2021 Vol. 41, No. 1
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2021, 41(1): 011401.
doi: 10.11883/bzycj-2020-0415
Abstract:
In the learning and research process of explosion/impact dynamics, “doubt” is the prelude of innovation. Several examples of my experiences are shared here, including as follows. Can statics equilibrium conditions be used for wave propagation analysis? Must satisfy the yield condition (σeff = Y) be in plastic state? Why are the viscoelastic relaxation times θ1 and θ2 in the ZWT equation independent of each other? Is there inertia where there is mass? Should inertial effect be considered in the dynamic constitutive response of materials? Is spalling a problem of material dynamic response or structural dynamic response? Is there any inherent relation between plastic hinge analysis and wave propagation analysis?
In the learning and research process of explosion/impact dynamics, “doubt” is the prelude of innovation. Several examples of my experiences are shared here, including as follows. Can statics equilibrium conditions be used for wave propagation analysis? Must satisfy the yield condition (σeff = Y) be in plastic state? Why are the viscoelastic relaxation times θ1 and θ2 in the ZWT equation independent of each other? Is there inertia where there is mass? Should inertial effect be considered in the dynamic constitutive response of materials? Is spalling a problem of material dynamic response or structural dynamic response? Is there any inherent relation between plastic hinge analysis and wave propagation analysis?
2021, 41(1): 011402.
doi: 10.11883/bzycj-2020-0351
Abstract:
The expansion fracture process of metallic shells under explosive loading is an important topic in fields of weapon design. This process contains a wealth of basic science problems in materials science and mechanics, which has attracted the long-term attention of many scholars. Based on the analysis of the expansion fracture behavior of metal shells under explosive loading, three key physical problems were clarified: dynamic tensile constitutive law of metals, expansion fracture mechanism of shells and mechanism of fragment size. The current status and research trends of the three physical problems were comprehensively analyzed. For the aspect of dynamic tensile constitutive law of metals, it is need to develop some new experimental methods to stretch the material at higher strain rates, to develop the experimental techniques of expanding cylindrical and spherical shells for studying the dynamic tensile constitutive relationship of materials under three dimentional stress state, and to develop the transient acceleration measurement technique and the interpretation method of expansion ring experimental data. For the expansion fracture mechanism, the main development trends are to develop the in-situ or freezing diagnostic techniques to capture key parameters in the fracture process of shells, to use the statistical method to study the fracture behavior, to reveal the essential mechanism of the fracture mode transition and the Ivanov plastic peak phenomena, and to study the mechanism of expanding fracture shells at the micro level. For the mechanism of fragment size, it is need to study the relationship between the fragment size and all the potential control variables with the experimental and modeling method, to analyze the relationship between the micro heterogeneity of the material and the statistical distribution of the fragment size by taking the probability distribution of fracture strain as a bridge, and to analyze the influence of two-dimensional or three-dimensional effects on fragment size distribution and develop new models.
The expansion fracture process of metallic shells under explosive loading is an important topic in fields of weapon design. This process contains a wealth of basic science problems in materials science and mechanics, which has attracted the long-term attention of many scholars. Based on the analysis of the expansion fracture behavior of metal shells under explosive loading, three key physical problems were clarified: dynamic tensile constitutive law of metals, expansion fracture mechanism of shells and mechanism of fragment size. The current status and research trends of the three physical problems were comprehensively analyzed. For the aspect of dynamic tensile constitutive law of metals, it is need to develop some new experimental methods to stretch the material at higher strain rates, to develop the experimental techniques of expanding cylindrical and spherical shells for studying the dynamic tensile constitutive relationship of materials under three dimentional stress state, and to develop the transient acceleration measurement technique and the interpretation method of expansion ring experimental data. For the expansion fracture mechanism, the main development trends are to develop the in-situ or freezing diagnostic techniques to capture key parameters in the fracture process of shells, to use the statistical method to study the fracture behavior, to reveal the essential mechanism of the fracture mode transition and the Ivanov plastic peak phenomena, and to study the mechanism of expanding fracture shells at the micro level. For the mechanism of fragment size, it is need to study the relationship between the fragment size and all the potential control variables with the experimental and modeling method, to analyze the relationship between the micro heterogeneity of the material and the statistical distribution of the fragment size by taking the probability distribution of fracture strain as a bridge, and to analyze the influence of two-dimensional or three-dimensional effects on fragment size distribution and develop new models.
