2022 Vol. 42, No. 5
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2022, 42(5): 052201.
doi: 10.11883/bzycj-2021-0280
Abstract:
In order to study the influence of different ways of eccentric initiation on the energy distribution and the gain of explosive charge, a theoretical model of eccentric initiation warhead is established, and the concept of energy distribution center is introduced. By introducing the variable of local loading ratio, the calculation formula of initial velocity of fragments of eccentric initiation warhead is formulated. In this paper, the velocity gain of fragments and energy gain with different initiation modes under the sextile condition are compared and analyzed by using numerical simulation and experimental verification. The results show that at the directional orientation, the maximum pressure at the edge of multi-line eccentric initiation is significantly greater than that of eccentric single line initiation and central initiation, and the detonation pressure at the edge of charge increases from 23.5 GPa of central initiation to 36.2 GPa of asymmetrical two lines 60° initiation; The distribution law of fragment velocity in the direction of 0°−30° is similar to the distribution law of maximum pressure at the edge of charge. Taking the central initiation as the benchmark, the relationship of velocity gain with the directional orientation takes the following relation: asymmetrical two lines 60°>asymmetrical three lines 120°>asymmetrical two lines 120°>asymmetrical one line. When asymmetrical two lines 60° initiation, the fragment velocity gain in the target direction is 25.47%. Finally, through the verification of experiments and theoretical calculation, it is concluded that the energy proportion in the directional area of adjacent asymmetrical two lines 60° is the highest, with the energy gain in this area being 47.42%; followed by asymmetrical three lines 120einitiation, with the energy gain being 38.84%; then symmetrical two lines 1202initiation, with the energy gain being 36.98%; and finally asymmetrical one line initiation, with the energy gain in the directional area being 32.72%.
In order to study the influence of different ways of eccentric initiation on the energy distribution and the gain of explosive charge, a theoretical model of eccentric initiation warhead is established, and the concept of energy distribution center is introduced. By introducing the variable of local loading ratio, the calculation formula of initial velocity of fragments of eccentric initiation warhead is formulated. In this paper, the velocity gain of fragments and energy gain with different initiation modes under the sextile condition are compared and analyzed by using numerical simulation and experimental verification. The results show that at the directional orientation, the maximum pressure at the edge of multi-line eccentric initiation is significantly greater than that of eccentric single line initiation and central initiation, and the detonation pressure at the edge of charge increases from 23.5 GPa of central initiation to 36.2 GPa of asymmetrical two lines 60° initiation; The distribution law of fragment velocity in the direction of 0°−30° is similar to the distribution law of maximum pressure at the edge of charge. Taking the central initiation as the benchmark, the relationship of velocity gain with the directional orientation takes the following relation: asymmetrical two lines 60°>asymmetrical three lines 120°>asymmetrical two lines 120°>asymmetrical one line. When asymmetrical two lines 60° initiation, the fragment velocity gain in the target direction is 25.47%. Finally, through the verification of experiments and theoretical calculation, it is concluded that the energy proportion in the directional area of adjacent asymmetrical two lines 60° is the highest, with the energy gain in this area being 47.42%; followed by asymmetrical three lines 120einitiation, with the energy gain being 38.84%; then symmetrical two lines 1202initiation, with the energy gain being 36.98%; and finally asymmetrical one line initiation, with the energy gain in the directional area being 32.72%.
2022, 42(5): 052301.
doi: 10.11883/bzycj-2021-0305
Abstract:
The detonation pressure and detonation reaction zone are important for the detonation performance evaluation of explosives. In order to obtain the reaction zone parameters of several common high explosives, the detonation wave profiles in TNT, PETN, RDX, HMX, TATB and CL-20 based explosives were experimentally measured with photon Doppler velocimetry (PDV). The explosive samples were initiated by explosive plane-wave lenses or a powder gun, and the thickness of the samples was more than 10 mm to insure a stable detonation in the test area. A transparent LiF window covered by a 0.7-μm-thick aluminum reflective coating on the distal side was attached to the explosive sample, and the particle velocity histories of the interface between the explosive and window were measured with PDV. The Chapman-Jouguet (CJ) point was determined by the inflexion point in the corresponding profile or the separation point of the particle velocity histories for samples of different lengths. The CJ pressure was calculated using the impedance matching method. The pressure at the von Neumann (VN) spike was also obtained. The results show that for ideal explosives such as PETN, RDX, HMX and CL-20, the interface particle velocity profiles show a distinct end of the reaction zone, and the detonation reaction zones are narrow. The detonation reaction time is between 7 ns and 15 ns for those ideal explosives. For TNT and TATB based explosives, measurements show an indistinct end of the reaction zone because the reaction of solid carbon formation is slow, and the detonation reaction time is about (100±15) ns and (255±20) ns, respectively. The ratio of the measured spike pressure to CJ pressure of the explosives ranges from 1.22 to 1.46. The analysis indicates that the relative expanded uncertainty of the detonation pressure measured with PDV is 4.4% at k=2, and the uncertainty of the detonation reaction time is 2－4 ns for those ideal explosives or 10－20 ns for those unideal explosives.
