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, Available online , doi: 10.11883/bzycj-2024-0248
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The penetration depth of the earth-penetrating projectile is a basic problem in the design of protection engineering. Scaled testing is an important method to study the penetration law. The size effect between the model test results and the prototype is a problem that must be solved to establish the calculation method of penetration using scaled tests. In this study, the stress and strain state evolution of the rock-like target medium subjected to the penetration of earth-penetrating projectiles and the penetration resistance function of the projectiles were derived using cavity expansion theory. The formula for the caliber coefficient characterizing the size effect was obtained, and a simplified analysis of the nose shape coefficient and caliber coefficient was conducted using curve fitting and Taylor expansion within the penetration velocity range of the conventional earth-penetrating weapons. A practical calculation formula for the penetration depth of conventional earth-penetrating weapons into rock-like media was proposed, whose coefficients can be directly determined by parameters of target and projectiles. The results show that the main influencing factor of the projectile’s penetration resistance is the impedance of the target. The source of the size effect is originated from the fact that the ranges of the target damage zones do not satisfy the geometric similarity law. The nose shape coefficient can be simplified into a linear function of the projectile’s aspect ratio, and the nose shape coefficient of a flat-nosed projectile is 0.57. The caliber coefficient of the projectile is determined by the ratio of the cavity radius of the penetration to the radius of the fracture zone and can be taken as 1.2−1.4 for conventional earth-penetrating weapons. The theoretical calculation formula of penetration depth is in good agreement with experimental results, and thus, has high reliability.
The penetration depth of the earth-penetrating projectile is a basic problem in the design of protection engineering. Scaled testing is an important method to study the penetration law. The size effect between the model test results and the prototype is a problem that must be solved to establish the calculation method of penetration using scaled tests. In this study, the stress and strain state evolution of the rock-like target medium subjected to the penetration of earth-penetrating projectiles and the penetration resistance function of the projectiles were derived using cavity expansion theory. The formula for the caliber coefficient characterizing the size effect was obtained, and a simplified analysis of the nose shape coefficient and caliber coefficient was conducted using curve fitting and Taylor expansion within the penetration velocity range of the conventional earth-penetrating weapons. A practical calculation formula for the penetration depth of conventional earth-penetrating weapons into rock-like media was proposed, whose coefficients can be directly determined by parameters of target and projectiles. The results show that the main influencing factor of the projectile’s penetration resistance is the impedance of the target. The source of the size effect is originated from the fact that the ranges of the target damage zones do not satisfy the geometric similarity law. The nose shape coefficient can be simplified into a linear function of the projectile’s aspect ratio, and the nose shape coefficient of a flat-nosed projectile is 0.57. The caliber coefficient of the projectile is determined by the ratio of the cavity radius of the penetration to the radius of the fracture zone and can be taken as 1.2−1.4 for conventional earth-penetrating weapons. The theoretical calculation formula of penetration depth is in good agreement with experimental results, and thus, has high reliability.
, Available online , doi: 10.11883/bzycj-2024-0203
Abstract:
The equation of state for the detonation products of explosives is one of the foundations in explosion physics. JWL equation of state has been widely applied to study the properties of various explosives. In order to obtain the equation of state of the detonation products, an underwater explosion method was used to study JWL equation of state for the detonation of RDX. It considered the explosion bubble expansion process based on the conservation of energy including Es0 (initial shock wave energy), Ept (potential energy of water), Ec (kinetic energy of water) and Er (energy loss by bubble expansion), which are related to the underwater explosion bubble radius (R-t) and shock wave front (Rs-t) measured in the underwater explosion experiments as functions of time. Based on the experimental results and using the same method to process the experimental data in cylinder experiment, the time functions of explosion bubble expansion radius and variation of shock wave front position were fitted and the parameters of the JWL equation of state for RDX detonation products were obtained. In order to analyze the accuracy of the parameters of the JWL equation of state obtained by the underwater explosion method, the time history of the underwater explosions bubble pulsating pressure wave was calculated using the bubble dynamics equation. It shows that the calculation results agree well with the bubble expansion radius and bubble pulsation period determined using the underwater explosion experiments in a pool. The calculated bubble radius obtained by the proposed measurement method has a smaller deviation from that obtained by the cylinder experimental value, especially in the low-pressure stage compare with the JWL state parameters obtained from cylinder method. This method provides a testing approach for the equation of state of detonation products with low cost, reduced size limitations and a wide pressure range.
The equation of state for the detonation products of explosives is one of the foundations in explosion physics. JWL equation of state has been widely applied to study the properties of various explosives. In order to obtain the equation of state of the detonation products, an underwater explosion method was used to study JWL equation of state for the detonation of RDX. It considered the explosion bubble expansion process based on the conservation of energy including Es0 (initial shock wave energy), Ept (potential energy of water), Ec (kinetic energy of water) and Er (energy loss by bubble expansion), which are related to the underwater explosion bubble radius (R-t) and shock wave front (Rs-t) measured in the underwater explosion experiments as functions of time. Based on the experimental results and using the same method to process the experimental data in cylinder experiment, the time functions of explosion bubble expansion radius and variation of shock wave front position were fitted and the parameters of the JWL equation of state for RDX detonation products were obtained. In order to analyze the accuracy of the parameters of the JWL equation of state obtained by the underwater explosion method, the time history of the underwater explosions bubble pulsating pressure wave was calculated using the bubble dynamics equation. It shows that the calculation results agree well with the bubble expansion radius and bubble pulsation period determined using the underwater explosion experiments in a pool. The calculated bubble radius obtained by the proposed measurement method has a smaller deviation from that obtained by the cylinder experimental value, especially in the low-pressure stage compare with the JWL state parameters obtained from cylinder method. This method provides a testing approach for the equation of state of detonation products with low cost, reduced size limitations and a wide pressure range.
, Available online , doi: 10.11883/bzycj-2023-0463
Abstract:
The experimental and numerical investigation was carried out to clarify the influence of thickness and strength of foam concrete layer on blast resistance of the new composite protective structure. And the multilayer graded foam concrete was applied to adequately and rationally use the good wave dissipation performance of foam concrete. Then the advantage of new composite protective structure is verified by the comparison with the traditional layered structure with medium/coarse sand as the distribution layer. Finally, the design concept of composite protective structure based on controllability of blast load on structure layer is summarized. The foam concrete can be used as energy control layer of composite protective structure, which is mainly due to its long yield plateau and low wave impedance. The blast load acting on the structure layer can be exactly equal to the yield strength of foam concrete by choosing the appropriate thickness and strength (density) of foam concrete layer, as well as the use of the multilayer graded foam concrete. Based on the controllable design concept of blast load on structure layer in the new composite protective structure, the defects of traditional layered protective structure with medium/coarse sand as the distribution layer can be solved thoroughly, all of which can provide important reference for design of protective structure against new earth penetration weapons.
The experimental and numerical investigation was carried out to clarify the influence of thickness and strength of foam concrete layer on blast resistance of the new composite protective structure. And the multilayer graded foam concrete was applied to adequately and rationally use the good wave dissipation performance of foam concrete. Then the advantage of new composite protective structure is verified by the comparison with the traditional layered structure with medium/coarse sand as the distribution layer. Finally, the design concept of composite protective structure based on controllability of blast load on structure layer is summarized. The foam concrete can be used as energy control layer of composite protective structure, which is mainly due to its long yield plateau and low wave impedance. The blast load acting on the structure layer can be exactly equal to the yield strength of foam concrete by choosing the appropriate thickness and strength (density) of foam concrete layer, as well as the use of the multilayer graded foam concrete. Based on the controllable design concept of blast load on structure layer in the new composite protective structure, the defects of traditional layered protective structure with medium/coarse sand as the distribution layer can be solved thoroughly, all of which can provide important reference for design of protective structure against new earth penetration weapons.
, Available online , doi: 10.11883/bzycj-2024-0136
Abstract:
Aiming at the resistance evaluation and engineering design of the rock-rubble concrete shield under the combination of penetration and explosion of Earth Penetrating Weapons, firstly, a finite element modeling method for rock-rubble concrete shields was proposed. By conducting numerical simulations of quasi-static and penetration tests on ultra-high performance concrete targets containing different coarse aggregate types (corundum and basalt), particle sizes (5–15 mm, 5–20 mm, 35–45 mm, and 65–75 mm), and volume fractions (15% and 30%), the reliability of the finite element analysis approach was thoroughly verified. Then, using the semi-infinite rock-rubble concrete shield penetrated by the SDB as a case study, the quantitative influence of type (corundum, basalt, and granite) and dimensionless particle size of rock-rubble (ranging from 0.3 to 2.2 times the projectile diameter) on the penetration depth was analyzed, and optimal design recommendations were determined. Furthermore, the penetration analyses of three typical prototype warheads, i.e., SDB, WDU-43/B, and BLU-109/B, were carried out, and the corresponding penetration resistances of normal strength concrete (NSC), ultra-high performance concrete (UHPC), and corundum rubble concrete (CRC) shields against the above three warheads were quantitatively compared. Finally, the engineering design method for the CRC shield under the combined effects of penetration and explosion of prototype warheads was proposed. The results indicate that the CRC shield containing the particle size of 1.3 to 1.7 times the projectile diameter exhibits the most excellent penetration resistance. Under the penetration of three types of warheads, the penetration depths in CRC shield were 0.29, 0.78, and 0.68 m, respectively, which are reduced by 61.8%–69.1% and 43.3%–58.0% compared to those in NSC and UHPC shields. Under the combined effects of penetration and explosion, the perforation limits of the CRC shield are 0.55, 1.41, and 1.48 m, while the scabbing limits are 1.11, 2.26, and 3.17 m. Compared with NSC and UHPC shields, the perforation limits are reduced by 58.5%–61.2% and 43.2%–58.1%, respectively, and the scabbing limits are reduced by 61.8%–69.2% and 34.7%–40.5%, respectively.
Aiming at the resistance evaluation and engineering design of the rock-rubble concrete shield under the combination of penetration and explosion of Earth Penetrating Weapons, firstly, a finite element modeling method for rock-rubble concrete shields was proposed. By conducting numerical simulations of quasi-static and penetration tests on ultra-high performance concrete targets containing different coarse aggregate types (corundum and basalt), particle sizes (5–15 mm, 5–20 mm, 35–45 mm, and 65–75 mm), and volume fractions (15% and 30%), the reliability of the finite element analysis approach was thoroughly verified. Then, using the semi-infinite rock-rubble concrete shield penetrated by the SDB as a case study, the quantitative influence of type (corundum, basalt, and granite) and dimensionless particle size of rock-rubble (ranging from 0.3 to 2.2 times the projectile diameter) on the penetration depth was analyzed, and optimal design recommendations were determined. Furthermore, the penetration analyses of three typical prototype warheads, i.e., SDB, WDU-43/B, and BLU-109/B, were carried out, and the corresponding penetration resistances of normal strength concrete (NSC), ultra-high performance concrete (UHPC), and corundum rubble concrete (CRC) shields against the above three warheads were quantitatively compared. Finally, the engineering design method for the CRC shield under the combined effects of penetration and explosion of prototype warheads was proposed. The results indicate that the CRC shield containing the particle size of 1.3 to 1.7 times the projectile diameter exhibits the most excellent penetration resistance. Under the penetration of three types of warheads, the penetration depths in CRC shield were 0.29, 0.78, and 0.68 m, respectively, which are reduced by 61.8%–69.1% and 43.3%–58.0% compared to those in NSC and UHPC shields. Under the combined effects of penetration and explosion, the perforation limits of the CRC shield are 0.55, 1.41, and 1.48 m, while the scabbing limits are 1.11, 2.26, and 3.17 m. Compared with NSC and UHPC shields, the perforation limits are reduced by 58.5%–61.2% and 43.2%–58.1%, respectively, and the scabbing limits are reduced by 61.8%–69.2% and 34.7%–40.5%, respectively.
, Available online , doi: 10.11883/bzycj-2024-0096
Abstract:
An experimental investigation of typical projectiles penetrating multi-layer spaced Q355B steel targets was conducted to study the trajectory characteristics of elliptical cross-section projectiles penetrating multi-layer spaced steel targets. Numerical simulations were performed on LS-DYNA finite element software and typical results obtained were validated by experimental results. The attitude and trajectory parameters in the penetration process and the deflection mechanism of the projectile were obtained. The influence of cross-section shape, the minor-to-major axis length ratio of the projectile cross-section, initial velocity, rotation angle, and incident angle on the penetration trajectories and attitude deflection was investigated. The research results show that the penetration trajectory stability of the circular cross-section projectile is better than the elliptical and asymmetric elliptical cross-section projectiles when the rotation angle is 0°. As the minor-to-major axis length ratio increases, the trajectory is more stable. The trajectory deflection reduces with a higher initial velocity. When the rotation angle is 90°, the penetration trajectory of both symmetric and asymmetric elliptical cross-section projectiles in the incident plane is the most stable, and the trajectory deflection of the two projectiles in the horizontal plane reaches its maximum at rotation angles of 45° and 90°, respectively. The trajectory stability of an asymmetric elliptical projectile, when the rotation angle is obtuse, is better than that at the acute angle. When the incident angle is in the range of [0°, 50°], the trajectory instability and attitude deflection of the projectile increase with the increase of incident angle and then decrease, and both reach the largest when the incident angle is about 30°. It is also found that the projectile will separate from the target during the penetration stage of the projectile nose when penetrating a thin steel target in a stable attitude. When the projectile penetrates a thin steel target at a large attack angle, the attachment of the projectile and target mainly occurs on the upper surface of the projectile.
An experimental investigation of typical projectiles penetrating multi-layer spaced Q355B steel targets was conducted to study the trajectory characteristics of elliptical cross-section projectiles penetrating multi-layer spaced steel targets. Numerical simulations were performed on LS-DYNA finite element software and typical results obtained were validated by experimental results. The attitude and trajectory parameters in the penetration process and the deflection mechanism of the projectile were obtained. The influence of cross-section shape, the minor-to-major axis length ratio of the projectile cross-section, initial velocity, rotation angle, and incident angle on the penetration trajectories and attitude deflection was investigated. The research results show that the penetration trajectory stability of the circular cross-section projectile is better than the elliptical and asymmetric elliptical cross-section projectiles when the rotation angle is 0°. As the minor-to-major axis length ratio increases, the trajectory is more stable. The trajectory deflection reduces with a higher initial velocity. When the rotation angle is 90°, the penetration trajectory of both symmetric and asymmetric elliptical cross-section projectiles in the incident plane is the most stable, and the trajectory deflection of the two projectiles in the horizontal plane reaches its maximum at rotation angles of 45° and 90°, respectively. The trajectory stability of an asymmetric elliptical projectile, when the rotation angle is obtuse, is better than that at the acute angle. When the incident angle is in the range of [0°, 50°], the trajectory instability and attitude deflection of the projectile increase with the increase of incident angle and then decrease, and both reach the largest when the incident angle is about 30°. It is also found that the projectile will separate from the target during the penetration stage of the projectile nose when penetrating a thin steel target in a stable attitude. When the projectile penetrates a thin steel target at a large attack angle, the attachment of the projectile and target mainly occurs on the upper surface of the projectile.
, Available online , doi: 10.11883/bzycj-2024-0191
Abstract:
For the estimation of blast loading in complex structures, traditional numerical simulation methods were computationally intensive whereas rapid estimation methods based on neural networks can only provide estimates at local points without providing confidence intervals for the predicted results. To achieve fast and reliable estimation of the blast loading in complex structures, Bayesian theory was combined with deep learning to develop a Bayesian deep learning approach for rapid estimation of blast loading in complex structures. The approach initially utilized open-source numerical simulation software to generate a dataset of blast loading in complex structures, encompassing a wide range of parameters such as explosion equivalents, locations, and velocities. During this process, mesh sizes that balanced computational accuracy and speed were determined through mesh sensitivity analysis and the verification of the numerical simulation accuracy. Then, the deep learning model was extended into a Bayesian deep learning model based on Bayesian theory. By introducing probability distributions over the weights of the neural network, the model parameters were treated as random variables. Variational Bayesian inference was then employed to efficiently train the model, ensuring the accuracy of rapid blast loading estimation while also equipping the model with the ability to quantify uncertainty. Finally, metrics such as mean absolute percentage error (MAPE), normalized mean prediction interval width (NMPIW) and prediction interval coverage probability (PICP) were adopted to quantitatively assess the model's estimated accuracy and the precision of the uncertainty quantification. Additionally, an error decomposition of the estimation results was conducted to analyze model’s performance based on target parameters and scaled distance. The results indicate that the proposed method achieved an estimation error of 12.2% on the test set, with a confidence interval covering over 81.6% of true values, and less than 20 milliseconds of the estimation time for a single sample point. This method provides a novel approach for fast and accurate estimation of blast loading in complex structures with sufficient confidence for the estimation results.
For the estimation of blast loading in complex structures, traditional numerical simulation methods were computationally intensive whereas rapid estimation methods based on neural networks can only provide estimates at local points without providing confidence intervals for the predicted results. To achieve fast and reliable estimation of the blast loading in complex structures, Bayesian theory was combined with deep learning to develop a Bayesian deep learning approach for rapid estimation of blast loading in complex structures. The approach initially utilized open-source numerical simulation software to generate a dataset of blast loading in complex structures, encompassing a wide range of parameters such as explosion equivalents, locations, and velocities. During this process, mesh sizes that balanced computational accuracy and speed were determined through mesh sensitivity analysis and the verification of the numerical simulation accuracy. Then, the deep learning model was extended into a Bayesian deep learning model based on Bayesian theory. By introducing probability distributions over the weights of the neural network, the model parameters were treated as random variables. Variational Bayesian inference was then employed to efficiently train the model, ensuring the accuracy of rapid blast loading estimation while also equipping the model with the ability to quantify uncertainty. Finally, metrics such as mean absolute percentage error (MAPE), normalized mean prediction interval width (NMPIW) and prediction interval coverage probability (PICP) were adopted to quantitatively assess the model's estimated accuracy and the precision of the uncertainty quantification. Additionally, an error decomposition of the estimation results was conducted to analyze model’s performance based on target parameters and scaled distance. The results indicate that the proposed method achieved an estimation error of 12.2% on the test set, with a confidence interval covering over 81.6% of true values, and less than 20 milliseconds of the estimation time for a single sample point. This method provides a novel approach for fast and accurate estimation of blast loading in complex structures with sufficient confidence for the estimation results.
, Available online , doi: 10.11883/bzycj-2024-0320
Abstract:
In order to study the dynamic response mode and explosion ignition characteristics of lithium battery in light and small unmanned aerial vehicle (UAV) under high-energy impact, and evaluate the safety performance of lithium battery under dynamic impact, this paper takes the soft-package lithium battery as the research object, and have used the drop-hammer impact and gas gun impact test methods to carry out the drop hammer impact of the soft-package battery pack and the high-velocity impact of the battery on the aluminum plate. The deformation mode and ignition of the soft-package lithium battery under different battery power after impact were studied respectively. Combined with the mechanical deformation response and ignition characteristics of the battery, the impact safety of the small soft-package lithium battery was analyzed. The results show that the ignition risk of small soft-package lithium battery after being impacted by loads in the out-of-plane direction under the conditions of conventional battery shell protection is much higher than that under the condition of out-of-plane load impact. The ignition risk of lithium battery is obviously related to battery power and impact velocity. The thickness of the impacted aluminum plate has little effect on the ignition risk of lithium battery. Due to the buffering effect of the external battery shell, the lithium battery for light and small UAV has a relatively low risk of ignition after an unpredictable heading impact accident at low altitude in the urban environment.
