2023 Vol. 43, No. 5
Display Method:
PDF 
Cited by
Read OL
2023, 43(5): 052201.
doi: 10.11883/bzycj-2022-0161
Abstract:
Polymer materials have the characteristics of fast forming and good expansion performance. Their composite structures with gravel and reinforcement have obvious advantages in foundation treatment and urban road void removal and reinforcement. As reported in this paper, polymer gravel slabs and reinforced polymer slabs were designed and manufactured, and experimental study under contact explosion impact was carried out. The damage characteristics of the two kinds of slabs were investigated through the damage sizes and the measured shock wave data. Based on the ANSYS/AUTODYN nonlinear explicit finite element program, the damage modes and damage diameters of the reinforced polymer slabs were explored, and compared with the experimental results to verify the accuracy and applicability of the established finite element model. The sensitivity of the reinforced polymer slabs to explosive quantity and slab thickness was analyzed parametrically, and the prediction formula of the failure diameter of the top surface and bottom surface of the reinforced polymer slab was proposed by using a multi-parameter regression procedure. The results show that under the action of air contact explosion, the damage mode of the polymer gravel slab is mainly local collapse and perforation at the contact part. Under the impact load of contact explosion, punching and cutting explosion pits appear on the top surface of the slab, tensile failure and collapse area occur on the bottom surface, and a through failure hole is formed in the center of the slab, in addition to some damage cracks. Under the action of air contact explosion, the reinforced polymer slab mainly exhibits crater damage on the top surface, spalling damage on the bottom surface and central punching perforation damage. The reinforced polymer slab has a good attenuation effect on the explosion shock wave. The diffuse reflection effect of the closed bubble in the polymer structure on the shock wave can absorb more energy to alleviate the explosion shock wave, indicating that the polymer has the potential to be applied to the anti-explosion shock protection.
Polymer materials have the characteristics of fast forming and good expansion performance. Their composite structures with gravel and reinforcement have obvious advantages in foundation treatment and urban road void removal and reinforcement. As reported in this paper, polymer gravel slabs and reinforced polymer slabs were designed and manufactured, and experimental study under contact explosion impact was carried out. The damage characteristics of the two kinds of slabs were investigated through the damage sizes and the measured shock wave data. Based on the ANSYS/AUTODYN nonlinear explicit finite element program, the damage modes and damage diameters of the reinforced polymer slabs were explored, and compared with the experimental results to verify the accuracy and applicability of the established finite element model. The sensitivity of the reinforced polymer slabs to explosive quantity and slab thickness was analyzed parametrically, and the prediction formula of the failure diameter of the top surface and bottom surface of the reinforced polymer slab was proposed by using a multi-parameter regression procedure. The results show that under the action of air contact explosion, the damage mode of the polymer gravel slab is mainly local collapse and perforation at the contact part. Under the impact load of contact explosion, punching and cutting explosion pits appear on the top surface of the slab, tensile failure and collapse area occur on the bottom surface, and a through failure hole is formed in the center of the slab, in addition to some damage cracks. Under the action of air contact explosion, the reinforced polymer slab mainly exhibits crater damage on the top surface, spalling damage on the bottom surface and central punching perforation damage. The reinforced polymer slab has a good attenuation effect on the explosion shock wave. The diffuse reflection effect of the closed bubble in the polymer structure on the shock wave can absorb more energy to alleviate the explosion shock wave, indicating that the polymer has the potential to be applied to the anti-explosion shock protection.
2023, 43(5): 052202.
doi: 10.11883/bzycj-2022-0113
Abstract:
To investigate the standoff distance of underwater explosions on the damage to gravity dams and to explore whether there is an “optimal standoff distance”, a numerical model of a fully-coupled explosive-water-air-gravity dam was established. The numerical model was validated by comparing it with centrifuge test results. The results demonstrated that the employed numerical model could predict the dam failures and the effect of bubble pulse well. Then, a numerical scheme including 60 numerical calculations was designed. In these calculations, the water depth is 600 mm, the explosive mass is 2.2 g, and the geometrical scaling factor of the gravity dam model is 1/80. The detonation depth ranges from 50 to 250 mm with five detonation depths. Each detonation depth corresponds to 12 standoff distances ranging from 10 to 200 mm, with the scaled standoff distance ranging from 0.077 to 1.54 m/kg1/3. The damage degrees to the gravity dam under underwater explosions with different standoff distances are compared. Quantitative comparisons of dam average damage, element erosion rate, stress, and strain are also presented. The results show that for the overall structural failure of the gravity dam, such as the structural bending-induced tensile failure, there is an “optimal standoff distance” for the damage effects of underwater explosions on gravity dams, that is, with the increase of standoff distance, the damage degree of gravity dam increases first and then decreases. The quantitative results also indicate that with the increase of standoff distance, the average damage of the damaged area in the dam upstream face, the element erosion rate, the average value of the maximum tensile stress of the dam heel, and the average value of the maximum tensile strain of the dam heel all increase first and then decrease, and reach their maximum values around a standoff distance of 40 mm. With identical water depth, explosive mass, and geometrical model of gravity dam, the “optimal standoff distances” for the damage effects of near-surface underwater explosions at five different detonation depths on the gravity dam are all near 40 mm. It suggests that for near-surface underwater explosions, the detonation depth owns limited influence on the “optimal standoff distance”.