2021, 41(1): 011403.
doi: 10.11883/bzycj-2020-0246
Abstract:
Cylindrical shell chain can cause dispersion of waveform and has the potential to manipulate waveform. An equivalent continuum model and a mesoscopic finite element model of cylindrical shell chain structure were established, and the stress wave propagation process and its geometric dispersion characteristics in cylindrical shell chains under mass impact were studied. For the in-plane compression of a single cylindrical shell, the deformation in the out-of-plane direction is very small and the in-plane deformation perpendicular to the loading direction is relatively large. Thus, the out-of-plane Poisson’s ratio can be taken as 0, but the in-plane one cannot be ignored. For the simplification of analysis, the cylindrical shell chain is considered as a rod composed of anisotropic homogeneous continuum. Based on the Rayleigh-Love wave equation with the transverse inertia correction, the governing equation of elastic wave propagation in a cylindrical shell chain under mass impact was obtained and rewritten in a dimensionless form. The analytical solutions of displacement, velocity and strain fields were obtained by using Laplace transform and its inverse transform and expressed in the form of infinite series. A chain with 30 cylindrical shells was constructed numerically and its dynamic impact behavior was simulated with finite element code ABAQUS/Explicit. The theoretical predictions of mechanical responses are in good agreement with the results of mesoscopic finite element simulation. During the impact process, the peak values of strain and velocity decrease gradually. The peak strain, the oscillation amplitude of waveform and the width of waveform front are related to the in-plane Poisson's ratio and the radius of gyration of the cylindrical shell chain. The larger the in-plane Poisson's ratio and the radius of gyration of the cylindrical shell chain, the smaller the peak strain, the stronger the oscillation of the strain waveform and the wider the width of the waveform front.
Cylindrical shell chain can cause dispersion of waveform and has the potential to manipulate waveform. An equivalent continuum model and a mesoscopic finite element model of cylindrical shell chain structure were established, and the stress wave propagation process and its geometric dispersion characteristics in cylindrical shell chains under mass impact were studied. For the in-plane compression of a single cylindrical shell, the deformation in the out-of-plane direction is very small and the in-plane deformation perpendicular to the loading direction is relatively large. Thus, the out-of-plane Poisson’s ratio can be taken as 0, but the in-plane one cannot be ignored. For the simplification of analysis, the cylindrical shell chain is considered as a rod composed of anisotropic homogeneous continuum. Based on the Rayleigh-Love wave equation with the transverse inertia correction, the governing equation of elastic wave propagation in a cylindrical shell chain under mass impact was obtained and rewritten in a dimensionless form. The analytical solutions of displacement, velocity and strain fields were obtained by using Laplace transform and its inverse transform and expressed in the form of infinite series. A chain with 30 cylindrical shells was constructed numerically and its dynamic impact behavior was simulated with finite element code ABAQUS/Explicit. The theoretical predictions of mechanical responses are in good agreement with the results of mesoscopic finite element simulation. During the impact process, the peak values of strain and velocity decrease gradually. The peak strain, the oscillation amplitude of waveform and the width of waveform front are related to the in-plane Poisson's ratio and the radius of gyration of the cylindrical shell chain. The larger the in-plane Poisson's ratio and the radius of gyration of the cylindrical shell chain, the smaller the peak strain, the stronger the oscillation of the strain waveform and the wider the width of the waveform front.
