storage tanks, and other types of liquid filled structures may be threatened by blast waves, projectile penetration, and other impact loads during the engineering practice. The dynamic response of the liquid filled structure under impact load may be affected by various factors such as the characteristics of the load, the configuration of the structure, and the way of liquid filling. Accordingly, the protection mechanism of the liquid filled structure against various types of shock loads involves the fluid-solid interaction of multiphase media, wave propagation in different media, cavitation of liquid media, dynamic mechanical properties of the structure, and several other scientific issues. In this paper, the dynamic response and protection mechanism of the liquid filled structure under different impact loads are reviewed, the typical forms of the liquid filled structure in the engineering field are summarized, and the dynamic response processes, damage modes, load dissipation processes, energy conversion, and absorption processes of various types of the liquid filled structure under the loads of blast shock wave, projectile penetration and their combined effects are analyzed. Furthermore, the impact dynamic response characteristics of the liquid filled structure under the action of blast shock wave loading, projectile penetration loading, and the combined loads of blast shock wave and high-speed fragmentation group are summarized. The protection mechanisms of the liquid filled structure against various types of impact loads are summarized from the perspectives of attenuating and dissipating loads, and transferring and converting energy. In the end, the research on anti-impact characteristics of the liquid filled structure prospects from the perspectives of dynamic response and protection characteristics of the multi-cell liquid filled structure, mechanisms for destruction of the liquid filled structure by combined loads, efficient numerical computation methods, and dynamic response and protection mechanism of the liquid filled structure made of new materials.
, Available online ,
doi: 10.11883/bzycj-2023-0380
Abstract:
The stress-strain data obtained from split Hopkinson pressure bar (SHPB) tests include both strain rate effects and structural effects, where the structural effects result in non-uniform stress in the elastic phase of the stress-strain curve. The elastic phase is a critical focus of study for materials like concrete with low sound velocity or certain metals under high strain rate loading conditions. In this paper, we focus on one-dimensional rod systems and employ one-dimensional elastic incremental wave theory to derive analytical expressions for stress-strain curves and Young's modulus under one-dimensional stress wave conditions with linear incident waves. We investigate the effects and mechanisms of stress difference and velocity difference at both ends of the specimen on the accuracy of stress-strain curves and Young's modulus. Furthermore, we provide a method for determining stress-strain curves and tangent Young's modulus during the elastic phase for arbitrary incident waveforms. We analyze the influence of the incident wave slope and shape characteristics on the stress uniformity in specimens and stress-strain curves. We establish the inherent relationship between stress uniformity and experimental stress-strain curves, and clarify the relative accuracy and applicability conditions of tangent modulus and secant modulus. The results indicate that stress uniformity is a key factor affecting the accuracy of stress-strain curves and Young's modulus. However, the accuracy of Young's modulus is not solely dependent on the change in stress difference at both ends of the specimen; it is also related to the factors such as the incident wave slope, shape characteristics, and the elastic segment range of the specimen. An increase in the linear wave slope leads to a greater difference between the tangent modulus and the secant modulus from the actual values. For larger slopes, the accuracy of the secant modulus is higher than that of the tangent modulus. When the incident wave shape is considered as a reference, curves with low initial slopes, such as sine waves, have higher accuracy for the tangent modulus compared to the secant modulus, whereas curves with high initial slopes show the opposite trend. For concrete specimens, we verify the influence of incident wave slope on Young's modulus and evaluate the maximum incident wave slopes for concrete specimens to reach accurate values, which are 0.128 MPa/μs for the tangent modulus and 0.319 MPa/μs for the secant modulus.
The stress-strain data obtained from split Hopkinson pressure bar (SHPB) tests include both strain rate effects and structural effects, where the structural effects result in non-uniform stress in the elastic phase of the stress-strain curve. The elastic phase is a critical focus of study for materials like concrete with low sound velocity or certain metals under high strain rate loading conditions. In this paper, we focus on one-dimensional rod systems and employ one-dimensional elastic incremental wave theory to derive analytical expressions for stress-strain curves and Young's modulus under one-dimensional stress wave conditions with linear incident waves. We investigate the effects and mechanisms of stress difference and velocity difference at both ends of the specimen on the accuracy of stress-strain curves and Young's modulus. Furthermore, we provide a method for determining stress-strain curves and tangent Young's modulus during the elastic phase for arbitrary incident waveforms. We analyze the influence of the incident wave slope and shape characteristics on the stress uniformity in specimens and stress-strain curves. We establish the inherent relationship between stress uniformity and experimental stress-strain curves, and clarify the relative accuracy and applicability conditions of tangent modulus and secant modulus. The results indicate that stress uniformity is a key factor affecting the accuracy of stress-strain curves and Young's modulus. However, the accuracy of Young's modulus is not solely dependent on the change in stress difference at both ends of the specimen; it is also related to the factors such as the incident wave slope, shape characteristics, and the elastic segment range of the specimen. An increase in the linear wave slope leads to a greater difference between the tangent modulus and the secant modulus from the actual values. For larger slopes, the accuracy of the secant modulus is higher than that of the tangent modulus. When the incident wave shape is considered as a reference, curves with low initial slopes, such as sine waves, have higher accuracy for the tangent modulus compared to the secant modulus, whereas curves with high initial slopes show the opposite trend. For concrete specimens, we verify the influence of incident wave slope on Young's modulus and evaluate the maximum incident wave slopes for concrete specimens to reach accurate values, which are 0.128 MPa/μs for the tangent modulus and 0.319 MPa/μs for the secant modulus.
, Available online ,
doi: 10.11883/bzycj-2023-0366
Abstract:
In order to explore the underwater anti-explosion mechanism of different corrugated steel-concrete slab composite structures, the damage process of concrete slab under underwater contact explosion was simulated by smoothed particle hydrodynamics and finite element method (FEM-SPH), and the validity of the numerical method was verified by comparing with the experimental results. The FEM-SPH method was used to explore the damage process and failure mode of the wall panel under different protection schemes, reveal the underwater explosion-proof mechanism, and construct the prediction curve of the damage grade of the wall panel. The results show that the simulation results are in good agreement with the experimental results, which verifies the effectiveness of the simulation method. Under different protection schemes, the damage range of the wall panel with 12 mm thick corrugated steel composite structure (T-12), 75o angle corrugated steel composite structure (A-75) and 70 mm corrugated steel composite structure (WH-70) is 83 %, 81.6 % and 82.5 % lower than that of the unreinforced wall panel, respectively. In the composite structure, the explosion shock wave propagates to the corrugated steel in the form of incident wave and then propagates in the structure in the form of transmitted wave and reflected wave. When the transmitted wave reaches the lower surface of the corrugated steel, part of the shock wave will continue to propagate to the wall panel, while the remaining shock wave is reflected to form reflected longitudinal wave and reflected transverse wave, which further attenuates the transmitted shock wave acting on the wall panel to achieve the effect of wave clipping and energy absorption. The prediction curve can directly evaluate the influence of explosive amount and wave height change of corrugated steel in composite structure on the damage grade of wall panel.
In order to explore the underwater anti-explosion mechanism of different corrugated steel-concrete slab composite structures, the damage process of concrete slab under underwater contact explosion was simulated by smoothed particle hydrodynamics and finite element method (FEM-SPH), and the validity of the numerical method was verified by comparing with the experimental results. The FEM-SPH method was used to explore the damage process and failure mode of the wall panel under different protection schemes, reveal the underwater explosion-proof mechanism, and construct the prediction curve of the damage grade of the wall panel. The results show that the simulation results are in good agreement with the experimental results, which verifies the effectiveness of the simulation method. Under different protection schemes, the damage range of the wall panel with 12 mm thick corrugated steel composite structure (T-12), 75o angle corrugated steel composite structure (A-75) and 70 mm corrugated steel composite structure (WH-70) is 83 %, 81.6 % and 82.5 % lower than that of the unreinforced wall panel, respectively. In the composite structure, the explosion shock wave propagates to the corrugated steel in the form of incident wave and then propagates in the structure in the form of transmitted wave and reflected wave. When the transmitted wave reaches the lower surface of the corrugated steel, part of the shock wave will continue to propagate to the wall panel, while the remaining shock wave is reflected to form reflected longitudinal wave and reflected transverse wave, which further attenuates the transmitted shock wave acting on the wall panel to achieve the effect of wave clipping and energy absorption. The prediction curve can directly evaluate the influence of explosive amount and wave height change of corrugated steel in composite structure on the damage grade of wall panel.
, Available online ,
doi: 10.11883/bzycj-2023-0363
Abstract:
In the experiment conducted using a custom-built 5L dust explosion flame propagation apparatus, the focus was on studying the characteristics of the flame propagation of magnesium hydride (MgH2) dust explosions within a semi-enclosed space.The results of the experiment showed that as the concentration of MgH2 dust increased,the time required for the MgH2 dust explosion flame to transition from ignition to stable propagation decreased initially,but then increased as the dust concentration further increased.Similarly, the width of the preheating zone followed the same pattern.Initially, it decreased with increasing dust concentration,but once the concentration reached a certain threshold,it started to increase.Beyond that,the flame brightness, smoothness of the flame front, and flame propagation speed showed similar trends.They initially increased as the MgH2 dust concentration increased,suggesting enhanced combustion activity.However, as the concentration further increased,these characteristics started to decline,indicating a diminishing combustion efficiency.The best combustion state was observed at a dust concentration of 800 g/m3.The instantaneous speed of the MgH2 dust explosion flame propagation exhibited a fluctuating pattern across different concentrations.The fluctuation amplitude initially decreased as the dust concentration increased, suggesting a more stable flame propagation.However,beyond a certain concentration, the fluctuation amplitude began to increase again.It is worth noting that the change in instantaneous propagation speed variation displayed different trends as the concentration varied.The exact behaviors were found to be dependent on the particular concentration level.Finally,analysis of the X-ray diffraction (XRD) test results of the MgH2 explosion products revealed a complex reaction mechanism.The MgH2 dust explosion primarily involved the combustion reaction of MgH2 but also included multiple overall reactions such as the decomposition of MgH2 and Mg(OH)2,as well as the oxidation of Mg and H2.The final product of the explosion reaction was identified to be MgO.
In the experiment conducted using a custom-built 5L dust explosion flame propagation apparatus, the focus was on studying the characteristics of the flame propagation of magnesium hydride (MgH2) dust explosions within a semi-enclosed space.The results of the experiment showed that as the concentration of MgH2 dust increased,the time required for the MgH2 dust explosion flame to transition from ignition to stable propagation decreased initially,but then increased as the dust concentration further increased.Similarly, the width of the preheating zone followed the same pattern.Initially, it decreased with increasing dust concentration,but once the concentration reached a certain threshold,it started to increase.Beyond that,the flame brightness, smoothness of the flame front, and flame propagation speed showed similar trends.They initially increased as the MgH2 dust concentration increased,suggesting enhanced combustion activity.However, as the concentration further increased,these characteristics started to decline,indicating a diminishing combustion efficiency.The best combustion state was observed at a dust concentration of 800 g/m3.The instantaneous speed of the MgH2 dust explosion flame propagation exhibited a fluctuating pattern across different concentrations.The fluctuation amplitude initially decreased as the dust concentration increased, suggesting a more stable flame propagation.However,beyond a certain concentration, the fluctuation amplitude began to increase again.It is worth noting that the change in instantaneous propagation speed variation displayed different trends as the concentration varied.The exact behaviors were found to be dependent on the particular concentration level.Finally,analysis of the X-ray diffraction (XRD) test results of the MgH2 explosion products revealed a complex reaction mechanism.The MgH2 dust explosion primarily involved the combustion reaction of MgH2 but also included multiple overall reactions such as the decomposition of MgH2 and Mg(OH)2,as well as the oxidation of Mg and H2.The final product of the explosion reaction was identified to be MgO.
, Available online ,
doi: 10.11883/bzycj-2023-0346
Abstract:
A visual square tube water mist suppression system was independently designed in order to study the inhibition effect of water mist on RDX dust explosion. The system is composed of closed explosion chamber, powder spraying system, ignition system, high-speed photography system, water mist generation system, data acquisition system and time control system. The automatic control of powder injection and ignition is carried out by the time control system. Various experimental conditions such as different nozzle types, nozzle diameters, and atomization pressures were selected. The effect of water mist on RDX dust explosion characteristics was evaluated by comparing the changes in flame propagation dynamics, explosion pressure, and explosion temperature of RDX dust explosion. The results show that the explosion pressure, and temperature of RDX dust clouds increase with the increase of explosive mass. The inhibition effect of water mist on RDX dust explosions varies with different types of nozzles at the same atomization pressure. The water mist sprayed by centrifugal nozzle has the best explosion inhibition effect, and the spiral nozzle has the worst explosion inhibition effect. As the atomization pressure increases, the explosion inhibition effect of water mist enhances. The water mist sprayed by centrifugal nozzle with diameter of 1.5 mm shows the optimal explosion inhibition effect among the five centrifugal nozzles with diameters of 0.8, 1.2, 1.5, 2.0, and 2.4 mm used in the experiment. The explosion pressure and temperature attenuation of water mist on RDX dust explosion increased with the increase of spray pressure. The explosion pressure of RDX dust is only 0.1184 MPa at an atomization pressure of 4 MPa. the peak pressure is reduced by 74.0% compared to the situation without water mist where the explosion pressure of RDX dust is 0.4561 MPa. The explosion temperature is 234 ℃, which is 69.8% lower than the explosion temperature of RDX dust without water mist (774 ℃).
A visual square tube water mist suppression system was independently designed in order to study the inhibition effect of water mist on RDX dust explosion. The system is composed of closed explosion chamber, powder spraying system, ignition system, high-speed photography system, water mist generation system, data acquisition system and time control system. The automatic control of powder injection and ignition is carried out by the time control system. Various experimental conditions such as different nozzle types, nozzle diameters, and atomization pressures were selected. The effect of water mist on RDX dust explosion characteristics was evaluated by comparing the changes in flame propagation dynamics, explosion pressure, and explosion temperature of RDX dust explosion. The results show that the explosion pressure, and temperature of RDX dust clouds increase with the increase of explosive mass. The inhibition effect of water mist on RDX dust explosions varies with different types of nozzles at the same atomization pressure. The water mist sprayed by centrifugal nozzle has the best explosion inhibition effect, and the spiral nozzle has the worst explosion inhibition effect. As the atomization pressure increases, the explosion inhibition effect of water mist enhances. The water mist sprayed by centrifugal nozzle with diameter of 1.5 mm shows the optimal explosion inhibition effect among the five centrifugal nozzles with diameters of 0.8, 1.2, 1.5, 2.0, and 2.4 mm used in the experiment. The explosion pressure and temperature attenuation of water mist on RDX dust explosion increased with the increase of spray pressure. The explosion pressure of RDX dust is only 0.1184 MPa at an atomization pressure of 4 MPa. the peak pressure is reduced by 74.0% compared to the situation without water mist where the explosion pressure of RDX dust is 0.4561 MPa. The explosion temperature is 234 ℃, which is 69.8% lower than the explosion temperature of RDX dust without water mist (774 ℃).
, Available online ,
doi: 10.11883/bzycj-2023-0349
Abstract:
In order to explore the effect of the aspect ratio of rectangular tube on the propagation of the spinning detonation under the limiting detonation propagating conditions, the structure of the three-dimensional gas-phase spinning detonation wave and its propagation modes in rectangular cross-section tubes are numerically investigated based on Euler equations with a 5th-order WENO finite difference scheme and the two-step global reaction model. A linear stability theory of planar detonation wave based on the normal mode method is firstly adopted to examine the chemical reaction parameters for numerical simulations and then several cases with different aspect ratios in cross-section of rectangular tube are investigated to study the structure and propagation mode of three-dimensional gaseous spinning detonation waves. By recording motions of triple lines, flow-field distributions and high-pressure imprint of detonation wave under different sizes of tube cross-section, the effect of cross-sectional geometry on the stable propagation of gaseous detonation under the limiting detonation propagating condition is revealed. The results show that the spinning detonation propagation can be maintained within a certain range of small tube cross-section size, through the movements of horizontal and vertical triple lines and an oblique triple line that is produced by interaction between both horizontal and vertical triple lines. For a square tube with 1 of aspect ratio in cross-section, the high-pressure imprint of spinning detonation on the wall forms the helical strip pattern. With the increase of the aspect ratio of the cross-section size of the tube, the pattern of a high-pressure imprint formed by the spinning detonation on the channel wall varies from the strip structure to a dotted distribution structure, the trajectory of the oblique triple line on the wave front gradually develops from the circular motion in a single direction to a complex trajectory with varying direction. When the aspect ratio is further increased, there is a tendency for the three-dimensional spinning detonation wave to eventually degenerate into a two-dimensional single-head detonation wave structure.
In order to explore the effect of the aspect ratio of rectangular tube on the propagation of the spinning detonation under the limiting detonation propagating conditions, the structure of the three-dimensional gas-phase spinning detonation wave and its propagation modes in rectangular cross-section tubes are numerically investigated based on Euler equations with a 5th-order WENO finite difference scheme and the two-step global reaction model. A linear stability theory of planar detonation wave based on the normal mode method is firstly adopted to examine the chemical reaction parameters for numerical simulations and then several cases with different aspect ratios in cross-section of rectangular tube are investigated to study the structure and propagation mode of three-dimensional gaseous spinning detonation waves. By recording motions of triple lines, flow-field distributions and high-pressure imprint of detonation wave under different sizes of tube cross-section, the effect of cross-sectional geometry on the stable propagation of gaseous detonation under the limiting detonation propagating condition is revealed. The results show that the spinning detonation propagation can be maintained within a certain range of small tube cross-section size, through the movements of horizontal and vertical triple lines and an oblique triple line that is produced by interaction between both horizontal and vertical triple lines. For a square tube with 1 of aspect ratio in cross-section, the high-pressure imprint of spinning detonation on the wall forms the helical strip pattern. With the increase of the aspect ratio of the cross-section size of the tube, the pattern of a high-pressure imprint formed by the spinning detonation on the channel wall varies from the strip structure to a dotted distribution structure, the trajectory of the oblique triple line on the wave front gradually develops from the circular motion in a single direction to a complex trajectory with varying direction. When the aspect ratio is further increased, there is a tendency for the three-dimensional spinning detonation wave to eventually degenerate into a two-dimensional single-head detonation wave structure.