The detonation pressure and detonation reaction zone are important for the detonation performance evaluation of explosives. In order to obtain the reaction zone parameters of several common high explosives, the detonation wave profiles in TNT, PETN, RDX, HMX, TATB and CL-20 based explosives were experimentally measured with photon Doppler velocimetry (PDV). The explosive samples were initiated by explosive plane-wave lenses or a powder gun, and the thickness of the samples was more than 10 mm to insure a stable detonation in the test area. A transparent LiF window covered by a 0.7-μm-thick aluminum reflective coating on the distal side was attached to the explosive sample, and the particle velocity histories of the interface between the explosive and window were measured with PDV. The Chapman-Jouguet (CJ) point was determined by the inflexion point in the corresponding profile or the separation point of the particle velocity histories for samples of different lengths. The CJ pressure was calculated using the impedance matching method. The pressure at the von Neumann (VN) spike was also obtained. The results show that for ideal explosives such as PETN, RDX, HMX and CL-20, the interface particle velocity profiles show a distinct end of the reaction zone, and the detonation reaction zones are narrow. The detonation reaction time is between 7 ns and 15 ns for those ideal explosives. For TNT and TATB based explosives, measurements show an indistinct end of the reaction zone because the reaction of solid carbon formation is slow, and the detonation reaction time is about (100±15) ns and (255±20) ns, respectively. The ratio of the measured spike pressure to CJ pressure of the explosives ranges from 1.22 to 1.46. The analysis indicates that the relative expanded uncertainty of the detonation pressure measured with PDV is 4.4% at k=2, and the uncertainty of the detonation reaction time is 2－4 ns for those ideal explosives or 10－20 ns for those unideal explosives.
2022, 42(5): 053101.
doi: 10.11883/bzycj-2021-0328
Abstract:
Aiming at new technology of the kinked rebar which can improve the resistance of concrete beams to impact and blast loading, the mechanism of rapid tensile deformation of the kinked rebar was revealed through theoretical analysis combined with dynamic impact tensile tests. The influences of the tensile velocity and the bending height of the kinked rebar on its tensile strength were analyzed. According to the mechanism of tensile deformation, the calculation method of the static elastic ultimate strength of the kinked rebar was determined by using the classical plastic mechanics theory, and the proposed calculation method was modified based on the existing literature data to consider the error caused by the Bauschinger effect. A new concept of equivalent tensile strain rate of the kinked rebar was put forward, the kinked rebar was regarded as an equivalent material, and the average strain rate of the bending part of the rebar was defined as the equivalent tensile strain rate of the kinked rebar. Considering the influence of the tensile velocity and the bending height of the kinked rebar, the calculation model of dynamic increase factors (DIF) of the elastic ultimate strength was established, referring to the form of the Johnson-Cook material constitutive model. The results show that the pre-bending kink results in the section bending moment of the steel bar during force straightening and the mechanical properties of the kinked rebar have an obvious strain rate effect. The tensile yield strength first increases and then decreases with the increase of the bending height of the kinked rebar. There is an optimal bending height for the kinked rebar at high strain rates, which can maximize the dynamic amplification factor of the tensile strength of the kinked rebar. The research results can provide a basis for further promotion of the application of the kinked rebar technology in protection engineering.
Aiming at new technology of the kinked rebar which can improve the resistance of concrete beams to impact and blast loading, the mechanism of rapid tensile deformation of the kinked rebar was revealed through theoretical analysis combined with dynamic impact tensile tests. The influences of the tensile velocity and the bending height of the kinked rebar on its tensile strength were analyzed. According to the mechanism of tensile deformation, the calculation method of the static elastic ultimate strength of the kinked rebar was determined by using the classical plastic mechanics theory, and the proposed calculation method was modified based on the existing literature data to consider the error caused by the Bauschinger effect. A new concept of equivalent tensile strain rate of the kinked rebar was put forward, the kinked rebar was regarded as an equivalent material, and the average strain rate of the bending part of the rebar was defined as the equivalent tensile strain rate of the kinked rebar. Considering the influence of the tensile velocity and the bending height of the kinked rebar, the calculation model of dynamic increase factors (DIF) of the elastic ultimate strength was established, referring to the form of the Johnson-Cook material constitutive model. The results show that the pre-bending kink results in the section bending moment of the steel bar during force straightening and the mechanical properties of the kinked rebar have an obvious strain rate effect. The tensile yield strength first increases and then decreases with the increase of the bending height of the kinked rebar. There is an optimal bending height for the kinked rebar at high strain rates, which can maximize the dynamic amplification factor of the tensile strength of the kinked rebar. The research results can provide a basis for further promotion of the application of the kinked rebar technology in protection engineering.
2022, 42(5): 053102.
doi: 10.11883/bzycj-2021-0292
Abstract:
Compared with traditional transparent materials, transparent ceramics have excellent impact resistance at the same areal density, which contributes to its giant potential in the field of transparent armor protection. The studies of the damage response and damage evolution law of transparent ceramics under impact play a vital role in the structural design and protection of transparent ceramic armors. In order to compare the difference between traditional transparent materials and typical transparent ceramic materials under the impact damage process, a 9 mm-ballistic gun launch platform was used to conduct edge-on impact (EOI) tests on three transparent materials, including float glass, YAG transparent ceramics and magnesium aluminum spinel transparent ceramics. The impact process of the fragments was captured by a high-speed video camera, and the change rule of the crushing zone and the propagation distance of the main crack over time was analyzed. The results show that the area of the crushing zone in three materials was negatively correlated with the strength of the material when the fragment impact velocity ranged from 200 to 300 m/s. For the same material, within this velocity range, the impact velocity of the fragments had no significant effect on the propagation velocity of the main crack. Besides, the macroscale differences on the damage evolution characteristics of three materials are investigated. Through the scanning electron microscope (SEM) observation on the recovered ceramic fragments, the similarities and differences on the damage characteristics of the two transparent ceramic materials at the mesoscale are analyzed in detail. The change that intergranular fracture transformed into transgranular fracture on the radial crack occurred in both spinel and YAG transparent ceramics, while the ring fracture surfaces were almost all along the intergranular fracture. Compared with the magnesium aluminum spinel transparent ceramics, YAG transparent ceramics possessed “peel off” phenomenon that fracture occurred along the grain boundary. Besides, the transgranular fracture surface in MgAl2O4 transparent ceramics was in jagged irregular shape, while that of YAG transparent ceramics was smooth.