In order to study the dynamic response mode and explosion ignition characteristics of lithium battery in light and small unmanned aerial vehicle (UAV) under high-energy impact, and evaluate the safety performance of lithium battery under dynamic impact, this paper takes the soft-package lithium battery as the research object, and have used the drop-hammer impact and gas gun impact test methods to carry out the drop hammer impact of the soft-package battery pack and the high-velocity impact of the battery on the aluminum plate. The deformation mode and ignition of the soft-package lithium battery under different battery power after impact were studied respectively. Combined with the mechanical deformation response and ignition characteristics of the battery, the impact safety of the small soft-package lithium battery was analyzed. The results show that the ignition risk of small soft-package lithium battery after being impacted by loads in the out-of-plane direction under the conditions of conventional battery shell protection is much higher than that under the condition of out-of-plane load impact. The ignition risk of lithium battery is obviously related to battery power and impact velocity. The thickness of the impacted aluminum plate has little effect on the ignition risk of lithium battery. Due to the buffering effect of the external battery shell, the lithium battery for light and small UAV has a relatively low risk of ignition after an unpredictable heading impact accident at low altitude in the urban environment.
, Available online , doi: 10.11883/bzycj-2024-0089
Abstract:
Plasma blasting rock breaking technology is characterized by green, high efficiency, controllability, and has a good application prospect in deep rock breaking. In order to provide a new rock-breaking method for the rock-breaking engineering under deep stress, four groups of plasma sandstone blasting tests under different peripheral pressures were carried out. The morphology, structure and distribution of three-dimensional cracks inside the rock were comparatively analyzed by CT scanning and three-dimensional reconstruction, so as to study the effects of the plasma rock-breaking technology in rock-breaking under different peripheral pressures. Meanwhile numerical simulation is conducted by using LS-DYNA, and a plasma equivalent explosive model in the coupled stress field is established to assist the verification of the coupled stress field, the plasma blasting mechanism as well as the rock-breaking process in the blasting process. Numerical simulation is conducted by using LS-DYNA to establish the plasma equivalent explosive model, supplementing the verification of the role of plasma blasting in the coupled stress field, and investigating the mechanism of plasma blasting under different pressures, as well as the rock body in the blasting process of the internal crack expansion, distribution and damage evolution laws. The results show that under the same voltage, with the increase of the 3D peripheral pressure, the number and distribution range of cracks on the surface of the rock exhibit a trend of gradual reduction, while the complexity of the cracks within the sandstone and the degree of penetration are significantly reduced. Due to the dynamic stress field generated by plasma blasting and the static stress coupling field generated by the surrounding pressure, the shock wave generated by the plasma blasting in the initial stage of the explosion plays a major role for the effect of different pressures under the action of the rock crack morphology and the center of the expansion of the region does not show obvious differences. With the attenuation of the shock wave, the 3D surrounding pressure in the middle and late stages of the plasma blasting process plays a decisive role in inhibiting the cracks of the rock mass expansion and damage evolution. At the same time, with the increase of the surrounding pressure, the more significant inhibition effect on the expansion of cracks in the rock body, resulting in the body fractal dimension and damage degree of 3D cracks in the rock body, while the role of the surrounding pressure approximately follows a linearly decreasing relationship.
Plasma blasting rock breaking technology is characterized by green, high efficiency, controllability, and has a good application prospect in deep rock breaking. In order to provide a new rock-breaking method for the rock-breaking engineering under deep stress, four groups of plasma sandstone blasting tests under different peripheral pressures were carried out. The morphology, structure and distribution of three-dimensional cracks inside the rock were comparatively analyzed by CT scanning and three-dimensional reconstruction, so as to study the effects of the plasma rock-breaking technology in rock-breaking under different peripheral pressures. Meanwhile numerical simulation is conducted by using LS-DYNA, and a plasma equivalent explosive model in the coupled stress field is established to assist the verification of the coupled stress field, the plasma blasting mechanism as well as the rock-breaking process in the blasting process. Numerical simulation is conducted by using LS-DYNA to establish the plasma equivalent explosive model, supplementing the verification of the role of plasma blasting in the coupled stress field, and investigating the mechanism of plasma blasting under different pressures, as well as the rock body in the blasting process of the internal crack expansion, distribution and damage evolution laws. The results show that under the same voltage, with the increase of the 3D peripheral pressure, the number and distribution range of cracks on the surface of the rock exhibit a trend of gradual reduction, while the complexity of the cracks within the sandstone and the degree of penetration are significantly reduced. Due to the dynamic stress field generated by plasma blasting and the static stress coupling field generated by the surrounding pressure, the shock wave generated by the plasma blasting in the initial stage of the explosion plays a major role for the effect of different pressures under the action of the rock crack morphology and the center of the expansion of the region does not show obvious differences. With the attenuation of the shock wave, the 3D surrounding pressure in the middle and late stages of the plasma blasting process plays a decisive role in inhibiting the cracks of the rock mass expansion and damage evolution. At the same time, with the increase of the surrounding pressure, the more significant inhibition effect on the expansion of cracks in the rock body, resulting in the body fractal dimension and damage degree of 3D cracks in the rock body, while the role of the surrounding pressure approximately follows a linearly decreasing relationship.
, Available online , doi: 10.11883/bzycj-2024-0150
Abstract:
The protection level and domestic standard test level of commonly used passive flexible barriers against rockfall impact are not higher than 5 000 kJ, while bridges in mountains and other important transportation infrastructures are facing rockfall disaster threats with higher impact energy levels. Considering that the design method for passive flexible barriers with higher impact energy levels is lacking, to provide a feasible and reliable tool for the infrastructure engineers, the analysis and design of 8 000 kJ-level passive flexible barrier against rockfall impact were carried out at present based on the numerical simulation method. Firstly, by adopting the explicit dynamic software ANSYS/LS-DYNA, quasi-static tests, including the tensile test on single wire ring and three-ring chain, net puncturing test, and the dynamic impact test, i.e., 2 000 kJ rockfall impacting the full-scale passive flexible barrier, were numerically reproduced, and the reliability of the numerical simulation method was fully verified by comparing with the test data, i.e., the maximum breaking force and breaking displacement of the wire ring and its failure characteristics, the whole impact process of rockfall, and the cable force-time history curves, the influencing factors, i.e., the inclining angle, span, and height of the steel post and different specifications of energy dissipating devices ranging from 50 kJ to 70 kJ, on the dynamic behavior of the passive flexible barrier were further analyzed. The results show that the specification of the energy dissipation device is the most critical parameter controlling the internal force and displacement of the passive flexible barrier. The inclining angle of the steel post is recommended to be 10°. An increase in the post spacing can reduce the in-plane stiffness of the structure while having less effect on the transverse anchorage. An increase in the post height will cause a significant increase in the support reaction force at the post bottom. A reasonable adjustment of the anchorage position of each wire rope is required when the post height and spacing are changed. Finally, based on the results of parameter analysis, two design schemes for a passive flexible barrier against 8 000 kJ rockfall impact were given by adjusting the geometry of the structure, the specification of the energy dissipating device, and the addition of transmission support ropes. Both of them passed the test of the European standard EAD 340059-00-0106.
The protection level and domestic standard test level of commonly used passive flexible barriers against rockfall impact are not higher than 5 000 kJ, while bridges in mountains and other important transportation infrastructures are facing rockfall disaster threats with higher impact energy levels. Considering that the design method for passive flexible barriers with higher impact energy levels is lacking, to provide a feasible and reliable tool for the infrastructure engineers, the analysis and design of 8 000 kJ-level passive flexible barrier against rockfall impact were carried out at present based on the numerical simulation method. Firstly, by adopting the explicit dynamic software ANSYS/LS-DYNA, quasi-static tests, including the tensile test on single wire ring and three-ring chain, net puncturing test, and the dynamic impact test, i.e., 2 000 kJ rockfall impacting the full-scale passive flexible barrier, were numerically reproduced, and the reliability of the numerical simulation method was fully verified by comparing with the test data, i.e., the maximum breaking force and breaking displacement of the wire ring and its failure characteristics, the whole impact process of rockfall, and the cable force-time history curves, the influencing factors, i.e., the inclining angle, span, and height of the steel post and different specifications of energy dissipating devices ranging from 50 kJ to 70 kJ, on the dynamic behavior of the passive flexible barrier were further analyzed. The results show that the specification of the energy dissipation device is the most critical parameter controlling the internal force and displacement of the passive flexible barrier. The inclining angle of the steel post is recommended to be 10°. An increase in the post spacing can reduce the in-plane stiffness of the structure while having less effect on the transverse anchorage. An increase in the post height will cause a significant increase in the support reaction force at the post bottom. A reasonable adjustment of the anchorage position of each wire rope is required when the post height and spacing are changed. Finally, based on the results of parameter analysis, two design schemes for a passive flexible barrier against 8 000 kJ rockfall impact were given by adjusting the geometry of the structure, the specification of the energy dissipating device, and the addition of transmission support ropes. Both of them passed the test of the European standard EAD 340059-00-0106.
, Available online , doi: 10.11883/bzycj-2024-0117
Abstract:
In this paper, the microspheres in flying-ash are used as sensitizer and inert additive to prepare the low detonation velocity emulsion explosives. The detonation velocity and the parameters of explosive shock wave in the air of emulsion explosives were measured by the probe method, the lead column compression method and the air explosion method, respectively. The safety of emulsion explosives was tested by the storage life experiment and thermal analysis experiment. The experimental results show that the detonation velocity, the brisance, the peak pressure, the positive impulse and the positive pressure action time of shock wave of emulsion explosives increased first and then decreased with the increase of the content of flying-ash microspheres. When the content of flying-ash microspheres was 15%, the detonation performance of emulsion explosive was the best, and when the content of flying-ash microspheres was 45% , the detonation velocity of the explosive decreased obviously. Meanwhile, the detonation velocity ranged from 2191 to 2312 m/s, which can satisfy the condition of using explosive for explosive welding. In addition, it is found that the detonation performance of emulsion explosives with D50=79 μm flying-ash microspheres was higher than those of flying-ash microspheres with D50=116 and 47 μm. The storage life and thermal analysis results indicate that the storage life of low detonation velocity emulsion explosives with flying-ash microspheres is significantly better than that of traditional low detonation velocity emulsion explosive with clay particles, the activation energy of thermal decomposition of the emulsion explosive with 15% flying-ash microspheres was only 0.3% higher than that of emulsion matrix. The results also show that the addition of flying-ash microspheres has no obvious effect on the thermal stability of the emulsion matrix. The research results have important reference value for green resource disposal of coal-based solid waste and formulation design of the low detonation velocity emulsion explosive.
In this paper, the microspheres in flying-ash are used as sensitizer and inert additive to prepare the low detonation velocity emulsion explosives. The detonation velocity and the parameters of explosive shock wave in the air of emulsion explosives were measured by the probe method, the lead column compression method and the air explosion method, respectively. The safety of emulsion explosives was tested by the storage life experiment and thermal analysis experiment. The experimental results show that the detonation velocity, the brisance, the peak pressure, the positive impulse and the positive pressure action time of shock wave of emulsion explosives increased first and then decreased with the increase of the content of flying-ash microspheres. When the content of flying-ash microspheres was 15%, the detonation performance of emulsion explosive was the best, and when the content of flying-ash microspheres was 45% , the detonation velocity of the explosive decreased obviously. Meanwhile, the detonation velocity ranged from 2191 to 2312 m/s, which can satisfy the condition of using explosive for explosive welding. In addition, it is found that the detonation performance of emulsion explosives with D50=79 μm flying-ash microspheres was higher than those of flying-ash microspheres with D50=116 and 47 μm. The storage life and thermal analysis results indicate that the storage life of low detonation velocity emulsion explosives with flying-ash microspheres is significantly better than that of traditional low detonation velocity emulsion explosive with clay particles, the activation energy of thermal decomposition of the emulsion explosive with 15% flying-ash microspheres was only 0.3% higher than that of emulsion matrix. The results also show that the addition of flying-ash microspheres has no obvious effect on the thermal stability of the emulsion matrix. The research results have important reference value for green resource disposal of coal-based solid waste and formulation design of the low detonation velocity emulsion explosive.
, Available online , doi: 10.11883/bzycj-2024-0224
Abstract:
To reasonably describe the reaction evolution behavior of explosives after ignition under mechanical confinement, we conduct in-depth analysis of the deformation and movement characteristics of the shell, and divide the response process of the shell into three stages: elastoplastic stage, complete yield stage, and shell rupture stage with inertial motion constraint. The combustion rate theory and the combustion crack-network theory are employed as pivotal parameters for the reaction evolution of the explosives. In the initial stage, the mechanical properties of the shell are taken into consideration, with the material properties serving as the upper limit for structural constraint strength. During this stage, the deformation of the shell remains relatively small. In the second stage, a generalized equivalent stiffness concept is introduced in order to account for the inertial confinement effect of the shell movement. Furthermore, a mechanical deformation analysis of cylindrical shells and end caps is conducted, which takes into account the coupled effects of combustion crack network reaction evolution and shell deformation movement based on a kinematic theory. The third stage is building upon the foundation established in preceding stages, the impact of gas leakage following shell rupture on the progression of the explosive reaction process is considered, The integration of these three stages yields a formula for pressure, shell velocity, and time in the non-impact ignition reaction evolution process of solid explosives. A model for explosives reaction evolution is established to characterize the inertial confinement effects of the shell movement. This model and the related parameters are verified by comparing the calculating results with typical experimental data. It is found that the velocity of shell motion and the changes in internal pressure fundamentally characterize the relationship between the energy release of the explosives and the work done by the product gas. Considering the inertial confinement effects of shell motion is more indicative for the evolution process of explosives reaction, by using this model, the internal pressure of the shell, reaction rate and reaction degree of solid explosives can be calculated based on the historical changes in the velocity of the shell’s motion, thus providing a theoretical method for the explosive safety design and for evaluation under unexpected stimuli.
To reasonably describe the reaction evolution behavior of explosives after ignition under mechanical confinement, we conduct in-depth analysis of the deformation and movement characteristics of the shell, and divide the response process of the shell into three stages: elastoplastic stage, complete yield stage, and shell rupture stage with inertial motion constraint. The combustion rate theory and the combustion crack-network theory are employed as pivotal parameters for the reaction evolution of the explosives. In the initial stage, the mechanical properties of the shell are taken into consideration, with the material properties serving as the upper limit for structural constraint strength. During this stage, the deformation of the shell remains relatively small. In the second stage, a generalized equivalent stiffness concept is introduced in order to account for the inertial confinement effect of the shell movement. Furthermore, a mechanical deformation analysis of cylindrical shells and end caps is conducted, which takes into account the coupled effects of combustion crack network reaction evolution and shell deformation movement based on a kinematic theory. The third stage is building upon the foundation established in preceding stages, the impact of gas leakage following shell rupture on the progression of the explosive reaction process is considered, The integration of these three stages yields a formula for pressure, shell velocity, and time in the non-impact ignition reaction evolution process of solid explosives. A model for explosives reaction evolution is established to characterize the inertial confinement effects of the shell movement. This model and the related parameters are verified by comparing the calculating results with typical experimental data. It is found that the velocity of shell motion and the changes in internal pressure fundamentally characterize the relationship between the energy release of the explosives and the work done by the product gas. Considering the inertial confinement effects of shell motion is more indicative for the evolution process of explosives reaction, by using this model, the internal pressure of the shell, reaction rate and reaction degree of solid explosives can be calculated based on the historical changes in the velocity of the shell’s motion, thus providing a theoretical method for the explosive safety design and for evaluation under unexpected stimuli.
, Available online , doi: 10.11883/bzycj-2024-0138
Abstract:
In this study, AlSi10Mg alloy was prepared by selective laser melting (SLM) first, and then subjected to stress relieved annealing treatment. The microstructures of the alloy were analyzed by optical microscope (OM), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) technology. To understand the influence of coupling effects on the mechanical behavior of AlSi10Mg alloy under wide strain rates and wide temperatures, the mechanical behavior of the alloy under extreme conditions (high and low temperatures, high strain-rate) were analyzed by universal testing machine with an environmental chamber and split Hopkinson pressure bar. The results show that AlSi10Mg alloy possesses fine cellular dendritic microstructure, mainly including α-Al and Si phases, and annealing treatment can result in the discontinuous distribution of eutectic Si particles. The average grain size is 3.7 μm. AlSi10Mg alloy displays strain-rate strengthening effect under room temperature condition at 0.002–4 800 s−1, and has different strain-rate sensitivity in different strain-rate ranges. Under high strain-rate conditions, strain hardening effect still dominates. The material has higher yield strength and flow stress at 173 K. When the strain-rate is 0.002 s−1, the SLM AlSi10Mg alloy has different temperature sensitivities in different temperature ranges. The alloy does not have temperature sensitivity in the range of 173–243 K; the material exhibits temperature sensitivity ranging from 293 K to 573 K, and the softening effect due to temperature on the material intensifies with increasing temperature. Based on the J-C constitutive model, a modified J-C constitutive model expressed by piecewise functions is constructed and the experimental results are fitted. In addition, experimental verification was conducted on the modified J-C constitutive model, and the predicted results are basically consistent with the experimental results. Within the scope of the study, the modified J-C constitutive model effectively reflects the mechanical behavior of the alloy at high and low temperatures and under different strain-rate.
In this study, AlSi10Mg alloy was prepared by selective laser melting (SLM) first, and then subjected to stress relieved annealing treatment. The microstructures of the alloy were analyzed by optical microscope (OM), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) technology. To understand the influence of coupling effects on the mechanical behavior of AlSi10Mg alloy under wide strain rates and wide temperatures, the mechanical behavior of the alloy under extreme conditions (high and low temperatures, high strain-rate) were analyzed by universal testing machine with an environmental chamber and split Hopkinson pressure bar. The results show that AlSi10Mg alloy possesses fine cellular dendritic microstructure, mainly including α-Al and Si phases, and annealing treatment can result in the discontinuous distribution of eutectic Si particles. The average grain size is 3.7 μm. AlSi10Mg alloy displays strain-rate strengthening effect under room temperature condition at 0.002–4 800 s−1, and has different strain-rate sensitivity in different strain-rate ranges. Under high strain-rate conditions, strain hardening effect still dominates. The material has higher yield strength and flow stress at 173 K. When the strain-rate is 0.002 s−1, the SLM AlSi10Mg alloy has different temperature sensitivities in different temperature ranges. The alloy does not have temperature sensitivity in the range of 173–243 K; the material exhibits temperature sensitivity ranging from 293 K to 573 K, and the softening effect due to temperature on the material intensifies with increasing temperature. Based on the J-C constitutive model, a modified J-C constitutive model expressed by piecewise functions is constructed and the experimental results are fitted. In addition, experimental verification was conducted on the modified J-C constitutive model, and the predicted results are basically consistent with the experimental results. Within the scope of the study, the modified J-C constitutive model effectively reflects the mechanical behavior of the alloy at high and low temperatures and under different strain-rate.