, Available online ,
doi: 10.11883/bzycj-2023-0259
Abstract:
The solid rocket motor is the only power source of the system in the rocket sled test, the traditional monorail rocket sled generally consists of the rocket motor, the motor mounting components, the reinforced longitudinal beam and the slippers, in which only the test object and the motor charge are effective mass, the rest of the structures are additional mass, reducing the additional mass can improve the thrust-to-weight ratio of the rocket sled system. In response to the problem of excessive mass added to the components of the conventional monorail rocket sled system, an integrated rocket sled and motor structure consisting of motor and slippers was proposed. The three-dimensional Euler-Bernoulli beam unit was used to discretize the rocket sled system to obtain the optimal distribution position of the slippers, and it was found that the vibration was minimized when the middle slipper was distributed between the front slipper and the back slipper. Three options for connecting the slipper to the motor housing were designed, one where the slipper was wrapped and connected to the motor housing by serrated welds, one where the motor housing was to be stacked directly on the slipper body, and one where the motor housing was to be connected to the slipper by supported transition plates. A comparative analysis of the on-rail safety of the latter two options was performed using the sled-rail coupling dynamics method, which indicates that the mechanical environment of the integrated rocket sled is better when the sled slippers and the motor housing are connected by the supported plates as transition structures, and the additional mass of the system is reduced by 73% compared to that of the traditional monorail sled. Finally, the integrated motor with sled validation test was implemented and the collected data were analyzed, the results show that: the integrated motor with sled proposed in this paper is reasonable and feasible, and the motor vibration level is comparable to that of the traditional rocket sled.
The solid rocket motor is the only power source of the system in the rocket sled test, the traditional monorail rocket sled generally consists of the rocket motor, the motor mounting components, the reinforced longitudinal beam and the slippers, in which only the test object and the motor charge are effective mass, the rest of the structures are additional mass, reducing the additional mass can improve the thrust-to-weight ratio of the rocket sled system. In response to the problem of excessive mass added to the components of the conventional monorail rocket sled system, an integrated rocket sled and motor structure consisting of motor and slippers was proposed. The three-dimensional Euler-Bernoulli beam unit was used to discretize the rocket sled system to obtain the optimal distribution position of the slippers, and it was found that the vibration was minimized when the middle slipper was distributed between the front slipper and the back slipper. Three options for connecting the slipper to the motor housing were designed, one where the slipper was wrapped and connected to the motor housing by serrated welds, one where the motor housing was to be stacked directly on the slipper body, and one where the motor housing was to be connected to the slipper by supported transition plates. A comparative analysis of the on-rail safety of the latter two options was performed using the sled-rail coupling dynamics method, which indicates that the mechanical environment of the integrated rocket sled is better when the sled slippers and the motor housing are connected by the supported plates as transition structures, and the additional mass of the system is reduced by 73% compared to that of the traditional monorail sled. Finally, the integrated motor with sled validation test was implemented and the collected data were analyzed, the results show that: the integrated motor with sled proposed in this paper is reasonable and feasible, and the motor vibration level is comparable to that of the traditional rocket sled.
, Available online ,
doi: 10.11883/bzycj-2023-0391
Abstract:
Different initiation methods directly determined the stress wave propagation and explosion energy transmission law caused by drilling and blasting, thus affected the effect of rock fragmentations. In this paper, the collision mechanism of stress wave and rock fragmentation characteristics induced by blasting with different initiation methods were studied. Based on the theory of frontal and oblique collision of stress waves, the interaction mechanism of stress waves between holes was studied to prove stress enhancement effect caused by wave collision under the staggered initiation mode. By using the RHT model for rock and JWL state equation for explosive in the ANSYS/LS-DYNA software, the magnitude of stress waves between holes and the rock fragmentation characteristics were simulated under staggered, bottom and top initiation modes. Finally, combined with on-site experiments, the interaction of stress waves and the characteristics of fragmentation distribution for blasting of rock mass containing gravel under different initiation modes were compared and analysed. Results show that under the staggered initiation mode, a frontal collision of stress wave happens at the midpoint between two holes, and the pressure after collision is 2.4 times that of the stable propagation of the stress wave; An oblique collision occurs between 0° and 44°, and the ratio of collision pressure to the stable pressure ranges from 4.1 to 2.3; Mach reflection occurs between 44° and 90°, and the ratio of collision pressure to the stable pressure ranges from 3.5 to 1. The rates of rock fragmentations with the size less than 250mm under staggered and bottom initiation modes are 25.5% and 20.9%, respectively. And the rates of rock fragmentations with the size larger than 750mm under staggered and bottom initiation modes are 9.2% and 17.5%, respectively. The stress enhancement effect caused by wave collision under the staggered initiation mode can significantly improve the blasting fragmentation of rock mass containing gravel.
Different initiation methods directly determined the stress wave propagation and explosion energy transmission law caused by drilling and blasting, thus affected the effect of rock fragmentations. In this paper, the collision mechanism of stress wave and rock fragmentation characteristics induced by blasting with different initiation methods were studied. Based on the theory of frontal and oblique collision of stress waves, the interaction mechanism of stress waves between holes was studied to prove stress enhancement effect caused by wave collision under the staggered initiation mode. By using the RHT model for rock and JWL state equation for explosive in the ANSYS/LS-DYNA software, the magnitude of stress waves between holes and the rock fragmentation characteristics were simulated under staggered, bottom and top initiation modes. Finally, combined with on-site experiments, the interaction of stress waves and the characteristics of fragmentation distribution for blasting of rock mass containing gravel under different initiation modes were compared and analysed. Results show that under the staggered initiation mode, a frontal collision of stress wave happens at the midpoint between two holes, and the pressure after collision is 2.4 times that of the stable propagation of the stress wave; An oblique collision occurs between 0° and 44°, and the ratio of collision pressure to the stable pressure ranges from 4.1 to 2.3; Mach reflection occurs between 44° and 90°, and the ratio of collision pressure to the stable pressure ranges from 3.5 to 1. The rates of rock fragmentations with the size less than 250mm under staggered and bottom initiation modes are 25.5% and 20.9%, respectively. And the rates of rock fragmentations with the size larger than 750mm under staggered and bottom initiation modes are 9.2% and 17.5%, respectively. The stress enhancement effect caused by wave collision under the staggered initiation mode can significantly improve the blasting fragmentation of rock mass containing gravel.
, Available online ,
doi: 10.11883/bzycj-2023-0094
Abstract:
High-pressure-gas-driving blast wave simulation shock tube, commonly composed of driving section, throat section and expansion section, is an ideal platform for explosion damage effect research of long positive shock pressure duration time in the laboratory, as the ability of generating simulated shock wave with similar characteristics to real explosion wave. One of the core problems in the design of blast simulation shock tube, is the control method of the simulated wave attenuation process by modifying the variable section structure and the driving section shape of the shock tube. In this article, a numerical calculation model of one-dimensional flow in the shock tube is established based on the explosion simulation shock tube in the laboratory, a similarity evaluation method of simulated shock wave and standard explosion wave in a shock tube based on determination coefficient is proposed referring to the statistical theory. Then, based on the flow characteristics of the variable section shock tube, the influence of the shape of the driving section on the shock wave attenuation history is studied. The results show that, it is feasible to acquire simulated wave with approximate exponential attenuation history of real blast wave, by using variable cross-section driving tube, of which the section diameter decreases with the growth of distance to the throat, optimizing the variable cross-section structure due to the determination coefficient, and controlling the motion property of expansion and compression wave in the shock tube.
High-pressure-gas-driving blast wave simulation shock tube, commonly composed of driving section, throat section and expansion section, is an ideal platform for explosion damage effect research of long positive shock pressure duration time in the laboratory, as the ability of generating simulated shock wave with similar characteristics to real explosion wave. One of the core problems in the design of blast simulation shock tube, is the control method of the simulated wave attenuation process by modifying the variable section structure and the driving section shape of the shock tube. In this article, a numerical calculation model of one-dimensional flow in the shock tube is established based on the explosion simulation shock tube in the laboratory, a similarity evaluation method of simulated shock wave and standard explosion wave in a shock tube based on determination coefficient is proposed referring to the statistical theory. Then, based on the flow characteristics of the variable section shock tube, the influence of the shape of the driving section on the shock wave attenuation history is studied. The results show that, it is feasible to acquire simulated wave with approximate exponential attenuation history of real blast wave, by using variable cross-section driving tube, of which the section diameter decreases with the growth of distance to the throat, optimizing the variable cross-section structure due to the determination coefficient, and controlling the motion property of expansion and compression wave in the shock tube.
, Available online ,
doi: 10.11883/bzycj-2023-0336
Abstract:
The precise control of explosive energy to form an effective radial fracture network in shale is the key of shale gas dynamic extraction. In order to elucidate the damage and fracture mechanisms of shale under directional fracture-controlled blasting and establish a quantifiable relationship for shale damage and destruction under various blasting conditions, explosive tests were conducted on cubic shale specimens with four different fracture angles. The evolution of surface strain fields on the shale specimens was monitored using Digital Image Correlation (DIC) technology. Additionally, the fractal dimensions of surface cracks on the shale specimens at different fracture angles were computed based on the box-counting theory. A programmed analysis of post-blast fragment size distribution was carried out using Matlab software, resulting in the development of a fully automated particle size analysis program with visual delineation of particle sizes. The experimental results demonstrate a negative power-law relationship between crack density and scaled distance within different scaled distances. The angle between the fracture direction and the weak plane of the bedding significantly influences the location of micro-damaged areas. Particularly, when the weak plane of the bedding is parallel to the fracture direction, damaged areas tend to concentrate along the weak plane, affecting the macrocrack propagation path and favoring the formation of a single crack. Energy dissipation at the weak planes of the bedding is identified as a crucial factor leading to suboptimal fracturing effects in shale blasting. When the fracture direction aligns with the weak plane of the bedding, a higher proportion of large fragments is observed in the post-blast specimens. The average fractal dimension of fragment size distribution is the lowest among all groups, measuring only 0.7843. Conversely, when the fracture direction is perpendicular to the weak plane of the bedding, the distribution of post-blast fragment sizes becomes more uniform. The average fractal dimension of fragment size distribution increases to 2.5233, indicating relatively better blasting fragmentation results in such scenarios.
The precise control of explosive energy to form an effective radial fracture network in shale is the key of shale gas dynamic extraction. In order to elucidate the damage and fracture mechanisms of shale under directional fracture-controlled blasting and establish a quantifiable relationship for shale damage and destruction under various blasting conditions, explosive tests were conducted on cubic shale specimens with four different fracture angles. The evolution of surface strain fields on the shale specimens was monitored using Digital Image Correlation (DIC) technology. Additionally, the fractal dimensions of surface cracks on the shale specimens at different fracture angles were computed based on the box-counting theory. A programmed analysis of post-blast fragment size distribution was carried out using Matlab software, resulting in the development of a fully automated particle size analysis program with visual delineation of particle sizes. The experimental results demonstrate a negative power-law relationship between crack density and scaled distance within different scaled distances. The angle between the fracture direction and the weak plane of the bedding significantly influences the location of micro-damaged areas. Particularly, when the weak plane of the bedding is parallel to the fracture direction, damaged areas tend to concentrate along the weak plane, affecting the macrocrack propagation path and favoring the formation of a single crack. Energy dissipation at the weak planes of the bedding is identified as a crucial factor leading to suboptimal fracturing effects in shale blasting. When the fracture direction aligns with the weak plane of the bedding, a higher proportion of large fragments is observed in the post-blast specimens. The average fractal dimension of fragment size distribution is the lowest among all groups, measuring only 0.7843. Conversely, when the fracture direction is perpendicular to the weak plane of the bedding, the distribution of post-blast fragment sizes becomes more uniform. The average fractal dimension of fragment size distribution increases to 2.5233, indicating relatively better blasting fragmentation results in such scenarios.
, Available online ,
doi: 10.11883/bzycj-2023-0250
Abstract:
The liquid in partially filled tanks is prone to slosh under external excitation, and the additional forces and moments generated by liquid sloshing can have adverse effects on tank trucks. In order to avoid significant sloshing of the liquid in the tank when the tank truck brakes, several types of baffles were proposed, and the influence of baffles and their geometric parameters on the liquid sloshing inside the tank truck was studied. Firstly, a numerical model of liquid sloshing based on the Finite Volume Method was established. Secondly, a series of liquid sloshing experiments were conducted. The effectiveness of the numerical model was verified by comparing the free surface waveforms obtained from the experiments at different times with those obtained from numerical simulations under the same conditions. Finally, the validated numerical model was used to analyze the influence of the geometric parameters of the baffle on the liquid sloshing response parameters under different liquid-filling conditions. The research results indicate that the perforated baffle can not only effectively suppress the peak of the sloshing response parameters in the tank but also significantly shorten the time for liquid sloshing to reach stability. The position and number of baffle orifices have little effect on the peak longitudinal force caused by liquid sloshing during vehicle braking, while the peak pitch moment is more significantly affected by the geometric parameters of the baffle. By studying liquid sloshing in the tank at different filling heights, it is found that the decrease rate of the peak value of the sloshing response parameter will first decrease and then increase with the increase of the filling height. When the peak value of pitch moment reaches its maximum value, the baffle has the worst suppression effect on liquid sloshing in a partially filled tank.
The liquid in partially filled tanks is prone to slosh under external excitation, and the additional forces and moments generated by liquid sloshing can have adverse effects on tank trucks. In order to avoid significant sloshing of the liquid in the tank when the tank truck brakes, several types of baffles were proposed, and the influence of baffles and their geometric parameters on the liquid sloshing inside the tank truck was studied. Firstly, a numerical model of liquid sloshing based on the Finite Volume Method was established. Secondly, a series of liquid sloshing experiments were conducted. The effectiveness of the numerical model was verified by comparing the free surface waveforms obtained from the experiments at different times with those obtained from numerical simulations under the same conditions. Finally, the validated numerical model was used to analyze the influence of the geometric parameters of the baffle on the liquid sloshing response parameters under different liquid-filling conditions. The research results indicate that the perforated baffle can not only effectively suppress the peak of the sloshing response parameters in the tank but also significantly shorten the time for liquid sloshing to reach stability. The position and number of baffle orifices have little effect on the peak longitudinal force caused by liquid sloshing during vehicle braking, while the peak pitch moment is more significantly affected by the geometric parameters of the baffle. By studying liquid sloshing in the tank at different filling heights, it is found that the decrease rate of the peak value of the sloshing response parameter will first decrease and then increase with the increase of the filling height. When the peak value of pitch moment reaches its maximum value, the baffle has the worst suppression effect on liquid sloshing in a partially filled tank.
, Available online ,
doi: 10.11883/bzycj-2023-0322
Abstract:
Aiming at the problem that the traditional single-phase explosion suppression medium is not effective, it is proposed that the gas-solid two-phase medium cooperates with different explosion suppression principles to achieve efficient and rapid suppression of gas explosion. The method of using NaHCO3 powder and CO2 gas to synergistically suppress gas explosion was studied. The standard 20 L spherical explosion test device was selected, and the configuration optimization of reactants, transition states and products in the microscopic reaction mechanism of methane explosion was carried out by DFT theory. On this basis, the subsequent calculation was carried out. The results show that the single-phase medium with a volume fraction of 16%CO2 and 0.35 g/LNaHCO3 has an excellent effect on suppressing gas explosion, but the presence of 0.1 g/L powder will increase the maximum boosting rate by 18.9%. Compared with single-phase CO2 and single-phase NaHCO3 powder, the gas-solid two-phase medium explosion suppression phase reduces the maximum explosion pressure. When 8% volume fraction CO2 is used in conjunction with 0.125 g/L powder, the maximum explosion pressure of gas explosion is reduced by 72.42%, and the maximum pressure rise rate is reduced to 2.345 MPa/·s. The suppression effect is optimal; however, when 4% volume fraction CO2 cooperates with 0.05 g/L powder, the maximum explosion pressure rise rate increases by 93.68%, and the reaction shows a certain intensification phenomenon. The quantum chemical calculation shows that in the process of gas-solid two-phase medium synergistic inhibition of gas explosion, the decomposition of NaHCO3 powder will absorb the heat in the reaction system, and its decomposition products will preferentially react with OH· and H· in the mixed system, hindering the generation of O·, inhibiting the chain process in the CH2O stage, and then inhibiting the transfer process of chain reaction. The CO2 produced by the decomposition of NaHCO3 powder and the CO2 in the mixed system dilute the volume fraction of methane in the mixed system, reduce the probability of collision between methane and oxygen molecules, and effectively inhibit the reaction process.
Aiming at the problem that the traditional single-phase explosion suppression medium is not effective, it is proposed that the gas-solid two-phase medium cooperates with different explosion suppression principles to achieve efficient and rapid suppression of gas explosion. The method of using NaHCO3 powder and CO2 gas to synergistically suppress gas explosion was studied. The standard 20 L spherical explosion test device was selected, and the configuration optimization of reactants, transition states and products in the microscopic reaction mechanism of methane explosion was carried out by DFT theory. On this basis, the subsequent calculation was carried out. The results show that the single-phase medium with a volume fraction of 16%CO2 and 0.35 g/LNaHCO3 has an excellent effect on suppressing gas explosion, but the presence of 0.1 g/L powder will increase the maximum boosting rate by 18.9%. Compared with single-phase CO2 and single-phase NaHCO3 powder, the gas-solid two-phase medium explosion suppression phase reduces the maximum explosion pressure. When 8% volume fraction CO2 is used in conjunction with 0.125 g/L powder, the maximum explosion pressure of gas explosion is reduced by 72.42%, and the maximum pressure rise rate is reduced to 2.345 MPa/·s. The suppression effect is optimal; however, when 4% volume fraction CO2 cooperates with 0.05 g/L powder, the maximum explosion pressure rise rate increases by 93.68%, and the reaction shows a certain intensification phenomenon. The quantum chemical calculation shows that in the process of gas-solid two-phase medium synergistic inhibition of gas explosion, the decomposition of NaHCO3 powder will absorb the heat in the reaction system, and its decomposition products will preferentially react with OH· and H· in the mixed system, hindering the generation of O·, inhibiting the chain process in the CH2O stage, and then inhibiting the transfer process of chain reaction. The CO2 produced by the decomposition of NaHCO3 powder and the CO2 in the mixed system dilute the volume fraction of methane in the mixed system, reduce the probability of collision between methane and oxygen molecules, and effectively inhibit the reaction process.
