2021 Vol. 41, No. 8
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2021, 41(8): 082101.
doi: 10.11883/bzycj-2020-0349
Abstract:
The reaction model of aluminum particles is the key to successfully simulate the two-phase detonation of aluminum suspensions. In this study, by considering the endothermic decomposition reaction of the aluminum oxide (Al2O3) product at high temperature, a diffusion combustion model for the aluminum particles was improved and was incorporated into the homemade numerical code for 3D simulation of gas-solid two-phase detonation. The numerical program is based on the theory of two-phase flows, both gaseous and solid phases are assumed to be continuous media with inter-phase transfer of mass, momentum and energy. The system of 3D governing equations is solved in Cartesian x-y-z coordinates using an Eulerian grid, the numerical simulation code uses an explicit finite difference scheme based on the space-time conservation element and solution element (CE/SE) method, and the fourth order Runge-Kutta method is used to solve the source terms of the governing equations. In addition, the stability is assured by the Courant-Friedrichs-Lewy (CFL) criterion. Program parallelization is realized based on the message-passing-interface (MPI) technique, and the reliability of the program is demonstrated by simulating the shock tube problem successfully. Based on the program and the improved reaction model for the aluminum particles, numerical simulations for detonations of Al/air mixtures and Al/O2 mixtures were performed, respectively, the simulated results of the steady detonation wave speeds are in agreement with the experimental results or the literature value, with the error of less than 5.5%, which demonstrate the validity of the improved reaction model for Al suspensions detonation in different oxidizing atmosphere. Moreover, the detonation parameters and the distributions of the physical quantities around the detonation wave are analyzed, and the influence law of the reaction model on the detonation wave structure is obtained.
The reaction model of aluminum particles is the key to successfully simulate the two-phase detonation of aluminum suspensions. In this study, by considering the endothermic decomposition reaction of the aluminum oxide (Al2O3) product at high temperature, a diffusion combustion model for the aluminum particles was improved and was incorporated into the homemade numerical code for 3D simulation of gas-solid two-phase detonation. The numerical program is based on the theory of two-phase flows, both gaseous and solid phases are assumed to be continuous media with inter-phase transfer of mass, momentum and energy. The system of 3D governing equations is solved in Cartesian x-y-z coordinates using an Eulerian grid, the numerical simulation code uses an explicit finite difference scheme based on the space-time conservation element and solution element (CE/SE) method, and the fourth order Runge-Kutta method is used to solve the source terms of the governing equations. In addition, the stability is assured by the Courant-Friedrichs-Lewy (CFL) criterion. Program parallelization is realized based on the message-passing-interface (MPI) technique, and the reliability of the program is demonstrated by simulating the shock tube problem successfully. Based on the program and the improved reaction model for the aluminum particles, numerical simulations for detonations of Al/air mixtures and Al/O2 mixtures were performed, respectively, the simulated results of the steady detonation wave speeds are in agreement with the experimental results or the literature value, with the error of less than 5.5%, which demonstrate the validity of the improved reaction model for Al suspensions detonation in different oxidizing atmosphere. Moreover, the detonation parameters and the distributions of the physical quantities around the detonation wave are analyzed, and the influence law of the reaction model on the detonation wave structure is obtained.
2021, 41(8): 082301.
doi: 10.11883/bzycj-2020-0350
Abstract:
In order to investigate the characters of the four-component HTPB solid propellant containing RDX initiated by shock waves and evaluate its adaptability to low temperature, Lagrange analytical experiments were carried out in normal and low temperature conditions. In the Lagrange analytical experiments, sensors were embedded in different locations of the material, and the dynamic mechanical behavior of the material was obtained by analyzing the variation of some mechanical parameters (such as stress or pressure, particle velocity, strain or specific volume and temperature) measured by the sensors. Since the thickness of gap affected the initiation pressure, the manganese-copper sensors were used to measure the pressure changes in different positions of the propellant with the gap thicknesses of 40, 45 and 50 mm, respectively. When the gap thickness was 40 mm, the propellant detonated. In contrast, the propellant burned for the gap thicknesses of 45 and 50 mm. The ionization probes were used to collect the detonation velocity of the propellant. In normal temperature conditions, the detonation velocities with the gap thicknesses of 10 and 40 mm were measured. In low temperature conditions, the detonation velocities with the gap thicknesses of 10, 30 and 40 mm were measured. The growth laws of the detonation were analyzed, and the parameters such as detonation pressure, detonation velocity and detonation distance of the solid propellant were obtained. Numerical simulation was carried out to calculate the shock initiation process of the propellant, and the parameters of the ignition and growth model and the JWL state equation of the nonreactive propellant were determined by fitting the experimental data. The results show that the detonation pressure of the solid propellant is about 12.5 GPa, the critical initiation pressure is 5.16−5.61 GPa, the detonation distance is about 13.3 mm, and the detonation velocity is 5.719−6.013 km/s. The research results indicate that the low temperature has little effect on the shock initiation characteristics of the solid propellant.
In order to investigate the characters of the four-component HTPB solid propellant containing RDX initiated by shock waves and evaluate its adaptability to low temperature, Lagrange analytical experiments were carried out in normal and low temperature conditions. In the Lagrange analytical experiments, sensors were embedded in different locations of the material, and the dynamic mechanical behavior of the material was obtained by analyzing the variation of some mechanical parameters (such as stress or pressure, particle velocity, strain or specific volume and temperature) measured by the sensors. Since the thickness of gap affected the initiation pressure, the manganese-copper sensors were used to measure the pressure changes in different positions of the propellant with the gap thicknesses of 40, 45 and 50 mm, respectively. When the gap thickness was 40 mm, the propellant detonated. In contrast, the propellant burned for the gap thicknesses of 45 and 50 mm. The ionization probes were used to collect the detonation velocity of the propellant. In normal temperature conditions, the detonation velocities with the gap thicknesses of 10 and 40 mm were measured. In low temperature conditions, the detonation velocities with the gap thicknesses of 10, 30 and 40 mm were measured. The growth laws of the detonation were analyzed, and the parameters such as detonation pressure, detonation velocity and detonation distance of the solid propellant were obtained. Numerical simulation was carried out to calculate the shock initiation process of the propellant, and the parameters of the ignition and growth model and the JWL state equation of the nonreactive propellant were determined by fitting the experimental data. The results show that the detonation pressure of the solid propellant is about 12.5 GPa, the critical initiation pressure is 5.16−5.61 GPa, the detonation distance is about 13.3 mm, and the detonation velocity is 5.719−6.013 km/s. The research results indicate that the low temperature has little effect on the shock initiation characteristics of the solid propellant.