To investigate the standoff distance of underwater explosions on the damage to gravity dams and to explore whether there is an “optimal standoff distance”, a numerical model of a fully-coupled explosive-water-air-gravity dam was established. The numerical model was validated by comparing it with centrifuge test results. The results demonstrated that the employed numerical model could predict the dam failures and the effect of bubble pulse well. Then, a numerical scheme including 60 numerical calculations was designed. In these calculations, the water depth is 600 mm, the explosive mass is 2.2 g, and the geometrical scaling factor of the gravity dam model is 1/80. The detonation depth ranges from 50 to 250 mm with five detonation depths. Each detonation depth corresponds to 12 standoff distances ranging from 10 to 200 mm, with the scaled standoff distance ranging from 0.077 to 1.54 m/kg1/3. The damage degrees to the gravity dam under underwater explosions with different standoff distances are compared. Quantitative comparisons of dam average damage, element erosion rate, stress, and strain are also presented. The results show that for the overall structural failure of the gravity dam, such as the structural bending-induced tensile failure, there is an “optimal standoff distance” for the damage effects of underwater explosions on gravity dams, that is, with the increase of standoff distance, the damage degree of gravity dam increases first and then decreases. The quantitative results also indicate that with the increase of standoff distance, the average damage of the damaged area in the dam upstream face, the element erosion rate, the average value of the maximum tensile stress of the dam heel, and the average value of the maximum tensile strain of the dam heel all increase first and then decrease, and reach their maximum values around a standoff distance of 40 mm. With identical water depth, explosive mass, and geometrical model of gravity dam, the “optimal standoff distances” for the damage effects of near-surface underwater explosions at five different detonation depths on the gravity dam are all near 40 mm. It suggests that for near-surface underwater explosions, the detonation depth owns limited influence on the “optimal standoff distance”.
2023, 43(5): 052301.
doi: 10.11883/bzycj-2022-0234
Abstract:
To determine the critical vent area over which a warhead can burn stably under the fast cook-off condition, the gas pressure rise inside the casing after the ignition of the warhead charge was studied under the fast cook-off stimulation based on the mass conservation law and state equation of gases. A gas pressure rise model was established in the current work by considering the initial temperature of the explosive and gas venting in a warhead. A composition B explosive (Comp-B) cylindrical warhead was used as the research object. The numerical calculation of the model was carried out to determine the AV0/SB ratio (critical vent area/external surface area of the explosive) at which the warhead could be in stable combustion after it was accidentally ignited. And the results were compared with experimental values. It is found that the change of pc (pressure inside the warhead casing) after the thermal stimulation and ignition of Comp-B occurred in four stages of Ⅰ-Ⅳ: increased sharply, increased rapidly, decreased slowly, and finally, leveled off. The peak pressure of the warhead decreased linearly with the increase of AV/SB. When AV/SB corresponding to the peak pressure (pcmax) of 10 MPa in the warhead was taken as the critical AV/SB ratio, AV/SB could better separate the stable combustion reaction from the explosion reaction inside the warhead. The effects of the warhead charge surface area, the explosive initial temperature, the air volume ratio, and the explosive burning rate on AV0/SB were investigated, and the model predictions at different temperatures were compared with the experimental results. The predicted values of AV0/SB agree well with the experimental results. It is found that the warhead charge surface area has little effect on AV0/SB, andAV0/SB is positively correlated with the temperature and burning rate of the explosive and negatively correlated with the air volume ratio. The proposed model can well predict the critical vent area of the Comp-B warhead. Therefore, the findings of this study provide a theoretical basis for the design of thermally stimulated venting structures of ammunition.
To determine the critical vent area over which a warhead can burn stably under the fast cook-off condition, the gas pressure rise inside the casing after the ignition of the warhead charge was studied under the fast cook-off stimulation based on the mass conservation law and state equation of gases. A gas pressure rise model was established in the current work by considering the initial temperature of the explosive and gas venting in a warhead. A composition B explosive (Comp-B) cylindrical warhead was used as the research object. The numerical calculation of the model was carried out to determine the AV0/SB ratio (critical vent area/external surface area of the explosive) at which the warhead could be in stable combustion after it was accidentally ignited. And the results were compared with experimental values. It is found that the change of pc (pressure inside the warhead casing) after the thermal stimulation and ignition of Comp-B occurred in four stages of Ⅰ-Ⅳ: increased sharply, increased rapidly, decreased slowly, and finally, leveled off. The peak pressure of the warhead decreased linearly with the increase of AV/SB. When AV/SB corresponding to the peak pressure (pcmax) of 10 MPa in the warhead was taken as the critical AV/SB ratio, AV/SB could better separate the stable combustion reaction from the explosion reaction inside the warhead. The effects of the warhead charge surface area, the explosive initial temperature, the air volume ratio, and the explosive burning rate on AV0/SB were investigated, and the model predictions at different temperatures were compared with the experimental results. The predicted values of AV0/SB agree well with the experimental results. It is found that the warhead charge surface area has little effect on AV0/SB, andAV0/SB is positively correlated with the temperature and burning rate of the explosive and negatively correlated with the air volume ratio. The proposed model can well predict the critical vent area of the Comp-B warhead. Therefore, the findings of this study provide a theoretical basis for the design of thermally stimulated venting structures of ammunition.