Compared with traditional transparent materials, transparent ceramics have excellent impact resistance at the same areal density, which contributes to its giant potential in the field of transparent armor protection. The studies of the damage response and damage evolution law of transparent ceramics under impact play a vital role in the structural design and protection of transparent ceramic armors. In order to compare the difference between traditional transparent materials and typical transparent ceramic materials under the impact damage process, a 9 mm-ballistic gun launch platform was used to conduct edge-on impact (EOI) tests on three transparent materials, including float glass, YAG transparent ceramics and magnesium aluminum spinel transparent ceramics. The impact process of the fragments was captured by a high-speed video camera, and the change rule of the crushing zone and the propagation distance of the main crack over time was analyzed. The results show that the area of the crushing zone in three materials was negatively correlated with the strength of the material when the fragment impact velocity ranged from 200 to 300 m/s. For the same material, within this velocity range, the impact velocity of the fragments had no significant effect on the propagation velocity of the main crack. Besides, the macroscale differences on the damage evolution characteristics of three materials are investigated. Through the scanning electron microscope (SEM) observation on the recovered ceramic fragments, the similarities and differences on the damage characteristics of the two transparent ceramic materials at the mesoscale are analyzed in detail. The change that intergranular fracture transformed into transgranular fracture on the radial crack occurred in both spinel and YAG transparent ceramics, while the ring fracture surfaces were almost all along the intergranular fracture. Compared with the magnesium aluminum spinel transparent ceramics, YAG transparent ceramics possessed “peel off” phenomenon that fracture occurred along the grain boundary. Besides, the transgranular fracture surface in MgAl2O4 transparent ceramics was in jagged irregular shape, while that of YAG transparent ceramics was smooth.
2022, 42(5): 053201.
doi: 10.11883/bzycj-2021-0494
Abstract:
To study the influence of side-direction ventilation on the surface loads of a revolving body during water entry, based on the VOF (volume of fluid) model and the Realizable k-ε two-layer turbulence model, the numerical prediction of the flow field evolution and analysis of the surface load characteristics when a side-direction ventilated revolving body into the water at a low-speed are carried out. By comparing the cavity shape between the numerical predictions and the experimental results, the validity of the numerical method is verified. The effects of different ventilation rates on the cavity shape, the flow field evolution, and the surface load characteristics are then analyzed. The results show that ventilation changes the process of the cavity evolution and the pressure on the sidewall surface of the revolving body. With the effect of ventilation, the time when the first cavity falls off is delayed, and the ventilation gas flows to the area behind the cavitator, which improves the negative pressure situation behind the cavitator. The ventilation gas forms an obvious vortex structure near the spout, which then merges with another vortex formed by the cavitator at the cavity wall, leading to an increase in the vortex intensity in the middle of the cavity. With the increase of the ventilation rate, the closure time of the cavity becomes later, the volume of the cavity gets bigger, and the cavity near the tail of the revolving body is less likely to fall off. Compared to the non-ventilation situation, the ventilation will reduce the fluctuations of the surface loads. The greater the ventilation rate, the less the surface load fluctuations are. In general, the side-direction ventilation improves the flow field and the surface load characteristics of the revolving body during low-speed water entry.
To study the influence of side-direction ventilation on the surface loads of a revolving body during water entry, based on the VOF (volume of fluid) model and the Realizable k-ε two-layer turbulence model, the numerical prediction of the flow field evolution and analysis of the surface load characteristics when a side-direction ventilated revolving body into the water at a low-speed are carried out. By comparing the cavity shape between the numerical predictions and the experimental results, the validity of the numerical method is verified. The effects of different ventilation rates on the cavity shape, the flow field evolution, and the surface load characteristics are then analyzed. The results show that ventilation changes the process of the cavity evolution and the pressure on the sidewall surface of the revolving body. With the effect of ventilation, the time when the first cavity falls off is delayed, and the ventilation gas flows to the area behind the cavitator, which improves the negative pressure situation behind the cavitator. The ventilation gas forms an obvious vortex structure near the spout, which then merges with another vortex formed by the cavitator at the cavity wall, leading to an increase in the vortex intensity in the middle of the cavity. With the increase of the ventilation rate, the closure time of the cavity becomes later, the volume of the cavity gets bigger, and the cavity near the tail of the revolving body is less likely to fall off. Compared to the non-ventilation situation, the ventilation will reduce the fluctuations of the surface loads. The greater the ventilation rate, the less the surface load fluctuations are. In general, the side-direction ventilation improves the flow field and the surface load characteristics of the revolving body during low-speed water entry.