, Available online , doi: 10.11883/bzycj-2024-0351
Abstract:
As lithium-ion batteries are widely used in the industry represented by electric vehicles, their collision-induced safety problems have aroused widespread concern in the industry and society. Under the collision condition of electric vehicles, on the one hand, the deformation of the battery will lead to direct fire and explosion, and on the other hand, the unknown deformation of the battery caused by the collision will bring safety risks to the subsequent use. For the unknown deformation of batteries after collision, abnormal batteries are only sensed by physical signals such as voltage, temperature and current, and there is no direct monitoring method for battery deformation. To bridge this gap, this paper uses small piezoelectric plates and realizes deformation and collision monitoring of lithium-ion batteries based on ultrasonic guided waves. Firstly, an experimental platform for different loads of lithium-ion batteries was built, and quasi-static and micro-collision experiments were carried out. Further, the experimental results were analyzed and discussed to clarify the change law of ultrasonic signal under different loads. The results showed that: in the quasi-static battery experiment, the ultrasonic amplitude signal was negatively correlated with the deformation degree of the battery. When the battery was subjected to gradually increasing load and the deformation became more serious, the amplitude would gradually decrease; when the battery was deformed to failure, the amplitude signal would also drop instantaneously. In ball-dropped experiment, the impact deformation will affect the change of amplitude and energy integration of the ultrasonic signal, which can be used as a basis to judge whether the battery collision occurs. Finally, the mapping relationship between ultrasonic and battery deformation failure monitoring under large deformation is established, and the criteria based on ultrasonic sensor under collision deformation is proposed. The results of this paper propose a new method for the safety monitoring of lithium-ion batteries, which is expected to be applied in electric vehicles and other fields.
As lithium-ion batteries are widely used in the industry represented by electric vehicles, their collision-induced safety problems have aroused widespread concern in the industry and society. Under the collision condition of electric vehicles, on the one hand, the deformation of the battery will lead to direct fire and explosion, and on the other hand, the unknown deformation of the battery caused by the collision will bring safety risks to the subsequent use. For the unknown deformation of batteries after collision, abnormal batteries are only sensed by physical signals such as voltage, temperature and current, and there is no direct monitoring method for battery deformation. To bridge this gap, this paper uses small piezoelectric plates and realizes deformation and collision monitoring of lithium-ion batteries based on ultrasonic guided waves. Firstly, an experimental platform for different loads of lithium-ion batteries was built, and quasi-static and micro-collision experiments were carried out. Further, the experimental results were analyzed and discussed to clarify the change law of ultrasonic signal under different loads. The results showed that: in the quasi-static battery experiment, the ultrasonic amplitude signal was negatively correlated with the deformation degree of the battery. When the battery was subjected to gradually increasing load and the deformation became more serious, the amplitude would gradually decrease; when the battery was deformed to failure, the amplitude signal would also drop instantaneously. In ball-dropped experiment, the impact deformation will affect the change of amplitude and energy integration of the ultrasonic signal, which can be used as a basis to judge whether the battery collision occurs. Finally, the mapping relationship between ultrasonic and battery deformation failure monitoring under large deformation is established, and the criteria based on ultrasonic sensor under collision deformation is proposed. The results of this paper propose a new method for the safety monitoring of lithium-ion batteries, which is expected to be applied in electric vehicles and other fields.
, Available online , doi: 10.11883/bzycj-2024-0097
Abstract:
Concrete materials are widely used in the construction of infrastructure and defense facilities. In order to study the dynamic mechanical properties of high-temperature concrete with different cooling methods, the dynamic mechanical properties of C30 cylindrical concrete samples at different temperatures with different cooling methods were tested by\begin{document}$\varnothing $\end{document} ![]()
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Concrete materials are widely used in the construction of infrastructure and defense facilities. In order to study the dynamic mechanical properties of high-temperature concrete with different cooling methods, the dynamic mechanical properties of C30 cylindrical concrete samples at different temperatures with different cooling methods were tested by
, Available online , doi: 10.11883/bzycj-2024-0239
Abstract:
In order to explore the underwater anti-explosion protection effect of steel fiber reinforced cellular concrete materials, the damage process of reinforced concrete slabs under underwater contact explosion was reproduced by the coupling method of smoothed particle hydrodynamics and finite element method (SPH-FEM). The validity of the simulation method was verified by comparing with the experimental results. On this basis, a three-dimensional refined simulation model of water-explosive-protective layer-reinforced concrete slab was established by the SPH-FEM coupling method. The damage evolution process, failure mode and failure mechanism of protective layer of steel fiber reinforced cellular concrete (SAP10S5, SAP10S10, SAP10S15 and SAP10S20) with different fiber ratios and explosive mass were studied, and the prediction curve of damage level of reinforced concrete slabs was constructed. The results show that the numerical simulation results are in good agreement with the experimental results, which verifies the effectiveness of the simulation method. Under the underwater contact explosion, the addition of protective layer of steel fiber reinforced cellular concrete can effectively reduce the damage degree of protected reinforced concrete (RC) slab, and its influence on the damage degree of RC slab decreases first and then increases with the increase of steel fiber volume fraction in the protective layer. Among them, the anti-explosion protection effect of protective layer of SAP10S15 ratio is the best. When the amount of explosive increases within a certain range, the protective layer of SAP10S15 ratio can still maintain a high proportion of energy consumption and effectively reduce the damage degree of the RC plate. When the amount of explosive is 0.25 kg, the damage index of RC slabs strengthened with protective layer of SAP10S15 has the most obvious attenuation compared with the unprotected scheme, which is 42.5%, and the damage level is reduced from serious damage to moderate damage. The prediction curve of constructed damage level can directly evaluate the influence of steel fiber volume fraction/explosive amount on the damage degree of RC panel. The above research results can provide reference for the anti-explosion protection design of wading concrete structures.
In order to explore the underwater anti-explosion protection effect of steel fiber reinforced cellular concrete materials, the damage process of reinforced concrete slabs under underwater contact explosion was reproduced by the coupling method of smoothed particle hydrodynamics and finite element method (SPH-FEM). The validity of the simulation method was verified by comparing with the experimental results. On this basis, a three-dimensional refined simulation model of water-explosive-protective layer-reinforced concrete slab was established by the SPH-FEM coupling method. The damage evolution process, failure mode and failure mechanism of protective layer of steel fiber reinforced cellular concrete (SAP10S5, SAP10S10, SAP10S15 and SAP10S20) with different fiber ratios and explosive mass were studied, and the prediction curve of damage level of reinforced concrete slabs was constructed. The results show that the numerical simulation results are in good agreement with the experimental results, which verifies the effectiveness of the simulation method. Under the underwater contact explosion, the addition of protective layer of steel fiber reinforced cellular concrete can effectively reduce the damage degree of protected reinforced concrete (RC) slab, and its influence on the damage degree of RC slab decreases first and then increases with the increase of steel fiber volume fraction in the protective layer. Among them, the anti-explosion protection effect of protective layer of SAP10S15 ratio is the best. When the amount of explosive increases within a certain range, the protective layer of SAP10S15 ratio can still maintain a high proportion of energy consumption and effectively reduce the damage degree of the RC plate. When the amount of explosive is 0.25 kg, the damage index of RC slabs strengthened with protective layer of SAP10S15 has the most obvious attenuation compared with the unprotected scheme, which is 42.5%, and the damage level is reduced from serious damage to moderate damage. The prediction curve of constructed damage level can directly evaluate the influence of steel fiber volume fraction/explosive amount on the damage degree of RC panel. The above research results can provide reference for the anti-explosion protection design of wading concrete structures.
, Available online , doi: 10.11883/bzycj-2024-0318
Abstract:
The battery pack of electric vehicles is highly susceptible to failure under side pole collision. To accurately and quickly evaluate the safety of battery packs under such conditions, this paper introduces a local region refined battery pack model that can effectively characterize the deformation and mechanical response of the jellyroll of battery. Simulation analyses were conducted under varying impact velocity, angles, positions, and vehicle loading configuration, with the latter achieved by uniformly applying mass compensation to the side wall of the battery pack. A simulation matrix was designed using an optimized Latin hypercube sampling (LHS) strategy, and a dataset was generated through image recognition methods. This dataset includes parameters such as the maximum intrusion depth, intrusion location, intrusion width of the battery pack side wall, and the deformation of the jellyroll of battery. New features, including collision energy and velocity components in the x and y directions, were derived and selected as input features for model training through correlation analysis. Support vector machine (SVM), random forest (RF), and back propagation neural networks (BPNN) were employed to build a data-driven predictive model. The SVM model demonstrated superior performance, achieving an average R2 of 0.96 across prediction parameters. The prediction of the maximum intrusion depth of the battery pack side wall was particularly accurate, with an R2 exceeding 0.95 for all three models. Additionally, the robustness of the models was tested by introducing Gaussian noise, where the BP neural network exhibited better robustness. Even with the addition of Gaussian noise with a standard deviation of 0.5, the BP model maintained an average R2 of 0.91 for the prediction parameters. The established data-driven model can effectively predict mechanical response of battery packs under side pole collisions and provide a reliable tool for evaluating battery pack safety.
The battery pack of electric vehicles is highly susceptible to failure under side pole collision. To accurately and quickly evaluate the safety of battery packs under such conditions, this paper introduces a local region refined battery pack model that can effectively characterize the deformation and mechanical response of the jellyroll of battery. Simulation analyses were conducted under varying impact velocity, angles, positions, and vehicle loading configuration, with the latter achieved by uniformly applying mass compensation to the side wall of the battery pack. A simulation matrix was designed using an optimized Latin hypercube sampling (LHS) strategy, and a dataset was generated through image recognition methods. This dataset includes parameters such as the maximum intrusion depth, intrusion location, intrusion width of the battery pack side wall, and the deformation of the jellyroll of battery. New features, including collision energy and velocity components in the x and y directions, were derived and selected as input features for model training through correlation analysis. Support vector machine (SVM), random forest (RF), and back propagation neural networks (BPNN) were employed to build a data-driven predictive model. The SVM model demonstrated superior performance, achieving an average R2 of 0.96 across prediction parameters. The prediction of the maximum intrusion depth of the battery pack side wall was particularly accurate, with an R2 exceeding 0.95 for all three models. Additionally, the robustness of the models was tested by introducing Gaussian noise, where the BP neural network exhibited better robustness. Even with the addition of Gaussian noise with a standard deviation of 0.5, the BP model maintained an average R2 of 0.91 for the prediction parameters. The established data-driven model can effectively predict mechanical response of battery packs under side pole collisions and provide a reliable tool for evaluating battery pack safety.
, Available online , doi: 10.11883/bzycj-2024-0339
Abstract:
The deformation and failure of the internal separator in lithium-ion batteries under external impact are key factors in triggering internal short circuits. The surface of the battery electrodes is usually not smooth, which can cause stress concentration in the separator, affecting the mechanical stability of the battery. Therefore, this study, based on numerical simulation and theoretical analysis, deeply explores the mechanical behavior of the battery separator under compression on uneven surfaces and its short-circuit safety boundary. The model is established using the finite element software ABAQUS, selecting a section of a separator with a width of 50 μm and the nearby positive and negative electrode coatings as a representative unit cell for two-dimensional finite element modeling and numerical calculation. The study compares the surface morphology of three forms: (1) ideal plane; (2) densely packed granular surface; (3) single granular protrusion plane, as well as the effects of particle size, separator thickness, and loading rate. By analyzing the stress-strain curve of the separator, it is found that the separator compressed by uneven surfaces exhibits a "softening phenomenon" compared to compression on an ideal plane. For the ideal plane case, the strain distribution is very uniform, so the battery’s load-bearing capacity is larger. However, for densely packed granular and single granular protrusion cases, under the same loading displacement, the loaded area is smaller, and the generated reaction force is also smaller. As the loading progresses, the gaps are gradually filled, the loaded area increases, and gradually tends to be loaded on the entire surface, and the load difference gradually decreases. Through parametric analysis of the failure stress, it is found that as the particle diameter increases, the separator thickness decreases, or within a certain range of loading rates increases, the separator exhibits a softening behavior, that is, the average stress decreases, the yield point shifts backward, and the short-circuit failure stress also decreases. Furthermore, this study also establishes an equivalent compression constitutive model of the separator under compression on uneven surfaces, thereby theoretically explaining the effect of roughness on failure stress and deriving a quantitative relationship between the two.
The deformation and failure of the internal separator in lithium-ion batteries under external impact are key factors in triggering internal short circuits. The surface of the battery electrodes is usually not smooth, which can cause stress concentration in the separator, affecting the mechanical stability of the battery. Therefore, this study, based on numerical simulation and theoretical analysis, deeply explores the mechanical behavior of the battery separator under compression on uneven surfaces and its short-circuit safety boundary. The model is established using the finite element software ABAQUS, selecting a section of a separator with a width of 50 μm and the nearby positive and negative electrode coatings as a representative unit cell for two-dimensional finite element modeling and numerical calculation. The study compares the surface morphology of three forms: (1) ideal plane; (2) densely packed granular surface; (3) single granular protrusion plane, as well as the effects of particle size, separator thickness, and loading rate. By analyzing the stress-strain curve of the separator, it is found that the separator compressed by uneven surfaces exhibits a "softening phenomenon" compared to compression on an ideal plane. For the ideal plane case, the strain distribution is very uniform, so the battery’s load-bearing capacity is larger. However, for densely packed granular and single granular protrusion cases, under the same loading displacement, the loaded area is smaller, and the generated reaction force is also smaller. As the loading progresses, the gaps are gradually filled, the loaded area increases, and gradually tends to be loaded on the entire surface, and the load difference gradually decreases. Through parametric analysis of the failure stress, it is found that as the particle diameter increases, the separator thickness decreases, or within a certain range of loading rates increases, the separator exhibits a softening behavior, that is, the average stress decreases, the yield point shifts backward, and the short-circuit failure stress also decreases. Furthermore, this study also establishes an equivalent compression constitutive model of the separator under compression on uneven surfaces, thereby theoretically explaining the effect of roughness on failure stress and deriving a quantitative relationship between the two.
, Available online , doi: 10.11883/bzycj-2024-0329
Abstract:
As a crucial component to ensure the safety and reliability of lithium-ion batteries (LIBs), the polymer separator plays a significant role in ensuring the mechanical abuse safety of the battery, and its mechanical properties have become an important indicator of battery safety performance. This study focuses on the compressive mechanical behavior of separators in prismatic power batteries under coupled strain rate and temperature conditions. A comprehensive experiment has been conducted including quasi-static and dynamic compression tests across a wide range of strain rates and temperatures. These tests assessed the separator’s mechanical behavior under different strain rates and temperature conditions, with a specific focus on properties and damage mechanism at elevated temperatures and different strain rates. The mechanical response of the separator was meticulously explored, involving an in-depth analysis of strain rate-dependent and temperature-dependent mechanical properties. The results indicated that the separator's mechanical behavior is highly sensitive to both strain rate and temperature. As the strain rate increases, the yield point is reached earlier, causing the separator to yield sooner. Additionally, both the elastic modulus and the yield stress of the separator decrease as the temperature rises. At low strain rates, the yield point shifts forward, whereas at high strain rates, the yield strain increases with temperature. Additionally, the coupled effects of temperature and strain rate were found to alter the damage failure modes, subsequently affecting the separator’s mechanical properties and structural integrity. At low strain rates, the failure of the separator is primarily characterized by plastic deformation and local buckling, whereas complex dynamic failure modes may occur at high strain rates. Based on experimental data, a nonlinear viscoelastic constitutive model was developed, incorporating the effects of temperature-strain rate coupling. This model offers essential insights for the safe and optimized design of lithium-ion batteries. The comprehensive experimental analysis and model developed in this study provide critical references for advancing the design, manufacturing, and practical application of LIB separators, enhancing their reliability and safety across a diverse range of operational conditions.
As a crucial component to ensure the safety and reliability of lithium-ion batteries (LIBs), the polymer separator plays a significant role in ensuring the mechanical abuse safety of the battery, and its mechanical properties have become an important indicator of battery safety performance. This study focuses on the compressive mechanical behavior of separators in prismatic power batteries under coupled strain rate and temperature conditions. A comprehensive experiment has been conducted including quasi-static and dynamic compression tests across a wide range of strain rates and temperatures. These tests assessed the separator’s mechanical behavior under different strain rates and temperature conditions, with a specific focus on properties and damage mechanism at elevated temperatures and different strain rates. The mechanical response of the separator was meticulously explored, involving an in-depth analysis of strain rate-dependent and temperature-dependent mechanical properties. The results indicated that the separator's mechanical behavior is highly sensitive to both strain rate and temperature. As the strain rate increases, the yield point is reached earlier, causing the separator to yield sooner. Additionally, both the elastic modulus and the yield stress of the separator decrease as the temperature rises. At low strain rates, the yield point shifts forward, whereas at high strain rates, the yield strain increases with temperature. Additionally, the coupled effects of temperature and strain rate were found to alter the damage failure modes, subsequently affecting the separator’s mechanical properties and structural integrity. At low strain rates, the failure of the separator is primarily characterized by plastic deformation and local buckling, whereas complex dynamic failure modes may occur at high strain rates. Based on experimental data, a nonlinear viscoelastic constitutive model was developed, incorporating the effects of temperature-strain rate coupling. This model offers essential insights for the safe and optimized design of lithium-ion batteries. The comprehensive experimental analysis and model developed in this study provide critical references for advancing the design, manufacturing, and practical application of LIB separators, enhancing their reliability and safety across a diverse range of operational conditions.
, Available online , doi: 10.11883/bzycj-2024-0321
Abstract:
This investigation seeks to elucidate the impact of various discharge states on the dynamic mechanical responses and failure mechanisms of lithium-ion batteries through a comprehensive experimental study. Employing quasi-static compression tests, the research systematically analyzes the compression characteristics and safety performance of lithium-ion batteries preset to specific discharge levels. These tests were conducted at critical junctures: during discharge, following a 1-hour rest period, and after a 24-hour rest period. This methodology enabled a detailed examination of the force-displacement response characteristics, ultimate load-bearing capacity, and overall safety behaviors under varying electrochemical states. The experimental findings indicate that batteries in a discharged state exhibit lower force-displacement curves, suggesting a decrease in structural stiffness attributable to the electro-chemical reaction inside the battery during the discharge process. Notably, these batteries demonstrated a higher maximum load-bearing capacity compared to those tested after rest periods. Additionally, batteries undergoing compression tests in the midst of discharge were more susceptible to catastrophic failures, such as explosions, whereas those allowed to rest showed significantly enhanced safety characteristics. Further microscopic analysis using Scanning Electron Microscopy (SEM) provided insights into the internal structural changes, revealing extensive damage to electrode particles in batteries tested in the discharged state compared to those tested post-rest. The observed damage and increased risk of mechanical failure are primarily attributed to diffusive stresses generated during the discharge process, which accumulate and intensify the vulnerability of the battery structure under mechanical loads. This study contributes valuable experimental evidence and theoretical insights that are crucial for advancing the understanding of the mechanical integrity and safety of lithium-ion batteries under operational stresses. The findings underscore the importance of considering discharge states in the safety design and evaluation of lithium-ion batteries, potentially leading to enhanced durability and safer application in practical scenarios.