2023, 43(5): 053101.
doi: 10.11883/bzycj-2022-0050
Abstract:
In order to study the anti-penetration performance of concrete-filled steel tube (CFST) with honeycomb structure, six experiments on anti-penetration of the CFST with honeycomb structure were conducted by using a 125-mm smooth bore gun. The failure pattern and penetration depth of the targets under different working conditions were measured, and the typical failure modes of the CFST with honeycomb structure were analyzed. The differences of the failure pattern of the targets under different target-to-projectile size ratios were compared, while the influences of the impact point and steel tube wall thickness on the anti-penetration performance of the CFST with honeycomb structure were explored. Uniaxial compression tests on seven groups of hexagonal concrete-filled steel tube columns with different wall thicknesses and three groups of hexagonal concrete columns were carried out. The enhancement effects of the hexagonal steel tube on the strength and ductility of the core concrete under different wall thicknesses were studied, and the relationship between the strength enhancement coefficient of the core concrete and the hoop coefficient was obtained by data fitting. By refining the empirical formula for calculating the penetration depth of ordinary concrete, the formula for calculating the maximum penetration depth of the CFST targets with honeycomb structure was given. The results show that the wall thickness is an important factor that affects penetration depth, that is, the greater the wall thickness, the smaller the penetration depth. The locations of impact points have a great influence on the failure pattern of the target surface, but the influences of the locations of impact points on the penetration depth are complex. The existence of the steel tube can effectively increase the strength and ductility of the core concrete. The refined penetration depth formula can predict the maximum penetration depths of the projectiles to the CFST targets with honeycomb structure.
In order to study the anti-penetration performance of concrete-filled steel tube (CFST) with honeycomb structure, six experiments on anti-penetration of the CFST with honeycomb structure were conducted by using a 125-mm smooth bore gun. The failure pattern and penetration depth of the targets under different working conditions were measured, and the typical failure modes of the CFST with honeycomb structure were analyzed. The differences of the failure pattern of the targets under different target-to-projectile size ratios were compared, while the influences of the impact point and steel tube wall thickness on the anti-penetration performance of the CFST with honeycomb structure were explored. Uniaxial compression tests on seven groups of hexagonal concrete-filled steel tube columns with different wall thicknesses and three groups of hexagonal concrete columns were carried out. The enhancement effects of the hexagonal steel tube on the strength and ductility of the core concrete under different wall thicknesses were studied, and the relationship between the strength enhancement coefficient of the core concrete and the hoop coefficient was obtained by data fitting. By refining the empirical formula for calculating the penetration depth of ordinary concrete, the formula for calculating the maximum penetration depth of the CFST targets with honeycomb structure was given. The results show that the wall thickness is an important factor that affects penetration depth, that is, the greater the wall thickness, the smaller the penetration depth. The locations of impact points have a great influence on the failure pattern of the target surface, but the influences of the locations of impact points on the penetration depth are complex. The existence of the steel tube can effectively increase the strength and ductility of the core concrete. The refined penetration depth formula can predict the maximum penetration depths of the projectiles to the CFST targets with honeycomb structure.
2023, 43(5): 053102.
doi: 10.11883/bzycj-2022-0343
Abstract:
The parameters of the Holmquist-Johnson-Cook (HJC) constitutive model for ultra-high performance concrete (UHPC) were determined based on uniaxial compression test, split Hopkinson pressure bar (SHPB) test and existing tri-axial compression test and so on, in order to improve the calculation accuracy and design reliability. In the determination process of parameters, the parameters of the HJC constitutive model were divided into five categories. The yield-surface parameters were determined by the static failure surface equation, the parameters of state equation were determined by the p-μ relation, the damage parameters were determined according to relevant literature, the basic physical parameters were determined according to the test, and so on. LS_DYNA was used to simulate the explosion test of the one-way slab. Firstly, the finite element model of the one-way slab was established. The HJC constitutive model was used for the UHPC, and the linear reinforcement model was used for the reinforcement material. The reinforcement and UHPC were connected by common joints. The air and explosive models were established, and the fluid-solid coupling method was used for calculation. The effectiveness of the determined parameters was verified by comparing the simulation results with the damage degree and the maximum deflection of the one-way slab in the test. In order to further understand the anti-blast mechanism of the UHPC members, the determined parameters were used to conduct numerical simulation on the one-way slab explosion condition, and the influences of reinforcement and size effect on the explosion result were analyzed. Results show that during the explosion process, the maximum mid-span deflection of the one-way slab can be reduced by increasing the longitudinal reinforcement ratio, and the length of oblique cracks on the side of the one-way slab can be reduced by properly encrypted stirrups. The UHPC one-way slab has an obvious size effect, and the variation of its thickness and length has the greatest influence on the explosion result.
The parameters of the Holmquist-Johnson-Cook (HJC) constitutive model for ultra-high performance concrete (UHPC) were determined based on uniaxial compression test, split Hopkinson pressure bar (SHPB) test and existing tri-axial compression test and so on, in order to improve the calculation accuracy and design reliability. In the determination process of parameters, the parameters of the HJC constitutive model were divided into five categories. The yield-surface parameters were determined by the static failure surface equation, the parameters of state equation were determined by the p-μ relation, the damage parameters were determined according to relevant literature, the basic physical parameters were determined according to the test, and so on. LS_DYNA was used to simulate the explosion test of the one-way slab. Firstly, the finite element model of the one-way slab was established. The HJC constitutive model was used for the UHPC, and the linear reinforcement model was used for the reinforcement material. The reinforcement and UHPC were connected by common joints. The air and explosive models were established, and the fluid-solid coupling method was used for calculation. The effectiveness of the determined parameters was verified by comparing the simulation results with the damage degree and the maximum deflection of the one-way slab in the test. In order to further understand the anti-blast mechanism of the UHPC members, the determined parameters were used to conduct numerical simulation on the one-way slab explosion condition, and the influences of reinforcement and size effect on the explosion result were analyzed. Results show that during the explosion process, the maximum mid-span deflection of the one-way slab can be reduced by increasing the longitudinal reinforcement ratio, and the length of oblique cracks on the side of the one-way slab can be reduced by properly encrypted stirrups. The UHPC one-way slab has an obvious size effect, and the variation of its thickness and length has the greatest influence on the explosion result.