2022, 42(5): 053202.
doi: 10.11883/bzycj-2021-0485
Abstract:
The effect of the initial parameter setting of water medium on underwater explosion load characteristics in numerical simulation is studied. Firstly, based on the parameters under reference state, a kind of polynomial equation of state (EOS) is chosen as the EOS of water medium. Secondly, from the perspective of thermodynamics, two existing setting modes of initial parameters are analyzed, and a new setting mode following isothermal process is proposed. In addition, the results of initial compression ratio, initial internal energy and acoustic velocity of water under different depths given by INITIAL_EOS_ALE keyword in LS-DYNA program are investigated and compared with other three modes. Finally, by using the LS-DYNA program, numerical simulations of underwater explosion under different depths are conducted with a one-dimensional spherical charge model. The differences of shock wave load and bubble pulsation characteristics among the first three setting modes are discussed, which are also compared with previous studies. The results show that the parameters of water medium change with depths according to isochoric process if only the internal energy term of water medium is changed. Hence, it indicates that the pressures under different water depths are caused by thermal conduction from external environment, which is seriously inconsistent with the actual deep water condition. Initial parameters given by INITIAL_EOS_ALE keyword are close to the results obtained by only changing the density of water (i.e., following isometric energy process), but the changing laws of temperature for these two modes are both inconsistent with the real environment. When the parameters follow equal internal energy process or isothermal process, the calculated load characteristics are close to each other, which are consistent with existed studies. It is concluded, therefore, that initial parameter setting mode based on isothermal process is better than other three modes. This conclusion can provide an important reference to ensure the accuracy of underwater explosion numerical simulation, especially for deep water explosion.
The effect of the initial parameter setting of water medium on underwater explosion load characteristics in numerical simulation is studied. Firstly, based on the parameters under reference state, a kind of polynomial equation of state (EOS) is chosen as the EOS of water medium. Secondly, from the perspective of thermodynamics, two existing setting modes of initial parameters are analyzed, and a new setting mode following isothermal process is proposed. In addition, the results of initial compression ratio, initial internal energy and acoustic velocity of water under different depths given by INITIAL_EOS_ALE keyword in LS-DYNA program are investigated and compared with other three modes. Finally, by using the LS-DYNA program, numerical simulations of underwater explosion under different depths are conducted with a one-dimensional spherical charge model. The differences of shock wave load and bubble pulsation characteristics among the first three setting modes are discussed, which are also compared with previous studies. The results show that the parameters of water medium change with depths according to isochoric process if only the internal energy term of water medium is changed. Hence, it indicates that the pressures under different water depths are caused by thermal conduction from external environment, which is seriously inconsistent with the actual deep water condition. Initial parameters given by INITIAL_EOS_ALE keyword are close to the results obtained by only changing the density of water (i.e., following isometric energy process), but the changing laws of temperature for these two modes are both inconsistent with the real environment. When the parameters follow equal internal energy process or isothermal process, the calculated load characteristics are close to each other, which are consistent with existed studies. It is concluded, therefore, that initial parameter setting mode based on isothermal process is better than other three modes. This conclusion can provide an important reference to ensure the accuracy of underwater explosion numerical simulation, especially for deep water explosion.
2022, 42(5): 053203.
doi: 10.11883/bzycj-2021-0206
Abstract:
In marine warfare, the water jets formed by near-field underwater explosions can cause serious local damage to ship structures. With more knowledge on near-field underwater explosions, the phenomenon of water jet has become a hot research topic in recent years. To study the formation mechanism of water jet during near-field explosion under the bottom of a ship, an underwater explosion experiment was carried out, in which 2.5 g of TNT was detonated under the bottom of a clamped square plate at different explosion distances. A high-speed camera was used to record the evolution of the bubble jet. At the same time, a free-field underwater pressure sensor was used to measure the pressure field in the water tank. The experimental results show that with the increase of the burst distance, the process of bubbles evolving to form jets at the bottom of the square plate can be divided into two types; that is, the adsorption type and non-adsorption type. Then, by employing ABAQUS software andusing the CEL method, a series of numerical simulations were carried out for the experiment. The numerical simulation results show that the critical point for the conversion from the adsorption jet to the non-adsorption jet is between 0.821 times the maximum bubble radius and 0.867 times the maximum bubble radius. Because the upper part of the bubble is difficult to expand freely under the barrier of the steel plate, the corresponding burst distance when the bubble is adsorbed is smaller than the maximum bubble radius. By analyzing the velocity cloud diagram at the jet being formed, it is found that with the increase of the burst distance, because the clamped square plate accelerates the process of bubble collapse, the time of jet formation is advanced. The maximum velocity during the formation process of water jet and the velocity when water jet hits the steel plate both increase first and then decrease with the increase of the burst distance, reaching the maximum near the critical point. The maximum jet velocity can reach 621 m/s, the maximum jet velocity when jet hits the steel plate can reach 269 m/s. Because the larger the burst distance, the later the bubble collapses, and the more concentrated the energy in the bubble, which makes the jet velocity larger, but when the burst distance is too large, the Bjerknes effect of the steel plate on the bubble will be weakened, which will reduce the jet velocity. Consequently, a critical point of the burst distance exists, at which the jet velocity renders a maximum.