This investigation seeks to elucidate the impact of various discharge states on the dynamic mechanical responses and failure mechanisms of lithium-ion batteries through a comprehensive experimental study. Employing quasi-static compression tests, the research systematically analyzes the compression characteristics and safety performance of lithium-ion batteries preset to specific discharge levels. These tests were conducted at critical junctures: during discharge, following a 1-hour rest period, and after a 24-hour rest period. This methodology enabled a detailed examination of the force-displacement response characteristics, ultimate load-bearing capacity, and overall safety behaviors under varying electrochemical states. The experimental findings indicate that batteries in a discharged state exhibit lower force-displacement curves, suggesting a decrease in structural stiffness attributable to the electro-chemical reaction inside the battery during the discharge process. Notably, these batteries demonstrated a higher maximum load-bearing capacity compared to those tested after rest periods. Additionally, batteries undergoing compression tests in the midst of discharge were more susceptible to catastrophic failures, such as explosions, whereas those allowed to rest showed significantly enhanced safety characteristics. Further microscopic analysis using Scanning Electron Microscopy (SEM) provided insights into the internal structural changes, revealing extensive damage to electrode particles in batteries tested in the discharged state compared to those tested post-rest. The observed damage and increased risk of mechanical failure are primarily attributed to diffusive stresses generated during the discharge process, which accumulate and intensify the vulnerability of the battery structure under mechanical loads. This study contributes valuable experimental evidence and theoretical insights that are crucial for advancing the understanding of the mechanical integrity and safety of lithium-ion batteries under operational stresses. The findings underscore the importance of considering discharge states in the safety design and evaluation of lithium-ion batteries, potentially leading to enhanced durability and safer application in practical scenarios.
, Available online , doi: 10.11883/bzycj-2024-0279
Abstract:
Prefabricated concrete bursting layer has a very important application prospect in the field of protective engineering attributed to its technical advantages including high construction efficiency and construction quality. However, compared with the monolithic cast-in-situ concrete bursting layer, the impact resistance of the prefabricated concrete bursting layer may be significantly reduced because of the interfaces between the prefabricated blocks and the cast-in-situ part. Therefore, it is important for engineers to reasonably design the prefabricated concrete bursting layer to make its penetration resistance comparable to the monolithic one. To this end, a kind of prefabricated bursting layer connected by wet joints and rebars was proposed in our previous study. In order to apply the prefabricated bursting layer in protective engineering, a series of numerical models were developed to further study its penetration resistance. Firstly, based on the Kong-Fang model and smoothed particle Galerkin (SPG) method, the numerical models were developed and validated against the experimental data of projectile penetrating monolithic and prefabricated targets. Then, the validated numerical models were further used to investigate the influences of prefabricated block size, wet joint width and anchorage length, spacing and diameter of rebars on the penetration resistance of prefabricated targets. Numerical results indicate that increasing the width of wet joints, reducing the spacing between rebars, and extending the anchorage length of rebars can significantly enhance the penetration resistance of prefabricated targets. After clarifying the influences of these parameters, an engineering design method for a prefabricated concrete bursting layer was proposed. Finally, based on this method, two prefabricated high performance concrete targets subjected to two typical types of warhead penetration were designed. Numerical results show that the penetration resistances of two prefabricated targets were comparable to monolithic targets. The proposed engineering design method can provide a reference for engineering applications of prefabricated concrete bursting layers connected by the wet joints and rebars.
Prefabricated concrete bursting layer has a very important application prospect in the field of protective engineering attributed to its technical advantages including high construction efficiency and construction quality. However, compared with the monolithic cast-in-situ concrete bursting layer, the impact resistance of the prefabricated concrete bursting layer may be significantly reduced because of the interfaces between the prefabricated blocks and the cast-in-situ part. Therefore, it is important for engineers to reasonably design the prefabricated concrete bursting layer to make its penetration resistance comparable to the monolithic one. To this end, a kind of prefabricated bursting layer connected by wet joints and rebars was proposed in our previous study. In order to apply the prefabricated bursting layer in protective engineering, a series of numerical models were developed to further study its penetration resistance. Firstly, based on the Kong-Fang model and smoothed particle Galerkin (SPG) method, the numerical models were developed and validated against the experimental data of projectile penetrating monolithic and prefabricated targets. Then, the validated numerical models were further used to investigate the influences of prefabricated block size, wet joint width and anchorage length, spacing and diameter of rebars on the penetration resistance of prefabricated targets. Numerical results indicate that increasing the width of wet joints, reducing the spacing between rebars, and extending the anchorage length of rebars can significantly enhance the penetration resistance of prefabricated targets. After clarifying the influences of these parameters, an engineering design method for a prefabricated concrete bursting layer was proposed. Finally, based on this method, two prefabricated high performance concrete targets subjected to two typical types of warhead penetration were designed. Numerical results show that the penetration resistances of two prefabricated targets were comparable to monolithic targets. The proposed engineering design method can provide a reference for engineering applications of prefabricated concrete bursting layers connected by the wet joints and rebars.
, Available online , doi: 10.11883/bzycj-2024-0207
Abstract:
To investigate the dynamic mechanical characterization of non-pure and non-intact ice materials under impact loads, a modified split Hopkinson pressure bar (SHPB) was used. Rapid loading, rod end cooling and waveform shaping techniques were used to ensure the stability of the ice material and achieve dynamic stress balance during loading. The impact mechanical properties of complete ice (pure water, containing 2.5%, 3.5%, 4.5% salt, containing 2.0%, 4.5%, 8.5% coconut) and spliced ice (splicing interface inclination 30°, 60°) at freezing temperature of −10 ℃ were studied. The strain rate ranges from 150~250 s−1. The failure process was recorded by using the high-speed camera triggered simultaneously with the pressure rod. The correlation between the stress and strain of the sample, along with the failure process, was determined by analyzing the time history curve of sample. The failure mode of the spliced ice sample was analyzed by combining the Mohr-Coulomb strength criterion. The results show that the pure water ice exhibits the highest compressive strength, followed by the ice with coconut shreds, and both of them show a positive strain rate effect. However, the compressive strength of the ice with salt addition decreases significantly due to its loose structure and the strain rate effect is not obvious. The dynamic compressive strength of ice samples added with coconut fiber increases firstly and then decreases with the increase of coconut fiber content. Ice samples with high coconut fiber content are prone to "double peak" phenomenon due to the binding effect of coconut fiber on broken ice with small particle size. The splicing plane affects the crack growth, resulting in lower compressive strength than the intact ice sample, and affects the failure mode as well. The ice with small interface inclination is mainly damaged by interface slip, while the ice with large interface inclination is mainly damaged by whole ice, which is similar to the intact ice. The research results provide theoretical basis and method reference for the dynamic mechanical properties of non-pure and non-intact ice materials under impact loads.
To investigate the dynamic mechanical characterization of non-pure and non-intact ice materials under impact loads, a modified split Hopkinson pressure bar (SHPB) was used. Rapid loading, rod end cooling and waveform shaping techniques were used to ensure the stability of the ice material and achieve dynamic stress balance during loading. The impact mechanical properties of complete ice (pure water, containing 2.5%, 3.5%, 4.5% salt, containing 2.0%, 4.5%, 8.5% coconut) and spliced ice (splicing interface inclination 30°, 60°) at freezing temperature of −10 ℃ were studied. The strain rate ranges from 150~250 s−1. The failure process was recorded by using the high-speed camera triggered simultaneously with the pressure rod. The correlation between the stress and strain of the sample, along with the failure process, was determined by analyzing the time history curve of sample. The failure mode of the spliced ice sample was analyzed by combining the Mohr-Coulomb strength criterion. The results show that the pure water ice exhibits the highest compressive strength, followed by the ice with coconut shreds, and both of them show a positive strain rate effect. However, the compressive strength of the ice with salt addition decreases significantly due to its loose structure and the strain rate effect is not obvious. The dynamic compressive strength of ice samples added with coconut fiber increases firstly and then decreases with the increase of coconut fiber content. Ice samples with high coconut fiber content are prone to "double peak" phenomenon due to the binding effect of coconut fiber on broken ice with small particle size. The splicing plane affects the crack growth, resulting in lower compressive strength than the intact ice sample, and affects the failure mode as well. The ice with small interface inclination is mainly damaged by interface slip, while the ice with large interface inclination is mainly damaged by whole ice, which is similar to the intact ice. The research results provide theoretical basis and method reference for the dynamic mechanical properties of non-pure and non-intact ice materials under impact loads.
, Available online , doi: 10.11883/bzycj-2024-0229
Abstract:
To investigate the influence of the density of crushed ice region on the cavity evolution of a structure, an oblique water-entry experiment of the structure was conducted by high-speed photography technology under different crushed ice cover densities. Moreover, by comparing the water-entry process of the oblique structure in varying densities of crushed ice cover, the influence of crushed ice cover density on cavity evolution during the oblique water-entry process of the structure was obtained. Results indicate that during the cavity expansion, the presence of crushed ice reduces the cavity diameter by impeding the outward expansion of the fluid near the free surface, compared with the ice-free environment. When the cavity closes, crushed ice also impedes the inward contraction of the free surface fluid and prolongs the cavity expansion time. The augmentation in the total volume of air within the cavity results in a decrement of the pressure differential between the inside and outside of the cavity, ultimately leading to a retardation in the cavity closure time. As the coverage density of crushed ice gradually increases, the impedance exerted by the crushed ice on the inward contraction of fluid at the free surface progressively intensifies. This enhanced obstruction from the crushed ice further prolongs the cavity closure time and concurrently augments its length and maximum diameter. In conditions of lower crushed ice densities, jets point to the interior of the cavity when the cavity collapses. Besides, under conditions of higher crushed ice cover densities, the cavity wall is wrinkled by the irregular impact of the fluid. As the submerged depth of the structure increases, the cavity undergoes a deep necking under the influence of ambient pressure. As the coverage density of crushed ice gradually increases, the velocity of the underwater motion of the structure shows a trend of faster decay compared to ice-free environments.
To investigate the influence of the density of crushed ice region on the cavity evolution of a structure, an oblique water-entry experiment of the structure was conducted by high-speed photography technology under different crushed ice cover densities. Moreover, by comparing the water-entry process of the oblique structure in varying densities of crushed ice cover, the influence of crushed ice cover density on cavity evolution during the oblique water-entry process of the structure was obtained. Results indicate that during the cavity expansion, the presence of crushed ice reduces the cavity diameter by impeding the outward expansion of the fluid near the free surface, compared with the ice-free environment. When the cavity closes, crushed ice also impedes the inward contraction of the free surface fluid and prolongs the cavity expansion time. The augmentation in the total volume of air within the cavity results in a decrement of the pressure differential between the inside and outside of the cavity, ultimately leading to a retardation in the cavity closure time. As the coverage density of crushed ice gradually increases, the impedance exerted by the crushed ice on the inward contraction of fluid at the free surface progressively intensifies. This enhanced obstruction from the crushed ice further prolongs the cavity closure time and concurrently augments its length and maximum diameter. In conditions of lower crushed ice densities, jets point to the interior of the cavity when the cavity collapses. Besides, under conditions of higher crushed ice cover densities, the cavity wall is wrinkled by the irregular impact of the fluid. As the submerged depth of the structure increases, the cavity undergoes a deep necking under the influence of ambient pressure. As the coverage density of crushed ice gradually increases, the velocity of the underwater motion of the structure shows a trend of faster decay compared to ice-free environments.
, Available online , doi: 10.11883/bzycj-2024-0099
Abstract:
Artificial intelligence/machine learning methods can discover hidden physical patterns in data. By constructing an end-to-end surrogate model between state parameters and dynamic results, many complex engineering problems such as strong coupling, nonlinearity, and multiphysics can be efficiently solved. In the field of highly nonlinear explosion and shock dynamics, a classic detonation driving problem was chosen as the research object. Using numerical simulation results as training data for machine learning surrogate models, and combining forward simulation and reverse design organically. Based on deep neural network technology, an end-to-end surrogate model was constructed between feature position velocity profiles, material dynamic deformation, and engineering factors. And the calculation accuracy of the surrogate model was provided, verifying the ability to invert engineering factors from velocity profiles. The research results indicate that the end-to-end surrogate model has high predictive ability, with relative errors of less than 1% in both velocity profile prediction and engineering factor estimation. It can be applied to the rapid design, high-precision prediction, and agile iteration of highly nonlinear explosion and impact dynamics problems.
Artificial intelligence/machine learning methods can discover hidden physical patterns in data. By constructing an end-to-end surrogate model between state parameters and dynamic results, many complex engineering problems such as strong coupling, nonlinearity, and multiphysics can be efficiently solved. In the field of highly nonlinear explosion and shock dynamics, a classic detonation driving problem was chosen as the research object. Using numerical simulation results as training data for machine learning surrogate models, and combining forward simulation and reverse design organically. Based on deep neural network technology, an end-to-end surrogate model was constructed between feature position velocity profiles, material dynamic deformation, and engineering factors. And the calculation accuracy of the surrogate model was provided, verifying the ability to invert engineering factors from velocity profiles. The research results indicate that the end-to-end surrogate model has high predictive ability, with relative errors of less than 1% in both velocity profile prediction and engineering factor estimation. It can be applied to the rapid design, high-precision prediction, and agile iteration of highly nonlinear explosion and impact dynamics problems.
, Available online , doi: 10.11883/bzycj-2024-0118
Abstract:
With the wide application of new types of ammunition and large-caliber heavy artillery, the non-contact killing mode caused by explosive shock is rapidly replacing the original direct contact killing caused by bullets, fragments, etc., and its killing power, precision, etc., on the combat personnel and equipment is more threatening. This paper will start from the introduction of the typical test environment and methods of explosive shock wave, through an overview of the explosive impact monitoring and sensing technology and explosive impact flow field reconstruction technology analysis to summarize the development trend, and finally the application of portable explosive shock wave sensing system in the foreign military was briefly introduced for the research and development of China's related products to provide reference experience. At present, the most commonly used sensors in explosion impact tests are overpressure sensors and acceleration sensors. Among them, overpressure sensors can be divided into piezoresistive sensor, piezoelectric sensor and fiber-optic sensor; acceleration sensors cloud be divided into piezoresistive acceleration sensors, piezoelectric acceleration sensors, capacitive acceleration sensors, resonance acceleration sensors, electron tunneling acceleration sensors, thermal convection acceleration sensors and optical acceleration sensors (space light acceleration sensors, fiber-optic acceleration sensors). accelerometers, fiber optic accelerometers). The demanding testing environment requires all sensors to have high frequency response , good detection linear characteristics, high signal-to-noise ratio, high sensitivity, good anti-interference performance, and excellent characteristics such as small size and light weight. Shock wave over-pressure sensor toward miniaturization, standardization, integration and intelligent research direction, while vigorously developing new sensing technology research. Based on CFD data and experimental data, artificial intelligence technology is introduced into the explosion wave signal processing and flow field reconstruction; portable explosion impact detection and evaluation system with independent intellectual property rights in China is developed to provide rapid classification and rapid diagnosis and treatment basis for the protection and rescue of special industry practitioners in extreme environments.
With the wide application of new types of ammunition and large-caliber heavy artillery, the non-contact killing mode caused by explosive shock is rapidly replacing the original direct contact killing caused by bullets, fragments, etc., and its killing power, precision, etc., on the combat personnel and equipment is more threatening. This paper will start from the introduction of the typical test environment and methods of explosive shock wave, through an overview of the explosive impact monitoring and sensing technology and explosive impact flow field reconstruction technology analysis to summarize the development trend, and finally the application of portable explosive shock wave sensing system in the foreign military was briefly introduced for the research and development of China's related products to provide reference experience. At present, the most commonly used sensors in explosion impact tests are overpressure sensors and acceleration sensors. Among them, overpressure sensors can be divided into piezoresistive sensor, piezoelectric sensor and fiber-optic sensor; acceleration sensors cloud be divided into piezoresistive acceleration sensors, piezoelectric acceleration sensors, capacitive acceleration sensors, resonance acceleration sensors, electron tunneling acceleration sensors, thermal convection acceleration sensors and optical acceleration sensors (space light acceleration sensors, fiber-optic acceleration sensors). accelerometers, fiber optic accelerometers). The demanding testing environment requires all sensors to have high frequency response , good detection linear characteristics, high signal-to-noise ratio, high sensitivity, good anti-interference performance, and excellent characteristics such as small size and light weight. Shock wave over-pressure sensor toward miniaturization, standardization, integration and intelligent research direction, while vigorously developing new sensing technology research. Based on CFD data and experimental data, artificial intelligence technology is introduced into the explosion wave signal processing and flow field reconstruction; portable explosion impact detection and evaluation system with independent intellectual property rights in China is developed to provide rapid classification and rapid diagnosis and treatment basis for the protection and rescue of special industry practitioners in extreme environments.
, Available online , doi: 10.11883/bzycj-2024-0254
Abstract:
To address the issues of over-excavation at the tunnel arch foot due to the difficulty of forming the perimeter hole blasting and under-excavation at the tunnel face bottom, the damage characteristics of surrounding rock caused by perimeter hole blasting at the arch foot of a horseshoe-shaped tunnel were studied through a combination of theoretical calculations and numerical simulations. On the theoretical level, an in-depth analysis of the stress distribution and crack radius in the arch foot area was conducted based on the principles of blasting mechanics, and the theoretical charge length for the perimeter holes at the arch foot was derived. Building on this, a 3D numerical model of the perimeter holes at the arch foot was established through numerical simulation. During the modeling process, the damage evolution in the surrounding rock during blasting was simulated by introducing an appropriate damage model, and post-blast damage cloud maps were generated. By comparing the damage cloud maps under different conditions, the relationship between blasting effectiveness and parameters such as free surface shape, charge amount, and void deflection angle was analyzed, further revealing the mechanisms by which these parameters influence the blasting formation results, which were validated through field experiments. The research results indicate that the shape of the free surface significantly impacts the extent of surrounding rock damage and the energy utilization efficiency of explosives. A concave free surface results in a smaller damage range compared to a flat free surface, with greater rock confinement, making it difficult for the explosives to effectively fracture the surrounding rock, leading to an energy utilization rate of only 78%. The blasting effectiveness shows a trend of first increasing and then decreasing with the increase in charge amount, with the optimal blasting effectiveness achieved when the linear charge density of the perimeter holes at the arch foot is 0.624. Additionally, by setting voids and adjusting the void deflection angle, the blasting effectiveness of the perimeter holes at the arch foot can be improved. With the optimized blasting parameters, the maximum linear over-excavation at the arch foot was reduced by 53.1%, resulting in a smooth tunnel contour. The research outcomes are engineeringly feasible and provide valuable insights for similar projects.