2023, 43(5): 053103.
doi: 10.11883/bzycj-2022-0243
Abstract:
In order to better investigate the dynamic tensile properties and damage mechanism of ultra-high performance fibre reinforced concrete (UHPFRC), dynamic split tests with the strain rates of 1.72－7.42 s-1 were carried out by a split Hopkinson pressure bar for UHPFRC discs with the fibre volume fractions of 0－3%. The surface crack propagation processes of the UHPFRC discs were captured by a high-speed camera and the images were analyzed by the digital image correlation (DIC) technique for strain evolution. Micro X-ray computed tomography (μXCT) scanning of the UHPFRC disc specimens before and after the dynamic tests was also conducted. The 3D images of the internal micro structures of the specimens with a voxel resolution of 56.7 μm were reconstructed, and they were then processed to statistically quantify the distribution, volume fractions and sizes of pores, fibres and cracks. Moreover, the dynamic failure mechanisms, such as pullout from the matrix, bending and breakage of steel fibres, crack propagation and merging in the mortar, etc., were visualized and analyzed. The main results obtained are as follows. (1) The addition of 1%－3% steel fibres raises the static and dynamic splitting strength by 84%－131% and 47%－87%, respectively. The dynamic increase factor (ratio of dynamic to static strength) is 1.07－1.72. (2) DIC images demonstrate that the fibres lead to more dispersed cracks, slower crack propagation, higher energy consumption and higher ductility. (3) The μXCT image analysis shows that the fibre volume fraction is 1.04%－2.47%, consistent with the designed proportion, while the porosity is 0.98%－1.71%. Fibres reduce the porosity and the number of pores, but increase their average volume and equivalent diameter. The increase of crack-bridging fibres reduces the volume and width of main cracks and raises the surface roughness and the relative surface area of cracks, resulting in the increase of strength, energy dissipation, toughness and ductility of specimens. The research data are useful for improvement of dynamic design guidelines and optimization for UHPFRC materials and structures.
In order to better investigate the dynamic tensile properties and damage mechanism of ultra-high performance fibre reinforced concrete (UHPFRC), dynamic split tests with the strain rates of 1.72－7.42 s-1 were carried out by a split Hopkinson pressure bar for UHPFRC discs with the fibre volume fractions of 0－3%. The surface crack propagation processes of the UHPFRC discs were captured by a high-speed camera and the images were analyzed by the digital image correlation (DIC) technique for strain evolution. Micro X-ray computed tomography (μXCT) scanning of the UHPFRC disc specimens before and after the dynamic tests was also conducted. The 3D images of the internal micro structures of the specimens with a voxel resolution of 56.7 μm were reconstructed, and they were then processed to statistically quantify the distribution, volume fractions and sizes of pores, fibres and cracks. Moreover, the dynamic failure mechanisms, such as pullout from the matrix, bending and breakage of steel fibres, crack propagation and merging in the mortar, etc., were visualized and analyzed. The main results obtained are as follows. (1) The addition of 1%－3% steel fibres raises the static and dynamic splitting strength by 84%－131% and 47%－87%, respectively. The dynamic increase factor (ratio of dynamic to static strength) is 1.07－1.72. (2) DIC images demonstrate that the fibres lead to more dispersed cracks, slower crack propagation, higher energy consumption and higher ductility. (3) The μXCT image analysis shows that the fibre volume fraction is 1.04%－2.47%, consistent with the designed proportion, while the porosity is 0.98%－1.71%. Fibres reduce the porosity and the number of pores, but increase their average volume and equivalent diameter. The increase of crack-bridging fibres reduces the volume and width of main cracks and raises the surface roughness and the relative surface area of cracks, resulting in the increase of strength, energy dissipation, toughness and ductility of specimens. The research data are useful for improvement of dynamic design guidelines and optimization for UHPFRC materials and structures.
2023, 43(5): 053201.
doi: 10.11883/bzycj-2022-0117
Abstract:
Calcareous sand is widely distributed in coastal areas, and its engineering and mechanical properties are significantly different from terrestrial sands. To study the blast wave propagation in calcareous sand, a series of explosion tests with various charge weights on the ground surface were carried out in calcareous sand and silica sand. Pressure time-history curves at positions directly below the explosion center were measured. The propagation laws of two kinds of sands were investigated, including peak pressure, wave velocities of elastic and plastic waves, the rise time of pressure and size of cater. The results show that the blast wave propagation in calcareous sand differs from that in silica sand. Tests under 0.2 kg and 0.8 kg charge weight were conducted twice. And the results show that the explosion experiment is repeatable. Cater produced by the surface explosion in calcareous sand has a smaller size than in silica sand, and the shape of the cater is two-tier concentric circles, one of which is small in diameter and large in depth, and the other is large in diameter and small in depth. The elastic velocity in calcareous sand is 236 m/s to 300 m/s, and that in silica sand is 218 m/s to 337 m/s, while the elastic wave and plastic wave velocity increase with the increase of the explosive charge. The rise time of the blast wave pressure in calcareous sand increases with the increase of scaled distance. In silica sand, rise time does not change with the scaled distance and is much smaller than that in calcareous sand. The measured peak pressures are fitted by using a power function of scaled distance. The attenuation laws of peak pressure in calcareous sand and silica sand are derived. The attenuation coefficient of calcareous sand with low moisture content is 2.86, and 2.79 for silica sand.