In marine warfare, the water jets formed by near-field underwater explosions can cause serious local damage to ship structures. With more knowledge on near-field underwater explosions, the phenomenon of water jet has become a hot research topic in recent years. To study the formation mechanism of water jet during near-field explosion under the bottom of a ship, an underwater explosion experiment was carried out, in which 2.5 g of TNT was detonated under the bottom of a clamped square plate at different explosion distances. A high-speed camera was used to record the evolution of the bubble jet. At the same time, a free-field underwater pressure sensor was used to measure the pressure field in the water tank. The experimental results show that with the increase of the burst distance, the process of bubbles evolving to form jets at the bottom of the square plate can be divided into two types; that is, the adsorption type and non-adsorption type. Then, by employing ABAQUS software andusing the CEL method, a series of numerical simulations were carried out for the experiment. The numerical simulation results show that the critical point for the conversion from the adsorption jet to the non-adsorption jet is between 0.821 times the maximum bubble radius and 0.867 times the maximum bubble radius. Because the upper part of the bubble is difficult to expand freely under the barrier of the steel plate, the corresponding burst distance when the bubble is adsorbed is smaller than the maximum bubble radius. By analyzing the velocity cloud diagram at the jet being formed, it is found that with the increase of the burst distance, because the clamped square plate accelerates the process of bubble collapse, the time of jet formation is advanced. The maximum velocity during the formation process of water jet and the velocity when water jet hits the steel plate both increase first and then decrease with the increase of the burst distance, reaching the maximum near the critical point. The maximum jet velocity can reach 621 m/s, the maximum jet velocity when jet hits the steel plate can reach 269 m/s. Because the larger the burst distance, the later the bubble collapses, and the more concentrated the energy in the bubble, which makes the jet velocity larger, but when the burst distance is too large, the Bjerknes effect of the steel plate on the bubble will be weakened, which will reduce the jet velocity. Consequently, a critical point of the burst distance exists, at which the jet velocity renders a maximum.
2022, 42(5): 053204.
doi: 10.11883/bzycj-2021-0269
Abstract:
High-voltage power module is a key component to realize stable current output. In order to improve the structural reliability of the high-voltage power module and optimize the fixed modes under high-speed impact, the impact resistance characteristics with different fixed modes are studied. Based on the one-dimensional stress wave theory, the comparison of deformation energy and kinetic energy of the module with different fixed modes are obtained by analyzing the dynamic response and energy conversion form of the module on the free Hopkinson pulse bar (FHPB). The finite element method is used to simulate the processes of motion and deformation under impact velocity of 20 m/s. The stress distributions, the deflection curves, the velocity curves, and the acceleration curves of the module under the same impact are obtained. It is found that the maximum stress (427 MPa) appears at the ceramic layer, while the maximum deflection (773.8 μm) occurs at the metal substrate layer. The magnitude of the maximum displacement speed is up to 17.68 m/s, and the magnitude of the maximum acceleration is up to 51 110.7g. By comparing the impact response results of the four fixed modes, the deformation of bottom substrate from small to large is the surface mounting, four-corner point fixing, two-point fixing on the short side and two-point fixing on the long side. The highest kinetic energy and acceleration are produced on the surface mounting modules. The results indicate that a minimum failure probability exists on surface mounting module under high impact loading. In summary, surface mounting is the most reliable fixed method among the four fixed methods. Then, the selection priorities are as following: the four-corner fixing, two-point fixing on the short side and two-point fixing on the long side. Out study results would provide an important theoretical basis of the mounting and fixing methods for semiconductor high-voltage power modules in practical application.
High-voltage power module is a key component to realize stable current output. In order to improve the structural reliability of the high-voltage power module and optimize the fixed modes under high-speed impact, the impact resistance characteristics with different fixed modes are studied. Based on the one-dimensional stress wave theory, the comparison of deformation energy and kinetic energy of the module with different fixed modes are obtained by analyzing the dynamic response and energy conversion form of the module on the free Hopkinson pulse bar (FHPB). The finite element method is used to simulate the processes of motion and deformation under impact velocity of 20 m/s. The stress distributions, the deflection curves, the velocity curves, and the acceleration curves of the module under the same impact are obtained. It is found that the maximum stress (427 MPa) appears at the ceramic layer, while the maximum deflection (773.8 μm) occurs at the metal substrate layer. The magnitude of the maximum displacement speed is up to 17.68 m/s, and the magnitude of the maximum acceleration is up to 51 110.7g. By comparing the impact response results of the four fixed modes, the deformation of bottom substrate from small to large is the surface mounting, four-corner point fixing, two-point fixing on the short side and two-point fixing on the long side. The highest kinetic energy and acceleration are produced on the surface mounting modules. The results indicate that a minimum failure probability exists on surface mounting module under high impact loading. In summary, surface mounting is the most reliable fixed method among the four fixed methods. Then, the selection priorities are as following: the four-corner fixing, two-point fixing on the short side and two-point fixing on the long side. Out study results would provide an important theoretical basis of the mounting and fixing methods for semiconductor high-voltage power modules in practical application.
2022, 42(5): 053205.
doi: 10.11883/bzycj-2021-0452
Abstract:
In scaling the dynamic responses of thin-walled cylindrical shells subjected to axial impact loading, the thickness cannot be adjusted according to the same scale as the radius and height due to the thin wall characteristics. Hence, geometrically-distorted models would be used, and the traditional scaling law cannot describe the relationship between the dynamic responses of the prototype and the geometrically-distorted model. In this paper, the scaling law for this case was derived for elastic-ideal plastic thin-walled cylindrical shells under axial impact loading. For strain hardening and strain-rate hardening material, based on the average load, deformation energy, and displacement of the shell in the axisymmetric deformation mode, the dimensionless numbers of three key design parameters, namely the stress, mass, and displacement, were obtained through the law of energy conservation. Then, the optimal approximation of the flow stress predicted by the distorted scaled model to the flow stress of the prototype was established on a given strain and strain rate interval. In this way, the derived scaling law can be applied to the case considering the coupling effects of geometric distortion, strain-rate sensitivity, and strain hardening. Finally, several finite element models of thin-walled cylindrical shell models subject to axial mass impact were established. These models use the elastic-ideal plastic material model and the general material model with strain-rate hardening and strain hardening effects. The modified impact velocity and impact mass were obtained by the present method using the geometrically-distorted model, which verified the effectiveness and correctness of the proposed scaling law. The results show that the geometrically distorted model corrected by the method proposed in this article can quite accurately predict the dynamic responses of the prototype, and significantly reduce the errors in the dynamic responses of the thin-walled cylindrical shell subjected to axial impact loading, especially the average load and deformation energy.