2021, 41(8): 083101.
doi: 10.11883/bzycj-2021-0029
Abstract:
40Cr high strength steel is often used in aerospace and national defense fields due to its excellent mechanical properties. Therefore, the research on the mode Ⅱ dynamic fracture characteristics and failure mechanism of 40Cr high strength steel under high-speed impact has important scientific significance and engineering value. Experiments and numerical simulations were carried out to study the mode Ⅱ dynamic fracture properties of 40Cr material under high loading rates. Based on the newly designed specimen and the novel test technique for mode Ⅱ dynamic fracture, the experimental-numerical method was used to determine the dynamic stress intensity factor curve of the crack tip during the loading process. The crack initiation time of the specimen was obtained by the strain gauge pasted on the specimen, and the mode Ⅱ dynamic fracture toughness of 40Cr was finally determined. The effect of loading rate and the failure mechanism of the material were also studied. The results show that within the present loading rate range of this work (1.08−5.53 TPa·m1/2/s), the mode Ⅱ dynamic fracture toughness of 40Cr presents a positive correlation with the loading rate. Through the analysis of the fracture morphology of the recovered specimen, it is found that there exists a transition from tensile failure mode to adiabatic shear failure mode with the increase of loading rate, and the critical loading rate is about 2.92 TPa·m1/2/s. When KⅡd≤1.70 TPa·m1/2/s, the 40Cr steel mainly exhibits brittle fracture; when KⅡd is in the range of 2.12−2.92 TPa·m1/2/s, the fracture mainly presents the morphological characteristics of ductile fracture; when KⅡd ≥ 3.19 TPa·m1/2/s, the material failure is mainly caused by adiabatic shear bands. Brittle fracture is dominated by strain rate hardening mechanism, ductile fracture is dominated by strain/strain rate hardening and thermal softening mechanisms, and adiabatic shear fracture is dominated by thermal softening mechanism.
40Cr high strength steel is often used in aerospace and national defense fields due to its excellent mechanical properties. Therefore, the research on the mode Ⅱ dynamic fracture characteristics and failure mechanism of 40Cr high strength steel under high-speed impact has important scientific significance and engineering value. Experiments and numerical simulations were carried out to study the mode Ⅱ dynamic fracture properties of 40Cr material under high loading rates. Based on the newly designed specimen and the novel test technique for mode Ⅱ dynamic fracture, the experimental-numerical method was used to determine the dynamic stress intensity factor curve of the crack tip during the loading process. The crack initiation time of the specimen was obtained by the strain gauge pasted on the specimen, and the mode Ⅱ dynamic fracture toughness of 40Cr was finally determined. The effect of loading rate and the failure mechanism of the material were also studied. The results show that within the present loading rate range of this work (1.08−5.53 TPa·m1/2/s), the mode Ⅱ dynamic fracture toughness of 40Cr presents a positive correlation with the loading rate. Through the analysis of the fracture morphology of the recovered specimen, it is found that there exists a transition from tensile failure mode to adiabatic shear failure mode with the increase of loading rate, and the critical loading rate is about 2.92 TPa·m1/2/s. When KⅡd≤1.70 TPa·m1/2/s, the 40Cr steel mainly exhibits brittle fracture; when KⅡd is in the range of 2.12−2.92 TPa·m1/2/s, the fracture mainly presents the morphological characteristics of ductile fracture; when KⅡd ≥ 3.19 TPa·m1/2/s, the material failure is mainly caused by adiabatic shear bands. Brittle fracture is dominated by strain rate hardening mechanism, ductile fracture is dominated by strain/strain rate hardening and thermal softening mechanisms, and adiabatic shear fracture is dominated by thermal softening mechanism.
2021, 41(8): 083102.
doi: 10.11883/bzycj-2020-0275
Abstract:
To improve the crashworthiness of thin-walled sandwich structures, a series of bionic corrugated sandwich structures with triangular elements (the height-to-width ratios of the elements are defined as γ) were designed inspired by the structures of shrimp chelas, including single-layer, double-layer and three-layer corrugated sandwich structures (γ1, γ2 and γ3 denotes the height-to-width ratios of single-layer, double-layer and three-layer elements, respectively). To analyze the deformation and mechanical response of the bionic thin-walled structures, the finite element method was adopted based on LS-DYNA and HyperMesh. By taking the initial peak load Fp and specific energy absorption Es as crashworthiness indexes, the influences of γ on the crashworthiness of the corrugated sandwich structures were discussed. The crashworthiness of the single-layer sandwich structures becomes worse gradually when the parameters γ exceed a certain value. For the double-layer sandwich structures, the influences of the parameters γ2 in the lower layers on the crashworthiness is greater than that of the parameters γ1 in the upper layers.. The Fp decreases by 37.8% with the increase of γ2, which means the greater γ2 of the lower layer is beneficial to improve the crashworthiness of the structure. For the three-layer sandwich structures, the influence of γ on crashworthiness indexes was investigated by range and variance analysis methods. The results show that the γ3 has the most significant influence on Es, and the significance level reaches 0.1. Finally, the optimal parameters of the bionic corrugated sandwich structures were obtained by using the multi-objective particle swarm optimization method based on a polynomial regression (PR) meta model. The optimal results show that the crashworthiness of the single-layer corrugated sandwich structures improves with the increase of γ. For the double-layer corrugated sandwich structures, The γ of the lower layer affects the crashworthiness more significantly than the γ of the upper layer. The three-layer corrugated sandwich structure with lower γ has higher Es. The optimal dimensions of the single-layer, double-layer and three-layer structures are γ = 0.8; γ1 = 0.5 and γ2 = 1.2; γ1 = 0.6, γ2 = 0.6 and γ3 = 0.9, respectively. The above results are helpful for the design of the thin-walled sandwich structures.