2021, 41(1): 011404.
doi: 10.11883/bzycj-2020-0224
Abstract:
Adiabatic shear band (ASB) is a common failure mechanism of metals and alloys under high strain rate dynamic loading. The hat-shaped samples of Fe-24.86Ni-5.8Al-0.38C dual-phase steel with different microstructures were impacted by the Hopkinson pressure bar device to investigate their dynamic shear behaviors and microstructural deformation mechanisms. The coarse grained (CG) structure after solution treatment was subjected to cold rolling (CR) in order to obtain various microstructures. The evolution of microstructure during dynamic shear deformation was extensively studied using transmission electron microscopy (TEM) and scanning electron microscope (SEM). The results revealed that the FeNiAlC dual-phase steel has excellent dynamic shear properties with dynamic shear strength of 1.3 GPa and uniform dynamic shear strain of 1.5. The dual-phase steel was found to be composed of austenite phase (γ) and around 20% martensite phase (α) before deformation. The deformation process was found to be dominated by dislocations slip and twinning. Moreover, martensite transformation was found to be suppressed due to the high strain rates. ASBs were observed to be formed in all samples with various microstructures after impact, and dynamic recrystallization was found to occur with formed ultra-fined grains of about 300 nm and without transformation in ASBs. For the width of ASBs, the theoretical result (about 12.3 μm) was found to be in good agreement with the experimental value (about 14.6 μm) in CR samples. However, the measured width of ASBs was found to be about 15.8 μm, which is far smaller to the calculated value (about 30 μm) in CG samples. This may be attributed to the incompletely adiabatic conditions in CG samples. The adiabatic temperature rise due to the plastic work was found to be about 720 K (for CG sample) and 190 K (for CR sample). Through the analysis of the experimental results and the theory of the thermoplastic model, it can be concluded that the adiabatic temperature rise is not the only factor for ASB formation in the course of impact loading, and the localized deformation induced microstructure evolution in materials should also be considered.
Adiabatic shear band (ASB) is a common failure mechanism of metals and alloys under high strain rate dynamic loading. The hat-shaped samples of Fe-24.86Ni-5.8Al-0.38C dual-phase steel with different microstructures were impacted by the Hopkinson pressure bar device to investigate their dynamic shear behaviors and microstructural deformation mechanisms. The coarse grained (CG) structure after solution treatment was subjected to cold rolling (CR) in order to obtain various microstructures. The evolution of microstructure during dynamic shear deformation was extensively studied using transmission electron microscopy (TEM) and scanning electron microscope (SEM). The results revealed that the FeNiAlC dual-phase steel has excellent dynamic shear properties with dynamic shear strength of 1.3 GPa and uniform dynamic shear strain of 1.5. The dual-phase steel was found to be composed of austenite phase (γ) and around 20% martensite phase (α) before deformation. The deformation process was found to be dominated by dislocations slip and twinning. Moreover, martensite transformation was found to be suppressed due to the high strain rates. ASBs were observed to be formed in all samples with various microstructures after impact, and dynamic recrystallization was found to occur with formed ultra-fined grains of about 300 nm and without transformation in ASBs. For the width of ASBs, the theoretical result (about 12.3 μm) was found to be in good agreement with the experimental value (about 14.6 μm) in CR samples. However, the measured width of ASBs was found to be about 15.8 μm, which is far smaller to the calculated value (about 30 μm) in CG samples. This may be attributed to the incompletely adiabatic conditions in CG samples. The adiabatic temperature rise due to the plastic work was found to be about 720 K (for CG sample) and 190 K (for CR sample). Through the analysis of the experimental results and the theory of the thermoplastic model, it can be concluded that the adiabatic temperature rise is not the only factor for ASB formation in the course of impact loading, and the localized deformation induced microstructure evolution in materials should also be considered.
2021, 41(1): 012101.
doi: 10.11883/bzycj-2020-0054
Abstract:
To analyse the effect of gaps on the explosive loading process, we carried out an experiment by using high explosive to genarate a detonation impact on a tin sample through a piece of steel and tested the experimental results with a numerical simulation. Then, we explored variation of impacts due to different gap sizes with further numerical studies. The research shows that gaps of even sub-milimeter can emerge an obvious influence on the experimental results. The gap between the tin sample and the steel layer will lead to a stronger reflection of shock wave on the gap surface than that of the case with no gap, and the reflective rarefaction wave will reflect again at the interface between the steel layer and the high explosive to form a strong subsequent compression shock wave, which will lead to the significant increase of the loading pressure on the tin sample. On the other hand, the gap between the metal layer and the high explosive will lead to a certain extent decrease in loading pressure due to pressure release. Compared with the gap between metal layer and high explosive, the gap between tin sample and steel layer has a more serious effect on loading process. In addition, with the increase of gap size, the variation trend of gap effect is also different in the two cases.
