2023 Vol. 43, No. 4
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2023, 43(4): 042201.
doi: 10.11883/bzycj-2022-0239
Abstract:
Clearance of certain thickness often exists between two stacked metal flyers. When a double-layer metal flyer with clearance is loaded by detonation, the closing of the clearance may affect the form and shock intensity of the first and second loading waves inside of the outer flyer, and then affects the free surface velocity of the outer flyer. In order to better grasp the motion characteristics under detonation loading, the effect of clearance on the dynamic process needs to be studied. Firstly, a detonation driven two-layer steel flyers model is presented, in which a clearance of certain thickness is assumed to exist between two steel flyers. In this model, the free surface of the outer flyer is loaded twice. By comparing the simulation results and experimental results of free surface velocity at different positions, it is confirmed that the simulation can correctly catch the dynamic process. Then, the sources of the first and second loading in the outer flyer are given by the analysis of the simulated dynamic process. The first loading wave in the outer flyer comes from the clearance closing collision, and the second loading wave mainly comes from the sustained high pressure loading of detonation products. Finally, the simulation with various clearance thicknesses is carried out, and the effect of clearance thickness change is summarized. The simulated results of free surface velocity show that with the increase of clearance thickness from 0.1 mm to more than 1 mm, the peak value of the first take-off free surface velocity first decreases and then remains unchanged, and the peak value of the second take-off free surface velocity first increases and then remains unchanged. The dynamic analysis shows that the size of the clearance thickness directly affects whether the inner steel flyer has enough time to develop into spallation on the clearance side after detonation loading. If the size of clearance is small, the inner flyer cannot develop into a spallation on clearance side, and the first loading wave formed in the outer flyer has a triangular like pulse. In this stage, with the increase of the clearance thickness, the first loading peak pressure decreases and the second loading peak pressure increases. If the size of clearance is large, the inner flyer can form a spallation with constant thickness and stable velocity on clearance side, and the first loading wave formed in the outer flyer is an approximate square wave. In this stage, with the increase of clearance thickness, the peak pressures of the first and second loading remain basically unchanged, but the time interval between the first and second loading decreases. The understanding has guiding significance for the interpretation of the free surface velocity measurement results in experiments, and some unexpected physical phenomena caused by clearance in practical problems could be better understood, too.
Clearance of certain thickness often exists between two stacked metal flyers. When a double-layer metal flyer with clearance is loaded by detonation, the closing of the clearance may affect the form and shock intensity of the first and second loading waves inside of the outer flyer, and then affects the free surface velocity of the outer flyer. In order to better grasp the motion characteristics under detonation loading, the effect of clearance on the dynamic process needs to be studied. Firstly, a detonation driven two-layer steel flyers model is presented, in which a clearance of certain thickness is assumed to exist between two steel flyers. In this model, the free surface of the outer flyer is loaded twice. By comparing the simulation results and experimental results of free surface velocity at different positions, it is confirmed that the simulation can correctly catch the dynamic process. Then, the sources of the first and second loading in the outer flyer are given by the analysis of the simulated dynamic process. The first loading wave in the outer flyer comes from the clearance closing collision, and the second loading wave mainly comes from the sustained high pressure loading of detonation products. Finally, the simulation with various clearance thicknesses is carried out, and the effect of clearance thickness change is summarized. The simulated results of free surface velocity show that with the increase of clearance thickness from 0.1 mm to more than 1 mm, the peak value of the first take-off free surface velocity first decreases and then remains unchanged, and the peak value of the second take-off free surface velocity first increases and then remains unchanged. The dynamic analysis shows that the size of the clearance thickness directly affects whether the inner steel flyer has enough time to develop into spallation on the clearance side after detonation loading. If the size of clearance is small, the inner flyer cannot develop into a spallation on clearance side, and the first loading wave formed in the outer flyer has a triangular like pulse. In this stage, with the increase of the clearance thickness, the first loading peak pressure decreases and the second loading peak pressure increases. If the size of clearance is large, the inner flyer can form a spallation with constant thickness and stable velocity on clearance side, and the first loading wave formed in the outer flyer is an approximate square wave. In this stage, with the increase of clearance thickness, the peak pressures of the first and second loading remain basically unchanged, but the time interval between the first and second loading decreases. The understanding has guiding significance for the interpretation of the free surface velocity measurement results in experiments, and some unexpected physical phenomena caused by clearance in practical problems could be better understood, too.