Calcareous sand is widely distributed in coastal areas, and its engineering and mechanical properties are significantly different from terrestrial sands. To study the blast wave propagation in calcareous sand, a series of explosion tests with various charge weights on the ground surface were carried out in calcareous sand and silica sand. Pressure time-history curves at positions directly below the explosion center were measured. The propagation laws of two kinds of sands were investigated, including peak pressure, wave velocities of elastic and plastic waves, the rise time of pressure and size of cater. The results show that the blast wave propagation in calcareous sand differs from that in silica sand. Tests under 0.2 kg and 0.8 kg charge weight were conducted twice. And the results show that the explosion experiment is repeatable. Cater produced by the surface explosion in calcareous sand has a smaller size than in silica sand, and the shape of the cater is two-tier concentric circles, one of which is small in diameter and large in depth, and the other is large in diameter and small in depth. The elastic velocity in calcareous sand is 236 m/s to 300 m/s, and that in silica sand is 218 m/s to 337 m/s, while the elastic wave and plastic wave velocity increase with the increase of the explosive charge. The rise time of the blast wave pressure in calcareous sand increases with the increase of scaled distance. In silica sand, rise time does not change with the scaled distance and is much smaller than that in calcareous sand. The measured peak pressures are fitted by using a power function of scaled distance. The attenuation laws of peak pressure in calcareous sand and silica sand are derived. The attenuation coefficient of calcareous sand with low moisture content is 2.86, and 2.79 for silica sand.
2023, 43(5): 053301.
doi: 10.11883/bzycj-2022-0156
Abstract:
The dynamic response and failure of sandwich beams with gradient metal foam core subjected to high-velocity impact are studied experimentally. The impact resistance of five sandwich beams with different density gradient arrangements but the same surface density composed of three aluminum foams with different densities is analyzed. All the sandwich beams are simply-clamped. Combined with the quasi-static three-point bending tests, the impact resistance of the gradient sandwich beams is evaluated in terms of dynamic deformation and failure modes by considering the effects of core density gradient and impulsive intensity. The results show that the density gradient effect significantly influences the dynamic response and failure mode. The initial failure mode plays an important role in the structural response and the predominant energy absorption mechanism. Since the impact condition can not produce the local compression of the medium-density core, the initial failure mode of the uniform and negative gradient sandwich structures is the overall bending deformation, while the local core compression is the initial failure mode of the other structures with weak cores located in the first two layers. When the impulsive intensity is low, the gradient sandwich beam has superior impact resistance to the uniform counterpart. With increasing intensity, once a critical intensity is exceeded, the gradient sandwich beam shows low bending resistance to the uniform counterpart. Therefore, the optimal design of the core density gradient can efficiently improve the impact resistance of the sandwich beams under the high-velocity impact, which is a valuable reference for engineering applications.
The dynamic response and failure of sandwich beams with gradient metal foam core subjected to high-velocity impact are studied experimentally. The impact resistance of five sandwich beams with different density gradient arrangements but the same surface density composed of three aluminum foams with different densities is analyzed. All the sandwich beams are simply-clamped. Combined with the quasi-static three-point bending tests, the impact resistance of the gradient sandwich beams is evaluated in terms of dynamic deformation and failure modes by considering the effects of core density gradient and impulsive intensity. The results show that the density gradient effect significantly influences the dynamic response and failure mode. The initial failure mode plays an important role in the structural response and the predominant energy absorption mechanism. Since the impact condition can not produce the local compression of the medium-density core, the initial failure mode of the uniform and negative gradient sandwich structures is the overall bending deformation, while the local core compression is the initial failure mode of the other structures with weak cores located in the first two layers. When the impulsive intensity is low, the gradient sandwich beam has superior impact resistance to the uniform counterpart. With increasing intensity, once a critical intensity is exceeded, the gradient sandwich beam shows low bending resistance to the uniform counterpart. Therefore, the optimal design of the core density gradient can efficiently improve the impact resistance of the sandwich beams under the high-velocity impact, which is a valuable reference for engineering applications.
2023, 43(5): 053302.
doi: 10.11883/bzycj-2022-0079
Abstract:
To study the explosion characteristics of penetrator with elliptical cross-section, a static explosion experiment was designed and carried out. The penetrator with a mass of 255 kg was erected on a wooden cartridge, the centroid height was 2 m from the ground, and the test fuse was used to detonate the penetrator explosive. The aerial drone was used to record the whole explosion process in real time, the sector effecting steel plates were arranged in the major and minor axis directions to obtain the number and perforation rate of fragments, and the shock wave overpressure at the distance of 7, 10 and 12 m from the penetrator axis was measured. The macroscopic scene and the characteristics of fireball, fragment, and shock wave overpressure after explosion are analyzed in detail. Results show that the evolution morphology of the fireball and the fragment distribution area are symmetrically distributed with respect to the major axis and minor axis. The evolution of fireball can be divided into rapid growth stage, high temperature stability stage and free diffusion stage. The fireball size reached its maximum at 41.7 ms after explosion, and the maximum size in the minor axis and major axis directions was 21.86 and 19.29 m, respectively. Besides, the fireball size in the major axis direction had obvious secondary expansion. The fragments in the minor axis were small in size, large in number, and strong in perforation, while the fragments in the major axis had the opposite characteristics. The overpressure peak value, impulse, and velocity of shock wave decrease with the increase of propagation distance. Based on the experimental results, it can be concluded that the non-axisymmetric structure and non-uniform wall thickness of the elliptically cross-sectional penetrator have a great influence on the explosion characteristics, leading to the morphology of the non-axisymmetric distribution of the fireball and fragments.