To improve the crashworthiness of thin-walled sandwich structures, a series of bionic corrugated sandwich structures with triangular elements (the height-to-width ratios of the elements are defined as γ) were designed inspired by the structures of shrimp chelas, including single-layer, double-layer and three-layer corrugated sandwich structures (γ1, γ2 and γ3 denotes the height-to-width ratios of single-layer, double-layer and three-layer elements, respectively). To analyze the deformation and mechanical response of the bionic thin-walled structures, the finite element method was adopted based on LS-DYNA and HyperMesh. By taking the initial peak load Fp and specific energy absorption Es as crashworthiness indexes, the influences of γ on the crashworthiness of the corrugated sandwich structures were discussed. The crashworthiness of the single-layer sandwich structures becomes worse gradually when the parameters γ exceed a certain value. For the double-layer sandwich structures, the influences of the parameters γ2 in the lower layers on the crashworthiness is greater than that of the parameters γ1 in the upper layers.. The Fp decreases by 37.8% with the increase of γ2, which means the greater γ2 of the lower layer is beneficial to improve the crashworthiness of the structure. For the three-layer sandwich structures, the influence of γ on crashworthiness indexes was investigated by range and variance analysis methods. The results show that the γ3 has the most significant influence on Es, and the significance level reaches 0.1. Finally, the optimal parameters of the bionic corrugated sandwich structures were obtained by using the multi-objective particle swarm optimization method based on a polynomial regression (PR) meta model. The optimal results show that the crashworthiness of the single-layer corrugated sandwich structures improves with the increase of γ. For the double-layer corrugated sandwich structures, The γ of the lower layer affects the crashworthiness more significantly than the γ of the upper layer. The three-layer corrugated sandwich structure with lower γ has higher Es. The optimal dimensions of the single-layer, double-layer and three-layer structures are γ = 0.8; γ1 = 0.5 and γ2 = 1.2; γ1 = 0.6, γ2 = 0.6 and γ3 = 0.9, respectively. The above results are helpful for the design of the thin-walled sandwich structures.
2021, 41(8): 083103.
doi: 10.11883/bzycj-2020-0262
Abstract:
An aluminum honeycomb is widely used in the field of impact cushioning because of its excellent performance. In order to solve the problem of large difference between the in-plane and out-of-plane load-carrying capacities of traditional honeycombs, three new configurations of honeycombs were proposed as follows: bow-shaped, staggered and folded configurations. The finite element models for these new honeycombs were established, and their deformation modes and load-carrying capacities were analyzed. The results show that under the same relative density, compared with the traditional hexagonal honeycombs, the three new configurations can reduce the difference of load-carrying capacity in in-plane and out-of-plane directions. The average in-plane/out-of-plane (I/O) ratio of loading-carrying capacity of the bow-shaped honeycombs in two coplanar directions increased by 21.3 times. For the staggered honeycomb, the load-carrying capacity of each in-plane direction is of great difference, in which the I/O ratio of the excellent direction is increased by 42 times due to its special structure. For the folded honeycomb, the I/O ratio is increased by 21.3 times on average. The research results can provide a new idea and reference for the design of honeycomb structure under multi-directional impact load.
An aluminum honeycomb is widely used in the field of impact cushioning because of its excellent performance. In order to solve the problem of large difference between the in-plane and out-of-plane load-carrying capacities of traditional honeycombs, three new configurations of honeycombs were proposed as follows: bow-shaped, staggered and folded configurations. The finite element models for these new honeycombs were established, and their deformation modes and load-carrying capacities were analyzed. The results show that under the same relative density, compared with the traditional hexagonal honeycombs, the three new configurations can reduce the difference of load-carrying capacity in in-plane and out-of-plane directions. The average in-plane/out-of-plane (I/O) ratio of loading-carrying capacity of the bow-shaped honeycombs in two coplanar directions increased by 21.3 times. For the staggered honeycomb, the load-carrying capacity of each in-plane direction is of great difference, in which the I/O ratio of the excellent direction is increased by 42 times due to its special structure. For the folded honeycomb, the I/O ratio is increased by 21.3 times on average. The research results can provide a new idea and reference for the design of honeycomb structure under multi-directional impact load.
2021, 41(8): 083104.
doi: 10.11883/bzycj-2020-0392
Abstract:
All-metallic honeycomb sandwich structure is a new kind of ship protection structure, which has a broad application prospect in the field of ship protection. However, there is not enough research on the dynamic response of honeycomb sandwich structures under an actual underwater explosion load. The dynamic behavior and protective performance of honeycomb sandwich structures subjected to the underwater explosion load were investigated, both experimentally and numerically. A backplane stiffened honeycomb sandwich structure and the corresponding buoyant box were designed and fabricated for the subsequent experimental study in a large open water pool. The structural response was numerically simulated by using the coupled acoustic-structural approach (integrated in commercial FE code ABAQUS/Explicit). The numerical simulation results are in good agreement with the experimental measurements. Then, the deformation process and energy absorption characteristics of the honeycomb sandwich structure subjected to underwater explosion load were investigated. The effects of the load parameter (impact factor) and two geometric parameters (i.e., facesheet thickness ratio and core relative density) on the dynamic response of the sandwich structure were analyzed. Finally, the Pareto optimal designs with minimize value of non-dimensional areal density and minimize value of non-dimensional maximum deformation of the central point on back facesheet were obtained by using the NSGA-Ⅱ algorithm. The results show that with the increase of the impact factor, the overall deformation of the structure increases significantly. The honeycomb core is the main energy absorbing substructure during this process, and its energy absorption ratio gradually decreases. With the increase of either face sheet thickness ratio or core relative density, the deformation of the structure first decreases and then increases, accompanied by changes in deformation modes. The influence of core relative density is more significant. The optimized structures obtained from multi-objective optimal design effectively reduce the areal density and the maximum deformation, which can be used as a reference for the future design of honeycomb sandwich structures.