, Available online ,
doi: 10.11883/bzycj-2023-0370
Abstract:
Underwater explosions can cause serious damage to ships and other structures in the water, seriously endangering the vitality and combat capability of ships. Ships in the combat process by torpedoes or mines and other underwater weapons attack, the explosion produced by the breach continued multi-directional into the water, the ship unsinkability has a greater impact. In order to explore the underwater explosion damage distribution characteristics, carried out a real-scale near-field underwater explosion ship test, analyzed the test obtained along the direction of the ship's length of the acceleration as well as strain measurement point data, the use of acoustic-solid coupling method to calculate the shock wave and bubble jet load under the joint action of the whole ship structure of the damage, get the whole ship plastically deformed area of the depth of the depression is 85 cm, The depth of the plastic deformation area of the whole ship is 85 cm, the width of the “L” type breach is 30 cm, and the area of the breach is 0.2 m2. Comparing and analysing the experimental and simulation data, the error in the size of the computed breach is less than 20%, and the position of the breach matches well, which verifies the accuracy of the model. The model was used to carry out simulation calculations under different blast distances, analyse the structural damage distribution in the calculation results, put forward the distributed damage pattern of the barge under the action of near-field underwater explosion load, and make it clear that in addition to the overall fracture of the structure of the ship, there is also a wide distribution of small cracks in the bulkheads, the outboard side of the plate and other parts of the ship's structural damage, when the impact factor decreases from 5.84 to 1.91, the size of the bilge breach decreases, the size of the breach decreases, the location of the breach is a good match, and the accuracy of the model is verified. Bilge breach size decreases, the number of cracks in the cabin increases, which indicates that the larger the burst distance, the greater the scope of the underwater explosive load on the ship, the bubble pulsating load will make the barge appear “whiplash movement” will appear as a whole fracture of the barge to form a fatal damage to the overall structure of the impact factor of 1.91-2.87, the bilge breach for the The bilge breakage is scattered small breakage. Research results in the port side, bulkhead and bilge connection for the weak parts, small cracks are distributed more, in the ship design process can focus on strengthening the protection. This paper provides a design reference for the damage and protection of ships under the action of underwater explosive loads.
Underwater explosions can cause serious damage to ships and other structures in the water, seriously endangering the vitality and combat capability of ships. Ships in the combat process by torpedoes or mines and other underwater weapons attack, the explosion produced by the breach continued multi-directional into the water, the ship unsinkability has a greater impact. In order to explore the underwater explosion damage distribution characteristics, carried out a real-scale near-field underwater explosion ship test, analyzed the test obtained along the direction of the ship's length of the acceleration as well as strain measurement point data, the use of acoustic-solid coupling method to calculate the shock wave and bubble jet load under the joint action of the whole ship structure of the damage, get the whole ship plastically deformed area of the depth of the depression is 85 cm, The depth of the plastic deformation area of the whole ship is 85 cm, the width of the “L” type breach is 30 cm, and the area of the breach is 0.2 m2. Comparing and analysing the experimental and simulation data, the error in the size of the computed breach is less than 20%, and the position of the breach matches well, which verifies the accuracy of the model. The model was used to carry out simulation calculations under different blast distances, analyse the structural damage distribution in the calculation results, put forward the distributed damage pattern of the barge under the action of near-field underwater explosion load, and make it clear that in addition to the overall fracture of the structure of the ship, there is also a wide distribution of small cracks in the bulkheads, the outboard side of the plate and other parts of the ship's structural damage, when the impact factor decreases from 5.84 to 1.91, the size of the bilge breach decreases, the size of the breach decreases, the location of the breach is a good match, and the accuracy of the model is verified. Bilge breach size decreases, the number of cracks in the cabin increases, which indicates that the larger the burst distance, the greater the scope of the underwater explosive load on the ship, the bubble pulsating load will make the barge appear “whiplash movement” will appear as a whole fracture of the barge to form a fatal damage to the overall structure of the impact factor of 1.91-2.87, the bilge breach for the The bilge breakage is scattered small breakage. Research results in the port side, bulkhead and bilge connection for the weak parts, small cracks are distributed more, in the ship design process can focus on strengthening the protection. This paper provides a design reference for the damage and protection of ships under the action of underwater explosive loads.
, Available online ,
doi: 10.11883/bzycj-2023-0392
Abstract:
Compared to the reflection and transmission analysis process during the incident wave loading phase, the incident wave plateau phase lasts longer, and the elastic-plastic propagation and evolution behavior are much more complex. The effects of elastic-plastic wave interactions within the specimen during this phase are very pronounced. Using the elastic-plastic incremental wave theory, combined with numerical simulation, the calculations of elastic-plastic wave’s interactions inside the specimens under rectangular incident wave action and its elastic-plastic transmission and reflection behavior at the two interfaces are carried out. The attenuation characteristics of the reflected waves in the sandwich rod system are investigated. The results show that under strong incident wave action, the specimen internally forms a curve-shaped elastic-plastic interface due to the interactions of elastic-plastic waves. This causes the transmission end to reach the yield state significantly earlier. This elastic-plastic interface propagates towards the reflection end at a speed greater than the elastic sound speed. The attenuation of the reflected wave during the plastic phase is the sum of the increase in generalized wave impedance due to the increase in the specimen's cross-sectional area and the increase in the number of back-and-forth plastic waves caused by compression. Calculations also show that although the change of the specimen density significantly affects its wave speed and wave impedance, the sum of the attenuations caused by these two factors is close to zero. Hence, the effect of density changes on the transmission and reflection wave plateau phase can be ignored. An increase in the plastic modulus causes the reflection wave plateau to attenuate faster, but the effect of the specimen's diameter is not monotonous. When it increases from 4mm to 10mm, the reflection wave attenuation speed increases, but when it further increases to 12mm, the attenuation amount decreases. This study has certain reference value for in-depth analysis of split Hopkinson pressure bar test for the transmission waveforms as well as for the detailed test design and data processing.
Compared to the reflection and transmission analysis process during the incident wave loading phase, the incident wave plateau phase lasts longer, and the elastic-plastic propagation and evolution behavior are much more complex. The effects of elastic-plastic wave interactions within the specimen during this phase are very pronounced. Using the elastic-plastic incremental wave theory, combined with numerical simulation, the calculations of elastic-plastic wave’s interactions inside the specimens under rectangular incident wave action and its elastic-plastic transmission and reflection behavior at the two interfaces are carried out. The attenuation characteristics of the reflected waves in the sandwich rod system are investigated. The results show that under strong incident wave action, the specimen internally forms a curve-shaped elastic-plastic interface due to the interactions of elastic-plastic waves. This causes the transmission end to reach the yield state significantly earlier. This elastic-plastic interface propagates towards the reflection end at a speed greater than the elastic sound speed. The attenuation of the reflected wave during the plastic phase is the sum of the increase in generalized wave impedance due to the increase in the specimen's cross-sectional area and the increase in the number of back-and-forth plastic waves caused by compression. Calculations also show that although the change of the specimen density significantly affects its wave speed and wave impedance, the sum of the attenuations caused by these two factors is close to zero. Hence, the effect of density changes on the transmission and reflection wave plateau phase can be ignored. An increase in the plastic modulus causes the reflection wave plateau to attenuate faster, but the effect of the specimen's diameter is not monotonous. When it increases from 4mm to 10mm, the reflection wave attenuation speed increases, but when it further increases to 12mm, the attenuation amount decreases. This study has certain reference value for in-depth analysis of split Hopkinson pressure bar test for the transmission waveforms as well as for the detailed test design and data processing.
, Available online ,
doi: 10.11883/bzycj-2023-0243
Abstract:
In order to study the dynamic behaviors and energy dissipation characteristics of marble under cyclic impact loading, a split Hopkinson pressure bar system was first adopted to determine the five representative incident velocities of striking projectile through the trial impact method. Based on this, constant amplitude cyclic impact tests of the marble samples were performed, and stress uniformity of the samples was examined. Then, a systematic analysis is conducted on the test data from the aspects of strain rate time history curve, stress-strain relationship, impact times and energy dissipation properties. Finally, a damage variable is defined based on the energy evolution, and the associated mechanism between energy dissipation and damage development of the rock samples is further explored. The results show that the time-history curves of the strain rate of the samples exhibit a plateau segment with a constant rate of change at low projectile velocities, and the stress-strain curve has a certain rebound at the post-peak stage. The peak stress of the rock samples decreases with the increase of the number of cycles, while the peak strain, average strain rate and cumulative absorption specific energy take on the opposite trend, and their change rates all show a sudden increase phenomenon before sample’s break or fracture. The peak stress has a linear relationship with the average strain rate, while the variation of sample elastic modulus with average strain rate generally follows an exponential decay law. There is a positive linear correlation between the dissipated specific energy and the average strain rate of the marble samples. The damage variable defined based on energy dissipation analysis can better characterize the break or fracture process of the marble samples under dynamic loading. The research results of this study have certain reference value for revealing the evolution mechanism of rock internal damage under cyclic load disturbance.
In order to study the dynamic behaviors and energy dissipation characteristics of marble under cyclic impact loading, a split Hopkinson pressure bar system was first adopted to determine the five representative incident velocities of striking projectile through the trial impact method. Based on this, constant amplitude cyclic impact tests of the marble samples were performed, and stress uniformity of the samples was examined. Then, a systematic analysis is conducted on the test data from the aspects of strain rate time history curve, stress-strain relationship, impact times and energy dissipation properties. Finally, a damage variable is defined based on the energy evolution, and the associated mechanism between energy dissipation and damage development of the rock samples is further explored. The results show that the time-history curves of the strain rate of the samples exhibit a plateau segment with a constant rate of change at low projectile velocities, and the stress-strain curve has a certain rebound at the post-peak stage. The peak stress of the rock samples decreases with the increase of the number of cycles, while the peak strain, average strain rate and cumulative absorption specific energy take on the opposite trend, and their change rates all show a sudden increase phenomenon before sample’s break or fracture. The peak stress has a linear relationship with the average strain rate, while the variation of sample elastic modulus with average strain rate generally follows an exponential decay law. There is a positive linear correlation between the dissipated specific energy and the average strain rate of the marble samples. The damage variable defined based on energy dissipation analysis can better characterize the break or fracture process of the marble samples under dynamic loading. The research results of this study have certain reference value for revealing the evolution mechanism of rock internal damage under cyclic load disturbance.
, Available online ,
doi: 10.11883/bzycj-2023-0389
Abstract:
The reflected and transmitted waves in split Hopkinson Pressure Bar (SHPB) tests provide crucial information for obtaining the stress-strain relationship of materials. Accurately analyzing the formation process and influencing mechanisms of the reflected and incident waves is a key prerequisite for precise experimental design and accurate data processing. In this paper, the propagation and evolution of one-dimensional elastic-plastic waves in the loading stages of the SHPB test are presentedparticularlyfor asandwich bar system consisting of the incident wave, specimen, and transmitted bar. Based on the theory of elastic-plastic incremental waves and numerical simulation calculations, the propagation of elastic-plastic waves in the specimen, the transmission and reflection of elastic-plastic waves at the two interfaces, and the interaction of the resulting series of transmitted and reflected waves arequantitatively investigated. The research findings are as follows.Firstly, although the design principle of the SHPB apparatus is based on linear elastic wave theory, the elastic-plastic waves, especially the stress waves, have a major influence on the transmission and reflection at the elastic-plastic interface, while the transmission and propagation of purely elastic waves have a relatively minor effect. Secondly, when the loading interval of the incident wave has a certain width, the multiple transmission and reflection of elastic waves at the two interfaces in Bar 2 attenuate the reflected wave while further strengthening the transmitted wave. This attenuation causes the peak of the reflected wave for the half-sine wave to occur earlier than at 0.5 nondimensional time. Thirdly, in contrary to the preliminary laws of elastic wave transmission and reflection at interfaces in traditional SHPB analysis, variations in the Young's modulus and density of the specimen material have little effect on the waveform and peak intensity of the transmitted wave, regardless of whether the incident wave is rectangular, trapezoidal, or half-sine. This investigationprovides a scientific basis for the refined design of SHPB experiments and precise analysis of data.
The reflected and transmitted waves in split Hopkinson Pressure Bar (SHPB) tests provide crucial information for obtaining the stress-strain relationship of materials. Accurately analyzing the formation process and influencing mechanisms of the reflected and incident waves is a key prerequisite for precise experimental design and accurate data processing. In this paper, the propagation and evolution of one-dimensional elastic-plastic waves in the loading stages of the SHPB test are presentedparticularlyfor asandwich bar system consisting of the incident wave, specimen, and transmitted bar. Based on the theory of elastic-plastic incremental waves and numerical simulation calculations, the propagation of elastic-plastic waves in the specimen, the transmission and reflection of elastic-plastic waves at the two interfaces, and the interaction of the resulting series of transmitted and reflected waves arequantitatively investigated. The research findings are as follows.Firstly, although the design principle of the SHPB apparatus is based on linear elastic wave theory, the elastic-plastic waves, especially the stress waves, have a major influence on the transmission and reflection at the elastic-plastic interface, while the transmission and propagation of purely elastic waves have a relatively minor effect. Secondly, when the loading interval of the incident wave has a certain width, the multiple transmission and reflection of elastic waves at the two interfaces in Bar 2 attenuate the reflected wave while further strengthening the transmitted wave. This attenuation causes the peak of the reflected wave for the half-sine wave to occur earlier than at 0.5 nondimensional time. Thirdly, in contrary to the preliminary laws of elastic wave transmission and reflection at interfaces in traditional SHPB analysis, variations in the Young's modulus and density of the specimen material have little effect on the waveform and peak intensity of the transmitted wave, regardless of whether the incident wave is rectangular, trapezoidal, or half-sine. This investigationprovides a scientific basis for the refined design of SHPB experiments and precise analysis of data.
, Available online ,
doi: 10.11883/bzycj-2023-0365
Abstract:
Solid mediums, like rocks, concretes, shells and porous materials, etc., has the characteristics of microscopic discontinuity and macroscopic continuity. It is of great significance for material design, safety protection and other fields to reveal the influence of the meso-discontinuity on the dynamic response of the material. In this paper, based on the generalized Taylor’s formula under fractional definition, the governing equation of 1-D wave propagation in discontinuous medium is derived. Equivalent fractional order is introduced and the simplified form of the governing equation is presented for easily calculating. By using the finite difference method, the numerical solution of the governing equation is obtained. The influence of equivalent fractional order on wave propagation are analyzed. By the time domain analysis, the smaller the equivalent fractional order, the greater the degree of attenuation of the calculated waveform. By the frequency domain analysis, both high frequency wave and low frequency wave exhibit attenuation, and the attenuation of high frequency wave is higher than that of low frequency wave, which makes the pulse duration of the wave being larger. It is obvious that the equivalent fractional order has a certain relationship with the spatial structure of discontinuous medium. Based on the structural characteristics of some meso-discontinuous medium, e.g., porous materials and rocks, a randomly distributed pores model is established by using ABAQUS to verify the reliability of the governing equation and study the wave propagation of meso-discontinuous medium. The effects of porosity, material properties and input waves on wave propagation are analyzed. The degree of wave attenuation is positively related to the porosity of the medium, and negatively related to the wave velocity and the pulse duration of input wave. However, the equivalent fractional order is only related to the porosity and pore distribution of the discontinuous medium. When the spatial structure of the discontinuous medium remains unchanged, the corresponding equivalent fractional order does not change with the material property and the pulse duration of the input wave. By the randomly distributed pores model with various porosities, it is found that the equivalent fractional order decreases with the increase of porosity. Under the same porosity, the heterogeneity of pore distribution will result in different waveforms, while with the increase of porosity, this difference becomes more obvious, but the corresponding equivalent fractional order only has little difference. The statistical relation between equivalent fractional order and porosity is approximately linear when the pore distribution is almost the same. Compared with the randomly distributed pores medium, the statistical relation between equivalent fractional order and porosity of discontinuous medium with uniform distribution of different porosity shifts upward, indicating that the attenuation effect of random structure on wave is higher than that of uniform structure. This paper provides a new approach to investigate wave propagation in meso-discontinuous medium such as porous materials, rocks, shells, etc. It can be used as a basis to evaluate the dynamic response of discontinuous medium.
Solid mediums, like rocks, concretes, shells and porous materials, etc., has the characteristics of microscopic discontinuity and macroscopic continuity. It is of great significance for material design, safety protection and other fields to reveal the influence of the meso-discontinuity on the dynamic response of the material. In this paper, based on the generalized Taylor’s formula under fractional definition, the governing equation of 1-D wave propagation in discontinuous medium is derived. Equivalent fractional order is introduced and the simplified form of the governing equation is presented for easily calculating. By using the finite difference method, the numerical solution of the governing equation is obtained. The influence of equivalent fractional order on wave propagation are analyzed. By the time domain analysis, the smaller the equivalent fractional order, the greater the degree of attenuation of the calculated waveform. By the frequency domain analysis, both high frequency wave and low frequency wave exhibit attenuation, and the attenuation of high frequency wave is higher than that of low frequency wave, which makes the pulse duration of the wave being larger. It is obvious that the equivalent fractional order has a certain relationship with the spatial structure of discontinuous medium. Based on the structural characteristics of some meso-discontinuous medium, e.g., porous materials and rocks, a randomly distributed pores model is established by using ABAQUS to verify the reliability of the governing equation and study the wave propagation of meso-discontinuous medium. The effects of porosity, material properties and input waves on wave propagation are analyzed. The degree of wave attenuation is positively related to the porosity of the medium, and negatively related to the wave velocity and the pulse duration of input wave. However, the equivalent fractional order is only related to the porosity and pore distribution of the discontinuous medium. When the spatial structure of the discontinuous medium remains unchanged, the corresponding equivalent fractional order does not change with the material property and the pulse duration of the input wave. By the randomly distributed pores model with various porosities, it is found that the equivalent fractional order decreases with the increase of porosity. Under the same porosity, the heterogeneity of pore distribution will result in different waveforms, while with the increase of porosity, this difference becomes more obvious, but the corresponding equivalent fractional order only has little difference. The statistical relation between equivalent fractional order and porosity is approximately linear when the pore distribution is almost the same. Compared with the randomly distributed pores medium, the statistical relation between equivalent fractional order and porosity of discontinuous medium with uniform distribution of different porosity shifts upward, indicating that the attenuation effect of random structure on wave is higher than that of uniform structure. This paper provides a new approach to investigate wave propagation in meso-discontinuous medium such as porous materials, rocks, shells, etc. It can be used as a basis to evaluate the dynamic response of discontinuous medium.