To analyse the effect of gaps on the explosive loading process, we carried out an experiment by using high explosive to genarate a detonation impact on a tin sample through a piece of steel and tested the experimental results with a numerical simulation. Then, we explored variation of impacts due to different gap sizes with further numerical studies. The research shows that gaps of even sub-milimeter can emerge an obvious influence on the experimental results. The gap between the tin sample and the steel layer will lead to a stronger reflection of shock wave on the gap surface than that of the case with no gap, and the reflective rarefaction wave will reflect again at the interface between the steel layer and the high explosive to form a strong subsequent compression shock wave, which will lead to the significant increase of the loading pressure on the tin sample. On the other hand, the gap between the metal layer and the high explosive will lead to a certain extent decrease in loading pressure due to pressure release. Compared with the gap between metal layer and high explosive, the gap between tin sample and steel layer has a more serious effect on loading process. In addition, with the increase of gap size, the variation trend of gap effect is also different in the two cases.
2021, 41(1): 013201.
doi: 10.11883/bzycj-2020-0108
Abstract:
Phase transformation can seriously modify the properties of the materials and therefore impact the stress wave propagation features inside the materials. A simplified incremental phase transformation constitutive model, considering both the hydrostatic pressure and the deviatoric stress, is used to study the propagation of phase transformation coupled waves in a semi-infinite thin-walled tubes under the combined tension (compression) and torsion impact loading. The generalized characteristic theory is used to analyze the basic properties of the characteristic wave velocity and simple wave solution. Two kinds of typical solutions are studied by using numerical method. The stress paths and wave structure are related to the initial state and the loading amplitude, exhibiting the different properties from conventional elastoplastic materials.
Phase transformation can seriously modify the properties of the materials and therefore impact the stress wave propagation features inside the materials. A simplified incremental phase transformation constitutive model, considering both the hydrostatic pressure and the deviatoric stress, is used to study the propagation of phase transformation coupled waves in a semi-infinite thin-walled tubes under the combined tension (compression) and torsion impact loading. The generalized characteristic theory is used to analyze the basic properties of the characteristic wave velocity and simple wave solution. Two kinds of typical solutions are studied by using numerical method. The stress paths and wave structure are related to the initial state and the loading amplitude, exhibiting the different properties from conventional elastoplastic materials.
2021, 41(1): 013202.
doi: 10.11883/bzycj-2020-0313
Abstract:
Wave propagation in visco-elastic materials with gradient density is really complex. In order to understand the responses of the visco-elastic materials to impact load, a series of theoretical equations for wave propagation in density-graded visco-elastic materials were proposed by employing the Euler form of the governing equations and the Laplace transform method. According to these equations, the wave propagation in the two-layer periodically-superimposed media with perpendicular incidence was analyzed. The Ti-TiB2 material with gradient density characteristics and the carbon-fiber-reinforced resin composites with strong visco-elastic properties were selected as experimental subjects to carry out dynamic impact tests by applying a split Hopkinson pressure bar (SHPB) device. To better reflect the influences of the gradient characteristics on the dynamic responses of the materials, the experimental specimens were prepared by using different stacking directions and modes. The data obtained by the SHPB device were analyzed by the three-wave method. Moreover, according to the incident wave and transmission wave obtained by the SHPB device, the wave propagation equations proposed for the visco-elastic media with gradient density were applied to obtain the corresponding theoretical solutions. And the calculated theoretical solutions were compared with the experimental results. The comparisons display as follows. (1) Due to the internal interface and the superimposed interface, the graded Ti-TiB2 materials show certain viscosity properties. For single-layer Ti-TiB2 specimens, the theoretically calculated results are approximately consistent with the experimental ones analyzed by the three-wave method. But there lie some differences for two-layer Ti-TiB2 specimens. (2) The two-layer carbon fiber reinforced resin composites exhibit stronger visco-elastic characteristics, and the attenuation amplitude of stress wave is larger. There are obvious differences between the experimental results analyzed by the three-wave method and theoretically calculated ones. As a consequence, the influences of the viscosity produced by the meso-structures and the viscosity of the material itself on the dynamic behaviors of the macro medium cannot be ignored.