All-metallic honeycomb sandwich structure is a new kind of ship protection structure, which has a broad application prospect in the field of ship protection. However, there is not enough research on the dynamic response of honeycomb sandwich structures under an actual underwater explosion load. The dynamic behavior and protective performance of honeycomb sandwich structures subjected to the underwater explosion load were investigated, both experimentally and numerically. A backplane stiffened honeycomb sandwich structure and the corresponding buoyant box were designed and fabricated for the subsequent experimental study in a large open water pool. The structural response was numerically simulated by using the coupled acoustic-structural approach (integrated in commercial FE code ABAQUS/Explicit). The numerical simulation results are in good agreement with the experimental measurements. Then, the deformation process and energy absorption characteristics of the honeycomb sandwich structure subjected to underwater explosion load were investigated. The effects of the load parameter (impact factor) and two geometric parameters (i.e., facesheet thickness ratio and core relative density) on the dynamic response of the sandwich structure were analyzed. Finally, the Pareto optimal designs with minimize value of non-dimensional areal density and minimize value of non-dimensional maximum deformation of the central point on back facesheet were obtained by using the NSGA-Ⅱ algorithm. The results show that with the increase of the impact factor, the overall deformation of the structure increases significantly. The honeycomb core is the main energy absorbing substructure during this process, and its energy absorption ratio gradually decreases. With the increase of either face sheet thickness ratio or core relative density, the deformation of the structure first decreases and then increases, accompanied by changes in deformation modes. The influence of core relative density is more significant. The optimized structures obtained from multi-objective optimal design effectively reduce the areal density and the maximum deformation, which can be used as a reference for the future design of honeycomb sandwich structures.
2021, 41(8): 083105.
doi: 10.11883/bzycj-2021-0062
Abstract:
Cavities and crack defects usually coexist in deep earth rock mass structures, which together affect the structural safety and stability of rock masses. In order to study the effect of circular cavity on crack propagation behavior in rock mass under dynamic loads, circular opening specimens with straight crack cavity (COSSCC) specimen were proposed in this study, and a large-scale drop hammer impact device was applied to conduct impact tests. Crack propagation gauges were implemented to measure fracture mechanics parameters, such as dynamic crack initiation time and crack propagation velocity. Then a modified finite difference code Autodyn was applied to carry out the numerical simulation analysis of crack propagation path and stress field around the circular hole. The traditional finite element code Abaqus was also used to calculate the dynamic initiation toughness and dynamic propagation toughness. The results indicate that: (1) when the inclination θ of the circle hole is less than 10°, the crack propagation path deflects and passes through the surface of the circle hole; when the inclination θ of circle hole is 20° and 30°, the crack propagation paths deflects in the direction of the hole but does not pass through the circular hole, indicating that the circular hole has obvious guiding effect on crack propagation; when the inclination θ of circle hole is 40° and 50°, crack propagation path does not deflect, and the guiding effect of the circular hole is obvious weaken. (2) When the crack propagation path reaches the vicinity of the circular hole, the tensile stress zone at the crack tip coincides with the tensile stress zone at the edge of the circular hole. At this time, the crack propagation speed increases significantly, and the dynamic fracture toughness of the crack decreases significantly. (3) The deflection direction of the crack is basically the same as the direction of the maximum circumferential stress at the crack tip. (4) The dynamic fracture toughness of the crack is always smaller than the crack initiation toughness, and the dynamic fracture toughness of the crack has a linear relationship with the dynamic crack growth rate. The larger the dynamic crack growth rate, the smaller the dynamic fracture toughness of the crack.
Cavities and crack defects usually coexist in deep earth rock mass structures, which together affect the structural safety and stability of rock masses. In order to study the effect of circular cavity on crack propagation behavior in rock mass under dynamic loads, circular opening specimens with straight crack cavity (COSSCC) specimen were proposed in this study, and a large-scale drop hammer impact device was applied to conduct impact tests. Crack propagation gauges were implemented to measure fracture mechanics parameters, such as dynamic crack initiation time and crack propagation velocity. Then a modified finite difference code Autodyn was applied to carry out the numerical simulation analysis of crack propagation path and stress field around the circular hole. The traditional finite element code Abaqus was also used to calculate the dynamic initiation toughness and dynamic propagation toughness. The results indicate that: (1) when the inclination θ of the circle hole is less than 10°, the crack propagation path deflects and passes through the surface of the circle hole; when the inclination θ of circle hole is 20° and 30°, the crack propagation paths deflects in the direction of the hole but does not pass through the circular hole, indicating that the circular hole has obvious guiding effect on crack propagation; when the inclination θ of circle hole is 40° and 50°, crack propagation path does not deflect, and the guiding effect of the circular hole is obvious weaken. (2) When the crack propagation path reaches the vicinity of the circular hole, the tensile stress zone at the crack tip coincides with the tensile stress zone at the edge of the circular hole. At this time, the crack propagation speed increases significantly, and the dynamic fracture toughness of the crack decreases significantly. (3) The deflection direction of the crack is basically the same as the direction of the maximum circumferential stress at the crack tip. (4) The dynamic fracture toughness of the crack is always smaller than the crack initiation toughness, and the dynamic fracture toughness of the crack has a linear relationship with the dynamic crack growth rate. The larger the dynamic crack growth rate, the smaller the dynamic fracture toughness of the crack.
2021, 41(8): 083106.
doi: 10.11883/bzycj-2020-0204
Abstract:
In order to study the influence of long-term loading on the impact resistance of concrete-filled steel tubular (CFST) members, a finite element analysis (FEA) model was developed by using the software ABAQUS, which embeds the coupling analysis of long-term loading and lateral impact loading, along with the calculation of the residual compressive strength after impacting. The developed FEA models were verified by three tests. Based on the proposed method, the dynamic response of the CFST members under long-term loading was compared with that under primary loading. The residual compressive strength coefficient was used to quantitatively compare the residual compressive strength of the CFST members under those two loading modes and the influences of the steel ratio, steel yield strength, concrete strength, long-term loading ratio, slenderness ratio on the residual compressive strength coefficient were investigated as well. The results from the FEA show that compared with the primary loading mode, when considering the long-term loading, the peak and plateau values of the impact force decrease, the mid-span displacement increases, but the works done by the impact forces under two circumstances are equal. The work done by the axial load is more than that of the primary loading mode when the long-term loading is included, the excess work is mainly dissipated due to plastic deformation of the steel and the concrete has little contribution to the energy dissipation. At the same condition, the members that can continue to bear loads under the primary loading may lose their bearing capacity when considering the long-term loading. According to the parametric analysis, increasing the steel ratio and steel yield strength, and reducing the long-term loading ratio can effectively reduce the adverse effects of the long-term loading on the anti-impact performance of the members, with the increase of the slenderness ratio, the long-term loading will bring more adverse effects on the anti-impact performance of the members, the concrete strength has little effects on the impact resistance of the CFST members.