To address the issues of over-excavation at the tunnel arch foot due to the difficulty of forming the perimeter hole blasting and under-excavation at the tunnel face bottom, the damage characteristics of surrounding rock caused by perimeter hole blasting at the arch foot of a horseshoe-shaped tunnel were studied through a combination of theoretical calculations and numerical simulations. On the theoretical level, an in-depth analysis of the stress distribution and crack radius in the arch foot area was conducted based on the principles of blasting mechanics, and the theoretical charge length for the perimeter holes at the arch foot was derived. Building on this, a 3D numerical model of the perimeter holes at the arch foot was established through numerical simulation. During the modeling process, the damage evolution in the surrounding rock during blasting was simulated by introducing an appropriate damage model, and post-blast damage cloud maps were generated. By comparing the damage cloud maps under different conditions, the relationship between blasting effectiveness and parameters such as free surface shape, charge amount, and void deflection angle was analyzed, further revealing the mechanisms by which these parameters influence the blasting formation results, which were validated through field experiments. The research results indicate that the shape of the free surface significantly impacts the extent of surrounding rock damage and the energy utilization efficiency of explosives. A concave free surface results in a smaller damage range compared to a flat free surface, with greater rock confinement, making it difficult for the explosives to effectively fracture the surrounding rock, leading to an energy utilization rate of only 78%. The blasting effectiveness shows a trend of first increasing and then decreasing with the increase in charge amount, with the optimal blasting effectiveness achieved when the linear charge density of the perimeter holes at the arch foot is 0.624. Additionally, by setting voids and adjusting the void deflection angle, the blasting effectiveness of the perimeter holes at the arch foot can be improved. With the optimized blasting parameters, the maximum linear over-excavation at the arch foot was reduced by 53.1%, resulting in a smooth tunnel contour. The research outcomes are engineeringly feasible and provide valuable insights for similar projects.
, Available online , doi: 10.11883/bzycj-2024-0175
Abstract:
The safety of propulsion lithium batteries is a technical bottleneck problem restricting the operation and airworthiness certification of electric aircraft and affects the development of electric aviation worldwide. Failure events such as combustion and explosion triggered by thermal runaway of lithium batteries will cause the catastrophic consequences of aircraft destruction and casualties. This paper aims to introduce the status of aircraft lithium battery thermal runaway explosion characteristics for relevant researchers from three aspects, respectively, lithium-ion battery thermal runaway combustion and explosion behavior, thermal runaway gas explosion limit and thermal runaway gas explosion hazard assessment. In terms of lithium-ion battery thermal runaway explosion behaviors, introduced the lithium-ion battery thermal runaway development process, analyzed the determination of the parameters of the thermal runaway impact characteristics, summarized the evolution of the thermal jet mechanism and the simulation of jet flame and experimental methods; For the thermal runaway gas explosion limit, compared with national and international testing standards for the explosion limit of gases, concluded the theoretical calculation of the explosion limit of thermal runaway gas, as well as in-situ detection of the explosion limit of innovative methods are introduced; In the thermal runaway gas explosion risk assessment, a method of ageing lithium-ion battery risk assessment is proposed by innovatively combining CT non-destructive testing technology with explosion limit in-situ testing method. Based on the characteristics of lithium-ion battery thermal runaway gas explosion limit and pressure rise rate, the factors of explosion danger and explosion severity are obtained, and the explosion risk calculation formula explosion danger parameter indicators are innovated. It proposes that future research will focus on areas such as advanced diagnostic techniques, enhanced electrolyte stability, multi-scale modelling, advanced inhibition techniques, and the establishment of standardized testing processes and safety regulations. It proposes that future research will focus on areas such as advanced diagnostic techniques, enhanced electrolyte stability, multi-scale modeling, advanced inhibition techniques, and the establishment of standardized test procedures and technical regulations.
The safety of propulsion lithium batteries is a technical bottleneck problem restricting the operation and airworthiness certification of electric aircraft and affects the development of electric aviation worldwide. Failure events such as combustion and explosion triggered by thermal runaway of lithium batteries will cause the catastrophic consequences of aircraft destruction and casualties. This paper aims to introduce the status of aircraft lithium battery thermal runaway explosion characteristics for relevant researchers from three aspects, respectively, lithium-ion battery thermal runaway combustion and explosion behavior, thermal runaway gas explosion limit and thermal runaway gas explosion hazard assessment. In terms of lithium-ion battery thermal runaway explosion behaviors, introduced the lithium-ion battery thermal runaway development process, analyzed the determination of the parameters of the thermal runaway impact characteristics, summarized the evolution of the thermal jet mechanism and the simulation of jet flame and experimental methods; For the thermal runaway gas explosion limit, compared with national and international testing standards for the explosion limit of gases, concluded the theoretical calculation of the explosion limit of thermal runaway gas, as well as in-situ detection of the explosion limit of innovative methods are introduced; In the thermal runaway gas explosion risk assessment, a method of ageing lithium-ion battery risk assessment is proposed by innovatively combining CT non-destructive testing technology with explosion limit in-situ testing method. Based on the characteristics of lithium-ion battery thermal runaway gas explosion limit and pressure rise rate, the factors of explosion danger and explosion severity are obtained, and the explosion risk calculation formula explosion danger parameter indicators are innovated. It proposes that future research will focus on areas such as advanced diagnostic techniques, enhanced electrolyte stability, multi-scale modelling, advanced inhibition techniques, and the establishment of standardized testing processes and safety regulations. It proposes that future research will focus on areas such as advanced diagnostic techniques, enhanced electrolyte stability, multi-scale modeling, advanced inhibition techniques, and the establishment of standardized test procedures and technical regulations.
, Available online , doi: 10.11883/bzycj-2024-0069
Abstract:
In relation to the application of high-entropy alloy systems containing high-density and high-calorific value elements in the liner of shaped charge warheads, the Ta-Hf-Nb-Zr high-entropy alloy system is investigated. The study employed an INSTRON material testing machine and a split Hopkinson pressure bar testing platform to explore the mechanical response of this high-entropy alloy across a wide range of strain rates from 10−3 to 103 s−1, temperatures ranging from 25 to 900 °C, and stress triaxiality values ranging from 0.33 to 0.89. Yield strength and failure strain data were obtained from static round bar tensile tests and dynamic compression tests conducted under these varying conditions. By using least squares fitting, the parameters of the Johnson-Cook (J-C) constitutive equation as well as the damage failure model parameters, are derived. Subsequently, a simulation model for explosively formed projectile (EFP) made from high-entropy alloys under explosive loading conditions was developed. Pulse X-ray tests of the EFP formation were performed, and numerical simulations of the EFP formation process are conducted using LS-DYNA software. The results show that at 117 μs, the high-entropy alloy EFP remains largely intact, with a length of 51.1 mm and a diameter of 12.27 mm. At 187 μs, three fractures are observed at the tail of the EFP, with the head length measuring 24.3 mm, the diameter at 12.27 mm, and the EFP speed recorded at2496.3 m/s. The numerical simulations demonstrate that the EFP length, diameter, and velocity at these time instants match the test data with errors of less than 8.2%. Moreover, the fracture patterns observed experimentally align closely with those predicted by the simulations. This consistency indicates that the J-C model effectively predicts the formation characteristics of high-entropy alloy EFPs under explosive loading conditions, confirming its utility in accurately simulating the EFP formation process.
In relation to the application of high-entropy alloy systems containing high-density and high-calorific value elements in the liner of shaped charge warheads, the Ta-Hf-Nb-Zr high-entropy alloy system is investigated. The study employed an INSTRON material testing machine and a split Hopkinson pressure bar testing platform to explore the mechanical response of this high-entropy alloy across a wide range of strain rates from 10−3 to 103 s−1, temperatures ranging from 25 to 900 °C, and stress triaxiality values ranging from 0.33 to 0.89. Yield strength and failure strain data were obtained from static round bar tensile tests and dynamic compression tests conducted under these varying conditions. By using least squares fitting, the parameters of the Johnson-Cook (J-C) constitutive equation as well as the damage failure model parameters, are derived. Subsequently, a simulation model for explosively formed projectile (EFP) made from high-entropy alloys under explosive loading conditions was developed. Pulse X-ray tests of the EFP formation were performed, and numerical simulations of the EFP formation process are conducted using LS-DYNA software. The results show that at 117 μs, the high-entropy alloy EFP remains largely intact, with a length of 51.1 mm and a diameter of 12.27 mm. At 187 μs, three fractures are observed at the tail of the EFP, with the head length measuring 24.3 mm, the diameter at 12.27 mm, and the EFP speed recorded at
, Available online , doi: 10.11883/bzycj-2024-0095
Abstract:
As an environmentally friendly energy-absorbing material, shear-thickening fluid (STF) can be applied to protective structures to improve impact resistance. STF was obtained by mixing fumed silica particles with polyethylene glycol solution. It was then filled into a honeycomb core layer to make STF-filled honeycomb sandwich panels. Finally, the effect of STF on the impact resistance of the structure was explored. The impact force-displacement curves were obtained by using the drop weight impact experiment, and the effects of impact velocity (1.0, 1.5, 2.0 m/s), honeycomb aperture diameter (2.0, 2.5, 3.0 mm), and wall thickness (0.04, 0.06, 0.08 mm) on the mechanical properties of the sandwich panel were studied. At the same time, digital image correlation technology was utilized, which is an optical method for measuring the deformation of the surface of an object. By comparing the pixel displacements in multiple images, the strain history and deflection field distribution of the back panel of the structure were obtained, and the low-velocity impact response process of the structure was discussed. The experimental results show that under low-velocity impact, there is bump deformation in the center area of the back panel of the STF-unfilled honeycomb sandwich panel, and there is obvious bulging deformation in the surrounding area. The central area of the back panel of the STF-filled honeycomb sandwich panels has a wider range of bump deformations and no bulging around it. The shear-thickening effect of STF can increase the honeycomb elements involved in energy absorption, expand the local deformation area of the structure, and reduce the deflection of the back panel of the structure. Increasing the impact velocity, increasing the honeycomb aperture diameter, or decreasing the wall thickness are all more conducive to the shear-thickening effect of STF. The results provide a reference for the application of STF in protective structures.
As an environmentally friendly energy-absorbing material, shear-thickening fluid (STF) can be applied to protective structures to improve impact resistance. STF was obtained by mixing fumed silica particles with polyethylene glycol solution. It was then filled into a honeycomb core layer to make STF-filled honeycomb sandwich panels. Finally, the effect of STF on the impact resistance of the structure was explored. The impact force-displacement curves were obtained by using the drop weight impact experiment, and the effects of impact velocity (1.0, 1.5, 2.0 m/s), honeycomb aperture diameter (2.0, 2.5, 3.0 mm), and wall thickness (0.04, 0.06, 0.08 mm) on the mechanical properties of the sandwich panel were studied. At the same time, digital image correlation technology was utilized, which is an optical method for measuring the deformation of the surface of an object. By comparing the pixel displacements in multiple images, the strain history and deflection field distribution of the back panel of the structure were obtained, and the low-velocity impact response process of the structure was discussed. The experimental results show that under low-velocity impact, there is bump deformation in the center area of the back panel of the STF-unfilled honeycomb sandwich panel, and there is obvious bulging deformation in the surrounding area. The central area of the back panel of the STF-filled honeycomb sandwich panels has a wider range of bump deformations and no bulging around it. The shear-thickening effect of STF can increase the honeycomb elements involved in energy absorption, expand the local deformation area of the structure, and reduce the deflection of the back panel of the structure. Increasing the impact velocity, increasing the honeycomb aperture diameter, or decreasing the wall thickness are all more conducive to the shear-thickening effect of STF. The results provide a reference for the application of STF in protective structures.
, Available online , doi: 10.11883/bzycj-2024-0023
Abstract:
Simultaneous or slightly different explosions at multiple points in the concrete medium can generate a complex superposition and aggregation effect of ground shock waves, significantly enhancing the pressure of ground shock waves in a specific area and greatly improving the destructive power of the explosion. In order to obtain the explosion aggregation effect and ground shock propagation attenuation law under the different arrangement of multi-point explosive sources. Firstly, field tests were carried out on single and seven-point aggregated explosions in concrete. Then, the reliability of the RHT material model parameters and the SPH numerical algorithm were verified based on experimental data. On this basis through the orthogonal design method and gray system theory on the multi-point detonation parameters for the optimization of design. Gray correlation coefficients and gray correlations between scaled charge spacing, scaled active charge height, scaled detonation time difference and peak pressure at different proportional bursting center distances were established. Finally, single-objective factor optimization and multi-objective factor optimization were identified, a set of preferred combinations of each factor was determined, and simulation tests were conducted to verify the results. The analysis results show that the concrete material model of RHT and the SPH algorithm can reasonably predict the shock wave propagation attenuation characteristics of multipoint charge explosions at different scaled bursting center distances as well as the induced damage and destruction of concrete; The main factors affecting the impact of the ground shock aggregation of explosive effect, in order of magnitude: scaled charge spacing, scaled detonation time difference and scaled active charge height. The use of optimized detonation parameters, that is, in the case of this test, in the proportional charge spacing 0.549 m/kg1/3, the proportional detonation time difference of 0.239 m/kg1/3, the proportional active charge height of 0, the ground shock aggregation effect to achieve the best, up to the same amount of single-point group charging the same amount of ground shock pressure of 4.7 times.
Simultaneous or slightly different explosions at multiple points in the concrete medium can generate a complex superposition and aggregation effect of ground shock waves, significantly enhancing the pressure of ground shock waves in a specific area and greatly improving the destructive power of the explosion. In order to obtain the explosion aggregation effect and ground shock propagation attenuation law under the different arrangement of multi-point explosive sources. Firstly, field tests were carried out on single and seven-point aggregated explosions in concrete. Then, the reliability of the RHT material model parameters and the SPH numerical algorithm were verified based on experimental data. On this basis through the orthogonal design method and gray system theory on the multi-point detonation parameters for the optimization of design. Gray correlation coefficients and gray correlations between scaled charge spacing, scaled active charge height, scaled detonation time difference and peak pressure at different proportional bursting center distances were established. Finally, single-objective factor optimization and multi-objective factor optimization were identified, a set of preferred combinations of each factor was determined, and simulation tests were conducted to verify the results. The analysis results show that the concrete material model of RHT and the SPH algorithm can reasonably predict the shock wave propagation attenuation characteristics of multipoint charge explosions at different scaled bursting center distances as well as the induced damage and destruction of concrete; The main factors affecting the impact of the ground shock aggregation of explosive effect, in order of magnitude: scaled charge spacing, scaled detonation time difference and scaled active charge height. The use of optimized detonation parameters, that is, in the case of this test, in the proportional charge spacing 0.549 m/kg1/3, the proportional detonation time difference of 0.239 m/kg1/3, the proportional active charge height of 0, the ground shock aggregation effect to achieve the best, up to the same amount of single-point group charging the same amount of ground shock pressure of 4.7 times.
, Available online , doi: 10.11883/bzycj-2024-0312
Abstract:
Lithium-ion battery combustion accidents are known for their rapid onset and difficulty in extinguishment, raising significant safety concerns in environments with collision risks. These risks highlight the need for stringent damage assessment and failure prediction methods for power batteries. While severe collisions can cause immediate catastrophic damage and thermal runaway, most collisions occur at low speeds, where the impact may result in only minor external deformation without immediate failure. However, the potential safety risks associated with continued use of batteries after such minor collisions are not well understood. Current research and battery safety standards primarily focus on immediate or short-term failure after impact, leaving a gap in understanding the long-term effects of low-energy collisions on battery safety. This study addresses this gap by investigating the impact of low-energy collisions on the safety and reliability of lithium-ion batteries. A shock-compression sequential loading experiment was used to evaluate the mechanical response and failure behavior of pouch batteries under dynamic loading. The study also explored the deterioration of batteries subjected to weaker impact loads through electrochemical performance testing and internal structural damage analysis. The results reveal that even if a battery does not fail immediately under low-impact energy, its internal mechanical integrity may still be compromised, leading to a lower failure threshold under subsequent loads. Significant deterioration in capacity and internal resistance was observed, with the battery’s ability to withstand secondary loads and its electrochemical performance declining as impact energy increased. This indicates a clear correlation between impact-induced deformation and overall battery performance. The study also proposes a quantitative evaluation method for assessing the battery's condition after minor impacts, offering a valuable tool for predicting the risks associated with reusing impacted batteries. These insights are essential for understanding the response mechanisms of lithium-ion batteries under low-energy collision conditions and for optimizing safety standards for their continued use in collision-prone environments.
Lithium-ion battery combustion accidents are known for their rapid onset and difficulty in extinguishment, raising significant safety concerns in environments with collision risks. These risks highlight the need for stringent damage assessment and failure prediction methods for power batteries. While severe collisions can cause immediate catastrophic damage and thermal runaway, most collisions occur at low speeds, where the impact may result in only minor external deformation without immediate failure. However, the potential safety risks associated with continued use of batteries after such minor collisions are not well understood. Current research and battery safety standards primarily focus on immediate or short-term failure after impact, leaving a gap in understanding the long-term effects of low-energy collisions on battery safety. This study addresses this gap by investigating the impact of low-energy collisions on the safety and reliability of lithium-ion batteries. A shock-compression sequential loading experiment was used to evaluate the mechanical response and failure behavior of pouch batteries under dynamic loading. The study also explored the deterioration of batteries subjected to weaker impact loads through electrochemical performance testing and internal structural damage analysis. The results reveal that even if a battery does not fail immediately under low-impact energy, its internal mechanical integrity may still be compromised, leading to a lower failure threshold under subsequent loads. Significant deterioration in capacity and internal resistance was observed, with the battery’s ability to withstand secondary loads and its electrochemical performance declining as impact energy increased. This indicates a clear correlation between impact-induced deformation and overall battery performance. The study also proposes a quantitative evaluation method for assessing the battery's condition after minor impacts, offering a valuable tool for predicting the risks associated with reusing impacted batteries. These insights are essential for understanding the response mechanisms of lithium-ion batteries under low-energy collision conditions and for optimizing safety standards for their continued use in collision-prone environments.
, Available online , doi: 10.11883/bzycj-2024-0240
Abstract:
The thermal shock caused by thermal runaway of lithium batteries will damage the installation structure and pose a threat to the safety of surrounding personnel and equipment, which is a key issue limiting their aviation applications. Through a self-built high-temperature impact experimental platform for lithium battery thermal runaway, it was found that the impact pressure on the battery pack top plate from single-cell thermal shock can reach up to 13.23 kPa, causing the external surface temperature to exceed 274 ℃. The combined effect of high temperature and impact pressure increases the risk of the casing undergoing plastic deformation, buckling, or even failure. To effectively mitigate such risks, a passive protection method of coating the top plate of the battery pack with fireproof coating is proposed. Through large panel combustion experiments and cone calorimeter tests, it was found that the epoxy resin-based intumescent fireproof coatings can effectively block the impact pressure of lithium battery thermal runaway by expanding, and they absorb heat, reducing and delaying the temperature rise of the battery pack top plate, demonstrating excellent thermal shock resistance. By comparing the containment effects of fireproof coatings of different thicknesses, it was found that the 1mm coating is more suitable for practical application needs. Referring to relevant airworthiness regulations, verification tests were conducted on the containment of lithium battery thermal runaway. The analysis of the experiment results shows that the 1.0 mm thick E80S20 coating and E85S15B3 coating reduced the maximum temperature of the battery pack top plate by 52.16% and 55.80%, respectively. Additionally, the maximum structural deformation decreased by 72.2% and 44.4%, respectively. The study indicates that passive protection technology of fireproof coating can effectively enhance the containment of high temperatures and impact hazards caused by thermal runaway. This approach can serve as an effective measure in the safety design of aviation power lithium battery systems.