To study the explosion characteristics of penetrator with elliptical cross-section, a static explosion experiment was designed and carried out. The penetrator with a mass of 255 kg was erected on a wooden cartridge, the centroid height was 2 m from the ground, and the test fuse was used to detonate the penetrator explosive. The aerial drone was used to record the whole explosion process in real time, the sector effecting steel plates were arranged in the major and minor axis directions to obtain the number and perforation rate of fragments, and the shock wave overpressure at the distance of 7, 10 and 12 m from the penetrator axis was measured. The macroscopic scene and the characteristics of fireball, fragment, and shock wave overpressure after explosion are analyzed in detail. Results show that the evolution morphology of the fireball and the fragment distribution area are symmetrically distributed with respect to the major axis and minor axis. The evolution of fireball can be divided into rapid growth stage, high temperature stability stage and free diffusion stage. The fireball size reached its maximum at 41.7 ms after explosion, and the maximum size in the minor axis and major axis directions was 21.86 and 19.29 m, respectively. Besides, the fireball size in the major axis direction had obvious secondary expansion. The fragments in the minor axis were small in size, large in number, and strong in perforation, while the fragments in the major axis had the opposite characteristics. The overpressure peak value, impulse, and velocity of shock wave decrease with the increase of propagation distance. Based on the experimental results, it can be concluded that the non-axisymmetric structure and non-uniform wall thickness of the elliptically cross-sectional penetrator have a great influence on the explosion characteristics, leading to the morphology of the non-axisymmetric distribution of the fireball and fragments.
2023, 43(5): 054101.
doi: 10.11883/bzycj-2022-0314
Abstract:
The loading technology of cosine distributed load by chemical explosion is the main method for evaluating the dynamic response of space structures under the irradiation of high-altitude nuclear explosions with soft X-rays. A loading method of discretely-distributed sheet explosives synchronously detonated by a mild detonating fuse (MDF) network was proposed to meet the design requirements of complex configuration, high synchronicity and low specific impulse load in the structural assessment of new space vehicles. In terms of experimental study, the cross-shaped sheet explosive made by stacking explosive strips with a cross-sectional size of 0.33 mm×0.5 mm can be directly detonated by a mild detonating fuse with the diameter of 0.5 mm. Compared with strip distribution, the space uniformity of cross distribution is improved by 76.7%. A high-speed camera was used to record the shock wave luminescence during the detonation process. The results show that the detonation ratio of the 21-point MDF detonation network reaches 100%, and the detonation asynchrony is less than 1 μs. In terms of numerical simulation, a numerical model for the explosion of sheet explosives was established based on the multi-material arbitrary Lagrangian-Eulerian (ALE) algorithm. The numerical model has strong grid sensitivity, and the results by it tend to converge when the mesh size reaches 0.5 mm, with the deviation from the measured specific impulse results within 5%. Based on the numerically-simulated results, the following conclusions can be drawn. (1) Under the periodic discrete distribution condition, the peak specific impulse is determined by the surface density of the explosive, and the evolution process of the peak specific impulse is determined by the spacing. (2) The homogenization process of specific impulse can be divided into three stages: diffusion stage, superposition stage and uniform stage. The specific impulse is homogenized through free diffusion of shock wave in the diffusion stage, and through shock wave superposition and collision in the superposition stage, and finally enters the uniform stage with relatively uniform distribution. (3) The homogenization distance into the uniform stage required by the arrays of square and short rod explosives is about equal to the spacing of the explosives, while the arrays of cross explosives only need about 0.8 times the spacing, and the degree of homogenization in the uniform stage is higher, so the cross explosive has a greater advantage in the case of plane explosive loading. (4) The loading mode of synchronous initiation of discrete explosive group not only improves the load synchronization, but also improves the load uniformity, compared with the slip detonation loading of rod distributed charge. The structural response distortion caused by the excessive additional mass of rubber can also be avoided by using the air layer between the sheet explosives and the structure to homogenize the load.
The loading technology of cosine distributed load by chemical explosion is the main method for evaluating the dynamic response of space structures under the irradiation of high-altitude nuclear explosions with soft X-rays. A loading method of discretely-distributed sheet explosives synchronously detonated by a mild detonating fuse (MDF) network was proposed to meet the design requirements of complex configuration, high synchronicity and low specific impulse load in the structural assessment of new space vehicles. In terms of experimental study, the cross-shaped sheet explosive made by stacking explosive strips with a cross-sectional size of 0.33 mm×0.5 mm can be directly detonated by a mild detonating fuse with the diameter of 0.5 mm. Compared with strip distribution, the space uniformity of cross distribution is improved by 76.7%. A high-speed camera was used to record the shock wave luminescence during the detonation process. The results show that the detonation ratio of the 21-point MDF detonation network reaches 100%, and the detonation asynchrony is less than 1 μs. In terms of numerical simulation, a numerical model for the explosion of sheet explosives was established based on the multi-material arbitrary Lagrangian-Eulerian (ALE) algorithm. The numerical model has strong grid sensitivity, and the results by it tend to converge when the mesh size reaches 0.5 mm, with the deviation from the measured specific impulse results within 5%. Based on the numerically-simulated results, the following conclusions can be drawn. (1) Under the periodic discrete distribution condition, the peak specific impulse is determined by the surface density of the explosive, and the evolution process of the peak specific impulse is determined by the spacing. (2) The homogenization process of specific impulse can be divided into three stages: diffusion stage, superposition stage and uniform stage. The specific impulse is homogenized through free diffusion of shock wave in the diffusion stage, and through shock wave superposition and collision in the superposition stage, and finally enters the uniform stage with relatively uniform distribution. (3) The homogenization distance into the uniform stage required by the arrays of square and short rod explosives is about equal to the spacing of the explosives, while the arrays of cross explosives only need about 0.8 times the spacing, and the degree of homogenization in the uniform stage is higher, so the cross explosive has a greater advantage in the case of plane explosive loading. (4) The loading mode of synchronous initiation of discrete explosive group not only improves the load synchronization, but also improves the load uniformity, compared with the slip detonation loading of rod distributed charge. The structural response distortion caused by the excessive additional mass of rubber can also be avoided by using the air layer between the sheet explosives and the structure to homogenize the load.