In scaling the dynamic responses of thin-walled cylindrical shells subjected to axial impact loading, the thickness cannot be adjusted according to the same scale as the radius and height due to the thin wall characteristics. Hence, geometrically-distorted models would be used, and the traditional scaling law cannot describe the relationship between the dynamic responses of the prototype and the geometrically-distorted model. In this paper, the scaling law for this case was derived for elastic-ideal plastic thin-walled cylindrical shells under axial impact loading. For strain hardening and strain-rate hardening material, based on the average load, deformation energy, and displacement of the shell in the axisymmetric deformation mode, the dimensionless numbers of three key design parameters, namely the stress, mass, and displacement, were obtained through the law of energy conservation. Then, the optimal approximation of the flow stress predicted by the distorted scaled model to the flow stress of the prototype was established on a given strain and strain rate interval. In this way, the derived scaling law can be applied to the case considering the coupling effects of geometric distortion, strain-rate sensitivity, and strain hardening. Finally, several finite element models of thin-walled cylindrical shell models subject to axial mass impact were established. These models use the elastic-ideal plastic material model and the general material model with strain-rate hardening and strain hardening effects. The modified impact velocity and impact mass were obtained by the present method using the geometrically-distorted model, which verified the effectiveness and correctness of the proposed scaling law. The results show that the geometrically distorted model corrected by the method proposed in this article can quite accurately predict the dynamic responses of the prototype, and significantly reduce the errors in the dynamic responses of the thin-walled cylindrical shell subjected to axial impact loading, especially the average load and deformation energy.
2022, 42(5): 053206.
doi: 10.11883/bzycj-2021-0279
Abstract:
It is necessary to take into consideration the effects of elevated-altitude conditions on the propagation characteristics of blast waves when evaluating the explosion power of ammunitions under plateau environment. In order to study the propagation characteristics of blast wave under plateau environment with low pressure, experiments were carried out at simulated plateau environment at altitudes of 500, 2 500 and 4 500 m, respectively. Results show that when the ambient air pressure decreases by 20%, the overpressure, specific impulse and arrival time of blast wave decrease in average by about 9%, 10% and 6%, respectively. Calculated results corrected by Sachs' factor are compared with the test data. It is found that the method proposed in the present study can better predict the blast wave parameters under different environmental conditions. The effects of ambient temperature were also studied. It is concluded that the increase of the initial ambient temperature will reduce the arrival time of blast wave, however, the effects of ambient temperature on the overpressure and specific impulse are not significant. The results have reference significance for the evaluation of warhead explosion power at elevated altitude.
It is necessary to take into consideration the effects of elevated-altitude conditions on the propagation characteristics of blast waves when evaluating the explosion power of ammunitions under plateau environment. In order to study the propagation characteristics of blast wave under plateau environment with low pressure, experiments were carried out at simulated plateau environment at altitudes of 500, 2 500 and 4 500 m, respectively. Results show that when the ambient air pressure decreases by 20%, the overpressure, specific impulse and arrival time of blast wave decrease in average by about 9%, 10% and 6%, respectively. Calculated results corrected by Sachs' factor are compared with the test data. It is found that the method proposed in the present study can better predict the blast wave parameters under different environmental conditions. The effects of ambient temperature were also studied. It is concluded that the increase of the initial ambient temperature will reduce the arrival time of blast wave, however, the effects of ambient temperature on the overpressure and specific impulse are not significant. The results have reference significance for the evaluation of warhead explosion power at elevated altitude.
2022, 42(5): 053301.
doi: 10.11883/bzycj-2021-0307
Abstract:
In an inflatable capsule, a bearing layer, which consists of high-performance fiber fabrics, is always used to bear its internal pressure load and to provide space debris protection. The pre-tension of the fiber fabric bearing layer, resulting from the pressure load, has a significant effect on the characteristics of the fiber fabric under space debris hypervelocity impact, thereby affecting the space debris protection performance of the inflatable capsule. To consider the thermo-mechanical behavior during hypervelocity impact, a numerical model for hypervelocity impact on pre-tensioned fiber fabrics is developed by introducing the Johnson-Cook strength model and Mie-Grüneisen state equation. The finite element method-smoothed particle hydrodynamics (FEM-SPH) coupling algorithm is used to discrete the yarn weaving structure of fiber fabrics. A fabric panel that has a rectangular configuration is pre-stretched by applying tensile stress boundary conditions. A projectile is then launched at a preset velocity and hit the four-side clamped pre-tensioned fiber fabric to simulate the hypervelocity impact process. The thermal-mechanical properties and space debris protection performance of the pre-tensioned fiber fabrics under hypervelocity impact are analyzed. The results show that with an increase in pre-tension, the perforation diameter of the fiber fabric increases, while the diffusion angle of the debris, as well as the absorption rate of the projectile kinetic energy and the temperature of the impact area, decrease. As a result, the pre-tension significantly reduces the space debris protection performance of the fiber fabrics.