Wave propagation in visco-elastic materials with gradient density is really complex. In order to understand the responses of the visco-elastic materials to impact load, a series of theoretical equations for wave propagation in density-graded visco-elastic materials were proposed by employing the Euler form of the governing equations and the Laplace transform method. According to these equations, the wave propagation in the two-layer periodically-superimposed media with perpendicular incidence was analyzed. The Ti-TiB2 material with gradient density characteristics and the carbon-fiber-reinforced resin composites with strong visco-elastic properties were selected as experimental subjects to carry out dynamic impact tests by applying a split Hopkinson pressure bar (SHPB) device. To better reflect the influences of the gradient characteristics on the dynamic responses of the materials, the experimental specimens were prepared by using different stacking directions and modes. The data obtained by the SHPB device were analyzed by the three-wave method. Moreover, according to the incident wave and transmission wave obtained by the SHPB device, the wave propagation equations proposed for the visco-elastic media with gradient density were applied to obtain the corresponding theoretical solutions. And the calculated theoretical solutions were compared with the experimental results. The comparisons display as follows. (1) Due to the internal interface and the superimposed interface, the graded Ti-TiB2 materials show certain viscosity properties. For single-layer Ti-TiB2 specimens, the theoretically calculated results are approximately consistent with the experimental ones analyzed by the three-wave method. But there lie some differences for two-layer Ti-TiB2 specimens. (2) The two-layer carbon fiber reinforced resin composites exhibit stronger visco-elastic characteristics, and the attenuation amplitude of stress wave is larger. There are obvious differences between the experimental results analyzed by the three-wave method and theoretically calculated ones. As a consequence, the influences of the viscosity produced by the meso-structures and the viscosity of the material itself on the dynamic behaviors of the macro medium cannot be ignored.
2021, 41(1): 013301.
doi: 10.11883/bzycj-2020-0075
Abstract:
One of the main functions of liquid tanks in the passive protective systems of surface warships is to prevent the damage by high-velocity projectiles (explosive fragments) to important internal structures, equipments and personnels. The process of high-velocity projectile penetrating through a liquid tank involves complex energy transfer and dissipation. To explore the influences of the head shape of a projectile and its water-entry velocity on the velocity attenuation of the projectile in fluid, a series of truncated cone-shaped projectiles with different head shape factors were developed to numerically simulate the processes of the truncated cone-shaped projectiles vertically penetrating through the fluid at different initial water-entry velocities. The velocity attenuation characteristics were obtained for the projectiles vertically penetrating through the fluid. The above results display that the resistance factor of a high-velocity projectile moving in the fluid is related with the projectile shape and the ratio of the instantaneous velocity of the projectile to its initial water-entry velocity. Based on the numerical simulations and the corresponding fitting results, an empirical formula was proposed by considering the projectile head factor to predict the velocity attenuation of the truncated cone-shaped projectiles vertically penetrating through the fluid. And a series of calculation examples were carried out to verify the formula. These calculation examples show that the formula is feasible and can be used to accurately calculate the velocity attenuation of high-velocity projectiles in fluid media and it is helpful for the structural design of the protective tanks of warships.