2023, 43(4): 042202.
doi: 10.11883/bzycj-2022-0209
Abstract:
The most common hypervelocity propulsion systems are light gas guns. Especially, the ability of two-stage light gas guns is suitable to accelerate projectile at velocities ranging from 2 km/s to 9 km/s. However, velocities higher than 10 km/s are demanded eagerly for ballistic limit equations on on-orbit impacts and meteoroids. In order to enhance the launch performance of the light-gas guns, a concept of using density-gradient gas as the driving gas instead of single helium or hydrogen gas has been proposed. An analytical acceleration model of the projectile in the launch tube with constant cross-sectional area is deduced. The launch process can be divided into three stages. The first stage is the projectile driven by the first shock wave. The second stage is the projectile driven by shock waves reflected on the gas interface. The last stage is the projectile caught up by the rarefaction wave created by the suddenly stop of the piston. The comparison in launch performance between neon-helium density-gradient driving gas and helium driving gas is made, and the influences of parameters of the gradient gas on the launch performance are studied. Results show that the neon-helium density-gradient driving gas can improve the launch velocity by about 0.4−1.4 km/s or lower the maximum base pressure by about 0.2−0.9 GPa. The biggest influential factors for the launch velocity and the maximum base pressure are the density of high density gas and the piston velocity, following by the initial gas pressure and the gaseous polytrophic index. High density gas with both high density and high gaseous polytrophic index would be the prior choice due to the reason that higher gaseous polytrophic index could make the maximum base pressure lower. The launch velocity has little correlation with the ratio of high density gas. However, low ratio of high density gas could lower the maximum base pressure.
The most common hypervelocity propulsion systems are light gas guns. Especially, the ability of two-stage light gas guns is suitable to accelerate projectile at velocities ranging from 2 km/s to 9 km/s. However, velocities higher than 10 km/s are demanded eagerly for ballistic limit equations on on-orbit impacts and meteoroids. In order to enhance the launch performance of the light-gas guns, a concept of using density-gradient gas as the driving gas instead of single helium or hydrogen gas has been proposed. An analytical acceleration model of the projectile in the launch tube with constant cross-sectional area is deduced. The launch process can be divided into three stages. The first stage is the projectile driven by the first shock wave. The second stage is the projectile driven by shock waves reflected on the gas interface. The last stage is the projectile caught up by the rarefaction wave created by the suddenly stop of the piston. The comparison in launch performance between neon-helium density-gradient driving gas and helium driving gas is made, and the influences of parameters of the gradient gas on the launch performance are studied. Results show that the neon-helium density-gradient driving gas can improve the launch velocity by about 0.4−1.4 km/s or lower the maximum base pressure by about 0.2−0.9 GPa. The biggest influential factors for the launch velocity and the maximum base pressure are the density of high density gas and the piston velocity, following by the initial gas pressure and the gaseous polytrophic index. High density gas with both high density and high gaseous polytrophic index would be the prior choice due to the reason that higher gaseous polytrophic index could make the maximum base pressure lower. The launch velocity has little correlation with the ratio of high density gas. However, low ratio of high density gas could lower the maximum base pressure.
2023, 43(4): 042301.
doi: 10.11883/bzycj-2022-0316
Abstract:
In order to investigate the combustion characteristics of a new aluminum-containing solid propellant, the ignition and combustion process of the propellant at elevated pressure for simulating the solid propellant rocket engine were systematically studied by using a variable power fiber-laser and optical diagnostic techniques. The near-infrared fiber laser was employed to ignite the propellant slices placed in a high-pressure optical tank which was designed and manufactured for simulating solid propellant rocket engine conditions. The successive images of the laser-ignition and combustion process were captured by a high-speed camera while the optical emission spectroscopy was recorded with fiber-based spectrometers. Therewith, the regression rate, the ignition delay, and agglomerate particle size of the propellant were determined from the quantitative measurement and analysis of the former, likewise, the combustion temperatures were deduced by the latter. Accordingly, the maximum combustion temperature, the magnitude of the ignition delay, and rules of regression rate were mastered, as well as their dependence on laser power and ambient pressure. Firstly, the analysis of emission spectra shows that the maximum combustion temperature of this propellant should be higher than 3 300 K which grows with pressure. It reveals that the fundamental mechanisms of the propellant receding rate and ignition delay are affected by the ambient pressure from the perspective of chemical reaction dynamics. Meantime, the exponential decay law of ignition delay is determined while its formation mechanism is explored, based on the real-time monitoring of the propellant burning surface with high spatial and temporal resolution. Furthermore, it is also found that the regression rate of this propellant increases rapidly at low pressure, but appears to be saturated gradually when the ambient pressure exceeds 4 MPa. Whereafter, it is confirmed that the receding rate rules strictly follow the Summerfield burning rate equation. Finally, through the quantitative analysis of the luminous area of agglomerates in the combustion process, the effects of the agglomerate particle size in the propellant product by environmental parameters are concluded.