, Available online ,
doi: 10.11883/bzycj-2023-0258
Abstract:
Typical sandstones distributed in cold regions were chosen as the research object to study the impact mechanical properties of frozen rock mass and provide reasonable unit explosive consumption for frozen rock mass in blasting excavation engineering in cold regions. Sandstone specimens with different moisture contents were prepared by the controlled mass method. Comprehensive research methods of indoor split Hopkinson pressure bar (SHPB) test and theoretical analysis are used to study the impact mechanical properties and blasting fragmentation energy dissipation characteristics of frozen sandstones. The results are as follows. (1) The dynamic compressive strength and dynamic elastic modulus of frozen sandstone are overall improved compared to the room temperature state, while the peak strain is generally decreased. Comparing the dynamic and static load test results of the mechanical properties of sandstone, the difference between the compressive strength of sandstones with the same physical parameters under dynamic and static loads is small, and the dynamic elastic modulus is significantly higher than the static elastic modulus. (2) The energy dissipation of room-temperature and frozen sandstone specimens decreases gradually with the increase of moisture content, and the energy dissipation of frozen sandstone is higher than that at room temperature. Under the moisture content of 0, 0.25ω, 0.50ω, 0.75ω, and 1.00ω, the energy dissipation of frozen sandstone increased by 21.6%, 64.9%, 80.3%, 78.2%, and 83.3%, respectively compared with the room temperature state. (3) The unit explosive consumption of frozen sandstone with the same moisture content is higher than that at room temperature, with moisture contents of 0, 0.25ω, 0.50ω, 0.75ω and 1.00ω, the unit explosive consumption of sandstone in the frozen state is 20.4%, 61.3%, 60.0%, 55.6% and 66.7% higher than that in room temperature state. (4) By fitting the unit explosive consumption values of sandstone at room temperature and frozen state, a correction model for the unit consumption of sandstone blasting in different states is obtained, which can provide correction suggestions for the unit explosive consumption for sandstone blasting engineering in cold regions.
Typical sandstones distributed in cold regions were chosen as the research object to study the impact mechanical properties of frozen rock mass and provide reasonable unit explosive consumption for frozen rock mass in blasting excavation engineering in cold regions. Sandstone specimens with different moisture contents were prepared by the controlled mass method. Comprehensive research methods of indoor split Hopkinson pressure bar (SHPB) test and theoretical analysis are used to study the impact mechanical properties and blasting fragmentation energy dissipation characteristics of frozen sandstones. The results are as follows. (1) The dynamic compressive strength and dynamic elastic modulus of frozen sandstone are overall improved compared to the room temperature state, while the peak strain is generally decreased. Comparing the dynamic and static load test results of the mechanical properties of sandstone, the difference between the compressive strength of sandstones with the same physical parameters under dynamic and static loads is small, and the dynamic elastic modulus is significantly higher than the static elastic modulus. (2) The energy dissipation of room-temperature and frozen sandstone specimens decreases gradually with the increase of moisture content, and the energy dissipation of frozen sandstone is higher than that at room temperature. Under the moisture content of 0, 0.25ω, 0.50ω, 0.75ω, and 1.00ω, the energy dissipation of frozen sandstone increased by 21.6%, 64.9%, 80.3%, 78.2%, and 83.3%, respectively compared with the room temperature state. (3) The unit explosive consumption of frozen sandstone with the same moisture content is higher than that at room temperature, with moisture contents of 0, 0.25ω, 0.50ω, 0.75ω and 1.00ω, the unit explosive consumption of sandstone in the frozen state is 20.4%, 61.3%, 60.0%, 55.6% and 66.7% higher than that in room temperature state. (4) By fitting the unit explosive consumption values of sandstone at room temperature and frozen state, a correction model for the unit consumption of sandstone blasting in different states is obtained, which can provide correction suggestions for the unit explosive consumption for sandstone blasting engineering in cold regions.
, Available online ,
doi: 10.11883/bzycj-2024-0119
Abstract:
As a novel folded structure, truncated square pyramid (TSP) exhibits excellent impact resistance and energy absorption performance. It also has the merit of simple and modulated fabrication of its unit cell. To further verify the performance of TSP sandwich panels under local impact load, the impact tests are carried out in this work by using an air cannon testing system. The unit cell is firstly prepared by multi-stage mould-pressing and then modulated to form single and multi-layer sandwich panels. The impact protection performance and energy absorption properties of the back-supported cladding cases as well as unsupported sandwich structures are investigated under different impact scenarios. By measuring and comparing the displacement time histories of the single-layer sandwich structure, and their deformation modes after impact, their impact resistance performances are evaluated. For the back supported cladding cases, a measuring system with five load cells is placed behind the back plate of the cladding and is rigidly supported to record the time history and distribution of the transmitted force of the claddings under impact. Their impact mitigation performances are evaluated by analyzing the recorded force-time histories under various loading scenarios. It was found that the maximum displacement and residual displacement of the back plate increase with the increase of impact velocity for the unsupported cases. For the rigidly supported claddings, the double-layered cladding shows significantly improved energy absorption and impact mitigation performance than single layered one. It shows a larger area of the utilized core and leads to a reduced initial peak transmitted force. In addition, it is found that the impact position has a significant effect on the dynamic response of the claddings as it changes the peak transmitted force and the time of occurrence because of the change in deformation modes. The research results provide a reference for the engineering design and application of TSP sandwich structures.
As a novel folded structure, truncated square pyramid (TSP) exhibits excellent impact resistance and energy absorption performance. It also has the merit of simple and modulated fabrication of its unit cell. To further verify the performance of TSP sandwich panels under local impact load, the impact tests are carried out in this work by using an air cannon testing system. The unit cell is firstly prepared by multi-stage mould-pressing and then modulated to form single and multi-layer sandwich panels. The impact protection performance and energy absorption properties of the back-supported cladding cases as well as unsupported sandwich structures are investigated under different impact scenarios. By measuring and comparing the displacement time histories of the single-layer sandwich structure, and their deformation modes after impact, their impact resistance performances are evaluated. For the back supported cladding cases, a measuring system with five load cells is placed behind the back plate of the cladding and is rigidly supported to record the time history and distribution of the transmitted force of the claddings under impact. Their impact mitigation performances are evaluated by analyzing the recorded force-time histories under various loading scenarios. It was found that the maximum displacement and residual displacement of the back plate increase with the increase of impact velocity for the unsupported cases. For the rigidly supported claddings, the double-layered cladding shows significantly improved energy absorption and impact mitigation performance than single layered one. It shows a larger area of the utilized core and leads to a reduced initial peak transmitted force. In addition, it is found that the impact position has a significant effect on the dynamic response of the claddings as it changes the peak transmitted force and the time of occurrence because of the change in deformation modes. The research results provide a reference for the engineering design and application of TSP sandwich structures.
Abstract:
To investigate the effect of the steel ratio on the impact resistance of glass fiber reinforced polymer (GFRP) tube concrete-encased steel composite members, 15 numerical models of composite members were established. The whole impact process, the dynamic response and the stress distribution from each component of the composite member at the different characteristic moment during the low-velocity impact were analyzed. The direct bending moment contributions at the typical cross sections and the energy dissipation under the different impact moment were explored. Meanwhile, the corresponding failure mode was determined, based on the maximum principal plastic strain distribution of concrete, GFRP tube matrix tensile and compression damage, and equivalent plastic strain distribution of steel. Additionally, the effect of the steel ratio on the impact performance of members with different slenderness ratios was investigated by analyzing the time history curves of the impact force, displacement, energy transformation and energy consumption. The results show that the impact load-bearing capacity of GFRP tube concrete-encased steel members is improved by 7% to 134% and the lateral displacement is reduced by 13% to 68% compared with the GFRP tube concrete members. Furthermore, it can be found that the failure mode of the members is flexure-dominant and the concrete is crushed at the impact region. The flexural stiffness has a significant influence on the impact performance of the member under lateral impact loading. The impact force of the member increases with increasing the steel ratio. Whereas, the impact force of the member decreases with increasing the slenderness ratio. Moreover, the narrow flange section steel with a higher moment of inertia is more favorable for the impact resistance of the member when the difference in steel ratio is 1.5%. And energy consumption of the encased steel is a major contributor to the total energy consumption of the member when the slenderness ratio is greater than or equal to 20. The GFRP tube plays a dual role in both bearing the impact force and confining the concrete in a circumferential direction at the oscillation stage during impact process.
To investigate the effect of the steel ratio on the impact resistance of glass fiber reinforced polymer (GFRP) tube concrete-encased steel composite members, 15 numerical models of composite members were established. The whole impact process, the dynamic response and the stress distribution from each component of the composite member at the different characteristic moment during the low-velocity impact were analyzed. The direct bending moment contributions at the typical cross sections and the energy dissipation under the different impact moment were explored. Meanwhile, the corresponding failure mode was determined, based on the maximum principal plastic strain distribution of concrete, GFRP tube matrix tensile and compression damage, and equivalent plastic strain distribution of steel. Additionally, the effect of the steel ratio on the impact performance of members with different slenderness ratios was investigated by analyzing the time history curves of the impact force, displacement, energy transformation and energy consumption. The results show that the impact load-bearing capacity of GFRP tube concrete-encased steel members is improved by 7% to 134% and the lateral displacement is reduced by 13% to 68% compared with the GFRP tube concrete members. Furthermore, it can be found that the failure mode of the members is flexure-dominant and the concrete is crushed at the impact region. The flexural stiffness has a significant influence on the impact performance of the member under lateral impact loading. The impact force of the member increases with increasing the steel ratio. Whereas, the impact force of the member decreases with increasing the slenderness ratio. Moreover, the narrow flange section steel with a higher moment of inertia is more favorable for the impact resistance of the member when the difference in steel ratio is 1.5%. And energy consumption of the encased steel is a major contributor to the total energy consumption of the member when the slenderness ratio is greater than or equal to 20. The GFRP tube plays a dual role in both bearing the impact force and confining the concrete in a circumferential direction at the oscillation stage during impact process.
, Available online ,
doi: 10.11883/bzycj-2023-0375
Abstract:
The fiber back plate in ceramic/fiber composite armor cannot provide sufficient support for the ceramic panel due to its low stiffness, which weakens the erosion effect of the ceramic panel on the projectile. In order to enhance the overall structural stiffness of composite armor, a metal sandwich layer material was added to the ceramic/fiber composite armor. The ballistic performance of the sandwich composite armor against 12.7 mm incendiary projectiles was studied through experiments and numerical simulations. The experimental results indicate that the core of the penetrator exhibits a brittle fracture failure mode, while composite armor exhibits multiple failure modes, including petal shaped expansion of the sandwich layer, delamination and protrusion deformation of the UHMWPE (ultra-high molecular weight polyethylene) laminate. A three-dimensional numerical model was established to analyze the evolution of the entire ballistic response, and the accuracy of the simulation was verified through experimental results. The simulation results indicate that the armor of the 12.7 mm penetrator will cause damage to the ceramic, while the ceramic will erode the pointed oval head of the core, making the core head blunt and weakening the penetration ability of the core into the UHMWPE backing plate. Most of the kinetic energy of the residual projectile is absorbed by the UHMWPE layer, and the failure mode of the UHMWPE laminate will change from shear failure to tensile failure as the number of layers increases. In addition, as a sandwich layer, the porous TC4 board can provide support for the ceramic panel, increase the energy absorption effect of the ceramic panel and the erosion of the projectile, and the 12mm pore size TC4 sandwich layer can provide greater stiffness support, increase the energy absorption efficiency of the overall composite structure by 10%.
The fiber back plate in ceramic/fiber composite armor cannot provide sufficient support for the ceramic panel due to its low stiffness, which weakens the erosion effect of the ceramic panel on the projectile. In order to enhance the overall structural stiffness of composite armor, a metal sandwich layer material was added to the ceramic/fiber composite armor. The ballistic performance of the sandwich composite armor against 12.7 mm incendiary projectiles was studied through experiments and numerical simulations. The experimental results indicate that the core of the penetrator exhibits a brittle fracture failure mode, while composite armor exhibits multiple failure modes, including petal shaped expansion of the sandwich layer, delamination and protrusion deformation of the UHMWPE (ultra-high molecular weight polyethylene) laminate. A three-dimensional numerical model was established to analyze the evolution of the entire ballistic response, and the accuracy of the simulation was verified through experimental results. The simulation results indicate that the armor of the 12.7 mm penetrator will cause damage to the ceramic, while the ceramic will erode the pointed oval head of the core, making the core head blunt and weakening the penetration ability of the core into the UHMWPE backing plate. Most of the kinetic energy of the residual projectile is absorbed by the UHMWPE layer, and the failure mode of the UHMWPE laminate will change from shear failure to tensile failure as the number of layers increases. In addition, as a sandwich layer, the porous TC4 board can provide support for the ceramic panel, increase the energy absorption effect of the ceramic panel and the erosion of the projectile, and the 12mm pore size TC4 sandwich layer can provide greater stiffness support, increase the energy absorption efficiency of the overall composite structure by 10%.
, Available online ,
doi: 10.11883/bzycj-2023-0295
Abstract:
In order to further reveal the characteristic of metal mesh to inhibit the flame propagation of hydrogen-methane premixed mixture, hydrogen and methane mixed gas with hydrogen mixing ratio of 0%, 10%, 20% and 30% were selected to conduct the experimental investigation of the effect of hydrogen mixing ratio inhibiting the fire processing through wire mesh with varied size in an explosion pipeline with an inner diameter of 60 mm and a total visible length of 1024 mm. Firstly, the flame propagation process was recorded by a high-speed camera, and the effect of hydrogen mixing ratio on fire resistance of wire mesh with different mesh numbers and the change of flame morphology were analyzed. Secondly, the average speed of flame front movement was calculated according to the interval of 50 mm, and the flame propagation speed within the visible area of the pipeline was analyzed. The interaction law between the metal wire mesh and the flame was mainly characterized by the flame propagation speed on both sides of the metal wire mesh. The results show that with the increase of hydrogen content, the difficulty of flame retardancy of metal wire mesh increases, and the flame retardancy effect of metal wire mesh can transition from success to failure, and the impact on flame propagation may shift from inhibition to promotion. When the wire mesh fails to resist the fire, the wire mesh will cause the flame to fold and cause the flame to accelerate, but the first appearance of the tulip flame is delayed. With the increase of hydrogen mixing ratio, the acceleration phenomenon of flame passing through the wire mesh is more obvious. Increasing the mesh number of wire mesh can improve the fire resistance of wire mesh to hydrogen-methane premixed flame. The larger the mesh number, the stronger the fire resistance. More than 60 mesh wire mesh can effectively quench hydrogen and methane premixed flame.
In order to further reveal the characteristic of metal mesh to inhibit the flame propagation of hydrogen-methane premixed mixture, hydrogen and methane mixed gas with hydrogen mixing ratio of 0%, 10%, 20% and 30% were selected to conduct the experimental investigation of the effect of hydrogen mixing ratio inhibiting the fire processing through wire mesh with varied size in an explosion pipeline with an inner diameter of 60 mm and a total visible length of 1024 mm. Firstly, the flame propagation process was recorded by a high-speed camera, and the effect of hydrogen mixing ratio on fire resistance of wire mesh with different mesh numbers and the change of flame morphology were analyzed. Secondly, the average speed of flame front movement was calculated according to the interval of 50 mm, and the flame propagation speed within the visible area of the pipeline was analyzed. The interaction law between the metal wire mesh and the flame was mainly characterized by the flame propagation speed on both sides of the metal wire mesh. The results show that with the increase of hydrogen content, the difficulty of flame retardancy of metal wire mesh increases, and the flame retardancy effect of metal wire mesh can transition from success to failure, and the impact on flame propagation may shift from inhibition to promotion. When the wire mesh fails to resist the fire, the wire mesh will cause the flame to fold and cause the flame to accelerate, but the first appearance of the tulip flame is delayed. With the increase of hydrogen mixing ratio, the acceleration phenomenon of flame passing through the wire mesh is more obvious. Increasing the mesh number of wire mesh can improve the fire resistance of wire mesh to hydrogen-methane premixed flame. The larger the mesh number, the stronger the fire resistance. More than 60 mesh wire mesh can effectively quench hydrogen and methane premixed flame.
, Available online ,
doi: 10.11883/bzycj-2023-0388
Abstract:
To investigate the feasibility and characteristics of high-velocity formed projectile formation driven by electromagnetic loading, exploratory experiments of projectile formation by electromagnetically driven the linear liner were conducted using the pulsed power generator CQ-7. Photon Doppler velocimeter (PDV) was employed to measure the velocity of the electromagnetic-driven projectiles and validate their penetration into aluminum targets. A physical model and numerical simulation method for electromagnetic-driven projectile formation were established using fluid dynamics software and corresponding electromagnetic simulation modules. The changes in current density and magnetic pressure during the electromagnetic loading stage were studied and the dynamic processes of projectile formation and penetration into aluminum targets were simulated. The numerical simulation method was verified through the comparison between numerical results and experimental data. Based on this, the influences of liner configuration and loading energy on the projectile formation parameters of equal wall thickness hemispherical liner were explored. The results indicate that the outer curvature radius has a minor impact on the head velocity of the projectile, while the head velocity significantly increases with decreasing wall thickness and increasing loading energy. The aspect ratio of the projectile gradually increases with decreasing outer curvature radius and wall thickness, as well as increasing loading energy. The conversion between quasi-spherical and long rod-shaped projectile modes can be achieved by changing the structural parameters, and for the same structural parameter, the conversion between two modes can be achieved by controlling the loading energy. Finally, the feasibility of obtaining high-velocity and high-mass-formed projectiles using electromagnetic-driven technology was predicted using numerical simulation methods, and it can be figured out from the results that a projectile with a higher velocity and larger mass can be formed by increasing the loading energy and the sizes of the shaped liner, effectively breaking through the velocity limit of a traditional penetrator driven by explosive detonation.