In an inflatable capsule, a bearing layer, which consists of high-performance fiber fabrics, is always used to bear its internal pressure load and to provide space debris protection. The pre-tension of the fiber fabric bearing layer, resulting from the pressure load, has a significant effect on the characteristics of the fiber fabric under space debris hypervelocity impact, thereby affecting the space debris protection performance of the inflatable capsule. To consider the thermo-mechanical behavior during hypervelocity impact, a numerical model for hypervelocity impact on pre-tensioned fiber fabrics is developed by introducing the Johnson-Cook strength model and Mie-Grüneisen state equation. The finite element method-smoothed particle hydrodynamics (FEM-SPH) coupling algorithm is used to discrete the yarn weaving structure of fiber fabrics. A fabric panel that has a rectangular configuration is pre-stretched by applying tensile stress boundary conditions. A projectile is then launched at a preset velocity and hit the four-side clamped pre-tensioned fiber fabric to simulate the hypervelocity impact process. The thermal-mechanical properties and space debris protection performance of the pre-tensioned fiber fabrics under hypervelocity impact are analyzed. The results show that with an increase in pre-tension, the perforation diameter of the fiber fabric increases, while the diffusion angle of the debris, as well as the absorption rate of the projectile kinetic energy and the temperature of the impact area, decrease. As a result, the pre-tension significantly reduces the space debris protection performance of the fiber fabrics.
2022, 42(5): 053302.
doi: 10.11883/bzycj-2021-0278
Abstract:
Armor steel/ultra-high performance concrete (UHPC) composite structures have a wide application prospect in the protective structures against the high-speed projectile penetration. Aiming to evaluate the penetration resistance of the composite targets, both field tests and numerical simulations were carried out on two types of armor steel/UHPC composite targets. Firstly, twelve 30mm-caliber 30CrMnSiNi2A steel projectile penetration tests on different armor steel/UHPC composite targets were conducted with the striking velocities varying from 372 m/s to 646 m/s. Compared to the UHPC target, the armor/UHPC composite targets present high penetration resistance and low areal density. The test results show that the penetration resistance of the NP500/UHPC composite target with an armor steel thickness of 5 mm can be increased by 35.7% compared to that of the NP450/UHPC composite target. Besides, a series of static and dynamic mechanical tests for armor steels were conducted to calibrate the parameters of the constitutive model. Then, 3D finite element models were established and the corresponding numerical simulations were carried out. The parameters of the constitutive model of the armor steel were validated by comparing the experimental penetration depth, residual projectile length and failure mode of the armor steel plate with the numerical results. Furthermore, the impact resistance of the armor steel/UHPC composite targets was discussed quantitatively via the ballistic efficiency factor. For the cases in this study, the composite target with 8mm thick NP500 armor steel exhibits the best ballistic performance. Finally, the critical perforation velocities of two types of armor steels with different thicknesses in the composite targets were determined. The failure modes of the projectile and target were further discussed. As the strength and hardness of the armor steel increase, the failure mode changes from shear plugging failure to ductile hole expansion failure.
Armor steel/ultra-high performance concrete (UHPC) composite structures have a wide application prospect in the protective structures against the high-speed projectile penetration. Aiming to evaluate the penetration resistance of the composite targets, both field tests and numerical simulations were carried out on two types of armor steel/UHPC composite targets. Firstly, twelve 30mm-caliber 30CrMnSiNi2A steel projectile penetration tests on different armor steel/UHPC composite targets were conducted with the striking velocities varying from 372 m/s to 646 m/s. Compared to the UHPC target, the armor/UHPC composite targets present high penetration resistance and low areal density. The test results show that the penetration resistance of the NP500/UHPC composite target with an armor steel thickness of 5 mm can be increased by 35.7% compared to that of the NP450/UHPC composite target. Besides, a series of static and dynamic mechanical tests for armor steels were conducted to calibrate the parameters of the constitutive model. Then, 3D finite element models were established and the corresponding numerical simulations were carried out. The parameters of the constitutive model of the armor steel were validated by comparing the experimental penetration depth, residual projectile length and failure mode of the armor steel plate with the numerical results. Furthermore, the impact resistance of the armor steel/UHPC composite targets was discussed quantitatively via the ballistic efficiency factor. For the cases in this study, the composite target with 8mm thick NP500 armor steel exhibits the best ballistic performance. Finally, the critical perforation velocities of two types of armor steels with different thicknesses in the composite targets were determined. The failure modes of the projectile and target were further discussed. As the strength and hardness of the armor steel increase, the failure mode changes from shear plugging failure to ductile hole expansion failure.
2022, 42(5): 053303.
doi: 10.11883/bzycj-2021-0310
Abstract:
Based on the quantitative analysis of the external parameters in relation to ultra-high pressure water jet sprayers, an optimal method for the key parameters of water jets was proposed, aiming at improving the efficiency of the water jets. Firstly, according to the characteristics of the ultra-high pressure water jet rust removal nozzles, the three-dimensional models of the single-beam and rotating multi-beam nozzles were established and used for the numerical simulations in which taking the water compressibility and cavitation effects into account. By changing the relevant characteristic parameters, such as standoff distances, jet angles and rotating speeds, the hydrodynamic performances related to the ultra-high pressure water jet rust removal nozzles were investigated though the simulations. Secondly, the effects of the standoff distances and jet angles for the single-beam nozzle on the distributions of the wall shear stress and impact pressure as well as the relationship between the length of the potential core of the jet and the optimal standoff distance were analyzed. Results show that the wall shear stress reaches its maximum value when the standoff distance is equal to the length of the potential core of a jet. Finally, by analyzing the effects of entrainment and water cushion on the distributions of the wall shear stress and impact pressure, the optimal rotating speed and corresponding linear speed were obtained. The research results preliminarily clarify the rust removal mechanism of the water jet and the effect of the characteristic parameters related to the single-beam nozzle and rotating multi-beam nozzle on the jet effect, and can provide references for the design and assembly of an ultra-high pressure rust removal equipment.