In order to investigate the combustion characteristics of a new aluminum-containing solid propellant, the ignition and combustion process of the propellant at elevated pressure for simulating the solid propellant rocket engine were systematically studied by using a variable power fiber-laser and optical diagnostic techniques. The near-infrared fiber laser was employed to ignite the propellant slices placed in a high-pressure optical tank which was designed and manufactured for simulating solid propellant rocket engine conditions. The successive images of the laser-ignition and combustion process were captured by a high-speed camera while the optical emission spectroscopy was recorded with fiber-based spectrometers. Therewith, the regression rate, the ignition delay, and agglomerate particle size of the propellant were determined from the quantitative measurement and analysis of the former, likewise, the combustion temperatures were deduced by the latter. Accordingly, the maximum combustion temperature, the magnitude of the ignition delay, and rules of regression rate were mastered, as well as their dependence on laser power and ambient pressure. Firstly, the analysis of emission spectra shows that the maximum combustion temperature of this propellant should be higher than 3 300 K which grows with pressure. It reveals that the fundamental mechanisms of the propellant receding rate and ignition delay are affected by the ambient pressure from the perspective of chemical reaction dynamics. Meantime, the exponential decay law of ignition delay is determined while its formation mechanism is explored, based on the real-time monitoring of the propellant burning surface with high spatial and temporal resolution. Furthermore, it is also found that the regression rate of this propellant increases rapidly at low pressure, but appears to be saturated gradually when the ambient pressure exceeds 4 MPa. Whereafter, it is confirmed that the receding rate rules strictly follow the Summerfield burning rate equation. Finally, through the quantitative analysis of the luminous area of agglomerates in the combustion process, the effects of the agglomerate particle size in the propellant product by environmental parameters are concluded.
2023, 43(4): 043101.
doi: 10.11883/bzycj-2022-0137
Abstract:
To describe the dynamic mechanical properties of frozen sandy soil under active confining pressure, a dynamic damage constitutive model, which could consider the effect of active confining pressure on the dynamic strength and deformation characteristics of frozen sandy soil, was established by connecting a plastic body to the nonlinear Zhu-Wang-Tang model. The effects of damage parameters on the characteristics of stress-strain curves, yield point, peak stress, and peak strain were analyzed. In addition, the model parameters were determined based on the dynamic test data of frozen sandy soil. The applicability and accuracy of the established model were verified by comparing the model with the test data and analyzing its prediction errors under different test conditions. The results show that the damage parameters have no significant effect on the elastic stage and yield point of the dynamic stress-strain curves. However, it significantly affects the plastic and failure stages. The stress-strain curves predicted by the established constitutive model are in good agreement with the test results. The model is appropriate in predicting the characteristics including large portion of the plastic stage and obvious yield point caused by active confining pressure. Moreover, the model can also describe the enhancement effect of confining pressure on the dynamic compressive strength of frozen sandy soil. The predictions of the model on the peak stress and yield stress are better than those on the peak strain and yield strain under different negative temperatures and active confining pressures.