One of the main functions of liquid tanks in the passive protective systems of surface warships is to prevent the damage by high-velocity projectiles (explosive fragments) to important internal structures, equipments and personnels. The process of high-velocity projectile penetrating through a liquid tank involves complex energy transfer and dissipation. To explore the influences of the head shape of a projectile and its water-entry velocity on the velocity attenuation of the projectile in fluid, a series of truncated cone-shaped projectiles with different head shape factors were developed to numerically simulate the processes of the truncated cone-shaped projectiles vertically penetrating through the fluid at different initial water-entry velocities. The velocity attenuation characteristics were obtained for the projectiles vertically penetrating through the fluid. The above results display that the resistance factor of a high-velocity projectile moving in the fluid is related with the projectile shape and the ratio of the instantaneous velocity of the projectile to its initial water-entry velocity. Based on the numerical simulations and the corresponding fitting results, an empirical formula was proposed by considering the projectile head factor to predict the velocity attenuation of the truncated cone-shaped projectiles vertically penetrating through the fluid. And a series of calculation examples were carried out to verify the formula. These calculation examples show that the formula is feasible and can be used to accurately calculate the velocity attenuation of high-velocity projectiles in fluid media and it is helpful for the structural design of the protective tanks of warships.
2021, 41(1): 013302.
doi: 10.11883/bzycj-2020-0077
Abstract:
Explosion experiments were performed to explore the response law of typical stiffened skin structures of aircrafts under explosive loading. And in the experiments, the following data on the structural responses were obtained as the reflected overpressure history at the surface of the typical aircraft structure, the strain and displacement of the stiffened structure. By combining the experimental data, a finite element model at a high-confidence level was proposed to analyze the deformation distribution and plastical damage characteristics of the structure investigated in this paper. Results show that for the stiffened structure investigated in this paper, the plastical deformation can start commonly at the midpoints of stiffeners, stiffener-to-stiffener and stiffener-to-outer frame joints in addition. It is mainly due to biaxial tensile deformation and stress concentration in stiffeners. Furthermore, the effective impulse and the peak threshold of reflected overpressure which can cause plastic deformation of reinforced structures with the increase of positive pressure action time were summarized. The research results are of great significance in the aerodynamic design of an aircraft.
Explosion experiments were performed to explore the response law of typical stiffened skin structures of aircrafts under explosive loading. And in the experiments, the following data on the structural responses were obtained as the reflected overpressure history at the surface of the typical aircraft structure, the strain and displacement of the stiffened structure. By combining the experimental data, a finite element model at a high-confidence level was proposed to analyze the deformation distribution and plastical damage characteristics of the structure investigated in this paper. Results show that for the stiffened structure investigated in this paper, the plastical deformation can start commonly at the midpoints of stiffeners, stiffener-to-stiffener and stiffener-to-outer frame joints in addition. It is mainly due to biaxial tensile deformation and stress concentration in stiffeners. Furthermore, the effective impulse and the peak threshold of reflected overpressure which can cause plastic deformation of reinforced structures with the increase of positive pressure action time were summarized. The research results are of great significance in the aerodynamic design of an aircraft.
2021, 41(1): 014101.
doi: 10.11883/bzycj-2020-0049
Abstract:
A liquid-driving brittle expansion ring test technique has been developed. The precise centering of the brittle ring was realized by means of a liftable convex platform to avoid the bending fracture caused by eccentric expansion. The strain vs time curves in the process of tensile fracture were measured by the semiconductor strain gauges on the expansion ring. Then expansion tensile fracture experiments of silicon carbide (SiC) ceramics were carried out, and their dynamic tensile fracture strength and average size and distribution of fragments were obtained. The experimental results show as follows. (1) The liquid-driving expansion ring experiment can better achieve the tensile fracture of the ceramic material. At a strain rate of 101 s−1, the tensile fracture strain of SiC ceramic is 3.7×10−4−7.4×10−4, and the average tensile fracture stress is 206 MPa. (2) The dimensionless average fragment size of SiC ceramic falls within the reasonable interval of various brittle fracture prediction models. With the increase of loading strain rate, the average fragment size of SiC ceramic decreases. (3) The fragment distribution of SiC ceramic tensile fracture basically conforms to the Rayleigh distribution, but there are some deviations in the fine size and large size fragment distribution.