In order to study the influence of long-term loading on the impact resistance of concrete-filled steel tubular (CFST) members, a finite element analysis (FEA) model was developed by using the software ABAQUS, which embeds the coupling analysis of long-term loading and lateral impact loading, along with the calculation of the residual compressive strength after impacting. The developed FEA models were verified by three tests. Based on the proposed method, the dynamic response of the CFST members under long-term loading was compared with that under primary loading. The residual compressive strength coefficient was used to quantitatively compare the residual compressive strength of the CFST members under those two loading modes and the influences of the steel ratio, steel yield strength, concrete strength, long-term loading ratio, slenderness ratio on the residual compressive strength coefficient were investigated as well. The results from the FEA show that compared with the primary loading mode, when considering the long-term loading, the peak and plateau values of the impact force decrease, the mid-span displacement increases, but the works done by the impact forces under two circumstances are equal. The work done by the axial load is more than that of the primary loading mode when the long-term loading is included, the excess work is mainly dissipated due to plastic deformation of the steel and the concrete has little contribution to the energy dissipation. At the same condition, the members that can continue to bear loads under the primary loading may lose their bearing capacity when considering the long-term loading. According to the parametric analysis, increasing the steel ratio and steel yield strength, and reducing the long-term loading ratio can effectively reduce the adverse effects of the long-term loading on the anti-impact performance of the members, with the increase of the slenderness ratio, the long-term loading will bring more adverse effects on the anti-impact performance of the members, the concrete strength has little effects on the impact resistance of the CFST members.
2021, 41(8): 083201.
doi: 10.11883/bzycj-2020-0196
Abstract:
A method for measuring the shock wave overpressure of blasting warhead explosion based on seismic wave triggering was proposed. By the proposed method, the peak overpressure of the blast wave from dynamic explosion of a warhead can be obtained reliably. The air explosion shock waves of the blasting warhead with the target velocities of 0, 535 and 980 m/s were measured, respectively. And the measured results of the peak overpressure of the shock wave from dynamic explosion of the blasting warhead were compared with those by the empirical formula calculation. The influence of warhead velocity on the pressure field distribution of the shock wave was analyzed quantitatively. Finally, a three-dimensional visualization model for shock wave overpressure from dynamic explosion of the warhead was reconstructed by using the thin-plate-spline interpolation method. The reconstructed model can provide a basis for studying the characteristics of dynamic explosion shock wave based on the measured data in the complex environment of an actual combat.
A method for measuring the shock wave overpressure of blasting warhead explosion based on seismic wave triggering was proposed. By the proposed method, the peak overpressure of the blast wave from dynamic explosion of a warhead can be obtained reliably. The air explosion shock waves of the blasting warhead with the target velocities of 0, 535 and 980 m/s were measured, respectively. And the measured results of the peak overpressure of the shock wave from dynamic explosion of the blasting warhead were compared with those by the empirical formula calculation. The influence of warhead velocity on the pressure field distribution of the shock wave was analyzed quantitatively. Finally, a three-dimensional visualization model for shock wave overpressure from dynamic explosion of the warhead was reconstructed by using the thin-plate-spline interpolation method. The reconstructed model can provide a basis for studying the characteristics of dynamic explosion shock wave based on the measured data in the complex environment of an actual combat.
2021, 41(8): 083301.
doi: 10.11883/bzycj-2020-0250
Abstract:
When the projectile penetrates into the concrete medium at high speed, the mass loss and nose blunting occur due to the strong local interaction between the projectile and the target. In order to further explore the mass erosion effect of high-speed projectile penetrating concrete target and its influencing factors, based on the thermal melting mechanism and variable friction coefficient model, the mass erosion model of high-speed projectile penetrating concrete target was modified considering the change of projectile nose shape during penetration. In order to verify the reliability of the model, based on the 30 mm ballistic gun platform, the oval projectile penetrating typical concrete targets at high velocities ranging from 700 to 1000 m/s was carried out, and the mass erosion results of high-speed penetration were obtained. Combined with the theoretical model, the reliability of the modified model is verified by analyzing the test data in this paper and the literature. The results show that the sliding friction term accounts for 10%−40% of the total friction in the process of projectile penetration, and its influence on the penetration process can’t be ignored. The prediction results of mass erosion model considering the variation of friction coefficient are in good agreement with the existing test data, and the maximum error with the test data in this paper is less than 7%, which can accurately predict the mass loss of projectile under different working conditions.
When the projectile penetrates into the concrete medium at high speed, the mass loss and nose blunting occur due to the strong local interaction between the projectile and the target. In order to further explore the mass erosion effect of high-speed projectile penetrating concrete target and its influencing factors, based on the thermal melting mechanism and variable friction coefficient model, the mass erosion model of high-speed projectile penetrating concrete target was modified considering the change of projectile nose shape during penetration. In order to verify the reliability of the model, based on the 30 mm ballistic gun platform, the oval projectile penetrating typical concrete targets at high velocities ranging from 700 to 1000 m/s was carried out, and the mass erosion results of high-speed penetration were obtained. Combined with the theoretical model, the reliability of the modified model is verified by analyzing the test data in this paper and the literature. The results show that the sliding friction term accounts for 10%−40% of the total friction in the process of projectile penetration, and its influence on the penetration process can’t be ignored. The prediction results of mass erosion model considering the variation of friction coefficient are in good agreement with the existing test data, and the maximum error with the test data in this paper is less than 7%, which can accurately predict the mass loss of projectile under different working conditions.