The thermal shock caused by thermal runaway of lithium batteries will damage the installation structure and pose a threat to the safety of surrounding personnel and equipment, which is a key issue limiting their aviation applications. Through a self-built high-temperature impact experimental platform for lithium battery thermal runaway, it was found that the impact pressure on the battery pack top plate from single-cell thermal shock can reach up to 13.23 kPa, causing the external surface temperature to exceed 274 ℃. The combined effect of high temperature and impact pressure increases the risk of the casing undergoing plastic deformation, buckling, or even failure. To effectively mitigate such risks, a passive protection method of coating the top plate of the battery pack with fireproof coating is proposed. Through large panel combustion experiments and cone calorimeter tests, it was found that the epoxy resin-based intumescent fireproof coatings can effectively block the impact pressure of lithium battery thermal runaway by expanding, and they absorb heat, reducing and delaying the temperature rise of the battery pack top plate, demonstrating excellent thermal shock resistance. By comparing the containment effects of fireproof coatings of different thicknesses, it was found that the 1mm coating is more suitable for practical application needs. Referring to relevant airworthiness regulations, verification tests were conducted on the containment of lithium battery thermal runaway. The analysis of the experiment results shows that the 1.0 mm thick E80S20 coating and E85S15B3 coating reduced the maximum temperature of the battery pack top plate by 52.16% and 55.80%, respectively. Additionally, the maximum structural deformation decreased by 72.2% and 44.4%, respectively. The study indicates that passive protection technology of fireproof coating can effectively enhance the containment of high temperatures and impact hazards caused by thermal runaway. This approach can serve as an effective measure in the safety design of aviation power lithium battery systems.
, Available online , doi: 10.11883/bzycj-2024-0188
Abstract:
To improve the safety performance of cylindrical lithium-ion batteries under radial dynamic impacting, the dynamic response characteristics of the batteries under large deformation were investigated based on the membrane factor method. Firstly, the battery was simplified to sandwich beam including the casing and inner core. The plastic yield criterion and membrane factor of the battery cross-section were established based on tensile yield strengths. The membrane factor was introduced into the motion equation to solve the dynamic response under large deformation. Furthermore, the mechanical properties of the battery components were determined based on tensile and compression tests. Then the finite element (FE) model of the battery was developed. It has been shown that the theoretical results and FE results of the displacement responses and velocity responses of the battery were in good agreement. The larger the initial velocity of the battery under impact loading, the larger the effect of axial force effect on the dynamic response. The maximum deflection of the battery increases approximately linearly with initial velocity, and the actual response time shows saturation. The maximum deflection of the battery increases with the decrease of the ratio of casing yield strength to core yield strength. The effect of yield strength is significant under thin battery casings. The maximum deflection of the battery decreases with the increase of the casing thickness. Under high yield strength ratio, the effect of casing thickness is significant. The research can provide technical support for the failure prediction and structural safety design of the battery.
To improve the safety performance of cylindrical lithium-ion batteries under radial dynamic impacting, the dynamic response characteristics of the batteries under large deformation were investigated based on the membrane factor method. Firstly, the battery was simplified to sandwich beam including the casing and inner core. The plastic yield criterion and membrane factor of the battery cross-section were established based on tensile yield strengths. The membrane factor was introduced into the motion equation to solve the dynamic response under large deformation. Furthermore, the mechanical properties of the battery components were determined based on tensile and compression tests. Then the finite element (FE) model of the battery was developed. It has been shown that the theoretical results and FE results of the displacement responses and velocity responses of the battery were in good agreement. The larger the initial velocity of the battery under impact loading, the larger the effect of axial force effect on the dynamic response. The maximum deflection of the battery increases approximately linearly with initial velocity, and the actual response time shows saturation. The maximum deflection of the battery increases with the decrease of the ratio of casing yield strength to core yield strength. The effect of yield strength is significant under thin battery casings. The maximum deflection of the battery decreases with the increase of the casing thickness. Under high yield strength ratio, the effect of casing thickness is significant. The research can provide technical support for the failure prediction and structural safety design of the battery.
, Available online , doi: 10.11883/bzycj-2024-0158
Abstract:
Combined with the actual distribution characteristics of tungsten fibers and metallic glass matrix, a three-dimensional (3D) mesoscale finite element (FE) geometric model of a long rod of tungsten fiber-reinforced metallic glass composite was established, and the coupled thermo-mechanical constitutive model was used to describe the high strength and high shear sensitivity of metallic glass matrix. FE simulations on the oblique penetration/perforation of composite and tungsten alloy long rods into steel targets were carried out combined with related oblique penetrating tests, and comparative analyses on the deformation and failure characteristics of projectiles and targets were conducted. Furthermore, the influences of oblique angle and impact velocity on the ‘self-sharpening’ behavior of composite long rods and the corresponding ballistic performance were investigated in detail. Related analysis shows that in the oblique impact condition, due to the asymmetrical characteristics of target resistance on the rod, the rod nose gradually sharpens into an asymmetrical pointed configuration, and certain deflection occurs in the trajectory. Consequently, the ‘self-sharpening’ behavior in the composite long rod is weakened to a certain extent, and thus a decay occurs in its penetrating property. Besides, the impact velocity also contributes to the ‘self-sharpening’ characteristics and the corresponding ballistic behavior in the oblique impact condition, and the decay of penetrating capability derived from the oblique angle is more remarkable at lower impact velocities. When the oblique angle increases to 50°, the composite long rod is hard to effectively penetrate the target at an impact velocity lower than 900 m/s, and ricochet becomes easy when it impacts under a higher oblique angle. The results are of good significance in predicting the penetrating ability of tungsten fiber-reinforced metallic glass matrix composite long rods and optimizing its impact attitude.
Combined with the actual distribution characteristics of tungsten fibers and metallic glass matrix, a three-dimensional (3D) mesoscale finite element (FE) geometric model of a long rod of tungsten fiber-reinforced metallic glass composite was established, and the coupled thermo-mechanical constitutive model was used to describe the high strength and high shear sensitivity of metallic glass matrix. FE simulations on the oblique penetration/perforation of composite and tungsten alloy long rods into steel targets were carried out combined with related oblique penetrating tests, and comparative analyses on the deformation and failure characteristics of projectiles and targets were conducted. Furthermore, the influences of oblique angle and impact velocity on the ‘self-sharpening’ behavior of composite long rods and the corresponding ballistic performance were investigated in detail. Related analysis shows that in the oblique impact condition, due to the asymmetrical characteristics of target resistance on the rod, the rod nose gradually sharpens into an asymmetrical pointed configuration, and certain deflection occurs in the trajectory. Consequently, the ‘self-sharpening’ behavior in the composite long rod is weakened to a certain extent, and thus a decay occurs in its penetrating property. Besides, the impact velocity also contributes to the ‘self-sharpening’ characteristics and the corresponding ballistic behavior in the oblique impact condition, and the decay of penetrating capability derived from the oblique angle is more remarkable at lower impact velocities. When the oblique angle increases to 50°, the composite long rod is hard to effectively penetrate the target at an impact velocity lower than 900 m/s, and ricochet becomes easy when it impacts under a higher oblique angle. The results are of good significance in predicting the penetrating ability of tungsten fiber-reinforced metallic glass matrix composite long rods and optimizing its impact attitude.
, Available online , doi: 10.11883/bzycj-2024-0073
Abstract:
To improve the accuracy and robustness of the explicit FEM algorithm based on penalty method for simulating large deformation contact-impact problem, a new large-deformation non-penetration contact algorithm based on forward incremental displacement central difference (FIDCD) was developed. On the one hand, according to FIDCD, the solving step of the dynamic equation was decomposed into an estimated step without considering contact and a correction step considering contact constraint. At the current moment, a contact force was applied thorough the penalty method to make the deformation of entities satisfy the non-penetration condition. The contact force was calculated by a soft constraint penalty stiffness, which helped to maintain stability of contact localization. It enhanced the numerical accuracy of the explicit contact computation. On the other hand, to accurately calculate the large-deformation internal force of the next moment while only obtaining the displacement, the internal force term of the dynamic equation was mapped to a known configuration for solution based on the arbitrary reference configurations (ARC) theory. It avoided using the values of variables at intermediate configuration to approximate them, thereby improving the numerical accuracy of the large deformation computation. More rigorous contact algorithms and geometric nonlinear solution strategy can effectively suppress mesh distortion and non-physical penetration between entities during large-deformation impact simulation. This thus improved the robustness of the new explicit algorithm. Finally, the computational program written according to the new developed algorithm was applied to simulate several impact and penetration examples with different impact velocities. By comparing the simulation results with those obtained from commercial software, the correctness of the developed algorithm and computational program was verified. At the same time, it can also be proven that the algorithm proposed is more robust in simulating high-speed and large-deformation impact problems than the classical explicit contact-impact algorithm based on the frog jump center difference scheme combining with penalty method.
To improve the accuracy and robustness of the explicit FEM algorithm based on penalty method for simulating large deformation contact-impact problem, a new large-deformation non-penetration contact algorithm based on forward incremental displacement central difference (FIDCD) was developed. On the one hand, according to FIDCD, the solving step of the dynamic equation was decomposed into an estimated step without considering contact and a correction step considering contact constraint. At the current moment, a contact force was applied thorough the penalty method to make the deformation of entities satisfy the non-penetration condition. The contact force was calculated by a soft constraint penalty stiffness, which helped to maintain stability of contact localization. It enhanced the numerical accuracy of the explicit contact computation. On the other hand, to accurately calculate the large-deformation internal force of the next moment while only obtaining the displacement, the internal force term of the dynamic equation was mapped to a known configuration for solution based on the arbitrary reference configurations (ARC) theory. It avoided using the values of variables at intermediate configuration to approximate them, thereby improving the numerical accuracy of the large deformation computation. More rigorous contact algorithms and geometric nonlinear solution strategy can effectively suppress mesh distortion and non-physical penetration between entities during large-deformation impact simulation. This thus improved the robustness of the new explicit algorithm. Finally, the computational program written according to the new developed algorithm was applied to simulate several impact and penetration examples with different impact velocities. By comparing the simulation results with those obtained from commercial software, the correctness of the developed algorithm and computational program was verified. At the same time, it can also be proven that the algorithm proposed is more robust in simulating high-speed and large-deformation impact problems than the classical explicit contact-impact algorithm based on the frog jump center difference scheme combining with penalty method.
, Available online , doi: 10.11883/bzycj-2023-0452
Abstract:
To predict precisely the lower explosion limit of thermal runaway products of lithium iron phosphate batteries, thermal runaway tests of lithium iron phosphate batteries were carried out in a closed pressure vessel. The experiments were carried out at 25 ℃ and 0.1 MPa, and the method was used to analyze the thermal runaway gas production. The vent gas species composition of lithium iron phosphate batteries was analyzed by gas chromatography and mass spectrometry. Combined with the thermal runaway characteristics of the battery and gas chromatography-mass spectrometry (GC-MS) technology, the gas composition of thermal runaway products of lithium iron phosphate batteries was calculated. It was assumed that the thermal runway products released from the relief valve to the first injection were all dimethyl carbonate (DMC), and the secondary injection gas was the mixed gas generated by the internal chemical reaction, which is mainly composed of H2, CO2, CO, CH4, and C2H4. A prediction model of the lower explosion limit of thermal runaway products was established based on the energy conservation equation and adiabatic flame temperature. The prediction methods of lower explosion limit of multicomponent gases based on adiabatic flame temperature, Le Chatelier law method, and Jones method were verified, and the influence of electrolyte vapor on the lower explosion limit of thermal runaway production was also investigated. The smallest deviation of the lower explosion limit calculated by the Le Chatelier law method at normal temperature and pressure was 1.14%, and the largest deviation of the lower explosion limit calculated by the adiabatic flame temperature method was 10.02%. Within the range from 60% SOC to 100% SOC, the lower explosion limit of the thermal runaway gases increases first and then decreases. When the electrolyte vapor is considered in the thermal runaway products, the lower explosion limit of thermal runaway products of lithium iron phosphate batteries with 60% SOC is only 3.93%, which is 22.49% lower than that of the thermal runaway gas without considering the electrolyte vapor. Actually, the electrolyte vapor is contained in the thermal runaway products of lithium iron phosphate batteries. These results indicate that the addition of electrolyte vapor increases the explosion risk of thermal runaway production of lithium iron phosphate batteries.
To predict precisely the lower explosion limit of thermal runaway products of lithium iron phosphate batteries, thermal runaway tests of lithium iron phosphate batteries were carried out in a closed pressure vessel. The experiments were carried out at 25 ℃ and 0.1 MPa, and the method was used to analyze the thermal runaway gas production. The vent gas species composition of lithium iron phosphate batteries was analyzed by gas chromatography and mass spectrometry. Combined with the thermal runaway characteristics of the battery and gas chromatography-mass spectrometry (GC-MS) technology, the gas composition of thermal runaway products of lithium iron phosphate batteries was calculated. It was assumed that the thermal runway products released from the relief valve to the first injection were all dimethyl carbonate (DMC), and the secondary injection gas was the mixed gas generated by the internal chemical reaction, which is mainly composed of H2, CO2, CO, CH4, and C2H4. A prediction model of the lower explosion limit of thermal runaway products was established based on the energy conservation equation and adiabatic flame temperature. The prediction methods of lower explosion limit of multicomponent gases based on adiabatic flame temperature, Le Chatelier law method, and Jones method were verified, and the influence of electrolyte vapor on the lower explosion limit of thermal runaway production was also investigated. The smallest deviation of the lower explosion limit calculated by the Le Chatelier law method at normal temperature and pressure was 1.14%, and the largest deviation of the lower explosion limit calculated by the adiabatic flame temperature method was 10.02%. Within the range from 60% SOC to 100% SOC, the lower explosion limit of the thermal runaway gases increases first and then decreases. When the electrolyte vapor is considered in the thermal runaway products, the lower explosion limit of thermal runaway products of lithium iron phosphate batteries with 60% SOC is only 3.93%, which is 22.49% lower than that of the thermal runaway gas without considering the electrolyte vapor. Actually, the electrolyte vapor is contained in the thermal runaway products of lithium iron phosphate batteries. These results indicate that the addition of electrolyte vapor increases the explosion risk of thermal runaway production of lithium iron phosphate batteries.
, Available online , doi: 10.11883/bzycj-2024-0152
Abstract:
To investigate the dynamic mechanical properties of sandstone in deep strata under impact loads, an improved Hopkinson pressure bar experimental system was established. The traditional Hopkinson pressure bar's transmission rod was replaced with a long rod specimen made of gray sandstone to better simulate deep geological conditions. Point spalling treatment was applied to the specimen, and strain gauges were meticulously affixed at critical measurement points.Dynamic compression experiments were meticulously conducted on the gray sandstone long rod specimen at various loading rates (9.57 m/s, 14.78 m/s, 19.32 m/s, and 27.60 m/s). Utilizing high-speed digital image correlation (DIC) technology, the evolution of displacement and strain fields on the surface of the specimen throughout each test was closely monitored. This advanced technique enabled a detailed exploration of how the gray sandstone responded to near-field impact loading, particularly focusing on its tensile failure characteristics.Employing the Lagrangian analysis method, displacement-time curves for different mass points derived from the DIC analysis of displacement fields were extracted. These curves provided critical data to compute the stress-strain behavior of the gray sandstone material under dynamic loading conditions. The study reveals several key findings: the gray sandstone long rod specimen predominantly exhibits tensile failure, with distinct patterns of fragmentation near the loading end and layer cracking away from it. Moreover, the dynamic compressive strength factor of the gray sandstone long rod specimen shows a notable increase with higher strain rates, indicating a significant strain rate effect. Correspondingly, both stress and strain peaks observe an upward trend at various measurement points with increasing loading rates.Remarkably, under identical loading rates, stress-strain curves of the gray sandstone long rod specimen exhibit a unique phenomenon where curves from measurement points closer to the loading end envelop those from points farther away. This observation underscores the complex nature of dynamic loading responses in geological materials.Overall, this comprehensive investigation provides essential theoretical insights and methodological references for understanding the dynamic behavior of sandstone within deep geological formations under impact loads. The findings offer valuable contributions to engineering practices concerned with the stability and resilience of underground structures subjected to dynamic loading conditions.
To investigate the dynamic mechanical properties of sandstone in deep strata under impact loads, an improved Hopkinson pressure bar experimental system was established. The traditional Hopkinson pressure bar's transmission rod was replaced with a long rod specimen made of gray sandstone to better simulate deep geological conditions. Point spalling treatment was applied to the specimen, and strain gauges were meticulously affixed at critical measurement points.Dynamic compression experiments were meticulously conducted on the gray sandstone long rod specimen at various loading rates (9.57 m/s, 14.78 m/s, 19.32 m/s, and 27.60 m/s). Utilizing high-speed digital image correlation (DIC) technology, the evolution of displacement and strain fields on the surface of the specimen throughout each test was closely monitored. This advanced technique enabled a detailed exploration of how the gray sandstone responded to near-field impact loading, particularly focusing on its tensile failure characteristics.Employing the Lagrangian analysis method, displacement-time curves for different mass points derived from the DIC analysis of displacement fields were extracted. These curves provided critical data to compute the stress-strain behavior of the gray sandstone material under dynamic loading conditions. The study reveals several key findings: the gray sandstone long rod specimen predominantly exhibits tensile failure, with distinct patterns of fragmentation near the loading end and layer cracking away from it. Moreover, the dynamic compressive strength factor of the gray sandstone long rod specimen shows a notable increase with higher strain rates, indicating a significant strain rate effect. Correspondingly, both stress and strain peaks observe an upward trend at various measurement points with increasing loading rates.Remarkably, under identical loading rates, stress-strain curves of the gray sandstone long rod specimen exhibit a unique phenomenon where curves from measurement points closer to the loading end envelop those from points farther away. This observation underscores the complex nature of dynamic loading responses in geological materials.Overall, this comprehensive investigation provides essential theoretical insights and methodological references for understanding the dynamic behavior of sandstone within deep geological formations under impact loads. The findings offer valuable contributions to engineering practices concerned with the stability and resilience of underground structures subjected to dynamic loading conditions.