A liquid-driving brittle expansion ring test technique has been developed. The precise centering of the brittle ring was realized by means of a liftable convex platform to avoid the bending fracture caused by eccentric expansion. The strain vs time curves in the process of tensile fracture were measured by the semiconductor strain gauges on the expansion ring. Then expansion tensile fracture experiments of silicon carbide (SiC) ceramics were carried out, and their dynamic tensile fracture strength and average size and distribution of fragments were obtained. The experimental results show as follows. (1) The liquid-driving expansion ring experiment can better achieve the tensile fracture of the ceramic material. At a strain rate of 101 s−1, the tensile fracture strain of SiC ceramic is 3.7×10−4−7.4×10−4, and the average tensile fracture stress is 206 MPa. (2) The dimensionless average fragment size of SiC ceramic falls within the reasonable interval of various brittle fracture prediction models. With the increase of loading strain rate, the average fragment size of SiC ceramic decreases. (3) The fragment distribution of SiC ceramic tensile fracture basically conforms to the Rayleigh distribution, but there are some deviations in the fine size and large size fragment distribution.
2021, 41(1): 014201.
doi: 10.11883/bzycj-2020-0069
Abstract:
To improve the ballistic simulation accuracy of ceramic composite armors and glass composite armors (transparent armors) against small-caliber armor piercing bullets, the new FEM (finite element method) -SPH (smooth particle hydrodynamics) coupled model was proposed, which replaced the FEM model and JC (Johnson-Cook) material model of the armor-piercing-bullet core of traditional FEM-SPH coupled model with the SPH model and JH2 (Johnson-Holmquist-ceramics) material model. The results show that the new FEM-SPH coupled model can effectively simulate bullet core fragmentation and reduce FEM-SPH coupled calculation amount. So it can improve the computation accuracy and efficiency. And the FEM element/SPH particle size and armor modeling size of the new FEM-SPH coupled model are optimized.
To improve the ballistic simulation accuracy of ceramic composite armors and glass composite armors (transparent armors) against small-caliber armor piercing bullets, the new FEM (finite element method) -SPH (smooth particle hydrodynamics) coupled model was proposed, which replaced the FEM model and JC (Johnson-Cook) material model of the armor-piercing-bullet core of traditional FEM-SPH coupled model with the SPH model and JH2 (Johnson-Holmquist-ceramics) material model. The results show that the new FEM-SPH coupled model can effectively simulate bullet core fragmentation and reduce FEM-SPH coupled calculation amount. So it can improve the computation accuracy and efficiency. And the FEM element/SPH particle size and armor modeling size of the new FEM-SPH coupled model are optimized.
2021, 41(1): 014901.
doi: 10.11883/bzycj-2020-0078
Abstract:
A deep-water explosion test vessel is an important test equipment which is filled with water to simulate different water depth environment by loading different hydrostatic pressure, and it can be used to study deep water explosion theory and engineering technology based on the similarity principle. In order to ensure the safety of vessels used in deep-water explosion test, a random-interval dynamic reliability model based on intelligent prediction is proposed in this paper. A GRNN prediction network of vessel response is established through dynamic test data, and the maximum strain interval variable of the vessel is obtained. Considering the random characteristics of the vessel structure, the reliability analysis of the in-service deep-water explosion test vessel is carried out. During the period, three methods are used to calculate the reliability index, and the analysis shows that for the vessel structure with high reliability and lack of sample data, the hybrid reliability model based on dynamic prediction is established by the calculation of interval reliability index. The method is simple and feasible. At the same time, the interval variables of the model change with the structural dynamic test data, and the uncertainty analysis of the structure is also dynamic. Therefore, the reliability of the container obtained is also changing with the service process, and has dynamic characteristics, which can better reflect the performance changes of the container during the service period and provide the basis for the use and maintenance decision of the container.