To investigate the feasibility and characteristics of high-velocity formed projectile formation driven by electromagnetic loading, exploratory experiments of projectile formation by electromagnetically driven the linear liner were conducted using the pulsed power generator CQ-7. Photon Doppler velocimeter (PDV) was employed to measure the velocity of the electromagnetic-driven projectiles and validate their penetration into aluminum targets. A physical model and numerical simulation method for electromagnetic-driven projectile formation were established using fluid dynamics software and corresponding electromagnetic simulation modules. The changes in current density and magnetic pressure during the electromagnetic loading stage were studied and the dynamic processes of projectile formation and penetration into aluminum targets were simulated. The numerical simulation method was verified through the comparison between numerical results and experimental data. Based on this, the influences of liner configuration and loading energy on the projectile formation parameters of equal wall thickness hemispherical liner were explored. The results indicate that the outer curvature radius has a minor impact on the head velocity of the projectile, while the head velocity significantly increases with decreasing wall thickness and increasing loading energy. The aspect ratio of the projectile gradually increases with decreasing outer curvature radius and wall thickness, as well as increasing loading energy. The conversion between quasi-spherical and long rod-shaped projectile modes can be achieved by changing the structural parameters, and for the same structural parameter, the conversion between two modes can be achieved by controlling the loading energy. Finally, the feasibility of obtaining high-velocity and high-mass-formed projectiles using electromagnetic-driven technology was predicted using numerical simulation methods, and it can be figured out from the results that a projectile with a higher velocity and larger mass can be formed by increasing the loading energy and the sizes of the shaped liner, effectively breaking through the velocity limit of a traditional penetrator driven by explosive detonation.
, Available online ,
doi: 10.11883/bzycj-2023-0358
Abstract:
Decoupled charge structure is widely used in contour blasting for rock excavation engineering, and its efficacy in rock breaking is intricately tied to both the decoupling ratio and the transfer features of explosion energy. In this study, the analysis delves into the damage degree and failure patterns of cubic red sandstone samples through two groups of lab-scale blasting tests, utilizing various charging modes. To precisely quantify the features of rock fragmentation size distribution (FSD) induced by blasting load, a three-parameter generalized extreme value (GEV) function was introduced. In addition, a three-dimensional finite element model was developed in ANSYS software. The numerical model was calibrated based on the tested results of the sample R1 by comparing the fracture networks and FSDs curves. This validated model was then deployed to model the rock fracture behavior under decoupled charge blasting, and the evolution of blasting cracks and explosion pressure inside the rock sample was reproduced. Moreover, the effects of axial and radial decoupled ratios, as well as the choice of coupling medium on the rock fragmentation and fracture patterns were discussed. The results showed that the three-parameter GEV function can better characterize the rock fragmentation features resulting from blasting. Notably, the average size of the fragment exhibits a linear decrease trend with a reduction in the decoupling ratio, leading to a more uniform fragmentation degree. By comparing the energy distribution and damage levels of rock when using different coupling mediums, it was found that water as the coupling medium exhibits the highest efficiency in energy transfer, followed by wet sand and dry sand, while air has the lowest energy transfer efficiency. Furthermore, the theoretical stress transmission coefficient calculated by the equivalent wave impedance method can well reflect the rock fragmentation features, which can serve as a valuable reference for rock blasting in decoupled charge.
Decoupled charge structure is widely used in contour blasting for rock excavation engineering, and its efficacy in rock breaking is intricately tied to both the decoupling ratio and the transfer features of explosion energy. In this study, the analysis delves into the damage degree and failure patterns of cubic red sandstone samples through two groups of lab-scale blasting tests, utilizing various charging modes. To precisely quantify the features of rock fragmentation size distribution (FSD) induced by blasting load, a three-parameter generalized extreme value (GEV) function was introduced. In addition, a three-dimensional finite element model was developed in ANSYS software. The numerical model was calibrated based on the tested results of the sample R1 by comparing the fracture networks and FSDs curves. This validated model was then deployed to model the rock fracture behavior under decoupled charge blasting, and the evolution of blasting cracks and explosion pressure inside the rock sample was reproduced. Moreover, the effects of axial and radial decoupled ratios, as well as the choice of coupling medium on the rock fragmentation and fracture patterns were discussed. The results showed that the three-parameter GEV function can better characterize the rock fragmentation features resulting from blasting. Notably, the average size of the fragment exhibits a linear decrease trend with a reduction in the decoupling ratio, leading to a more uniform fragmentation degree. By comparing the energy distribution and damage levels of rock when using different coupling mediums, it was found that water as the coupling medium exhibits the highest efficiency in energy transfer, followed by wet sand and dry sand, while air has the lowest energy transfer efficiency. Furthermore, the theoretical stress transmission coefficient calculated by the equivalent wave impedance method can well reflect the rock fragmentation features, which can serve as a valuable reference for rock blasting in decoupled charge.
, Available online ,
doi: 10.11883/bzycj-2023-0367
Abstract:
In recent years, with the rapid development of technology and equipment in the fields of aerospace, defense and military industry, multilayer lightweight metal composite materials have attracted widespread attention in order to face complex service environments and reduce equipment weight. Titanium, aluminum, magnesium and other lightweight metals and their alloys have advantages such as high specific strength, high specific elastic modulus, high damping and shock absorption, high electrostatic shielding, and high machinability, making them the most promising lightweight metal materials for application. In this study, the explosive welding experiments of TA2/AZ31B/2024Al multilayer light metal plate were carried out using parallel explosive welding process. By means of scanning electron microscopy, electron backscatter diffraction, split Hopkinson pressure bar and three-dimensional contour scanning, the interfacial microstructure characteristics, material phase changes, dynamic mechanical properties and impact fracture characteristics of multilayer explosive welded composite plates were systematically studied. The results indicate that the four joining interfaces of the multilayer lightweight metal composite plate after welding present unique waveform structure characteristics of explosive welding, and there are no obvious defects at the joining interfaces. The overall welding quality is good. The grain refinement occurs at the joining interfaces and forms the fine grain region. The grain structure in the 1060Al transition layer exhibits typical elongated layered grain characteristics due to strong plastic deformation, and obvious deformation texture and recrystallization texture characteristics appear at all four joining interfaces. The maximum dynamic compressive strength of the sample along the X-direction is 605 MPa, and the three-dimensional morphology of the fracture interface present unique structural feature similar to the water ripples. The maximum dynamic compressive strength of the sample along the Z-direction is 390 MPa, and the three-dimensional morphology of the fracture interface presents obvious fibrous ductile fracture characteristics. Due to the different wave impedance of the metals, the delamination failure occurs in the X-direction sample, which is caused by the shear stress between the Al/Mg joining interfaces. Since the strength of 1060Al is lower than that of other metals, the Z-direction sample is first destroyed from the 1060Al layer and slip shear fracture occurs along the 45° direction.
In recent years, with the rapid development of technology and equipment in the fields of aerospace, defense and military industry, multilayer lightweight metal composite materials have attracted widespread attention in order to face complex service environments and reduce equipment weight. Titanium, aluminum, magnesium and other lightweight metals and their alloys have advantages such as high specific strength, high specific elastic modulus, high damping and shock absorption, high electrostatic shielding, and high machinability, making them the most promising lightweight metal materials for application. In this study, the explosive welding experiments of TA2/AZ31B/2024Al multilayer light metal plate were carried out using parallel explosive welding process. By means of scanning electron microscopy, electron backscatter diffraction, split Hopkinson pressure bar and three-dimensional contour scanning, the interfacial microstructure characteristics, material phase changes, dynamic mechanical properties and impact fracture characteristics of multilayer explosive welded composite plates were systematically studied. The results indicate that the four joining interfaces of the multilayer lightweight metal composite plate after welding present unique waveform structure characteristics of explosive welding, and there are no obvious defects at the joining interfaces. The overall welding quality is good. The grain refinement occurs at the joining interfaces and forms the fine grain region. The grain structure in the 1060Al transition layer exhibits typical elongated layered grain characteristics due to strong plastic deformation, and obvious deformation texture and recrystallization texture characteristics appear at all four joining interfaces. The maximum dynamic compressive strength of the sample along the X-direction is 605 MPa, and the three-dimensional morphology of the fracture interface present unique structural feature similar to the water ripples. The maximum dynamic compressive strength of the sample along the Z-direction is 390 MPa, and the three-dimensional morphology of the fracture interface presents obvious fibrous ductile fracture characteristics. Due to the different wave impedance of the metals, the delamination failure occurs in the X-direction sample, which is caused by the shear stress between the Al/Mg joining interfaces. Since the strength of 1060Al is lower than that of other metals, the Z-direction sample is first destroyed from the 1060Al layer and slip shear fracture occurs along the 45° direction.
, Available online ,
doi: 10.11883/bzycj-2023-0330
Abstract:
Hydrogen energy is an important component of the future national energy system. Mixing hydrogen with natural gas to form enriched hydrogen fuel can provide support for the transition towards renewable and green energy in the energy structure. However, it also brings more severe safety challenges. In order to systematically understand the current application status of enriched hydrogen methane fuel and its safe utilization, literature research was conducted to review and discuss the combustion characteristics and explosion suppression research of enriched hydrogen methane from several aspects, including propagation characteristics of deflagration flames, explosion characteristic parameters, deflagration mechanism, and explosion suppression materials. The research direction in recent years was also analyzed and summarized. The results showed that with an increase in the hydrogen addition ratio, parameters such as inherent flame instability, flame propagation speed, and explosion intensity were enhanced to varying degrees, while the suppression effect of explosion suppressants was continuously weakened. Currently, there is a lack of research on the explosion characteristics of enriched hydrogen methane under the coupling of multiple factors, and the co-suppression mechanism of explosion suppressants has not been clearly revealed. Based on this, the urgent directions and future research focus for the safe development of enriched hydrogen methane fuel are proposed, which can provide theoretical basis for the large-scale development of the enriched hydrogen natural gas industry.
Hydrogen energy is an important component of the future national energy system. Mixing hydrogen with natural gas to form enriched hydrogen fuel can provide support for the transition towards renewable and green energy in the energy structure. However, it also brings more severe safety challenges. In order to systematically understand the current application status of enriched hydrogen methane fuel and its safe utilization, literature research was conducted to review and discuss the combustion characteristics and explosion suppression research of enriched hydrogen methane from several aspects, including propagation characteristics of deflagration flames, explosion characteristic parameters, deflagration mechanism, and explosion suppression materials. The research direction in recent years was also analyzed and summarized. The results showed that with an increase in the hydrogen addition ratio, parameters such as inherent flame instability, flame propagation speed, and explosion intensity were enhanced to varying degrees, while the suppression effect of explosion suppressants was continuously weakened. Currently, there is a lack of research on the explosion characteristics of enriched hydrogen methane under the coupling of multiple factors, and the co-suppression mechanism of explosion suppressants has not been clearly revealed. Based on this, the urgent directions and future research focus for the safe development of enriched hydrogen methane fuel are proposed, which can provide theoretical basis for the large-scale development of the enriched hydrogen natural gas industry.
, Available online ,
doi: 10.11883/bzycj-2023-0257
Abstract:
In order to obtain the physical and mechanical properties of NiTi alloys at different initial phase transition temperatures under high strain rates, the dynamic responses of NiTi alloys with different initial phase transition temperatures were systematically studied under quasi-static compression and tensile at strain rate 10−3 s−1, quasi-isentropic compression at strain rate 105 s−1 and shock compression at strain rate of 107 s−1. Dog-bone specimens and cylindrical rod specimens were used in the quasi-static tension and compression experiments respectively. A series of quasi-isentropic compression and planar shock wave experiments were performed on pulsed power generator CQ-4, which can deliver pulsed currents with peak values of 3–4 MA and rise time of 470–600 ns to short circuit loads. Velocities were measured by a photonic Doppler velocimetry (PDV) system with accuracies of 1%. The quasi-static loading stress-strain curves showed twice modulus changes for both the initial martensitic and the initial austenitic NiTi alloy. The modulus changes were caused by crystal reorientation and plastic deformation of the martensitic NiTi alloy. In experiments of initial austenitic phase, the modulus changes were caused by martensitic phase transition and plastic deformation after phase change. The Lagrangian sound speed increased continuously with the particle velocity for the initial martensitic NiTi alloy under quasi-isentropic loading. However, there are discontinuities in the sound speed curves for initial austenite phase. The sound speed decreases intermittently from the transverse wave speed to the longitudinal wave speed, and then increases linearly with the particle velocity. In shock experiments of initial martensitic NiTi alloy, a double-wave structure appeared at the free surface velocity of about 34 and 100 m/s for the initial sample temperature of 302 and 402 K, respectively. Austenite-martensite phase transition was occurred during sample heating of initial martensitic NiTi alloy. The inflection points on the velocity curve were caused by plastic yielding of martensitic and austenitic phase separately. For initial austenite NiTi alloy, obvious elastic-plastic transformation of austenite NiTi alloy was observed at free surface velocity of approximately 260 m/s. The elastic limit of austenitic NiTi alloy increased from about 2 GPa to about 4 GPa with the increase of strain rate from about 105 s−1 to 107 s−1. And the elastic limit decreased to 1.7 GPa at strain rate of 107 s−1 with the initial sample temperature of 402 K. The results show that the elastic limit of NiTi alloy is greatly affected by temperature and strain rate.
In order to obtain the physical and mechanical properties of NiTi alloys at different initial phase transition temperatures under high strain rates, the dynamic responses of NiTi alloys with different initial phase transition temperatures were systematically studied under quasi-static compression and tensile at strain rate 10−3 s−1, quasi-isentropic compression at strain rate 105 s−1 and shock compression at strain rate of 107 s−1. Dog-bone specimens and cylindrical rod specimens were used in the quasi-static tension and compression experiments respectively. A series of quasi-isentropic compression and planar shock wave experiments were performed on pulsed power generator CQ-4, which can deliver pulsed currents with peak values of 3–4 MA and rise time of 470–600 ns to short circuit loads. Velocities were measured by a photonic Doppler velocimetry (PDV) system with accuracies of 1%. The quasi-static loading stress-strain curves showed twice modulus changes for both the initial martensitic and the initial austenitic NiTi alloy. The modulus changes were caused by crystal reorientation and plastic deformation of the martensitic NiTi alloy. In experiments of initial austenitic phase, the modulus changes were caused by martensitic phase transition and plastic deformation after phase change. The Lagrangian sound speed increased continuously with the particle velocity for the initial martensitic NiTi alloy under quasi-isentropic loading. However, there are discontinuities in the sound speed curves for initial austenite phase. The sound speed decreases intermittently from the transverse wave speed to the longitudinal wave speed, and then increases linearly with the particle velocity. In shock experiments of initial martensitic NiTi alloy, a double-wave structure appeared at the free surface velocity of about 34 and 100 m/s for the initial sample temperature of 302 and 402 K, respectively. Austenite-martensite phase transition was occurred during sample heating of initial martensitic NiTi alloy. The inflection points on the velocity curve were caused by plastic yielding of martensitic and austenitic phase separately. For initial austenite NiTi alloy, obvious elastic-plastic transformation of austenite NiTi alloy was observed at free surface velocity of approximately 260 m/s. The elastic limit of austenitic NiTi alloy increased from about 2 GPa to about 4 GPa with the increase of strain rate from about 105 s−1 to 107 s−1. And the elastic limit decreased to 1.7 GPa at strain rate of 107 s−1 with the initial sample temperature of 402 K. The results show that the elastic limit of NiTi alloy is greatly affected by temperature and strain rate.
, Available online ,
doi: 10.11883/bzycj-2023-0241
Abstract:
In order to study the effect of mass parameter on vibration displacement of beam member under air blast loading, an effective method was proposed to reduce vibration displacement of beam member by increasing mass. The equivalent single degree of freedom (SDOF) system was used to analyze vibration displacement for beam member. The displacement formulas with mass parameter for flexible beam member and rigid beam member in each stage under air blast loading were respectively established. These stages included elastic forced vibration, elastic free vibration, plastic forced vibration, plastic free vibration and rebound vibration. Rectangular section and circular section were selected as typical cross sections of beam members, and 13 typical calculation cases with mass parameters ranging from 1.00 to 1.20 were designed. The vibration displacement time-history curves, maximum elastic displacement, maximum elastic-plastic displacement and residual deformation of 13 typical calculation cases of flexible beam member and rigid beam member were calculated and analyzed respectively. Taking the data of mass parameter value with 1.0 as the benchmark value, the displacement reduction rate of the other calculation cases relative to the benchmark value could be obtained. The difference between the types of beam members for displacement reduction rate was further analyzed. The results show as follows. For flexible and rigid beam member subjected to air blast loading, increasing cross sectional area and considering only the mass parameter will result in a smaller reduction in vibration displacement. Therefore, the displacement should be analyzed according to the coupling effect of the mass parameter and additional stiffness parameter. For beam member with rectangular cross section, the reduction ranges for maximum elastic displacement, the maximum elastic-plastic displacement and the residual deformation calculated from coupled effect of mass parameter and stiffness parameter are about 4.75, 3.28, and 2.96 times that of mass parameter alone. For beam with circular cross section, the data are 3.75, 2.56, and 2.32 times. These conclusions are applicable to both flexible beam member and rigid beam member and there is no significant difference.
In order to study the effect of mass parameter on vibration displacement of beam member under air blast loading, an effective method was proposed to reduce vibration displacement of beam member by increasing mass. The equivalent single degree of freedom (SDOF) system was used to analyze vibration displacement for beam member. The displacement formulas with mass parameter for flexible beam member and rigid beam member in each stage under air blast loading were respectively established. These stages included elastic forced vibration, elastic free vibration, plastic forced vibration, plastic free vibration and rebound vibration. Rectangular section and circular section were selected as typical cross sections of beam members, and 13 typical calculation cases with mass parameters ranging from 1.00 to 1.20 were designed. The vibration displacement time-history curves, maximum elastic displacement, maximum elastic-plastic displacement and residual deformation of 13 typical calculation cases of flexible beam member and rigid beam member were calculated and analyzed respectively. Taking the data of mass parameter value with 1.0 as the benchmark value, the displacement reduction rate of the other calculation cases relative to the benchmark value could be obtained. The difference between the types of beam members for displacement reduction rate was further analyzed. The results show as follows. For flexible and rigid beam member subjected to air blast loading, increasing cross sectional area and considering only the mass parameter will result in a smaller reduction in vibration displacement. Therefore, the displacement should be analyzed according to the coupling effect of the mass parameter and additional stiffness parameter. For beam member with rectangular cross section, the reduction ranges for maximum elastic displacement, the maximum elastic-plastic displacement and the residual deformation calculated from coupled effect of mass parameter and stiffness parameter are about 4.75, 3.28, and 2.96 times that of mass parameter alone. For beam with circular cross section, the data are 3.75, 2.56, and 2.32 times. These conclusions are applicable to both flexible beam member and rigid beam member and there is no significant difference.