, Available online , doi: 10.11883/bzycj-2024-0064
Abstract:
Sympathetic detonation is defined as the phenomenon where the detonation pressure in one borehole causes explosives in another adjacent borehole to be detonated through an inert medium. It can increase the stress wave and the value of peak particle velocity, even causing fly rock to be thrown far away. These effects can impact the safety of blasting operation, slope stability, and blasting effects. Sympathetic detonation was identified by comparing the fluctuation difference of recorded blast-induced vibration signals. To investigate the mechanism of sympathetic detonation and methods of preventing sympathetic detonation in water-rich fissure open-pit mines, numerical simulation and field tests were adopted to analyze the effects of parameters on the occurrence of sympathetic detonation, such as the quantity of donor charge, crack width, and distance between charges. These results indicated that the borehole pressure increased with the decrease in decoupled charge coefficient, the increase of the crack width between boreholes (0.25-1.00 cm), and the decrease in the distance between boreholes. By using a wave-blocking tube, filling rock power, or setting up an air gap, the impact pressure produced by the donor charge was transmitted to the acceptor charge through the water-rich cracks. These methods made impact pressure lower than the critical detonation pressure of the emulsion explosive, which could prevent the sympathetic detonation of the accepted charge. Based on the field tests and simulated results, rock power filling was the best method of preventing sympathetic detonation when there was a single crack between the boreholes. Meanwhile, using a wave-blocking tube with a thickness of 2.6 mm was the best method of preventing sympathetic detonation when there were multiple cracks between the boreholes. Above all, the proposed detection method and obtained technologies provide the theory and guidance for preventing sympathetic detonation, which leads to improved blasting effects and the safety of blasting operations.
Sympathetic detonation is defined as the phenomenon where the detonation pressure in one borehole causes explosives in another adjacent borehole to be detonated through an inert medium. It can increase the stress wave and the value of peak particle velocity, even causing fly rock to be thrown far away. These effects can impact the safety of blasting operation, slope stability, and blasting effects. Sympathetic detonation was identified by comparing the fluctuation difference of recorded blast-induced vibration signals. To investigate the mechanism of sympathetic detonation and methods of preventing sympathetic detonation in water-rich fissure open-pit mines, numerical simulation and field tests were adopted to analyze the effects of parameters on the occurrence of sympathetic detonation, such as the quantity of donor charge, crack width, and distance between charges. These results indicated that the borehole pressure increased with the decrease in decoupled charge coefficient, the increase of the crack width between boreholes (0.25-1.00 cm), and the decrease in the distance between boreholes. By using a wave-blocking tube, filling rock power, or setting up an air gap, the impact pressure produced by the donor charge was transmitted to the acceptor charge through the water-rich cracks. These methods made impact pressure lower than the critical detonation pressure of the emulsion explosive, which could prevent the sympathetic detonation of the accepted charge. Based on the field tests and simulated results, rock power filling was the best method of preventing sympathetic detonation when there was a single crack between the boreholes. Meanwhile, using a wave-blocking tube with a thickness of 2.6 mm was the best method of preventing sympathetic detonation when there were multiple cracks between the boreholes. Above all, the proposed detection method and obtained technologies provide the theory and guidance for preventing sympathetic detonation, which leads to improved blasting effects and the safety of blasting operations.
, Available online , doi: 10.11883/bzycj-2024-0109
Abstract:
For the launch safety problem of the typical CL-20-based high detonation velocity pressed explosive (C-1, 94.5% CL-20+5.5% additive), the impact response characteristics of the explosive were studied by a large-scale hammer test with 400 kg, which has an impact loading curve similar to the loading characteristics of artillery chamber pressure. Meanwhile, the improved stress rate characterization method, the lower limit method, and the drop height method were used to characterize the drop hammer impact response characteristics of the explosive, and compared with the same kind of pressed explosives JO-8 and JH-2. The improved stress rate characterization method is obtained by improving the data processing process based on existing criteria and weakening the sensitivity of the original criterion formula to oscillatory waveforms. The measured stress curves and characterization parameters of the bottom of the three pressed explosives under different drop heights are obtained by tests, and the impact sensitivity differences of the explosives and influence factors of the impact sensitivity of C-1 are discussed. The results show that the improved stress rate characterization method has certain effectiveness and universality for characterizing the impact sensitivity of explosives. Meanwhile, the improved stress rate characterization method is consistent with other methods in reflecting the law. The drop height of C-1 (H50) is 1.0 m, which is 62.5% and 50.0% of JO-8 and JH-2, respectively; the peak stress of the backseat corresponding to non-detonation (σ0) is 748.90 MPa, which is 85.42% and 64.33% of JO-8 and JH-2, respectively; the safety stress rate parameter (C0) is 344 GPa2/s, which is 45.87% and 39.14% of JO-8 and JH-2, respectively. The molecular structure of CL-20, the mechanical properties, and the thermal-chemical characteristics of the C-1 explosive cylinder are the main factors that make its impact sensitivity higher than JO-8 and JH-2. The research results can provide a reference for the application and design calculation of CL-20-based high detonation velocity pressed explosives in a high overload environment.
For the launch safety problem of the typical CL-20-based high detonation velocity pressed explosive (C-1, 94.5% CL-20+5.5% additive), the impact response characteristics of the explosive were studied by a large-scale hammer test with 400 kg, which has an impact loading curve similar to the loading characteristics of artillery chamber pressure. Meanwhile, the improved stress rate characterization method, the lower limit method, and the drop height method were used to characterize the drop hammer impact response characteristics of the explosive, and compared with the same kind of pressed explosives JO-8 and JH-2. The improved stress rate characterization method is obtained by improving the data processing process based on existing criteria and weakening the sensitivity of the original criterion formula to oscillatory waveforms. The measured stress curves and characterization parameters of the bottom of the three pressed explosives under different drop heights are obtained by tests, and the impact sensitivity differences of the explosives and influence factors of the impact sensitivity of C-1 are discussed. The results show that the improved stress rate characterization method has certain effectiveness and universality for characterizing the impact sensitivity of explosives. Meanwhile, the improved stress rate characterization method is consistent with other methods in reflecting the law. The drop height of C-1 (H50) is 1.0 m, which is 62.5% and 50.0% of JO-8 and JH-2, respectively; the peak stress of the backseat corresponding to non-detonation (σ0) is 748.90 MPa, which is 85.42% and 64.33% of JO-8 and JH-2, respectively; the safety stress rate parameter (C0) is 344 GPa2/s, which is 45.87% and 39.14% of JO-8 and JH-2, respectively. The molecular structure of CL-20, the mechanical properties, and the thermal-chemical characteristics of the C-1 explosive cylinder are the main factors that make its impact sensitivity higher than JO-8 and JH-2. The research results can provide a reference for the application and design calculation of CL-20-based high detonation velocity pressed explosives in a high overload environment.
, Available online , doi: 10.11883/bzycj-2024-0074
Abstract:
The annular shaped charges serve as the precursor of a tandem warhead, prized for its ability to create large diameter perforation in targets. In an effort to enhance the penetration capacity of the annular shaped charge jet and mitigate the impact of the inner casing on subsequent sections induced by a reversed penetrator, a novel approach was taken to implement the investigation. Four different combinations of inner and outer casing materials based on steel and aluminum alloy were explored. It was found that when the inner casing was made of aluminum alloy, the average penetration depth in the rear target was 36.13% lower than that when the inner casing was made of steel. Selecting an inner casing of aluminum alloy and an outer casing of steel, the effects of tip offset, liner thickness, and standoff distance on the formation and penetration characteristics of the annular jet were further investigated. The results show that the jet formed by the non-eccentric liner exhibits radial offset, negatively influencing its penetration capability. However, by offsetting the liner tip to the outer side by 0.05d (where d represents the radial thickness of the annular shaped charge), both the forming and penetration performances of the jet are significantly improved. In addition, as the liner thickness increases, the velocity of the jet tip gradually decreases. Notably, the annular jet formed by an eccentric conical liner with a thickness of 0.045d exhibits superior penetration performance. Furthermore, the standoff distance emerges as a critical factor influencing the penetration capability of the annular jet. Optimal performance is achieved at a standoff distance of 1.12d. Under the same scenario, jet penetration tests were implemented. The difference between the radius of the penetration tunnel from numerical and experimental study lies within 12%. Subsequently, the reliability of the numerical simulation model and the conclusions are verified.
The annular shaped charges serve as the precursor of a tandem warhead, prized for its ability to create large diameter perforation in targets. In an effort to enhance the penetration capacity of the annular shaped charge jet and mitigate the impact of the inner casing on subsequent sections induced by a reversed penetrator, a novel approach was taken to implement the investigation. Four different combinations of inner and outer casing materials based on steel and aluminum alloy were explored. It was found that when the inner casing was made of aluminum alloy, the average penetration depth in the rear target was 36.13% lower than that when the inner casing was made of steel. Selecting an inner casing of aluminum alloy and an outer casing of steel, the effects of tip offset, liner thickness, and standoff distance on the formation and penetration characteristics of the annular jet were further investigated. The results show that the jet formed by the non-eccentric liner exhibits radial offset, negatively influencing its penetration capability. However, by offsetting the liner tip to the outer side by 0.05d (where d represents the radial thickness of the annular shaped charge), both the forming and penetration performances of the jet are significantly improved. In addition, as the liner thickness increases, the velocity of the jet tip gradually decreases. Notably, the annular jet formed by an eccentric conical liner with a thickness of 0.045d exhibits superior penetration performance. Furthermore, the standoff distance emerges as a critical factor influencing the penetration capability of the annular jet. Optimal performance is achieved at a standoff distance of 1.12d. Under the same scenario, jet penetration tests were implemented. The difference between the radius of the penetration tunnel from numerical and experimental study lies within 12%. Subsequently, the reliability of the numerical simulation model and the conclusions are verified.
, Available online , doi: 10.11883/bzycj-2024-0130
Abstract:
The high reactivity of hydrogen and oxygen poses a huge challenge to the stable propagation of rotating detonation waves. To study the propagation instability of hydrogen-oxygen rotating detonation waves, based on the RYrhoCentralFoam solver developed by OpenFOAM, numerical simulations were conducted on two-dimensional hydrogen-oxygen rotating detonation waves in small scale model by changing the equivalence ratio. The complex and variable propagation characteristics of hydrogen-oxygen rotating detonation waves were revealed, and the typical flow field was analyzed. The instability of propagation modes and the quenching and re-initiation mechanisms of detonation waves were explored. The results show that as the equivalence ratio increases, the flow field exhibits three propagation modes: extinction, single wave, and hybrid waves. The detonation wave velocity increases almost linearly with the increase of equivalence ratio, with a velocity deficit of 5% to 8%. The disturbance of shock waves causes significant distortion and wrinkling on the deflagration surface, while the high reactivity of hydrogen and oxygen results in obvious layering on the deflagration surface and different instability at the two interfaces. The upper interface exhibits Kelvin-Helmholt (K-H) instability, while the lower interface exhibits Rayleigh-Taylor (R-T) instability. As for the hybrid waves, the detonation wave is extremely unstable, maintaining a cycle between three states: quenching, single wave, and double wave collision. There are two ways in which detonation waves can be extinguished: firstly, the collision of two waves leads to the quenching of the detonation wave, and secondly, the intensification of combustion on the deflagration surface leads to the downward movement of the deflagration surface, ultimately resulting in the quenching of the detonation wave. The main reason for re-initiation is that the R-T instability induces detonation products and fresh premixed gas squeezing each other on the deflagration surface. The interaction between fresh premixed gas and products produces spikes and bubbles, enhances the reaction heat release on the deflagration surface, and generates local hotspots. The hotspots gradually increase into detonation waves, achieving the transition from deflagration to detonation.
The high reactivity of hydrogen and oxygen poses a huge challenge to the stable propagation of rotating detonation waves. To study the propagation instability of hydrogen-oxygen rotating detonation waves, based on the RYrhoCentralFoam solver developed by OpenFOAM, numerical simulations were conducted on two-dimensional hydrogen-oxygen rotating detonation waves in small scale model by changing the equivalence ratio. The complex and variable propagation characteristics of hydrogen-oxygen rotating detonation waves were revealed, and the typical flow field was analyzed. The instability of propagation modes and the quenching and re-initiation mechanisms of detonation waves were explored. The results show that as the equivalence ratio increases, the flow field exhibits three propagation modes: extinction, single wave, and hybrid waves. The detonation wave velocity increases almost linearly with the increase of equivalence ratio, with a velocity deficit of 5% to 8%. The disturbance of shock waves causes significant distortion and wrinkling on the deflagration surface, while the high reactivity of hydrogen and oxygen results in obvious layering on the deflagration surface and different instability at the two interfaces. The upper interface exhibits Kelvin-Helmholt (K-H) instability, while the lower interface exhibits Rayleigh-Taylor (R-T) instability. As for the hybrid waves, the detonation wave is extremely unstable, maintaining a cycle between three states: quenching, single wave, and double wave collision. There are two ways in which detonation waves can be extinguished: firstly, the collision of two waves leads to the quenching of the detonation wave, and secondly, the intensification of combustion on the deflagration surface leads to the downward movement of the deflagration surface, ultimately resulting in the quenching of the detonation wave. The main reason for re-initiation is that the R-T instability induces detonation products and fresh premixed gas squeezing each other on the deflagration surface. The interaction between fresh premixed gas and products produces spikes and bubbles, enhances the reaction heat release on the deflagration surface, and generates local hotspots. The hotspots gradually increase into detonation waves, achieving the transition from deflagration to detonation.
, Available online , doi: 10.11883/bzycj-2024-0145
Abstract:
In order to explore the structural response characteristics of projectile obliquely penetrating granite target, based on a 30 mm ballistic gun platform, the tests of projectile obliquely penetrating granite target were carried out, and the damage parameters of projectile structure under non-normal penetration were obtained. On this basis, combined with the numerical simulation, the deformation and fracture mechanism of the projectile structure of the projectile obliquely penetrating the granite target are studied, and the influence of the initial conditions of penetration on the structural response of the projectile is analyzed. The results show that the projectile is prone to bending and fracture when it is not penetrating the granite target. The asymmetric force on the head and tail of the projectile is the main factor affecting the response characteristics of the projectile. The degree of deformation and failure of the projectile is determined by the peak value of the angular velocity difference between the head and tail of the projectile. As the yaw increases, the bending degree of the projectile increases linearly, and the projectile breaks when the yaw increases to 8°. With the increase of the impact angle, the bending degree of the projectile increases first, followed by decrease and then increase again. When the impact angle is 15°, the bending degree of the projectile is the smallest. When the impact angle reaches 30°, the projectile breaks. Compared with the impact angle, the yaw has a more significant effect on the response behavior of the projectile structure. When the yaw and impact angle are combined, the introduction of the impact angle will increase the critical fracture positive yaw of the projectile, and the negative yaw will weaken the ability of the projectile to resist bending deformation and fracture. When the impact velocity is greater than1600 m/s, the impact velocity of the projectile becomes the main controlling factor for the different response behaviors of the projectile.
In order to explore the structural response characteristics of projectile obliquely penetrating granite target, based on a 30 mm ballistic gun platform, the tests of projectile obliquely penetrating granite target were carried out, and the damage parameters of projectile structure under non-normal penetration were obtained. On this basis, combined with the numerical simulation, the deformation and fracture mechanism of the projectile structure of the projectile obliquely penetrating the granite target are studied, and the influence of the initial conditions of penetration on the structural response of the projectile is analyzed. The results show that the projectile is prone to bending and fracture when it is not penetrating the granite target. The asymmetric force on the head and tail of the projectile is the main factor affecting the response characteristics of the projectile. The degree of deformation and failure of the projectile is determined by the peak value of the angular velocity difference between the head and tail of the projectile. As the yaw increases, the bending degree of the projectile increases linearly, and the projectile breaks when the yaw increases to 8°. With the increase of the impact angle, the bending degree of the projectile increases first, followed by decrease and then increase again. When the impact angle is 15°, the bending degree of the projectile is the smallest. When the impact angle reaches 30°, the projectile breaks. Compared with the impact angle, the yaw has a more significant effect on the response behavior of the projectile structure. When the yaw and impact angle are combined, the introduction of the impact angle will increase the critical fracture positive yaw of the projectile, and the negative yaw will weaken the ability of the projectile to resist bending deformation and fracture. When the impact velocity is greater than
, Available online , doi: 10.11883/bzycj-2024-0083
Abstract:
Reinforced concrete slabs, as the main load-bearing components in the structure of construction projects, are very likely to suffer serious damage in explosive accidents, while polyurea elastomers, with their better anti-blast and anti-impact properties, have been widely used in the field of protective engineering. It is well known that the mechanical properties and deformation mechanisms of thin slabs in the range from 100 mm to 250 mm and thick concrete slabs above 250 mm are not the same, and the thickness of reinforced concrete substrates studied so far is generally concentrated in the range from 100 mm to 250 mm, and there are relatively few studies on thick slabs of polyurea-coated reinforced concrete with a slab thickness of 250 mm or more. In order to study the anti-blast performance of the polyurea/reinforced concrete thick slab composite structure, firstly, the contact explosion tests were carried out on the polyurea/reinforced concrete thick slab composite structure with different charges, while the overall and local damage characteristics were analyzed. Secondly, numerical simulations were carried out using LS-DYNA finite element simulation software to verify the correctness of the numerical model by comparing with the experimental results. Based on LS-DYNA finite element simulations, the damage process of polyurea/reinforced concrete thick plate composite structure and the evolution of shock wave inside the polyurea/reinforced concrete thick plate were investigated, which revealed the anti-blast mechanism of the polyurea coating, and further analyzed the damage mode and damage characteristics of the polyurea/reinforced concrete thick plate composite structure. The test and finite element results showed that the polyurea/steel-reinforced concrete composite structure exhibited six damage modes under the contact explosion load (i.e., crate; spall; spall and bulge; threshold spall, bulging deformation of the polyurea coating; severe spall, serious bulging deformation of the polyurea coating; perforation). The investigation also demonstrated that the backside polyurea-coated reinforced concrete thick slabs effectively improved the anti-blast performance of the composite structure. The results of the study can provide a basis and reference for the design of blast resistance of polyurea/reinforced concrete thick slab composite structures.
Reinforced concrete slabs, as the main load-bearing components in the structure of construction projects, are very likely to suffer serious damage in explosive accidents, while polyurea elastomers, with their better anti-blast and anti-impact properties, have been widely used in the field of protective engineering. It is well known that the mechanical properties and deformation mechanisms of thin slabs in the range from 100 mm to 250 mm and thick concrete slabs above 250 mm are not the same, and the thickness of reinforced concrete substrates studied so far is generally concentrated in the range from 100 mm to 250 mm, and there are relatively few studies on thick slabs of polyurea-coated reinforced concrete with a slab thickness of 250 mm or more. In order to study the anti-blast performance of the polyurea/reinforced concrete thick slab composite structure, firstly, the contact explosion tests were carried out on the polyurea/reinforced concrete thick slab composite structure with different charges, while the overall and local damage characteristics were analyzed. Secondly, numerical simulations were carried out using LS-DYNA finite element simulation software to verify the correctness of the numerical model by comparing with the experimental results. Based on LS-DYNA finite element simulations, the damage process of polyurea/reinforced concrete thick plate composite structure and the evolution of shock wave inside the polyurea/reinforced concrete thick plate were investigated, which revealed the anti-blast mechanism of the polyurea coating, and further analyzed the damage mode and damage characteristics of the polyurea/reinforced concrete thick plate composite structure. The test and finite element results showed that the polyurea/steel-reinforced concrete composite structure exhibited six damage modes under the contact explosion load (i.e., crate; spall; spall and bulge; threshold spall, bulging deformation of the polyurea coating; severe spall, serious bulging deformation of the polyurea coating; perforation). The investigation also demonstrated that the backside polyurea-coated reinforced concrete thick slabs effectively improved the anti-blast performance of the composite structure. The results of the study can provide a basis and reference for the design of blast resistance of polyurea/reinforced concrete thick slab composite structures.