2021, 41(8): 084201.
doi: 10.11883/bzycj-2020-0252
Abstract:
In order to study the effect of the piston reset motion on the flow of propellant gas in a piston-controlled side spray gun, the propulsion process of the gun was modeled and simulated based on the one-dimensional two-phase flow interior ballistic theory. First, by considering the reciprocating motion of the piston-spring system that controls the opening and closing of the rear spray channel, a mathematical model of the gun propulsion process was established. It combines the gas-solid two-phase flow in the barrel, the fluid-solid coupling between the piston and the gas in the piston cavity, and the transient gas flow in the exhaust pipe. The flow field coupling between the barrel and the piston cavity, and the flow field coupling between the piston cavity and the exhaust pipe were modeled, respectively, and the solution procedure was displayed. The MacCormack scheme and the Runge-Kutta method were used in the simulations, and the accuracy of the numerical method was validated by the published data. Next, the propagation law of the rarefaction wave in the barrel during the firing cycle was gained. The projectile velocity and the pressure at the projectile base and the breech were presented. Then, the distributions of the pressure, the gas velocity, and the solid velocity in the barrel of the piston-controlled side spray gun were compared with those in the traditional gun. Finally, the effects of the piston reset motion on the propellant gas flow and the recoil reduction efficiency were analyzed. The results show that compared with the situation ignoring the piston reset motion, when the muzzle velocity is reduced by 1.52%, the recoil reduction efficiency of the case considering the reset motion drops from 38.86% to 32.88% because the piston closes the rear spray channel during the reset process. Therefore, the reset motion of the piston cannot be ignored in the numerical simulation on the gun firing process.
In order to study the effect of the piston reset motion on the flow of propellant gas in a piston-controlled side spray gun, the propulsion process of the gun was modeled and simulated based on the one-dimensional two-phase flow interior ballistic theory. First, by considering the reciprocating motion of the piston-spring system that controls the opening and closing of the rear spray channel, a mathematical model of the gun propulsion process was established. It combines the gas-solid two-phase flow in the barrel, the fluid-solid coupling between the piston and the gas in the piston cavity, and the transient gas flow in the exhaust pipe. The flow field coupling between the barrel and the piston cavity, and the flow field coupling between the piston cavity and the exhaust pipe were modeled, respectively, and the solution procedure was displayed. The MacCormack scheme and the Runge-Kutta method were used in the simulations, and the accuracy of the numerical method was validated by the published data. Next, the propagation law of the rarefaction wave in the barrel during the firing cycle was gained. The projectile velocity and the pressure at the projectile base and the breech were presented. Then, the distributions of the pressure, the gas velocity, and the solid velocity in the barrel of the piston-controlled side spray gun were compared with those in the traditional gun. Finally, the effects of the piston reset motion on the propellant gas flow and the recoil reduction efficiency were analyzed. The results show that compared with the situation ignoring the piston reset motion, when the muzzle velocity is reduced by 1.52%, the recoil reduction efficiency of the case considering the reset motion drops from 38.86% to 32.88% because the piston closes the rear spray channel during the reset process. Therefore, the reset motion of the piston cannot be ignored in the numerical simulation on the gun firing process.
2021, 41(8): 084202.
doi: 10.11883/bzycj-2020-0467
Abstract:
The spallation characteristics of ductile tantalum metal under planar plate impact was analyzed through a multi-scale perspective. And the typical characteristics of the free-surface velocity curve on the macro-scale were interpreted from the micro-scale to reveal the physical meanings corresponding to these typical characteristics. On the macro-scale, the spallation behaviors of the ductile tantalum metal under planar-plate impact were numerically simulated through the smooth particle hydrodynamics (SPH) and Lagrange methods, and the free-surface velocity curves of the tantalum during spallation were obtained. In addition, the free-surface velocity curves obtained by the Johnson-Cook model, Steinberg-Cochran-Guinan model and Zerilli-Armstrong model were compared in the numerical simulations. Comparison with the experimental data shows that the Steinberg-Cochran-Guinan constitutive model has a better performance in the macro-level simulation. The free-surface velocity curves at different strain rates were obtained by changing the loading conditions, and the typical characteristics of the free-surface velocity curves at different strain rates were discussed. Results show that there is an exponential relationship between spall strength and strain rate, and the spall strength obtained from the simulation has a good agreement with the experimental data. On the micro-scale, the damage evolution in the spallation region was obtained by molecular dynamics simulation conducted in the LAMMPS software, and the loading strain rate was consistent with that on the macro-scale. The micro-scale simulation reveals the physical connotation of the typical characteristics of the macro-scale free-surface velocity curve. Micro-scale analysis shows that spallation is the response of damage evolution of nucleation, growth, and aggregation of voids. From the multi-scale perspective analysis, the typical characteristics on the free-surface velocity curve are closely related to the damage evolution in the spallation area: the pullback signal is a macroscopic response of the void nucleation in the spall area; the decline amplitude of the free-surface velocity curve reflects the void nucleation condition, and the spall strength reflects the nucleation strength of the voids. What’s more, the velocity rises to the first peak beyond the minima after the pullback signal reflects the rate of damage evolution. The multi-scale perspective analysis is helpful to fully understand the physical mechanism of the spallation under planar-plate impact.