, Available online ,
doi: 10.11883/bzycj-2023-0263
Abstract:
In order to find a new, clean and efficient inhibitor of PE dust explosion, the Mg-Al hydrotalcite was used to inhibit PE dust explosion by using standard 20 L spherical explosion test system and minimum ignition temperature test system of dust cloud. The inhibition properties of Mg-Al hydrotalcite for PE dust explosion are analyzed from the aspects of explosion overpressure and minimum ignition temperature, and are compared with aluminum hydroxide and magnesium hydroxide. The results showed that the inhibition effect of Mg-Al hydrotalcite on explosion overpressure and minimum ignition temperature of polyethylene dust is superior to that of aluminum hydroxide and magnesium hydroxide. In terms of explosion overpressure, when the inhibition ratio is 2, Mg-Al hydrotalcite can completely inhibit the explosion of polyethylene dust, while the inhibition ratios required for aluminum hydroxide and magnesium hydroxide to achieve complete explosion suppression of polyethylene are 4 and 5 respectively. With the increase of inhibition ratio, the maximum explosion pressure rise rate of polyethylene dust decreased. The inhibition effect of Mg-Al hydrotalcite on the explosion pressure rise rate of polyethylene dust is also better than that of aluminum hydroxide and magnesium hydroxide. In terms of minimum ignition temperature, when the inhibition ratio was 1, Mg-Al hydrotalcite increased the minimum ignition temperature of polyethylene dust to 710 ℃, which was 290 ℃ higher than that of pure polyethylene dust. Under the same conditions, aluminum hydroxide and magnesium hydroxide can increase the minimum ignition temperature of polyethylene dust by 260 ℃ and 250 ℃ respectively. Therefore, the inhibition effect of Mg-Al hydrotalcite on the minimum ignition temperature of polyethylene is also greater than that of aluminum hydroxide and magnesium hydroxide. In addition, the inhibition mechanism of Mg-Al hydrotalcite on polyethylene dust explosion was analyzed based on its pyrolysis characteristics and infrared spectra.The physical effect is mainly realized by absorbing heat from the reaction system and diluting the oxygen concentration. The chemical action is mainly achieved by the pyrolysis products carbon dioxide and water participating in and blocking the polyethylene explosion chain reaction.
In order to find a new, clean and efficient inhibitor of PE dust explosion, the Mg-Al hydrotalcite was used to inhibit PE dust explosion by using standard 20 L spherical explosion test system and minimum ignition temperature test system of dust cloud. The inhibition properties of Mg-Al hydrotalcite for PE dust explosion are analyzed from the aspects of explosion overpressure and minimum ignition temperature, and are compared with aluminum hydroxide and magnesium hydroxide. The results showed that the inhibition effect of Mg-Al hydrotalcite on explosion overpressure and minimum ignition temperature of polyethylene dust is superior to that of aluminum hydroxide and magnesium hydroxide. In terms of explosion overpressure, when the inhibition ratio is 2, Mg-Al hydrotalcite can completely inhibit the explosion of polyethylene dust, while the inhibition ratios required for aluminum hydroxide and magnesium hydroxide to achieve complete explosion suppression of polyethylene are 4 and 5 respectively. With the increase of inhibition ratio, the maximum explosion pressure rise rate of polyethylene dust decreased. The inhibition effect of Mg-Al hydrotalcite on the explosion pressure rise rate of polyethylene dust is also better than that of aluminum hydroxide and magnesium hydroxide. In terms of minimum ignition temperature, when the inhibition ratio was 1, Mg-Al hydrotalcite increased the minimum ignition temperature of polyethylene dust to 710 ℃, which was 290 ℃ higher than that of pure polyethylene dust. Under the same conditions, aluminum hydroxide and magnesium hydroxide can increase the minimum ignition temperature of polyethylene dust by 260 ℃ and 250 ℃ respectively. Therefore, the inhibition effect of Mg-Al hydrotalcite on the minimum ignition temperature of polyethylene is also greater than that of aluminum hydroxide and magnesium hydroxide. In addition, the inhibition mechanism of Mg-Al hydrotalcite on polyethylene dust explosion was analyzed based on its pyrolysis characteristics and infrared spectra.The physical effect is mainly realized by absorbing heat from the reaction system and diluting the oxygen concentration. The chemical action is mainly achieved by the pyrolysis products carbon dioxide and water participating in and blocking the polyethylene explosion chain reaction.
Abstract:
In order to investigate the failure mechanism of tantalum capacitors under shock loads, shock experiments were conducted on tantalum capacitors using shock waves generated by underwater explosions with an electronic detonator. Five groups of experiments with different shock intensities were designed by varying the distance between the capacitor and the electronic detonator. The transient voltage characteristics of tantalum capacitors under different intensity shock loads were studied. The voltage variations of tantalum capacitors were explained based on changes in internal leakage current and external charging current, and the failure modes of tantalum capacitors were analyzed. Scanning electron microscopy was utilized to observe the microstructure of damaged areas in tantalum capacitors, and the micro-failure mechanisms of tantalum capacitors under shock loads were discussed. The results indicate that tantalum capacitors experience short-circuit failures after shocks, with a significant decrease in voltage initially, followed by a slow rise self-recovery. As the shock wave overpressure increases, the probability of tantalum capacitor failure increases, with a critical overpressure threshold of approximately 32.004 MPa. Different types of voltage variations correspond to different failure modes, including instant self-recovery after breakdown, slow self-recovery after breakdown, and repetitive breakdown with self-recovery. Different types of voltage variations exhibit significant differences in the peak values of initial leakage currents, with the first type ranging from 2.5 A to 5 A, the second type ranging from 1 A to 2 A, and the third type ranging from 8 A to 9 A. Moreover, larger peak values of leakage currents result in narrower peak widths. The micro-failure mechanisms of tantalum capacitors under shock loads include the propagation of microcracks within the oxide film leading to excessive local electric field strength and breakdown, impurities and surrounding crystalline oxide film protrude to form conductive channels in the region of thinner oxide film, and the formation of through-cracks followed by gas ionization leading to breakdown.
In order to investigate the failure mechanism of tantalum capacitors under shock loads, shock experiments were conducted on tantalum capacitors using shock waves generated by underwater explosions with an electronic detonator. Five groups of experiments with different shock intensities were designed by varying the distance between the capacitor and the electronic detonator. The transient voltage characteristics of tantalum capacitors under different intensity shock loads were studied. The voltage variations of tantalum capacitors were explained based on changes in internal leakage current and external charging current, and the failure modes of tantalum capacitors were analyzed. Scanning electron microscopy was utilized to observe the microstructure of damaged areas in tantalum capacitors, and the micro-failure mechanisms of tantalum capacitors under shock loads were discussed. The results indicate that tantalum capacitors experience short-circuit failures after shocks, with a significant decrease in voltage initially, followed by a slow rise self-recovery. As the shock wave overpressure increases, the probability of tantalum capacitor failure increases, with a critical overpressure threshold of approximately 32.004 MPa. Different types of voltage variations correspond to different failure modes, including instant self-recovery after breakdown, slow self-recovery after breakdown, and repetitive breakdown with self-recovery. Different types of voltage variations exhibit significant differences in the peak values of initial leakage currents, with the first type ranging from 2.5 A to 5 A, the second type ranging from 1 A to 2 A, and the third type ranging from 8 A to 9 A. Moreover, larger peak values of leakage currents result in narrower peak widths. The micro-failure mechanisms of tantalum capacitors under shock loads include the propagation of microcracks within the oxide film leading to excessive local electric field strength and breakdown, impurities and surrounding crystalline oxide film protrude to form conductive channels in the region of thinner oxide film, and the formation of through-cracks followed by gas ionization leading to breakdown.
Display Method:
2024, 44(3): 031400.
doi: 10.11883/bzycj-2024-0057
Abstract:
2024, 44(3): 031401.
doi: 10.11883/bzycj-2023-0324
Abstract:
High-entropy alloy (HEA) materials exhibit different failure modes and mechanical properties under high strain rate dynamic response. Because its potential mechanism cannot be fully explained from a macro perspective, it is necessary to study the atomic structure change, dislocation distribution change, evolution mechanism and deformation mechanism in the dynamic response process from a microscopic perspective. This study provides a reference for optimizing the processing technology and preparation method of HEA protective materials. The molecular dynamics simulation is adopted to design the compression, tensile at different strain rates and impact tests of [110], [111] and [100] three oriented Al0.3CoCrFeNi HEA. The atomic structure changes, dislocation distribution change, evolution mechanism and deformation mechanism in the dynamic response process are then analyzed. In the compression test: the yield strength of Al0.3CoCrFeNi high-entropy alloy with [110] orientation structure is the highest, followed by [111] and [100]. The main deformation mechanism of the [100] orientation structure is twin deformation, [110] orientation structure is slip deformation, and [111] orientation structure is dislocation deformation. In the tensile test: the yield strength of Al0.3CoCrFeNi high-entropy alloy with [111] orientation structure is the highest, followed by [100] and [110]. [100] orientation structure presents more twin structure during the tensile process; [110] exhibits more regular hexagonal close-packed structure slip surface; while [111] does not produce any slip surface. With the increase of strain rate, the compressive and tensile yield strength increased greatly, and the corresponding elongation increased, too. The plastic deformation mechanism at low strain rate (1×109 s−1) is mainly slip deformation, but the number of slip systems is small. The plastic deformation mechanism at medium strain rate (1×1010 s−1) is mainly slip deformation mechanism, but many slip systems appear. The plastic deformation mechanism at high strain rate (1×1011 s−1) is induced by amorphous atoms with disordered atomic arrangement. The Al0.3CoCrFeNi high-entropy alloy with [110] orientation structure has the best impact resistance, which is attributed to its highest yield strength and the highest stress at the end of the yield stage.
High-entropy alloy (HEA) materials exhibit different failure modes and mechanical properties under high strain rate dynamic response. Because its potential mechanism cannot be fully explained from a macro perspective, it is necessary to study the atomic structure change, dislocation distribution change, evolution mechanism and deformation mechanism in the dynamic response process from a microscopic perspective. This study provides a reference for optimizing the processing technology and preparation method of HEA protective materials. The molecular dynamics simulation is adopted to design the compression, tensile at different strain rates and impact tests of [110], [111] and [100] three oriented Al0.3CoCrFeNi HEA. The atomic structure changes, dislocation distribution change, evolution mechanism and deformation mechanism in the dynamic response process are then analyzed. In the compression test: the yield strength of Al0.3CoCrFeNi high-entropy alloy with [110] orientation structure is the highest, followed by [111] and [100]. The main deformation mechanism of the [100] orientation structure is twin deformation, [110] orientation structure is slip deformation, and [111] orientation structure is dislocation deformation. In the tensile test: the yield strength of Al0.3CoCrFeNi high-entropy alloy with [111] orientation structure is the highest, followed by [100] and [110]. [100] orientation structure presents more twin structure during the tensile process; [110] exhibits more regular hexagonal close-packed structure slip surface; while [111] does not produce any slip surface. With the increase of strain rate, the compressive and tensile yield strength increased greatly, and the corresponding elongation increased, too. The plastic deformation mechanism at low strain rate (1×109 s−1) is mainly slip deformation, but the number of slip systems is small. The plastic deformation mechanism at medium strain rate (1×1010 s−1) is mainly slip deformation mechanism, but many slip systems appear. The plastic deformation mechanism at high strain rate (1×1011 s−1) is induced by amorphous atoms with disordered atomic arrangement. The Al0.3CoCrFeNi high-entropy alloy with [110] orientation structure has the best impact resistance, which is attributed to its highest yield strength and the highest stress at the end of the yield stage.
2024, 44(3): 031402.
doi: 10.11883/bzycj-2023-0308
Abstract:
Stiffened panels are widely used in the explosion and impact protection, thus a fast and accurate method for solving their dynamic response is highly desired in engineering. Based on the idea of stiffness superposition, a novel equivalent-isotropic-plate method is proposed in this paper to convert the radial and uniformly stiffened circular plate into an isotropic flat plate, so as to analyze its dynamic response in the elastic stage under uniform pulse loading. Since obtaining the dynamic response of an isotropic plate is mature and convenient, the equivalent analysis can overcome the computational difficulty of anisotropy in direct modeling, thus greatly improving the solving efficiency. Through the linear superposition of the plate and stiffener dynamic equations, a concise formula of the equivalent plate thickness is derived explicitly. The equivalent parameter in the formula is obtained with the assistance of simulation and numerical fitting, which directly measures the strengthening effect of the stiffeners on the plate. Employing the equivalent-isotropic-plate model, the overall dynamic response of a stiffened circular plate can be represented by that of an equivalent isotropic plate with acceptable accuracy, especially for low-order vibrations and center deflections. It is verified that the equivalent method can be successfully applied to a variety of stiffening types, materials, and load forms. The deviation of the maximum deflection response of the equivalent flat plate from that of the original stiffened circular plate does not exceed 6%, and the deviation of the response frequency does not exceed 10%. This completely meets the engineering requirements. The equivalent-isotropic-plate model verifies the feasibility of isotropic equivalence, and reveals the intrinsic connection between the radial stiffened circular plate and the homogeneous circular plate, which is of great significance in engineering applications such as response prediction and structural optimization.
Stiffened panels are widely used in the explosion and impact protection, thus a fast and accurate method for solving their dynamic response is highly desired in engineering. Based on the idea of stiffness superposition, a novel equivalent-isotropic-plate method is proposed in this paper to convert the radial and uniformly stiffened circular plate into an isotropic flat plate, so as to analyze its dynamic response in the elastic stage under uniform pulse loading. Since obtaining the dynamic response of an isotropic plate is mature and convenient, the equivalent analysis can overcome the computational difficulty of anisotropy in direct modeling, thus greatly improving the solving efficiency. Through the linear superposition of the plate and stiffener dynamic equations, a concise formula of the equivalent plate thickness is derived explicitly. The equivalent parameter in the formula is obtained with the assistance of simulation and numerical fitting, which directly measures the strengthening effect of the stiffeners on the plate. Employing the equivalent-isotropic-plate model, the overall dynamic response of a stiffened circular plate can be represented by that of an equivalent isotropic plate with acceptable accuracy, especially for low-order vibrations and center deflections. It is verified that the equivalent method can be successfully applied to a variety of stiffening types, materials, and load forms. The deviation of the maximum deflection response of the equivalent flat plate from that of the original stiffened circular plate does not exceed 6%, and the deviation of the response frequency does not exceed 10%. This completely meets the engineering requirements. The equivalent-isotropic-plate model verifies the feasibility of isotropic equivalence, and reveals the intrinsic connection between the radial stiffened circular plate and the homogeneous circular plate, which is of great significance in engineering applications such as response prediction and structural optimization.
2024, 44(3): 031403.
doi: 10.11883/bzycj-2023-0317
Abstract:
To adjust the fragment lethality field of the anti-ground ammunition, the paper studies the power characteristics of a drum-shaped warhead under static and dynamic detonation. Aiming at the ground armored vehicles, the damage efficiency of the drum-shaped warhead under different initiation modes is analyzed. The fragment power characteristics of a drum-shaped warhead under static detonation and the damage area to vehicle target under dynamic detonation are studied by numerical simulation under two initiation modes of end face center single point and center single point compared with cylindrical warhead of the same caliber. On this basis, further by adjusting the drum-shaped warhead initiation mode into three kinds of eccentric two-line synchronous initiation, eccentric two-line sequential initiation and eccentric two-line synchronous-sequential initiation. The fragment velocity and dispersion angle of the drum-shaped warhead during static detonation, the damage area to the vehicle target and the distribution of the effective fragment landing kinetic energy during dynamic detonation are calculated under different eccentric initiation. The effect of adjusting the detonating mode on the destruction power field of the fragment of the drum-shaped warhead is analyzed by comparing the power characteristics of the fragment of the drum-shaped warhead during the static detonation and the damage results of the vehicle target during dynamic detonation with the corresponding results under the end face center single-point initiation of the drum-shaped warhead. The results show that compared with the cylindrical warhead structure with the same caliber, the fragment dispersion angle of the drum-shaped warhead is increased by 55.98%, and the damaged area of the ground military vehicles is increased by the maximum 59.3%. Compared with the eccentric two-line synchronous initiation, the drum-shaped warhead with eccentric two lines synchronous-sequential initiation can increase the fragment dispersion angle by 18.0%, and increase the dispersion of fragments by 11.48%. Compared with the single-point initiation of charge center, the damage area of the drum-shaped warhead under eccentric two-line sequential initiation is less affected by the burst height, and the damage area reaches 47.15 m2 when the falling angle is 50°, the falling velocity is 200 m/s and the burst height is 9 m. By adjusting the structure and the initiation mode of the warhead, the dispersion angle of fragments can be effectively increased, the coverage area of fragments to the target can be increased, and the damage efficiency of the warhead can be improved.
To adjust the fragment lethality field of the anti-ground ammunition, the paper studies the power characteristics of a drum-shaped warhead under static and dynamic detonation. Aiming at the ground armored vehicles, the damage efficiency of the drum-shaped warhead under different initiation modes is analyzed. The fragment power characteristics of a drum-shaped warhead under static detonation and the damage area to vehicle target under dynamic detonation are studied by numerical simulation under two initiation modes of end face center single point and center single point compared with cylindrical warhead of the same caliber. On this basis, further by adjusting the drum-shaped warhead initiation mode into three kinds of eccentric two-line synchronous initiation, eccentric two-line sequential initiation and eccentric two-line synchronous-sequential initiation. The fragment velocity and dispersion angle of the drum-shaped warhead during static detonation, the damage area to the vehicle target and the distribution of the effective fragment landing kinetic energy during dynamic detonation are calculated under different eccentric initiation. The effect of adjusting the detonating mode on the destruction power field of the fragment of the drum-shaped warhead is analyzed by comparing the power characteristics of the fragment of the drum-shaped warhead during the static detonation and the damage results of the vehicle target during dynamic detonation with the corresponding results under the end face center single-point initiation of the drum-shaped warhead. The results show that compared with the cylindrical warhead structure with the same caliber, the fragment dispersion angle of the drum-shaped warhead is increased by 55.98%, and the damaged area of the ground military vehicles is increased by the maximum 59.3%. Compared with the eccentric two-line synchronous initiation, the drum-shaped warhead with eccentric two lines synchronous-sequential initiation can increase the fragment dispersion angle by 18.0%, and increase the dispersion of fragments by 11.48%. Compared with the single-point initiation of charge center, the damage area of the drum-shaped warhead under eccentric two-line sequential initiation is less affected by the burst height, and the damage area reaches 47.15 m2 when the falling angle is 50°, the falling velocity is 200 m/s and the burst height is 9 m. By adjusting the structure and the initiation mode of the warhead, the dispersion angle of fragments can be effectively increased, the coverage area of fragments to the target can be increased, and the damage efficiency of the warhead can be improved.