A deep-water explosion test vessel is an important test equipment which is filled with water to simulate different water depth environment by loading different hydrostatic pressure, and it can be used to study deep water explosion theory and engineering technology based on the similarity principle. In order to ensure the safety of vessels used in deep-water explosion test, a random-interval dynamic reliability model based on intelligent prediction is proposed in this paper. A GRNN prediction network of vessel response is established through dynamic test data, and the maximum strain interval variable of the vessel is obtained. Considering the random characteristics of the vessel structure, the reliability analysis of the in-service deep-water explosion test vessel is carried out. During the period, three methods are used to calculate the reliability index, and the analysis shows that for the vessel structure with high reliability and lack of sample data, the hybrid reliability model based on dynamic prediction is established by the calculation of interval reliability index. The method is simple and feasible. At the same time, the interval variables of the model change with the structural dynamic test data, and the uncertainty analysis of the structure is also dynamic. Therefore, the reliability of the container obtained is also changing with the service process, and has dynamic characteristics, which can better reflect the performance changes of the container during the service period and provide the basis for the use and maintenance decision of the container.
2021, 41(1): 015901.
doi: 10.11883/bzycj-2020-0073
Abstract:
For a military vehicle, an unbuffered platform airdrop test was performed at a height of 1 m. And a seat-crew model was built. The impact signals at the seat installation point were obtained by the test. The obtained signals were used as the input of the simulation model, and the reliability of the model was verified by comparing the test and simulation data. Based on the aeronautical engineering related research, a weight evaluation index named weighted injury criteria (WIC) was presented by normalizing each key damage index. The influence of two posture parameters, namely the crew’s supine angle and the angle between the calf and the thigh, on the crew’s injury was studied. With the WIC as the optimization target, the genetic algorithm was used to obtain the optimized parameters. The study finds that to restrain the motion of the crew’s calf can reduce his overall injury response. The optimal posture of the crew against the landing impact is the supine angle range from 47° to 56°, and the angle between the upper and lower legs is from 62° to 68°.
For a military vehicle, an unbuffered platform airdrop test was performed at a height of 1 m. And a seat-crew model was built. The impact signals at the seat installation point were obtained by the test. The obtained signals were used as the input of the simulation model, and the reliability of the model was verified by comparing the test and simulation data. Based on the aeronautical engineering related research, a weight evaluation index named weighted injury criteria (WIC) was presented by normalizing each key damage index. The influence of two posture parameters, namely the crew’s supine angle and the angle between the calf and the thigh, on the crew’s injury was studied. With the WIC as the optimization target, the genetic algorithm was used to obtain the optimized parameters. The study finds that to restrain the motion of the crew’s calf can reduce his overall injury response. The optimal posture of the crew against the landing impact is the supine angle range from 47° to 56°, and the angle between the upper and lower legs is from 62° to 68°.
2021, 41(1): 015902.
doi: 10.11883/bzycj-2020-0059
Abstract:
In order to research the influence of the time interval between the vertical impact of the lower legs of passenger and seat on the pelvis and lumbar injuries under explosive impact environment, Hyperworks and LS-DYNA were used to model and simulation analysis, and the research was carried out in combination with the lower legs impact test and the seat drop test. The results show that the positive and negative peaks are generated by the pelvic acceleration, dynamic response index and the z-direction force of the lumbar spine when the passenger’s lower legs and seat mounting points are impacted separately, but the positive and negative peaks do not weaken when the impact time interval is controlled. When the lower legs and seat mounting points are impacted at different time, injuries to the pelvis and lumbar spine of the passenger will be aggravated, and the damage degree of the lower legs impacted preferentially is more serious than that when the seat mounting points are impacted first.
In order to research the influence of the time interval between the vertical impact of the lower legs of passenger and seat on the pelvis and lumbar injuries under explosive impact environment, Hyperworks and LS-DYNA were used to model and simulation analysis, and the research was carried out in combination with the lower legs impact test and the seat drop test. The results show that the positive and negative peaks are generated by the pelvic acceleration, dynamic response index and the z-direction force of the lumbar spine when the passenger’s lower legs and seat mounting points are impacted separately, but the positive and negative peaks do not weaken when the impact time interval is controlled. When the lower legs and seat mounting points are impacted at different time, injuries to the pelvis and lumbar spine of the passenger will be aggravated, and the damage degree of the lower legs impacted preferentially is more serious than that when the seat mounting points are impacted first.