The spallation characteristics of ductile tantalum metal under planar plate impact was analyzed through a multi-scale perspective. And the typical characteristics of the free-surface velocity curve on the macro-scale were interpreted from the micro-scale to reveal the physical meanings corresponding to these typical characteristics. On the macro-scale, the spallation behaviors of the ductile tantalum metal under planar-plate impact were numerically simulated through the smooth particle hydrodynamics (SPH) and Lagrange methods, and the free-surface velocity curves of the tantalum during spallation were obtained. In addition, the free-surface velocity curves obtained by the Johnson-Cook model, Steinberg-Cochran-Guinan model and Zerilli-Armstrong model were compared in the numerical simulations. Comparison with the experimental data shows that the Steinberg-Cochran-Guinan constitutive model has a better performance in the macro-level simulation. The free-surface velocity curves at different strain rates were obtained by changing the loading conditions, and the typical characteristics of the free-surface velocity curves at different strain rates were discussed. Results show that there is an exponential relationship between spall strength and strain rate, and the spall strength obtained from the simulation has a good agreement with the experimental data. On the micro-scale, the damage evolution in the spallation region was obtained by molecular dynamics simulation conducted in the LAMMPS software, and the loading strain rate was consistent with that on the macro-scale. The micro-scale simulation reveals the physical connotation of the typical characteristics of the macro-scale free-surface velocity curve. Micro-scale analysis shows that spallation is the response of damage evolution of nucleation, growth, and aggregation of voids. From the multi-scale perspective analysis, the typical characteristics on the free-surface velocity curve are closely related to the damage evolution in the spallation area: the pullback signal is a macroscopic response of the void nucleation in the spall area; the decline amplitude of the free-surface velocity curve reflects the void nucleation condition, and the spall strength reflects the nucleation strength of the voids. What’s more, the velocity rises to the first peak beyond the minima after the pullback signal reflects the rate of damage evolution. The multi-scale perspective analysis is helpful to fully understand the physical mechanism of the spallation under planar-plate impact.
2021, 41(8): 085101.
doi: 10.11883/bzycj-2020-0229
Abstract:
Military personnels need to wear equipment in combat, which will affect the damage to the occupants of the vehicle when they are subjected to the vertical impact of the explosion at the bottom of the vehicle. Through the method of vertical impact test and simulation, the influence of the distribution of the wearable equipment on the occupant injury is studied in the three directions of the weight of the wearable equipment, the position of the wearable equipment, and the tightness of the contact between the wearable equipment and the body. According to the AEP55 occupant injury criterion, the pelvic z-direction acceleration and the axial force of the lumbar spine are the reference targets for occupant injury. First, through the vertical impact test, the impact of different wearing equipment weight on occupant injury is studied; then the finite element model is used. The test is verified and optimized, and the influence of the position and tightness of the worn equipment on the occupant damage under vertical impact is studied. The results show that as the weight of wearing equipment increases, the lumbar spine injury of the occupant increases, and the probability of spinal injury decreases; the closer the equipment is to the upper part of the torso, the tighter the contact with the body, the smaller the load on the lumbar spine and the spine of the occupant, the less likely to be injured. On the contrary, the closer the equipment is to the upper part of the trunk, the tighter the contact with the body, the greater the load on the lumbar and spine of the occupant, the more likely to be injured. However, compared with the other two, the effect of tightness coefficient on the results is even less obvious. The results obtained above will provide reference for the subsequent research on reducing the impact of wearing equipment on occupant injury during the vertical impact of the bottom explosion of the vehicle.
Military personnels need to wear equipment in combat, which will affect the damage to the occupants of the vehicle when they are subjected to the vertical impact of the explosion at the bottom of the vehicle. Through the method of vertical impact test and simulation, the influence of the distribution of the wearable equipment on the occupant injury is studied in the three directions of the weight of the wearable equipment, the position of the wearable equipment, and the tightness of the contact between the wearable equipment and the body. According to the AEP55 occupant injury criterion, the pelvic z-direction acceleration and the axial force of the lumbar spine are the reference targets for occupant injury. First, through the vertical impact test, the impact of different wearing equipment weight on occupant injury is studied; then the finite element model is used. The test is verified and optimized, and the influence of the position and tightness of the worn equipment on the occupant damage under vertical impact is studied. The results show that as the weight of wearing equipment increases, the lumbar spine injury of the occupant increases, and the probability of spinal injury decreases; the closer the equipment is to the upper part of the torso, the tighter the contact with the body, the smaller the load on the lumbar spine and the spine of the occupant, the less likely to be injured. On the contrary, the closer the equipment is to the upper part of the trunk, the tighter the contact with the body, the greater the load on the lumbar and spine of the occupant, the more likely to be injured. However, compared with the other two, the effect of tightness coefficient on the results is even less obvious. The results obtained above will provide reference for the subsequent research on reducing the impact of wearing equipment on occupant injury during the vertical impact of the bottom explosion of the vehicle.
2021, 41(8): 085201.
doi: 10.11883/bzycj-2020-0433
Abstract:
The interfacial coupling structure between the backfill and ore rock body in the filling mining method will be continuously disturbed by the influence of mining and blasting. In the filling-rock interfacial coupling, it is easy to produce the behaviors of debonding and fissure expansion, which will bring potential safety hazards to underground production. Because the field experiment is time-consuming and laborious, and it is difficult to observe the impact effect and the rock crack propagation process when the explosive is detonated, the simulation method was adopted for research. In the simulation, reasonable simplification is particularly important. According to the actual situation of blasting hole layout, the three rows of blasting holes that were detonated at one time were simplified into a single-row blasting hole model and an edge blasting hole model. According to the research results in related literatures, the coupling surfaces of the filling bodies and the ore rocks were simplified into three kinds (a flat interface, wavy interface and serrated interface). The three different shapes of the interfaces correspond to the different roughnesses of the interfaces, respectively. By considering that the hole arrangement method used in stope blasting is vertical hole arrangement, the holes are parallel, and at the same time, in order to improve the calculation of the software efficiency, simplified the three-dimensional model of the stope into a two-dimensional plane model. After a series of simplifications, a physical model for the filling-rock interface coupling body was proposed, and the corresponding geometric analysis model was established by using the ANSYS/LS-DYNA software And different material parameters were assigned to the different parts of the model, and the blasting effect was analyzed by software calculation. The mechanical influence of the interface coupling body structure was obtained, and the response law of different interface roughness, the curing age of the filling body and the blasting method on the blasting shock was obtained, and the mechanism of the blasting dynamics was discussed. The research results can reveal mechanical behaviors such as debonding and crack propagation at the coupling of filling-rock interface, and clarify the influence of different factors on the law of blasting shock response and the mechanism of blasting dynamics, which has certain guiding significance for downhole safety production. The results show as follows. (1) The blasting impact has three mechanical effects in the interface coupling body: tension, pressure and shear. When the stress wave passes through the interface, the peak acceleration of the monitoring point at the interface will increase due to different degrees of refraction. After passing through the coupling interface, the stress wave energy decays rapidly. (2) The impact of different interface roughness on blasting action is different. The joint roughness coefficient (JRC) represents the roughness of the interface coupling body. With the increase of the JRC value, the interface stress tends to rise first and then decline, but the overall damage decreases. (3) As the curing time of the backfill increases, the fracture range at the coupling interface shrinks, and the interface damage gradually changes from tensile damage to shear damage. (4) The damage of different detonation modes to the interface coupling body is different, and the damage of simultaneous detonation to the coupling interface is weaker than that of hole-by-hole detonation.