2024, 44(3): 031404.
doi: 10.11883/bzycj-2023-0316
Abstract:
When assessing the damage effectiveness of blast-fragmentation ammunitions against ground targets, the traditional approach involves calculating the overall target damage probability based on component damage criteria. Typically, the shooting line tracing method is used to determine the specific location on the target where fragments from the munition hit. However, this computation process is time-consuming. Therefore, to rapidly and accurately evaluate the ammunition damage effectiveness on the target, this study proposes a method called the multiple rectangular cookie cutter damage function. This method adopts the concept of the trapezoidal rule and performs equivalent processing on different regions corresponding to different damage probability intervals based on the gradient of damage probability changes within the actual damage area. This method can effectively retain the distribution pattern of damage probability values in the practical damage area, thus ensuring the accuracy of the computations. When describing ammunition delivery accuracy, a two-dimensional normal distribution is commonly employed to simulate the impact point locations of projectiles. Therefore, when calculating the mean of damage probability of the ammunition on the target, integration operations on the normal distribution function are necessary. However, due to the absence of an analytical solution for integrating the normal distribution function, polynomial equations are introduced as substitutes to enhance computational efficiency. The effects of ammunition drop angle and accuracy on the mean of damage probability of the target were investigated through example analysis, and the results were compared with those of methods based on the rectangular cookie cutter and Carlton damage function. The results show that within the ammunition drop angle range from 30° to 75°, and the circular error probable (CEP) precision range from 5 m to 50 m, compared with the rectangular cookie cutter damage function, the calculation method based on the multiple rectangular cookie cutter damage function improves the accuracy of damage effectiveness calculation by up to 26.4%. At the same time, the computational efficiency is improved by a factor of 518 compared with the Carlton damage function.
When assessing the damage effectiveness of blast-fragmentation ammunitions against ground targets, the traditional approach involves calculating the overall target damage probability based on component damage criteria. Typically, the shooting line tracing method is used to determine the specific location on the target where fragments from the munition hit. However, this computation process is time-consuming. Therefore, to rapidly and accurately evaluate the ammunition damage effectiveness on the target, this study proposes a method called the multiple rectangular cookie cutter damage function. This method adopts the concept of the trapezoidal rule and performs equivalent processing on different regions corresponding to different damage probability intervals based on the gradient of damage probability changes within the actual damage area. This method can effectively retain the distribution pattern of damage probability values in the practical damage area, thus ensuring the accuracy of the computations. When describing ammunition delivery accuracy, a two-dimensional normal distribution is commonly employed to simulate the impact point locations of projectiles. Therefore, when calculating the mean of damage probability of the ammunition on the target, integration operations on the normal distribution function are necessary. However, due to the absence of an analytical solution for integrating the normal distribution function, polynomial equations are introduced as substitutes to enhance computational efficiency. The effects of ammunition drop angle and accuracy on the mean of damage probability of the target were investigated through example analysis, and the results were compared with those of methods based on the rectangular cookie cutter and Carlton damage function. The results show that within the ammunition drop angle range from 30° to 75°, and the circular error probable (CEP) precision range from 5 m to 50 m, compared with the rectangular cookie cutter damage function, the calculation method based on the multiple rectangular cookie cutter damage function improves the accuracy of damage effectiveness calculation by up to 26.4%. At the same time, the computational efficiency is improved by a factor of 518 compared with the Carlton damage function.
2024, 44(3): 031405.
doi: 10.11883/bzycj-2023-0289
Abstract:
The explosion of missiles penetrating the interior cabin could cause extensive damage to the warship structure. How to evaluate the damage range of the ship structure under the coupling of multiple loads in the inner explosion is a big challenge for engineering researchers. In order to establish a theory method of ship structural damage caused by cabin inner implosion, a large-scale cabin model was designed in this paper, and an inner explosion experiment was carried out on the cabin model. The damage range of the cabin structure was measured and typical failure models were acquired. The damage mechanism of the ship structure under the coupling effect of multiple loads (including extensive shock wave loading and quasi-static pressure loading) under inner implosion was analyzed. Based on experimental results, the theory method of ship structure damage range under inner blast was established. It was indicated that: (1) the cabin model would be subjected to shock wave and quasi-static pressure loadings after the explosive charge was detonated, which led to large area damage and complex failure models; (2) quasi-static pressure was the major destroying element for cabin model damage under inner blast; (3) the theory analysis method proposed by this paper simultaneously considered the coupling effect of shock wave and quasi-static pressure loadings for the damage of the cabin model, the theory results well coincided with the experimental ones. The established calculation method can be applied to evaluate the damage range of ship structure subjected to implosion loading.
The explosion of missiles penetrating the interior cabin could cause extensive damage to the warship structure. How to evaluate the damage range of the ship structure under the coupling of multiple loads in the inner explosion is a big challenge for engineering researchers. In order to establish a theory method of ship structural damage caused by cabin inner implosion, a large-scale cabin model was designed in this paper, and an inner explosion experiment was carried out on the cabin model. The damage range of the cabin structure was measured and typical failure models were acquired. The damage mechanism of the ship structure under the coupling effect of multiple loads (including extensive shock wave loading and quasi-static pressure loading) under inner implosion was analyzed. Based on experimental results, the theory method of ship structure damage range under inner blast was established. It was indicated that: (1) the cabin model would be subjected to shock wave and quasi-static pressure loadings after the explosive charge was detonated, which led to large area damage and complex failure models; (2) quasi-static pressure was the major destroying element for cabin model damage under inner blast; (3) the theory analysis method proposed by this paper simultaneously considered the coupling effect of shock wave and quasi-static pressure loadings for the damage of the cabin model, the theory results well coincided with the experimental ones. The established calculation method can be applied to evaluate the damage range of ship structure subjected to implosion loading.
2024, 44(3): 031406.
doi: 10.11883/bzycj-2023-0287
Abstract:
Data quality is the basis for the validity and accuracy of data-driven models, and there may be a large number of anomalies in the raw concrete targets penetration depth data. Therefore, to ensure the accuracy of the subsequent data-driven model, it is necessary to eliminate the outlier of the raw data. Compared with the traditional anomaly detection method, the anomaly detection method based on neural network models is more suitable for complex multi-dimensional and unevenly distributed concrete target penetration depth data. However, relying only on the neural network model to fit the raw experimental data ignores the abundant and effective expert prior knowledge, which will reduce the accuracy of the model, and even lead to wrong prediction results due to the limited amount of data of the training sample, data bad pixels, poor data distribution, etc. To this end, an algorithm for outlier detection of concrete target penetration depth data combined with prior knowledge was proposed. Firstly, the back propagation (BP) neural network model is used to fit the distribution of the experiment samples, then the outlier is screened out based on the deviation index, and at last, the anomaly detection performance of the model is evaluated by the empirical algorithm. Based on the characteristics of the experimental data, the batch gradient descent combined with the momentum optimization method is selected to improve the stability and efficiency during training. Furthermore, by adding domain prior knowledge with the BP neural network model to constrain the fitting of the sample data, the model can reflect the influence of additional features during training. The research results show that the BP neural network model is suitable for the outlier detection of the rigid projectile penetrating concrete experiment data. The fusion of reasonable prior knowledge can improve the detection accuracy and the convergence speed of the model, furthermore, integrating different prior knowledge will cause different results.
Data quality is the basis for the validity and accuracy of data-driven models, and there may be a large number of anomalies in the raw concrete targets penetration depth data. Therefore, to ensure the accuracy of the subsequent data-driven model, it is necessary to eliminate the outlier of the raw data. Compared with the traditional anomaly detection method, the anomaly detection method based on neural network models is more suitable for complex multi-dimensional and unevenly distributed concrete target penetration depth data. However, relying only on the neural network model to fit the raw experimental data ignores the abundant and effective expert prior knowledge, which will reduce the accuracy of the model, and even lead to wrong prediction results due to the limited amount of data of the training sample, data bad pixels, poor data distribution, etc. To this end, an algorithm for outlier detection of concrete target penetration depth data combined with prior knowledge was proposed. Firstly, the back propagation (BP) neural network model is used to fit the distribution of the experiment samples, then the outlier is screened out based on the deviation index, and at last, the anomaly detection performance of the model is evaluated by the empirical algorithm. Based on the characteristics of the experimental data, the batch gradient descent combined with the momentum optimization method is selected to improve the stability and efficiency during training. Furthermore, by adding domain prior knowledge with the BP neural network model to constrain the fitting of the sample data, the model can reflect the influence of additional features during training. The research results show that the BP neural network model is suitable for the outlier detection of the rigid projectile penetrating concrete experiment data. The fusion of reasonable prior knowledge can improve the detection accuracy and the convergence speed of the model, furthermore, integrating different prior knowledge will cause different results.
2024, 44(3): 031407.
doi: 10.11883/bzycj-2023-0331
Abstract:
To address challenges in the field of large-scale explosive building damage assessment, where the explosion process is too complex for high-precision numerical simulation, and relying solely on change detection from remote sensing imagery cannot capture detailed internal information and lacks the capability of predicting in advance, this paper establishes a building damage assessment model for large-scale explosive events by coupling empirical mechanics models with remote sensing image interpretation and big data analysis. The study initially constructs a damage dataset based on specific historical cases of large-scale explosions. This involves extracting building damage information (including building types and damage levels) from remote sensing imagery and supplementing damage details with additional big data sources such as collected online images, videos, and news reports to enhance the precision of the sampled data. Geographic information systems spatial analysis is employed to digitize the damage information, obtaining data on building types, damage levels, and the distance from the target building to the explosion center, forming the damage dataset. Subsequently, the empirical model parameters are refined based on the training samples from the damage dataset, creating damage assessment models applicable to different building types for large-scale explosive events. The performance of the model is then tested using validation samples from the damage dataset. Experimental results demonstrate a model fitting goodness of over 96%, accuracy on validation samples exceeding 84%, and an overall error within an acceptable range. The model, under certain accuracy requirements, can provide guidance for site selection of storage locations for chemicals and hazardous materials, emergency evacuation of people in the event of a risk of large-scale explosions, critical equipment evacuation during an emergency, resource dispatching for rescue and relief after an accident, and building damage assessment.
To address challenges in the field of large-scale explosive building damage assessment, where the explosion process is too complex for high-precision numerical simulation, and relying solely on change detection from remote sensing imagery cannot capture detailed internal information and lacks the capability of predicting in advance, this paper establishes a building damage assessment model for large-scale explosive events by coupling empirical mechanics models with remote sensing image interpretation and big data analysis. The study initially constructs a damage dataset based on specific historical cases of large-scale explosions. This involves extracting building damage information (including building types and damage levels) from remote sensing imagery and supplementing damage details with additional big data sources such as collected online images, videos, and news reports to enhance the precision of the sampled data. Geographic information systems spatial analysis is employed to digitize the damage information, obtaining data on building types, damage levels, and the distance from the target building to the explosion center, forming the damage dataset. Subsequently, the empirical model parameters are refined based on the training samples from the damage dataset, creating damage assessment models applicable to different building types for large-scale explosive events. The performance of the model is then tested using validation samples from the damage dataset. Experimental results demonstrate a model fitting goodness of over 96%, accuracy on validation samples exceeding 84%, and an overall error within an acceptable range. The model, under certain accuracy requirements, can provide guidance for site selection of storage locations for chemicals and hazardous materials, emergency evacuation of people in the event of a risk of large-scale explosions, critical equipment evacuation during an emergency, resource dispatching for rescue and relief after an accident, and building damage assessment.
2024, 44(3): 032101.
doi: 10.11883/bzycj-2023-0123
Abstract:
There are frequent gas explosion accidents in urban rain and sewage drainage pipes, which pose a serious threat to people’s lives and property safety. To study the propagation characteristics of gas explosion and the law of gas-liquid two-phase coupling in urban underground drainage pipes, based on the gas-liquid two-phase flow theory and computational fluid dynamics method, a numerical simulation study of the explosion-acceleration-decay process of gas/air mixture under different water depth ratio was conducted. The results show that when the water depth ratio is less than 0.7, as the water depth ratio increases, the long-diameter ratio of the gas phase space increases, the fuel combustion intensifies, and the flame acceleration phenomenon gradually becomes significant, which leads to a gradual increase in peak overpressure, a gradual reduction in peak overpressure time, and a more significant effect of peak overpressure along the axial direction. When the water depth ratio reaches 0.7, the propagation of the flame in the pipeline is blocked, and the fluctuation caused by the water shock and the fine water column quickly occupy a small gas phase space, blocking the continuous propagation of the flame, which makes the explosion overpressure appear only near the ignition source. Under different water depth ratios, in the same zone of the pipeline and at the same moment, the height of the water being rolled up and the velocity field of the gas phase region is different, and the cryogenic liquid is rolled up to cool and block the high-temperature flame in the adjacent zone. Then, due to the macroscopic flow of the gas, the cryogenic gas adjacent to the liquid surface flows to the high-temperature region in the pipeline, resulting in a decrease in the flame temperature in the pipeline. The shock of water and the flying of fine water columns greatly reduce the risk of explosion overpressure. The research results provide a scientific basis for the explosion protection of urban gas lifelines.
There are frequent gas explosion accidents in urban rain and sewage drainage pipes, which pose a serious threat to people’s lives and property safety. To study the propagation characteristics of gas explosion and the law of gas-liquid two-phase coupling in urban underground drainage pipes, based on the gas-liquid two-phase flow theory and computational fluid dynamics method, a numerical simulation study of the explosion-acceleration-decay process of gas/air mixture under different water depth ratio was conducted. The results show that when the water depth ratio is less than 0.7, as the water depth ratio increases, the long-diameter ratio of the gas phase space increases, the fuel combustion intensifies, and the flame acceleration phenomenon gradually becomes significant, which leads to a gradual increase in peak overpressure, a gradual reduction in peak overpressure time, and a more significant effect of peak overpressure along the axial direction. When the water depth ratio reaches 0.7, the propagation of the flame in the pipeline is blocked, and the fluctuation caused by the water shock and the fine water column quickly occupy a small gas phase space, blocking the continuous propagation of the flame, which makes the explosion overpressure appear only near the ignition source. Under different water depth ratios, in the same zone of the pipeline and at the same moment, the height of the water being rolled up and the velocity field of the gas phase region is different, and the cryogenic liquid is rolled up to cool and block the high-temperature flame in the adjacent zone. Then, due to the macroscopic flow of the gas, the cryogenic gas adjacent to the liquid surface flows to the high-temperature region in the pipeline, resulting in a decrease in the flame temperature in the pipeline. The shock of water and the flying of fine water columns greatly reduce the risk of explosion overpressure. The research results provide a scientific basis for the explosion protection of urban gas lifelines.
2024, 44(3): 032201.
doi: 10.11883/bzycj-2023-0230
Abstract:
To effectively characterize the propagation characteristics of the explosion shock waves in tunnels at different altitudes, nonlinear explicit dynamics finite element software AUTODYN and dimensional analysis were used to study the influence of altitude on the propagation of explosion shock waves in long straight tunnels, and the influence characteristics of high altitude environments on the propagation of shock waves in tunnels were explored. First of all, the accuracy of the computational method was verified by comparing the peak overpressure and the time of overpressure rise of the small-scale shock tube test and the numerical simulation at the same measurement point. Then based on the AUTODYN-2D Euler symmetric algorithm and standard atmospheric parameters, the shock wave parameters of TNT explosion with 10 kg TNT spherical charge explosion in a tunnel with a diameter of 2.5 m and a length of 40 m at altitudes from 0 to 4000 m were computed, which were arranged with gauges with an axial interval of 2 m and a radial interval of 0.25 m, such as plane wave formation distance, peak overpressure, shock wave front propagation velocity, impulse, etc. In the end, a polynomial theoretic calculation model for shock wave peak overpressure in a tunnel at different altitudes was proposed with coefficients least-squares fitted from numerical simulation data at sea level, and the variables were obtained by dimensional analysis and the extended Sachs scaling law. The results show that, with the increase of altitude, the deviations between the propagation velocity of the explosion shock wave front and the radial parameters of the shock wave in the tunnel increases, the formation distance of the plane wave increases, and the peak overpressure of the shock wave decreases. Within the altitude range of 0 to 4000 m, the average value of shock wave impulse decreases by about 0.91% for every 1000 m increase. By combining the extended Sachs scaling law with dimensional analysis, a theoretical analysis model for calculating peak overpressure of shock waves at different altitudes with no more than 10% deviation is derived, which can provide a theoretical basis for explosion shock wave propagation in tunnels at high altitudes.
To effectively characterize the propagation characteristics of the explosion shock waves in tunnels at different altitudes, nonlinear explicit dynamics finite element software AUTODYN and dimensional analysis were used to study the influence of altitude on the propagation of explosion shock waves in long straight tunnels, and the influence characteristics of high altitude environments on the propagation of shock waves in tunnels were explored. First of all, the accuracy of the computational method was verified by comparing the peak overpressure and the time of overpressure rise of the small-scale shock tube test and the numerical simulation at the same measurement point. Then based on the AUTODYN-2D Euler symmetric algorithm and standard atmospheric parameters, the shock wave parameters of TNT explosion with 10 kg TNT spherical charge explosion in a tunnel with a diameter of 2.5 m and a length of 40 m at altitudes from 0 to 4000 m were computed, which were arranged with gauges with an axial interval of 2 m and a radial interval of 0.25 m, such as plane wave formation distance, peak overpressure, shock wave front propagation velocity, impulse, etc. In the end, a polynomial theoretic calculation model for shock wave peak overpressure in a tunnel at different altitudes was proposed with coefficients least-squares fitted from numerical simulation data at sea level, and the variables were obtained by dimensional analysis and the extended Sachs scaling law. The results show that, with the increase of altitude, the deviations between the propagation velocity of the explosion shock wave front and the radial parameters of the shock wave in the tunnel increases, the formation distance of the plane wave increases, and the peak overpressure of the shock wave decreases. Within the altitude range of 0 to 4000 m, the average value of shock wave impulse decreases by about 0.91% for every 1000 m increase. By combining the extended Sachs scaling law with dimensional analysis, a theoretical analysis model for calculating peak overpressure of shock waves at different altitudes with no more than 10% deviation is derived, which can provide a theoretical basis for explosion shock wave propagation in tunnels at high altitudes.