To describe the dynamic mechanical properties of frozen sandy soil under active confining pressure, a dynamic damage constitutive model, which could consider the effect of active confining pressure on the dynamic strength and deformation characteristics of frozen sandy soil, was established by connecting a plastic body to the nonlinear Zhu-Wang-Tang model. The effects of damage parameters on the characteristics of stress-strain curves, yield point, peak stress, and peak strain were analyzed. In addition, the model parameters were determined based on the dynamic test data of frozen sandy soil. The applicability and accuracy of the established model were verified by comparing the model with the test data and analyzing its prediction errors under different test conditions. The results show that the damage parameters have no significant effect on the elastic stage and yield point of the dynamic stress-strain curves. However, it significantly affects the plastic and failure stages. The stress-strain curves predicted by the established constitutive model are in good agreement with the test results. The model is appropriate in predicting the characteristics including large portion of the plastic stage and obvious yield point caused by active confining pressure. Moreover, the model can also describe the enhancement effect of confining pressure on the dynamic compressive strength of frozen sandy soil. The predictions of the model on the peak stress and yield stress are better than those on the peak strain and yield strain under different negative temperatures and active confining pressures.
2023, 43(4): 043102.
doi: 10.11883/bzycj-2022-0253
Abstract:
Dynamic triaxial cyclic impact experiments on the coal rock samples with the bedding angles of 0°, 30°, 45°, 60°, and 90°, respectively, were conducted using a 50-mm split Hopkinson pressure bar (SHPB) system to study the dynamic mechanical behaviors of the coal rock with characteristic bedding under complex ground conditions. A 3D profile scanner was utilized to quantify the fracture interface roughness and to investigate the bedding effect on the dynamic fracture process of the coal rock. The bedding angle effect and confining pressure effect on the dynamic properties of the coal rock were explored by combining dynamic parameters such as compressive strength, elastic modulus, energy distribution evolution with the fracture surface roughness variation. The research shows that when confining pressure is applied, the stress-strain curve of the coal rock has an elastic aftereffect. The dynamic compressive strength and failure strain of the bedding coal rock with confining pressure are respectively 3.9−4.2 and 2.59−3.05 times higher than those without confining pressure. As the bedding angle increases, the dynamic compressive strength, elastic modulus, and energy transmitted ratio of the coal rock display the U-shaped distribution, which decreases first and then increases, reaching the minimum at the bedding angle of 45°. Meanwhile, the energy absorbed ratio and fracture surface roughness show the ∩-shaped distribution, first increasing and then decreasing, and the damage variable shows the N-shaped distribution, reaching the maximum at the bedding angle of 45°. The failure of the coal rock with 45° bedding is the most serious, which is more prone to intergranular and spalling fractures. However, the 90° bedding coal rock is more likely to absorb energy and to form transgranular fractures, resulting in a large number of mesoscopic fractures. Variation of the damage characteristics of the coal rocks with bedding angle can be summarized as a tensile damage (0°)-shear damage (30°, 45°, 60°)-splitting damage (90°) evolution process. The relevant characteristic results obtained from the experiments can provide a theoretical support for the safe and efficient exploitation of coalbed methane resources in the complex environment under practical working conditions.
Dynamic triaxial cyclic impact experiments on the coal rock samples with the bedding angles of 0°, 30°, 45°, 60°, and 90°, respectively, were conducted using a 50-mm split Hopkinson pressure bar (SHPB) system to study the dynamic mechanical behaviors of the coal rock with characteristic bedding under complex ground conditions. A 3D profile scanner was utilized to quantify the fracture interface roughness and to investigate the bedding effect on the dynamic fracture process of the coal rock. The bedding angle effect and confining pressure effect on the dynamic properties of the coal rock were explored by combining dynamic parameters such as compressive strength, elastic modulus, energy distribution evolution with the fracture surface roughness variation. The research shows that when confining pressure is applied, the stress-strain curve of the coal rock has an elastic aftereffect. The dynamic compressive strength and failure strain of the bedding coal rock with confining pressure are respectively 3.9−4.2 and 2.59−3.05 times higher than those without confining pressure. As the bedding angle increases, the dynamic compressive strength, elastic modulus, and energy transmitted ratio of the coal rock display the U-shaped distribution, which decreases first and then increases, reaching the minimum at the bedding angle of 45°. Meanwhile, the energy absorbed ratio and fracture surface roughness show the ∩-shaped distribution, first increasing and then decreasing, and the damage variable shows the N-shaped distribution, reaching the maximum at the bedding angle of 45°. The failure of the coal rock with 45° bedding is the most serious, which is more prone to intergranular and spalling fractures. However, the 90° bedding coal rock is more likely to absorb energy and to form transgranular fractures, resulting in a large number of mesoscopic fractures. Variation of the damage characteristics of the coal rocks with bedding angle can be summarized as a tensile damage (0°)-shear damage (30°, 45°, 60°)-splitting damage (90°) evolution process. The relevant characteristic results obtained from the experiments can provide a theoretical support for the safe and efficient exploitation of coalbed methane resources in the complex environment under practical working conditions.