2023, 43(5): 054201.
doi: 10.11883/bzycj-2023-0006
Abstract:
In order to obtain the material constitutive model parameters of polymethyl methacrylate (PMMA) in the numerical simulation of explosive cutting, and to avoid the multiple tests required by the traditional method of obtaining the material constitutive model parameters, a neural network-based inversion method of the Johnson Holmquist Ceramics (JH-2) constitutive model parameters of PMMA was established. Firstly, a 2.5-mm-wide linear shaped charge was used to cut 14 mm PMMA flat plate, and the results of the explosive cutting test were analyzed to classify and quantify the damage of PMMA flat plate into three kinds of damage data: penetration depth, impact fracture thickness and spallation damage thickness. Based on the empirical parameters of the JH-2 constitutive model obtained from the explosive cutting experiments and existing studies, the adjustment interval of the constitutive model parameters was determined. LS-DYNA was used to simulate the process of cutting 14 mm PMMA flat plate with 2.5 mm wide linear shaped charge and to collect a flat plate damage data set containing the three kinds of damage data. A neural network model between the parameters of the PMMA flat plate constitutive model and the damage data was developed, and the model was trained using the plate damage data set. The inversion of the JH-2 constitutive model parameters of the PMMA flat plate was performed by the trained neural network model. In order to verify the reliability of the parameters obtained by the inversion method, a 4.2 mm wide linear shaped charge cutting 19 mm PMMA flat plate experiments and finite element numerical simulation were conducted, and the fracture characteristics and damage data of the PMMA flat plate in the calculation results were less different from the experiment results, indicating that the JH-2 constitutive model parameters obtained by the inversion can be better applied to PMMA flat plate explosive cutting numerical simulation. The parameter inversion method can obtain more accurate material constitutive model parameters with less experiments and tests than the traditional material parameter acquisition method.
In order to obtain the material constitutive model parameters of polymethyl methacrylate (PMMA) in the numerical simulation of explosive cutting, and to avoid the multiple tests required by the traditional method of obtaining the material constitutive model parameters, a neural network-based inversion method of the Johnson Holmquist Ceramics (JH-2) constitutive model parameters of PMMA was established. Firstly, a 2.5-mm-wide linear shaped charge was used to cut 14 mm PMMA flat plate, and the results of the explosive cutting test were analyzed to classify and quantify the damage of PMMA flat plate into three kinds of damage data: penetration depth, impact fracture thickness and spallation damage thickness. Based on the empirical parameters of the JH-2 constitutive model obtained from the explosive cutting experiments and existing studies, the adjustment interval of the constitutive model parameters was determined. LS-DYNA was used to simulate the process of cutting 14 mm PMMA flat plate with 2.5 mm wide linear shaped charge and to collect a flat plate damage data set containing the three kinds of damage data. A neural network model between the parameters of the PMMA flat plate constitutive model and the damage data was developed, and the model was trained using the plate damage data set. The inversion of the JH-2 constitutive model parameters of the PMMA flat plate was performed by the trained neural network model. In order to verify the reliability of the parameters obtained by the inversion method, a 4.2 mm wide linear shaped charge cutting 19 mm PMMA flat plate experiments and finite element numerical simulation were conducted, and the fracture characteristics and damage data of the PMMA flat plate in the calculation results were less different from the experiment results, indicating that the JH-2 constitutive model parameters obtained by the inversion can be better applied to PMMA flat plate explosive cutting numerical simulation. The parameter inversion method can obtain more accurate material constitutive model parameters with less experiments and tests than the traditional material parameter acquisition method.
2023, 43(5): 054202.
doi: 10.11883/bzycj-2022-0171
Abstract:
The physical mechanism of electrically exploding wires has caused much attention recently; fruitful experimental results have been reported by domestic researchers. Modeling and studying of the electrical metal wire explosion problems can help to understand the basic physics of Z pinches and other related magnetically driven plasma problems, and to evaluate the parameters of the state equation and electrical conductivity. A zero-dimensional (0D) dynamical model of the underwater electrical wire explosion is developed, in which the single wire is modeled as a plasma cylinder undergoing self-similar radial motion with uniform density, temperature and pressure, while its velocity varies linearly with radius. The kinetic equation and internal energy equation are derived from the hydrodynamic equations and used as the basic governing equations. To close the 0D model, other parameters are supplemented, with the real gas quotidian equation of state (QEOS) model for pressure and internal energy, the modified Lee-More electrical conductivity model for resistivity, and an external circuit model for the current density. The boundary conditions are constructed from the shock Hugoniot relations in water, the pressure at the wire boundary is assumed to be equal to the water pressure behind the shock. The calculations are carried out from a cold start of wires with density and temperature in laboratory status. Results of the 0D model are validated by comparing with the results from simulations of one-dimensional (1D) magneto-hydrodynamic (MHD) model and experiments. Examples of electrical explosion of copper wires in water are taken in the applications, the rise time of the short-circuit current pulse is 5 μs and the wires vary from 50 μm to 200 μm in diameter. Results from the 0D-dynamical model agree well with the MHD simulation results and experimental data, typical discharging modes are achieved by varying the parameters of the wires. The 0D model can be used for parameters optimizing and data analysis in similar experiments.