, Available online , doi: 10.11883/bzycj-2024-0053
Abstract:
Damage assessment of building structures plays an important role in military operations and engineering protection design. However, there is a lack of high-efficiency and validated damage assessment methods due to the complexity, variety, and large size of building structures. Therefore, a structural damage assessment method was proposed based on the high-precision numerical simulation analysis, in which the blast loadings, as well as the damage degrees of members, rooms, and building structures, were comprehensively considered. Firstly, the typical explosion tests and collapse accidents of reinforced concrete (RC) structures and masonry walls were numerically reproduced to verify the reliability of the numerical simulation approach for masonry-infilled RC frame structures. Subsequently, the blast-resistant analysis of a typical three-story masonry-infilled RC frame structure was conducted under internal explosions of different charge weights (25−200kg TNT), including the propagation of blast waves, structural damage, and scattering of infilled walls. Besides, the proposed high-efficiency assessment method exhibited four key characteristics: (1) the concept of mirror explosion source and the non-linear shock addition rules were combined to predict the internal blast loadings in central and adjacent rooms; (2) the damage degrees of structural and non-structural members, i.e., beams, slabs, columns, and infilled walls, were determined by the equivalent single degree of freedom method; (3) the importance factor of members was considered and weighted to evaluate the damage degree of the room; (4) the influence of usage and location of each room on the damage degree of the building structure was considered. Finally, the proposed assessment method was employed to predict the aforementioned explosion scenarios. It derives that the RC frame structures exhibit slight, moderate, and severe damage under the explosions of 25, 100, and 200 kg TNT, respectively. The predicted damage degrees are identical to the simulation results, while the calculation time is reduced by over 99%. Therefore, the proposed method possesses reliability and timeliness in damage assessment of building structures.
Damage assessment of building structures plays an important role in military operations and engineering protection design. However, there is a lack of high-efficiency and validated damage assessment methods due to the complexity, variety, and large size of building structures. Therefore, a structural damage assessment method was proposed based on the high-precision numerical simulation analysis, in which the blast loadings, as well as the damage degrees of members, rooms, and building structures, were comprehensively considered. Firstly, the typical explosion tests and collapse accidents of reinforced concrete (RC) structures and masonry walls were numerically reproduced to verify the reliability of the numerical simulation approach for masonry-infilled RC frame structures. Subsequently, the blast-resistant analysis of a typical three-story masonry-infilled RC frame structure was conducted under internal explosions of different charge weights (25−200kg TNT), including the propagation of blast waves, structural damage, and scattering of infilled walls. Besides, the proposed high-efficiency assessment method exhibited four key characteristics: (1) the concept of mirror explosion source and the non-linear shock addition rules were combined to predict the internal blast loadings in central and adjacent rooms; (2) the damage degrees of structural and non-structural members, i.e., beams, slabs, columns, and infilled walls, were determined by the equivalent single degree of freedom method; (3) the importance factor of members was considered and weighted to evaluate the damage degree of the room; (4) the influence of usage and location of each room on the damage degree of the building structure was considered. Finally, the proposed assessment method was employed to predict the aforementioned explosion scenarios. It derives that the RC frame structures exhibit slight, moderate, and severe damage under the explosions of 25, 100, and 200 kg TNT, respectively. The predicted damage degrees are identical to the simulation results, while the calculation time is reduced by over 99%. Therefore, the proposed method possesses reliability and timeliness in damage assessment of building structures.
, Available online , doi: 10.11883/bzycj-2024-0061
Abstract:
Due to the high compressive/tensile strengths and fracture toughness, ultra-high performance concrete (UHPC) has great application potential in protective structures against the attack of earth penetrating weapons. Accurately evaluating the damage and failure and establishing reliable design methods of UHPC shields against the combination of penetration and explosion of warheads can provide a helpful reference for protective structure design and resistance improvement. In this study, combined tests of 105 mm-caliber projectile penetration test and 5 kg TNT explosion test on semi-infinite UHPC target were conducted first. The detailed test data of the projectile and target under penetration and the combined effect of penetration and explosion were recorded. Then, a finite element model of UHPC under penetration and explosion was established. By conducting the numerical simulations of the above-conducted test and the existing prefabricated hole charge explosion test on the finite UHPC slab, as well as comprehensively comparing the destroy depth and cracking dimension of the target, the reliability of the established finite element model and the corresponding analysis approach in predicting the damage and failure of UHPC shield against the combination of penetration and explosion of warheads were validated. Finally, the perforation limit and scabbing limit of the UHPC shield under the combination of penetration and explosion of three typical prototype warheads, i.e., SDB, WDU-43/B, and BLU-109/B, were determined and compared with those of normal strength concrete shield. The results show that, the perforation limit and scabbing limit of the UHPC shield against the above three warheads are in ranges of 1.30−2.60 m and 1.70−5.00 m, respectively. The corresponding critical perforation and scabbing coefficients are in the ranges of 1.81−2.17 and 2.46−4.17, respectively. Compared with the normal strength concrete shield, the cracking diameter of the UHPC shield is reduced by 34.4%−42.4%. The perforation limit and scabbing limit are reduced by 7.1%−31.6% and 39.7%−52.8%, respectively. The present work can provide an analysis method and reference for the resistance evaluation and design of the UHPC shield.
Due to the high compressive/tensile strengths and fracture toughness, ultra-high performance concrete (UHPC) has great application potential in protective structures against the attack of earth penetrating weapons. Accurately evaluating the damage and failure and establishing reliable design methods of UHPC shields against the combination of penetration and explosion of warheads can provide a helpful reference for protective structure design and resistance improvement. In this study, combined tests of 105 mm-caliber projectile penetration test and 5 kg TNT explosion test on semi-infinite UHPC target were conducted first. The detailed test data of the projectile and target under penetration and the combined effect of penetration and explosion were recorded. Then, a finite element model of UHPC under penetration and explosion was established. By conducting the numerical simulations of the above-conducted test and the existing prefabricated hole charge explosion test on the finite UHPC slab, as well as comprehensively comparing the destroy depth and cracking dimension of the target, the reliability of the established finite element model and the corresponding analysis approach in predicting the damage and failure of UHPC shield against the combination of penetration and explosion of warheads were validated. Finally, the perforation limit and scabbing limit of the UHPC shield under the combination of penetration and explosion of three typical prototype warheads, i.e., SDB, WDU-43/B, and BLU-109/B, were determined and compared with those of normal strength concrete shield. The results show that, the perforation limit and scabbing limit of the UHPC shield against the above three warheads are in ranges of 1.30−2.60 m and 1.70−5.00 m, respectively. The corresponding critical perforation and scabbing coefficients are in the ranges of 1.81−2.17 and 2.46−4.17, respectively. Compared with the normal strength concrete shield, the cracking diameter of the UHPC shield is reduced by 34.4%−42.4%. The perforation limit and scabbing limit are reduced by 7.1%−31.6% and 39.7%−52.8%, respectively. The present work can provide an analysis method and reference for the resistance evaluation and design of the UHPC shield.
, Available online , doi: 10.11883/bzycj-2024-0070
Abstract:
Silicone rubber has been widely used as a typical sandwich-structure or cushion-structure material in various high pressure loading environments. Under pressure loading of up to tens of GPa, silicone rubber may undergo shock decomposition reaction, and the decomposition products contain gas-solid mixture. Numerical simulation without the shock decomposition of silicone rubber can’t interpret some complex physical phenomena observed in detonation driven experiment. In order to illustrate the shock decomposition effect of silicone rubber, a simple shock decomposition model for silicone rubber is proposed based on the existing physical knowledge. By using the simple shock decomposition model for silicone rubber, the simulations of the experiment setup of detonation driven silicone rubber foam are carried out, and the simulated free surface velocities are compared with the experiments. The results show that the shock decomposition of silicone rubber can reasonably interpret the two grotesque phenomena observed in the experiment. During the shock decomposition process, the first incident pressure of silicone rubber would relax around the critical shock decomposition pressure for a period of time. As a result, the free surface velocity of steel plate exhibits a platform as observed in the experiment during the first take-off process. The compressibility of gas phase products of silicone rubber after shock decomposition is much higher than the solid/fluid materials, so more energy in the first incident wave is consumed to compress gas products to do work, leading to energy attenuation and peak pressure reduction when the first incident wave propagates to the outer surface of steel plate. Consequently, the peak value of the first take-off free surface velocity of steel plate decreases. Insight into the dynamic behavior of silicone rubber at high pressures is particularly valuable for predicting their response to extreme conditions, and it contributes to a deeper understanding of such experimental phenomena and to the proposal of a more refined shock decomposition model for silicone rubber.
Silicone rubber has been widely used as a typical sandwich-structure or cushion-structure material in various high pressure loading environments. Under pressure loading of up to tens of GPa, silicone rubber may undergo shock decomposition reaction, and the decomposition products contain gas-solid mixture. Numerical simulation without the shock decomposition of silicone rubber can’t interpret some complex physical phenomena observed in detonation driven experiment. In order to illustrate the shock decomposition effect of silicone rubber, a simple shock decomposition model for silicone rubber is proposed based on the existing physical knowledge. By using the simple shock decomposition model for silicone rubber, the simulations of the experiment setup of detonation driven silicone rubber foam are carried out, and the simulated free surface velocities are compared with the experiments. The results show that the shock decomposition of silicone rubber can reasonably interpret the two grotesque phenomena observed in the experiment. During the shock decomposition process, the first incident pressure of silicone rubber would relax around the critical shock decomposition pressure for a period of time. As a result, the free surface velocity of steel plate exhibits a platform as observed in the experiment during the first take-off process. The compressibility of gas phase products of silicone rubber after shock decomposition is much higher than the solid/fluid materials, so more energy in the first incident wave is consumed to compress gas products to do work, leading to energy attenuation and peak pressure reduction when the first incident wave propagates to the outer surface of steel plate. Consequently, the peak value of the first take-off free surface velocity of steel plate decreases. Insight into the dynamic behavior of silicone rubber at high pressures is particularly valuable for predicting their response to extreme conditions, and it contributes to a deeper understanding of such experimental phenomena and to the proposal of a more refined shock decomposition model for silicone rubber.
, Available online , doi: 10.11883/bzycj-2024-0082
Abstract:
When X-rays generated by high-altitude nuclear detonation irradiates on the shell structure of missile, blow-off impulse (BOI) and thermal shock waves generated may produce dynamic response and damage on it. The existing three one-dimensional theoretical models, Whitener, BBAY, and MBBAY, can only provide approximate BOI values and accurate results of peak pressure and other information are inaccessible. Solving this problem requires numerical calculations based on real physical laws. The numerical simulation program TSHOCK3D for X-ray thermal excitation wave is used to calculate the BOI and peak pressure to make a comparative analysis. An aluminum plate with a length and width of 0.4 centimeters and a thickness of 0.1 centimeters is set as the target for X-ray radiation. The range of the working conditions is 0.1−3.0 keV for the Planck's blackbody temperatures and radiant energy flux are in the range of 220−400 J/cm2. The results indicate that the TSHOCK3D can give the results effectively and reliably. The simulation results are consistent with the theoretical models mentioned above. The BOI and peak pressure are approximately linear with the energy flux, while the maximum value exist for different blackbody temperatures.
When X-rays generated by high-altitude nuclear detonation irradiates on the shell structure of missile, blow-off impulse (BOI) and thermal shock waves generated may produce dynamic response and damage on it. The existing three one-dimensional theoretical models, Whitener, BBAY, and MBBAY, can only provide approximate BOI values and accurate results of peak pressure and other information are inaccessible. Solving this problem requires numerical calculations based on real physical laws. The numerical simulation program TSHOCK3D for X-ray thermal excitation wave is used to calculate the BOI and peak pressure to make a comparative analysis. An aluminum plate with a length and width of 0.4 centimeters and a thickness of 0.1 centimeters is set as the target for X-ray radiation. The range of the working conditions is 0.1−3.0 keV for the Planck's blackbody temperatures and radiant energy flux are in the range of 220−400 J/cm2. The results indicate that the TSHOCK3D can give the results effectively and reliably. The simulation results are consistent with the theoretical models mentioned above. The BOI and peak pressure are approximately linear with the energy flux, while the maximum value exist for different blackbody temperatures.
, Available online , doi: 10.11883/bzycj-2024-0036
Abstract:
X-ray diffraction test was used to analyze the changes in the mineral composition of the granite before and after filling with water to study the effects of saturated water and initial damage degree on macroscopic and microscopic failure characteristics of granite under impact load. The Hopkinson device was used to carry out dynamic mechanical tests on the granite samples under different states to analyze the dynamic mechanical properties of the granite and the block size characteristics under different states. In addition, some of the granite fragments after impact were selected for electron microscope scanning test to analyze the fracture failure characteristics. The fractal dimension was used to analyze the fragmentation degree of the granite fragments after impact and the scanning images of the fracture under electron microscopy. The influence of the image magnification selected during electron microscope scanning on the fractal dimension is discussed. The micro-cracking mechanism of granite induced by saturated water under impact load is briefly analyzed. The results show that the mineral composition of the saturated granite changes compared with the natural granite. The proportions of hornblende, albite, microcline, and quartz in the saturated granite decrease, while the proportion of kaolinite increases significantly. With the increase of initial damage, the dynamic peak stress of granite gradually decreases while the fragmentation degree and the fractal dimension of the block increase gradually, and the influence of initial damage on the fractal dimension of the block is greater than that of saturated water. With the increase of initial damage, more micro-cracks and debris appear in the fracture image, and the fractal dimension of the fracture image increases gradually. In a certain range, the fractal dimension of electron microscope scanning images increases with the increase of image magnification, but when the image exceeds a certain multiple, the fractal dimension will decrease. The research results can provide some theoretical and engineering references for the failure and instability mechanism analysis of disturbed water-saturated granite with initial damage in geotechnical engineering.
X-ray diffraction test was used to analyze the changes in the mineral composition of the granite before and after filling with water to study the effects of saturated water and initial damage degree on macroscopic and microscopic failure characteristics of granite under impact load. The Hopkinson device was used to carry out dynamic mechanical tests on the granite samples under different states to analyze the dynamic mechanical properties of the granite and the block size characteristics under different states. In addition, some of the granite fragments after impact were selected for electron microscope scanning test to analyze the fracture failure characteristics. The fractal dimension was used to analyze the fragmentation degree of the granite fragments after impact and the scanning images of the fracture under electron microscopy. The influence of the image magnification selected during electron microscope scanning on the fractal dimension is discussed. The micro-cracking mechanism of granite induced by saturated water under impact load is briefly analyzed. The results show that the mineral composition of the saturated granite changes compared with the natural granite. The proportions of hornblende, albite, microcline, and quartz in the saturated granite decrease, while the proportion of kaolinite increases significantly. With the increase of initial damage, the dynamic peak stress of granite gradually decreases while the fragmentation degree and the fractal dimension of the block increase gradually, and the influence of initial damage on the fractal dimension of the block is greater than that of saturated water. With the increase of initial damage, more micro-cracks and debris appear in the fracture image, and the fractal dimension of the fracture image increases gradually. In a certain range, the fractal dimension of electron microscope scanning images increases with the increase of image magnification, but when the image exceeds a certain multiple, the fractal dimension will decrease. The research results can provide some theoretical and engineering references for the failure and instability mechanism analysis of disturbed water-saturated granite with initial damage in geotechnical engineering.
, Available online , doi: 10.11883/bzycj-2024-0217
Abstract:
To study the penetration resistance to the projectile by the reinforced concrete, the mechanical response of reinforcing bars under the dynamic constraint of both the projectile and concrete was analysed and the limitation of existing finite-length rigid beam models have been obtained. Based on this foundation, a shear-plastic hinge model was used to analyze the case of a projectile directly hitting the reinforcing bars, and a plastic string model was used to analyze the case of a projectile colliding with the side of the reinforcing bars, resulting in a more accurate equation for penetration resistance. In the shear plastic hinge model, stress analysis was performed based on the shear sliding of the reinforcing bar before fracture, and energy dissipation was calculated based on the deformation of the plastic hinge after the reinforcing bar fractures. In the plastic string model, the yield criterion of reinforcing bars under the combined action of bending moment and axial force was analyzed, and the plastic energy dissipation equations for reinforcing bar tension and bending were established. At the same time, the influence of changes in reinforcing bar kinetic energy was considered. Based on the theoretical model of cavity expansion and the empirical formula for the depth of projectile penetration, the concrete resistance equation under the indirect influence of steel reinforcement was obtained. By comparing with existing experimental data, the rationality of the theoretical models was verified. By analyzing the yield strength, diameter, mesh size of reinforcing bars, as well as the impact location of projectile, suggestions for the reinforcement design of the bulletproof layer were given. The adjacent two layers of reinforcing bars mesh should be staggered. The ratio of steel mesh to projectile diameter should be set between 0.5 and 0.8. It is not advisable to simply pursue high-strength reinforcing bars, and the ultimate plastic strain of reinforcing bars should also be considered as an important factor.
To study the penetration resistance to the projectile by the reinforced concrete, the mechanical response of reinforcing bars under the dynamic constraint of both the projectile and concrete was analysed and the limitation of existing finite-length rigid beam models have been obtained. Based on this foundation, a shear-plastic hinge model was used to analyze the case of a projectile directly hitting the reinforcing bars, and a plastic string model was used to analyze the case of a projectile colliding with the side of the reinforcing bars, resulting in a more accurate equation for penetration resistance. In the shear plastic hinge model, stress analysis was performed based on the shear sliding of the reinforcing bar before fracture, and energy dissipation was calculated based on the deformation of the plastic hinge after the reinforcing bar fractures. In the plastic string model, the yield criterion of reinforcing bars under the combined action of bending moment and axial force was analyzed, and the plastic energy dissipation equations for reinforcing bar tension and bending were established. At the same time, the influence of changes in reinforcing bar kinetic energy was considered. Based on the theoretical model of cavity expansion and the empirical formula for the depth of projectile penetration, the concrete resistance equation under the indirect influence of steel reinforcement was obtained. By comparing with existing experimental data, the rationality of the theoretical models was verified. By analyzing the yield strength, diameter, mesh size of reinforcing bars, as well as the impact location of projectile, suggestions for the reinforcement design of the bulletproof layer were given. The adjacent two layers of reinforcing bars mesh should be staggered. The ratio of steel mesh to projectile diameter should be set between 0.5 and 0.8. It is not advisable to simply pursue high-strength reinforcing bars, and the ultimate plastic strain of reinforcing bars should also be considered as an important factor.