Based on the quantitative analysis of the external parameters in relation to ultra-high pressure water jet sprayers, an optimal method for the key parameters of water jets was proposed, aiming at improving the efficiency of the water jets. Firstly, according to the characteristics of the ultra-high pressure water jet rust removal nozzles, the three-dimensional models of the single-beam and rotating multi-beam nozzles were established and used for the numerical simulations in which taking the water compressibility and cavitation effects into account. By changing the relevant characteristic parameters, such as standoff distances, jet angles and rotating speeds, the hydrodynamic performances related to the ultra-high pressure water jet rust removal nozzles were investigated though the simulations. Secondly, the effects of the standoff distances and jet angles for the single-beam nozzle on the distributions of the wall shear stress and impact pressure as well as the relationship between the length of the potential core of the jet and the optimal standoff distance were analyzed. Results show that the wall shear stress reaches its maximum value when the standoff distance is equal to the length of the potential core of a jet. Finally, by analyzing the effects of entrainment and water cushion on the distributions of the wall shear stress and impact pressure, the optimal rotating speed and corresponding linear speed were obtained. The research results preliminarily clarify the rust removal mechanism of the water jet and the effect of the characteristic parameters related to the single-beam nozzle and rotating multi-beam nozzle on the jet effect, and can provide references for the design and assembly of an ultra-high pressure rust removal equipment.
2022, 42(5): 055201.
doi: 10.11883/bzycj-2021-0414
Abstract:
As a hidden storage space for explosive hazards, the underground cavern has a potential risk of an internal explosion. To study the mechanism of the dynamic response of the surrounding rock under an internal explosion load, a new coupled damage and virtual crack model based on the HJC (Holmquist-Johnson-Cook) constitutive model of rock and the tensile failure cohesion element of the joint is proposed. And the quasi-static uniaxial compression, Brazilian splitting experiments, and dynamic SHPB experiments were calibrated. Therefore, this model is available for the simulation of middle-high strain rate problems, such as an underground explosion. Based on the new method, a series of underground explosions in spherical caverns is simulated by the multi-material ALE algorithm. The damage range and zoning failure law of the surrounding rock are analyzed. The research shows that the insertion of cohesive elements compensates for the deficiency of the HJC materials which cannot simulate tensile failure at low hydrostatic pressure. And the size effect of the model proposed in the paper is easy to deal with. The new method in this paper considers both the propagation of tensile crack by cohesive elements and the plastic damage by the HJC model, which can reflect the failure process of rock more accurately and completely. According to the numerical simulation results, the failure law of red sandstone during filling (coupling charge) explosion shows zonal characteristics with crashed zone and fracture zone from inside to outside. The proportional radius of the crashed zone is about 0.26 m/kg1/3, and that of the fracture zone is 0.47 m/kg1/3. The existence of the air chamber changes the loading form and reduces the load intensity acting on the cavern. Therefore, with the increase of the chamber size, the interval effect of air can reduce the damage of the surrounding rock during the explosion. Taking the red sandstone as an example, when the proportional radius reaches 0.52 m/kg1/3, there was no damage and no fracture generated by the explosion load. The conclusions above can be used as guidance for the anti-explosion design and protection of underground works.
As a hidden storage space for explosive hazards, the underground cavern has a potential risk of an internal explosion. To study the mechanism of the dynamic response of the surrounding rock under an internal explosion load, a new coupled damage and virtual crack model based on the HJC (Holmquist-Johnson-Cook) constitutive model of rock and the tensile failure cohesion element of the joint is proposed. And the quasi-static uniaxial compression, Brazilian splitting experiments, and dynamic SHPB experiments were calibrated. Therefore, this model is available for the simulation of middle-high strain rate problems, such as an underground explosion. Based on the new method, a series of underground explosions in spherical caverns is simulated by the multi-material ALE algorithm. The damage range and zoning failure law of the surrounding rock are analyzed. The research shows that the insertion of cohesive elements compensates for the deficiency of the HJC materials which cannot simulate tensile failure at low hydrostatic pressure. And the size effect of the model proposed in the paper is easy to deal with. The new method in this paper considers both the propagation of tensile crack by cohesive elements and the plastic damage by the HJC model, which can reflect the failure process of rock more accurately and completely. According to the numerical simulation results, the failure law of red sandstone during filling (coupling charge) explosion shows zonal characteristics with crashed zone and fracture zone from inside to outside. The proportional radius of the crashed zone is about 0.26 m/kg1/3, and that of the fracture zone is 0.47 m/kg1/3. The existence of the air chamber changes the loading form and reduces the load intensity acting on the cavern. Therefore, with the increase of the chamber size, the interval effect of air can reduce the damage of the surrounding rock during the explosion. Taking the red sandstone as an example, when the proportional radius reaches 0.52 m/kg1/3, there was no damage and no fracture generated by the explosion load. The conclusions above can be used as guidance for the anti-explosion design and protection of underground works.