2024, 44(3): 032301.
doi: 10.11883/bzycj-2023-0011
Abstract:
Multiple damage effects can be generated when thermobaric explosives (TBX) detonated inside a tunnel, posing serious threats to people and equipment. Based on the explosion tests with different explosive masses, the explosion characteristics of the TBX detonated inside a tunnel are investigated. The thermal effects of fireball and the propagation law of the shock wave inside the tunnel are analyzed, the reduction degree of oxygen concentration is elucidated as well. Besides, the constraint effect of the tunnel on the afterburning of aluminum powders and the explosive mass conditions for the formation of afterburning effects at high intensity are discussed. It is shown that the radiation brightness of the fireball induced by the TBX is higher than TNT, and the temperature peak of TBX fireball is 1.3 times higher than that of TNT. During the process of fireball evolution, the temperature peak of the TBX fireball in the afterburning stage can increase by more than 10% compared to the temperature peak at the moment when the fireball is just stable. Regarding the propagation law of shock waves, the TNT equivalent coefficients of the overpressure peak and positive pressure time are approximately 1.4 and 1.65, respectively. In addition, the compressive waves generated by the afterburning of aluminum powders can provide various supplementary effects on the propagation of shock wave. The compressive wave with quickly rising process can be benefit for the increase in the pressure peak of the shock wave. In terms of the compressive wave with long duration and slow rising process, it can limit the attenuation of the shock wave and can extend the overall positive pressure time. Due to the constraint effect of the tunnel, the TBX fireball could interact with tunnel walls. As a consequence, the combustion intensity of aluminum powders will be enhanced. When the ratio between the cubic root of the TBX mass and the equivalent tunnel diameter is greater than 0.28 kg1/3/m, the afterburning effect at high intensity will emerge.
Multiple damage effects can be generated when thermobaric explosives (TBX) detonated inside a tunnel, posing serious threats to people and equipment. Based on the explosion tests with different explosive masses, the explosion characteristics of the TBX detonated inside a tunnel are investigated. The thermal effects of fireball and the propagation law of the shock wave inside the tunnel are analyzed, the reduction degree of oxygen concentration is elucidated as well. Besides, the constraint effect of the tunnel on the afterburning of aluminum powders and the explosive mass conditions for the formation of afterburning effects at high intensity are discussed. It is shown that the radiation brightness of the fireball induced by the TBX is higher than TNT, and the temperature peak of TBX fireball is 1.3 times higher than that of TNT. During the process of fireball evolution, the temperature peak of the TBX fireball in the afterburning stage can increase by more than 10% compared to the temperature peak at the moment when the fireball is just stable. Regarding the propagation law of shock waves, the TNT equivalent coefficients of the overpressure peak and positive pressure time are approximately 1.4 and 1.65, respectively. In addition, the compressive waves generated by the afterburning of aluminum powders can provide various supplementary effects on the propagation of shock wave. The compressive wave with quickly rising process can be benefit for the increase in the pressure peak of the shock wave. In terms of the compressive wave with long duration and slow rising process, it can limit the attenuation of the shock wave and can extend the overall positive pressure time. Due to the constraint effect of the tunnel, the TBX fireball could interact with tunnel walls. As a consequence, the combustion intensity of aluminum powders will be enhanced. When the ratio between the cubic root of the TBX mass and the equivalent tunnel diameter is greater than 0.28 kg1/3/m, the afterburning effect at high intensity will emerge.
2024, 44(3): 032901.
doi: 10.11883/bzycj-2023-0222
Abstract:
The issue of charge launch safety under the environment of high rifling pressure, high overload and high initial velocity has been one of the research hot topics. To investigate the impact mechanism of bottom gap on charge launch safety, a thermo-mechanical-solid coupling combustion model of the charge affected by bottom gap under impact loads based on the material point method is established. In this procedure, the formula for calculating temperature of air in the bottom gap during adiabatic compression is deduced, the relationship between the compression amount and the air temperature is quantitatively analyzed, the criteria and equation of state of the multi-material hybrid is constructed, and the calculation method of the temperature at the charge bottom affected by bottom gap in the launch process is established. The launch process of PBX charge with different bottom gap thicknesses is simulated by using the model, and the bottom temperature variation of PBX charge under different conditions are consistent with the experimental results, which verifies the correctness of the model. This model is then used to simulate the launch process of Composition B (COM B) charge with different bottom gap thickness in the launch environment, and the bottom temperature variation of charge is analyzed. The simulation results show that the charge temperature decreases gradually from the bottom to the top in the launch process and the area most likely to experience an ignition reaction is located at the charge bottom. The bottom temperature of COM B charge increases with the increase of the bottom gap thickness. The thickness of the bottom gap shall not be greater than 0.062 cm when the charge is in the launch safety state under the action of loading peak value of 324.7 MPa, which means that the presence of bottom gap seriously affects charge launch safety. From the simulation results, it is clear that the air in the bottom gap can be compressed in the launch process, and its temperature can rise rapidly; while in turn, it transfers heat to the charge bottom adjacent to the air, causing the temperature of the charge bottom to rise and making the charge bottom more susceptible to ignition reactions. The combustion model provides a theoretical basis for studying the charge launch safety.
The issue of charge launch safety under the environment of high rifling pressure, high overload and high initial velocity has been one of the research hot topics. To investigate the impact mechanism of bottom gap on charge launch safety, a thermo-mechanical-solid coupling combustion model of the charge affected by bottom gap under impact loads based on the material point method is established. In this procedure, the formula for calculating temperature of air in the bottom gap during adiabatic compression is deduced, the relationship between the compression amount and the air temperature is quantitatively analyzed, the criteria and equation of state of the multi-material hybrid is constructed, and the calculation method of the temperature at the charge bottom affected by bottom gap in the launch process is established. The launch process of PBX charge with different bottom gap thicknesses is simulated by using the model, and the bottom temperature variation of PBX charge under different conditions are consistent with the experimental results, which verifies the correctness of the model. This model is then used to simulate the launch process of Composition B (COM B) charge with different bottom gap thickness in the launch environment, and the bottom temperature variation of charge is analyzed. The simulation results show that the charge temperature decreases gradually from the bottom to the top in the launch process and the area most likely to experience an ignition reaction is located at the charge bottom. The bottom temperature of COM B charge increases with the increase of the bottom gap thickness. The thickness of the bottom gap shall not be greater than 0.062 cm when the charge is in the launch safety state under the action of loading peak value of 324.7 MPa, which means that the presence of bottom gap seriously affects charge launch safety. From the simulation results, it is clear that the air in the bottom gap can be compressed in the launch process, and its temperature can rise rapidly; while in turn, it transfers heat to the charge bottom adjacent to the air, causing the temperature of the charge bottom to rise and making the charge bottom more susceptible to ignition reactions. The combustion model provides a theoretical basis for studying the charge launch safety.
2024, 44(3): 033101.
doi: 10.11883/bzycj-2023-0124
Abstract:
Lattice sandwich structures often exhibit discontinuous characteristics under impact, with damage behaviors involving multiple scales, from micro-scale cell fracture to macro-scale structural collapse. Traditional methods based on continuum mechanics have difficulty in accurately describing non-continuum problems such as material interfaces and fracture behavior, so usually they can only handle single-scale problems. Besides, lattice materials have complex geometric shapes, and mesh-dependent numerical methods such as finite element analysis may suffer mesh sensitivity and may even struggle to obtain an ideal mesh. In order to effectively simulate the damage behavior of 3D printed lattice sandwich structures under projectile impact, a lattice sandwich structure modeling method based on the theory of peridynamics and micro-polar model, and by considering plastic bonds, is proposed. The simulation results of uniaxial compression and large-mass low-speed impact tests are compared with experimental results to verify the accuracy of the peridynamics model for lattice sandwich structures. This model is then used to analyze the damage patterns and failure mechanisms of lattice sandwich panels under projectile impact from low to high velocities. The results show that under low-speed impact, the failure mode of 3D printed lattice sandwich structures is mainly localized plastic deformation, which causes small-scale fractures in the lattice structure near the impact location after arriving at a certain level of strain; while under high-speed impact, it usually exhibits collapse, hole piercing, and fragment ejection, accompanied by extensive plastic deformation. The plastic yield range of 3D printed lattice sandwich structures shows different patterns under high-speed and low-speed impacts, with the plastic deformation range increasing as the impact velocity increases under low-speed impact, and decreasing under high-speed impact. This is mainly influenced by the characteristics of the lattice structure and the material crack propagation during the impact process. Under high-speed impact, the process of projectile penetration will go through four stages; i.e., panel contact, local yield, core material compression, and penetration. Because the material characteristics at each stage are different, the projectile will experience a “sharp-slow-sharp” deceleration process featured by to two acceleration peaks, with the second peak value being 50% lower than the first. Compared with high-speed impact, the projectile under low-speed impact only experiences one deceleration process, and the peak acceleration increases with increasing impact velocity. When the plastic deformation and damage process of the lattice sandwich structure cannot fully dissipate the kinetic energy of the projectile, the release of elastic strain energy in the sandwich structure will cause the projectile to bounce back. The rebound speed in this study is less than 30% of the initial velocity. The research results can provide theoretical support and new analytical methods for the design and application of lattice materials.
Lattice sandwich structures often exhibit discontinuous characteristics under impact, with damage behaviors involving multiple scales, from micro-scale cell fracture to macro-scale structural collapse. Traditional methods based on continuum mechanics have difficulty in accurately describing non-continuum problems such as material interfaces and fracture behavior, so usually they can only handle single-scale problems. Besides, lattice materials have complex geometric shapes, and mesh-dependent numerical methods such as finite element analysis may suffer mesh sensitivity and may even struggle to obtain an ideal mesh. In order to effectively simulate the damage behavior of 3D printed lattice sandwich structures under projectile impact, a lattice sandwich structure modeling method based on the theory of peridynamics and micro-polar model, and by considering plastic bonds, is proposed. The simulation results of uniaxial compression and large-mass low-speed impact tests are compared with experimental results to verify the accuracy of the peridynamics model for lattice sandwich structures. This model is then used to analyze the damage patterns and failure mechanisms of lattice sandwich panels under projectile impact from low to high velocities. The results show that under low-speed impact, the failure mode of 3D printed lattice sandwich structures is mainly localized plastic deformation, which causes small-scale fractures in the lattice structure near the impact location after arriving at a certain level of strain; while under high-speed impact, it usually exhibits collapse, hole piercing, and fragment ejection, accompanied by extensive plastic deformation. The plastic yield range of 3D printed lattice sandwich structures shows different patterns under high-speed and low-speed impacts, with the plastic deformation range increasing as the impact velocity increases under low-speed impact, and decreasing under high-speed impact. This is mainly influenced by the characteristics of the lattice structure and the material crack propagation during the impact process. Under high-speed impact, the process of projectile penetration will go through four stages; i.e., panel contact, local yield, core material compression, and penetration. Because the material characteristics at each stage are different, the projectile will experience a “sharp-slow-sharp” deceleration process featured by to two acceleration peaks, with the second peak value being 50% lower than the first. Compared with high-speed impact, the projectile under low-speed impact only experiences one deceleration process, and the peak acceleration increases with increasing impact velocity. When the plastic deformation and damage process of the lattice sandwich structure cannot fully dissipate the kinetic energy of the projectile, the release of elastic strain energy in the sandwich structure will cause the projectile to bounce back. The rebound speed in this study is less than 30% of the initial velocity. The research results can provide theoretical support and new analytical methods for the design and application of lattice materials.
2024, 44(3): 034101.
doi: 10.11883/bzycj-2023-0089
Abstract:
The Asay foil has been a widely applied diagnostic in ejecta measurement since its design was first reported in 1976. An Asay foil is a foil of a known mass (or areal density), whose velocity changed when it is impacted by ejecta. The Foil velocity is measured using velocimetry and the ejecta velocity is inferred from the initial gap between foil and free surface and the ejecta fly time. The mass of the impacting ejecta can then be inferred from the change in momentum of the foil. In some cases, the ejecta spray out from complex loading conditions such as double shock loading condition, the initial gap and fly time are unable to measure accurately, thus the Asay foil method doesn’t work. Therefore, it is necessary to develop an Asay foil method that does not depend on the initial gap and fly time. An improved Asay foil method is then developed based on the traditional Asay foil method. This method uses photonic Doppler velocimetry (PDV) to obtain the ejecta velocity in the testing area of the Asay foil probe, and the Asay foil probe obtains the foil velocity curve after the ejecta collides with the foil. Based on spatial position constraints and precise temporal correlation, the combination of the two velocity curve results can provide the total amount and distribution of ejecta under complex loading conditions. A numerical experimental method was used to generate ejecta particle groups with different distribution states, as well as the PDV velocity curve and Asay foil velocity curve to analyze the applicability of the method. In addition, the numerical experimental analysis results were verified using light gas gun experiments. The numerical experimental analysis results show that this method has good applicability in three typical ejecta distribution cases, with a deviation of less than 20% between the measured value and the theoretical value. The results of the light gas gun tests indicate that the deviation between the improved method and the traditional Asay foil method is less than 20%.
The Asay foil has been a widely applied diagnostic in ejecta measurement since its design was first reported in 1976. An Asay foil is a foil of a known mass (or areal density), whose velocity changed when it is impacted by ejecta. The Foil velocity is measured using velocimetry and the ejecta velocity is inferred from the initial gap between foil and free surface and the ejecta fly time. The mass of the impacting ejecta can then be inferred from the change in momentum of the foil. In some cases, the ejecta spray out from complex loading conditions such as double shock loading condition, the initial gap and fly time are unable to measure accurately, thus the Asay foil method doesn’t work. Therefore, it is necessary to develop an Asay foil method that does not depend on the initial gap and fly time. An improved Asay foil method is then developed based on the traditional Asay foil method. This method uses photonic Doppler velocimetry (PDV) to obtain the ejecta velocity in the testing area of the Asay foil probe, and the Asay foil probe obtains the foil velocity curve after the ejecta collides with the foil. Based on spatial position constraints and precise temporal correlation, the combination of the two velocity curve results can provide the total amount and distribution of ejecta under complex loading conditions. A numerical experimental method was used to generate ejecta particle groups with different distribution states, as well as the PDV velocity curve and Asay foil velocity curve to analyze the applicability of the method. In addition, the numerical experimental analysis results were verified using light gas gun experiments. The numerical experimental analysis results show that this method has good applicability in three typical ejecta distribution cases, with a deviation of less than 20% between the measured value and the theoretical value. The results of the light gas gun tests indicate that the deviation between the improved method and the traditional Asay foil method is less than 20%.
2024, 44(3): 035201.
doi: 10.11883/bzycj-2023-0206
Abstract:
Due to the deficiency that dynamic processes of rock blasting and rock failure zones around a blasthole are not simultaneously considered, the explosion load history of rock blasting considering rock failure zones and its reliability were investigated. Combining theoretical solutions of the dynamic processes of rock blasting and the rock failure zones around a blasthole, a theoretical formula of the explosive load history considering rock failure zones was derived, and a comparison was made between the derived explosive load history and a measured explosion pressure curve inside a blasthole. Both the field test on an ideal site and the numerical simulation including three explosion load conditions of single hole blasting were carried out, and the field and numerical results of blasting vibration were compared. The results show that the explosive load history considering rock failure zones consists of an ascending stage and three attenuation stages Ⅰ, Ⅱ, and Ⅲ, among which the ascending stage lasts for an extremely short time, while the attenuation stages last for a long time and are controlled by the stemming conditions. The change tendency of the calculated explosive load history considering rock failure zones is consistent with that of the measured explosion pressure curve, indicating the reliability of the explosive load history considering rock failure zones. The numerical results of single hole blasting vibration waveforms under the theoretical explosive load condition are consistent with the filed results, and the deviation ratios between the calculated peak particle velocity (PPV) results under the theoretical explosive load condition and the field PPV results are the smallest, most of which are within 7%, indicting the explosive load history considering rock failure zones has strong reliability. The explosive load history considering rock failure zones can be adjusted as the rock blasting system changes, and it has wide adaptability and good application potentials. The research results may help provide a theoretical basis for realizing efficient and accurate calculation about rock blasting.
Due to the deficiency that dynamic processes of rock blasting and rock failure zones around a blasthole are not simultaneously considered, the explosion load history of rock blasting considering rock failure zones and its reliability were investigated. Combining theoretical solutions of the dynamic processes of rock blasting and the rock failure zones around a blasthole, a theoretical formula of the explosive load history considering rock failure zones was derived, and a comparison was made between the derived explosive load history and a measured explosion pressure curve inside a blasthole. Both the field test on an ideal site and the numerical simulation including three explosion load conditions of single hole blasting were carried out, and the field and numerical results of blasting vibration were compared. The results show that the explosive load history considering rock failure zones consists of an ascending stage and three attenuation stages Ⅰ, Ⅱ, and Ⅲ, among which the ascending stage lasts for an extremely short time, while the attenuation stages last for a long time and are controlled by the stemming conditions. The change tendency of the calculated explosive load history considering rock failure zones is consistent with that of the measured explosion pressure curve, indicating the reliability of the explosive load history considering rock failure zones. The numerical results of single hole blasting vibration waveforms under the theoretical explosive load condition are consistent with the filed results, and the deviation ratios between the calculated peak particle velocity (PPV) results under the theoretical explosive load condition and the field PPV results are the smallest, most of which are within 7%, indicting the explosive load history considering rock failure zones has strong reliability. The explosive load history considering rock failure zones can be adjusted as the rock blasting system changes, and it has wide adaptability and good application potentials. The research results may help provide a theoretical basis for realizing efficient and accurate calculation about rock blasting.
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Institude of Fluid Physics, CAEP
Editor-in-ChiefCangli Liu