The interfacial coupling structure between the backfill and ore rock body in the filling mining method will be continuously disturbed by the influence of mining and blasting. In the filling-rock interfacial coupling, it is easy to produce the behaviors of debonding and fissure expansion, which will bring potential safety hazards to underground production. Because the field experiment is time-consuming and laborious, and it is difficult to observe the impact effect and the rock crack propagation process when the explosive is detonated, the simulation method was adopted for research. In the simulation, reasonable simplification is particularly important. According to the actual situation of blasting hole layout, the three rows of blasting holes that were detonated at one time were simplified into a single-row blasting hole model and an edge blasting hole model. According to the research results in related literatures, the coupling surfaces of the filling bodies and the ore rocks were simplified into three kinds (a flat interface, wavy interface and serrated interface). The three different shapes of the interfaces correspond to the different roughnesses of the interfaces, respectively. By considering that the hole arrangement method used in stope blasting is vertical hole arrangement, the holes are parallel, and at the same time, in order to improve the calculation of the software efficiency, simplified the three-dimensional model of the stope into a two-dimensional plane model. After a series of simplifications, a physical model for the filling-rock interface coupling body was proposed, and the corresponding geometric analysis model was established by using the ANSYS/LS-DYNA software And different material parameters were assigned to the different parts of the model, and the blasting effect was analyzed by software calculation. The mechanical influence of the interface coupling body structure was obtained, and the response law of different interface roughness, the curing age of the filling body and the blasting method on the blasting shock was obtained, and the mechanism of the blasting dynamics was discussed. The research results can reveal mechanical behaviors such as debonding and crack propagation at the coupling of filling-rock interface, and clarify the influence of different factors on the law of blasting shock response and the mechanism of blasting dynamics, which has certain guiding significance for downhole safety production. The results show as follows. (1) The blasting impact has three mechanical effects in the interface coupling body: tension, pressure and shear. When the stress wave passes through the interface, the peak acceleration of the monitoring point at the interface will increase due to different degrees of refraction. After passing through the coupling interface, the stress wave energy decays rapidly. (2) The impact of different interface roughness on blasting action is different. The joint roughness coefficient (JRC) represents the roughness of the interface coupling body. With the increase of the JRC value, the interface stress tends to rise first and then decline, but the overall damage decreases. (3) As the curing time of the backfill increases, the fracture range at the coupling interface shrinks, and the interface damage gradually changes from tensile damage to shear damage. (4) The damage of different detonation modes to the interface coupling body is different, and the damage of simultaneous detonation to the coupling interface is weaker than that of hole-by-hole detonation.
2021, 41(8): 085901.
doi: 10.11883/bzycj-2020-0395
Abstract:
In order to optimize the structure and improve the performance of the head and face protective equipment for an individual soldier, firstly, the blast wave resistance tests of the bare-head model were carried out in real explosion field and shock tube environments, respectively. On this basis, the forward and lateral blast shockwave protective performance tests for helmet-head systems with different structures and protection levels were carried out by using the shock tube method. Finally, the peak values and durations of shockwave overpressure in the front, forehead, top, back, ear and eye areas of the helmet-head systems were compared and analyzed. The experimental results show that the blast shockwave test using a shock tube can be a substitute for the real explosion field test. When subjected to the effect of frontal shock wave, the peak value of the shockwave overpressure measured at the top measuring point of the two-half-helmet head model is about 1/6 compared with that of the nozzle outlet and 1/3 of the bare-head model as well as the integrated-helmet head model. The shockwave splits and relieves pressure at the split structure on the top of the two-half helmets and forms a superimposed reflection, resulting in a prolonged action time (5.5−8.5 ms), but a significantly decreased peak overpressure. For the rear measuring points, the peak overpressure (365 kPa) of shockwave measured by the integrated-helmet head model is slightly higher than that (303 kPa) measured by the two-half-helmet head model, and about 2.5 times as high as that (148 kPa) measured by the bare head model. By improving the structural airtightness of individual head and face protective equipments (such as wearing glasses, earmuffs or protective masks), shockwaves can be effectively prevented from entering the helmet-head systems, the stacking convergence effect can be weakened, and the protective performance of individual head and face equipments can be improved.
In order to optimize the structure and improve the performance of the head and face protective equipment for an individual soldier, firstly, the blast wave resistance tests of the bare-head model were carried out in real explosion field and shock tube environments, respectively. On this basis, the forward and lateral blast shockwave protective performance tests for helmet-head systems with different structures and protection levels were carried out by using the shock tube method. Finally, the peak values and durations of shockwave overpressure in the front, forehead, top, back, ear and eye areas of the helmet-head systems were compared and analyzed. The experimental results show that the blast shockwave test using a shock tube can be a substitute for the real explosion field test. When subjected to the effect of frontal shock wave, the peak value of the shockwave overpressure measured at the top measuring point of the two-half-helmet head model is about 1/6 compared with that of the nozzle outlet and 1/3 of the bare-head model as well as the integrated-helmet head model. The shockwave splits and relieves pressure at the split structure on the top of the two-half helmets and forms a superimposed reflection, resulting in a prolonged action time (5.5−8.5 ms), but a significantly decreased peak overpressure. For the rear measuring points, the peak overpressure (365 kPa) of shockwave measured by the integrated-helmet head model is slightly higher than that (303 kPa) measured by the two-half-helmet head model, and about 2.5 times as high as that (148 kPa) measured by the bare head model. By improving the structural airtightness of individual head and face protective equipments (such as wearing glasses, earmuffs or protective masks), shockwaves can be effectively prevented from entering the helmet-head systems, the stacking convergence effect can be weakened, and the protective performance of individual head and face equipments can be improved.