The physical mechanism of electrically exploding wires has caused much attention recently; fruitful experimental results have been reported by domestic researchers. Modeling and studying of the electrical metal wire explosion problems can help to understand the basic physics of Z pinches and other related magnetically driven plasma problems, and to evaluate the parameters of the state equation and electrical conductivity. A zero-dimensional (0D) dynamical model of the underwater electrical wire explosion is developed, in which the single wire is modeled as a plasma cylinder undergoing self-similar radial motion with uniform density, temperature and pressure, while its velocity varies linearly with radius. The kinetic equation and internal energy equation are derived from the hydrodynamic equations and used as the basic governing equations. To close the 0D model, other parameters are supplemented, with the real gas quotidian equation of state (QEOS) model for pressure and internal energy, the modified Lee-More electrical conductivity model for resistivity, and an external circuit model for the current density. The boundary conditions are constructed from the shock Hugoniot relations in water, the pressure at the wire boundary is assumed to be equal to the water pressure behind the shock. The calculations are carried out from a cold start of wires with density and temperature in laboratory status. Results of the 0D model are validated by comparing with the results from simulations of one-dimensional (1D) magneto-hydrodynamic (MHD) model and experiments. Examples of electrical explosion of copper wires in water are taken in the applications, the rise time of the short-circuit current pulse is 5 μs and the wires vary from 50 μm to 200 μm in diameter. Results from the 0D-dynamical model agree well with the MHD simulation results and experimental data, typical discharging modes are achieved by varying the parameters of the wires. The 0D model can be used for parameters optimizing and data analysis in similar experiments.
2023, 43(5): 055201.
doi: 10.11883/bzycj-2022-0164
Abstract:
In order to improve the permeability of coal seam with high gas and low permeability and effectively control the disaster of coal and gas outburst, the mechanism of permeability enhancement of coal seam by shaped charge blasting is studied. Firstly, the comparative experiments of concrete cracking caused by shaped charge blasting and conventional blasting were carried out, and the sizes of concrete crushing area and fracture area after blasting were compared. Meanwhile, the strain data of the strain bricks with time were collected by the super dynamic strain gauges. Then, ANSYS/LS-DYNA is used to reproduce the whole process of the formation, migration and penetration into concrete of shaped energy jet. The stress wave propagation characteristics of shaped charge blasting and conventional blasting are compared and analyzed. Finally, the coal seam antireflection tests were carried out in Pingmei No. 10 mine, and the gas volume fraction of the extraction hole after blasting was compared. The results show that after shaped charge blasting, the crack width of concrete in the direction of energy accumulation and in its perpendicular direction was 1.1 cm and 0.4 cm, respectively; while the width of four main cracks formed in concrete after conventional blasting was 0.3 cm. Comparing the strain peaks measured from strain gauges at the same distance, it is found that the strain gauge in the direction of energy accumulation is the maximum, followed by the perpendicular direction, and the strain at the diagonal direction is the minimum. In addition, the strain peak value in the direction of energy accumulation is much larger than that under conventional blasting, and the strain peak value in the perpendicular direction is basically equal to that of conventional blasting, while the strain peak value of the diagonal direction is smaller than that under the conventional blasting. The numerical simulation results show that the crushing region of concrete after shaped charge blasting is of “dumbbell type”, and the area of crushing region is smaller than that under conventional blasting. While the fracture region is of “spindle type”, the fracture is better developed. The field test shows that the gas volume fraction of the extraction hole after shaped charge blasting is significantly higher than that under conventional blasting. It is seen that shaped charge blasting can effectively improve the permeability of coal seam with high gas and low permeability.
In order to improve the permeability of coal seam with high gas and low permeability and effectively control the disaster of coal and gas outburst, the mechanism of permeability enhancement of coal seam by shaped charge blasting is studied. Firstly, the comparative experiments of concrete cracking caused by shaped charge blasting and conventional blasting were carried out, and the sizes of concrete crushing area and fracture area after blasting were compared. Meanwhile, the strain data of the strain bricks with time were collected by the super dynamic strain gauges. Then, ANSYS/LS-DYNA is used to reproduce the whole process of the formation, migration and penetration into concrete of shaped energy jet. The stress wave propagation characteristics of shaped charge blasting and conventional blasting are compared and analyzed. Finally, the coal seam antireflection tests were carried out in Pingmei No. 10 mine, and the gas volume fraction of the extraction hole after blasting was compared. The results show that after shaped charge blasting, the crack width of concrete in the direction of energy accumulation and in its perpendicular direction was 1.1 cm and 0.4 cm, respectively; while the width of four main cracks formed in concrete after conventional blasting was 0.3 cm. Comparing the strain peaks measured from strain gauges at the same distance, it is found that the strain gauge in the direction of energy accumulation is the maximum, followed by the perpendicular direction, and the strain at the diagonal direction is the minimum. In addition, the strain peak value in the direction of energy accumulation is much larger than that under conventional blasting, and the strain peak value in the perpendicular direction is basically equal to that of conventional blasting, while the strain peak value of the diagonal direction is smaller than that under the conventional blasting. The numerical simulation results show that the crushing region of concrete after shaped charge blasting is of “dumbbell type”, and the area of crushing region is smaller than that under conventional blasting. While the fracture region is of “spindle type”, the fracture is better developed. The field test shows that the gas volume fraction of the extraction hole after shaped charge blasting is significantly higher than that under conventional blasting. It is seen that shaped charge blasting can effectively improve the permeability of coal seam with high gas and low permeability.