2023, 43(4): 043103.
doi: 10.11883/bzycj-2022-0357
Abstract:
The microstructure of adiabatic shear band (ASB) is influenced by the specimen geometric shape. High-speed impact tests were performed on specimens of three different shapes of cylinder, hat-shaped, and shear-compression by a split Hopkinson pressure bar, to study the effect of the specimen shape on the formation and microstructure of the adiabatic shear band in the bearing steel. The results show that at the strain rate from 1800 to 3100 s-1, the flow stress remains almost the same with increasing the strain rate in three different shapes of sepcimens, indicating that the material shows low strain rate sensitivity. At high strain rates, the cylindrical specimen exhibits a strong strain hardening, while the hat-shaped specimen and the shear-compression specimen (SCS) show both strain hardening and no strain hardening features at different strain rates, but their flow stresses are not increased due to hardening effect. The fracture surface of the cylindrical specimen presents a large number of dense and tiny elliptical dimples. The number of dimples is greatly reduced on the hat-shaped specimen. The dimple, however, has a width that is twice of that of the cylindrical specimen. There is a distinct shearing path of carbides. In contrast, the SCS has even fewer but much larger dimples, with the width of 1.6 μm, twice of the hat-shaped specimen, and the shearing path of carbides reaches 7 μm. Local melting occurs on both the hat-shaped specimen and SCS, especially the SCS, a massive melting is displayed. A long and narrow ASB was produced in the cylindrical specimen, and only strain-induced grain refinement occurred in the ASB, which belongs to the deformed ASB. Large patch of ASBs is generated in the hat-shaped specimen and SCS. The ASBs consist of equiaxed grains and belong to the transformed ASB as the phase transformation from martensite to austenite occurred. In particular, the equiaxed grains in the ASB of the SCS have very clear grain boundaries, which are typical dynamic recrystallization grains. It can conclude that the shape of the specimen has a great influence on the microscopic morphologies and microstructures of ASB. The cylindrical specimen is in a typical compressive stress state, while the hat-shaped specimen and SCS are in complicated stress dominated by shear. The temperature rise int the ASB of the cylindrical specimen is much lower than the austenite transformation temperature, while it is higher than the melting point of martensite in the hat-shaped specimen and SCS, leading to local melting and microstructural change.
The microstructure of adiabatic shear band (ASB) is influenced by the specimen geometric shape. High-speed impact tests were performed on specimens of three different shapes of cylinder, hat-shaped, and shear-compression by a split Hopkinson pressure bar, to study the effect of the specimen shape on the formation and microstructure of the adiabatic shear band in the bearing steel. The results show that at the strain rate from 1800 to 3100 s-1, the flow stress remains almost the same with increasing the strain rate in three different shapes of sepcimens, indicating that the material shows low strain rate sensitivity. At high strain rates, the cylindrical specimen exhibits a strong strain hardening, while the hat-shaped specimen and the shear-compression specimen (SCS) show both strain hardening and no strain hardening features at different strain rates, but their flow stresses are not increased due to hardening effect. The fracture surface of the cylindrical specimen presents a large number of dense and tiny elliptical dimples. The number of dimples is greatly reduced on the hat-shaped specimen. The dimple, however, has a width that is twice of that of the cylindrical specimen. There is a distinct shearing path of carbides. In contrast, the SCS has even fewer but much larger dimples, with the width of 1.6 μm, twice of the hat-shaped specimen, and the shearing path of carbides reaches 7 μm. Local melting occurs on both the hat-shaped specimen and SCS, especially the SCS, a massive melting is displayed. A long and narrow ASB was produced in the cylindrical specimen, and only strain-induced grain refinement occurred in the ASB, which belongs to the deformed ASB. Large patch of ASBs is generated in the hat-shaped specimen and SCS. The ASBs consist of equiaxed grains and belong to the transformed ASB as the phase transformation from martensite to austenite occurred. In particular, the equiaxed grains in the ASB of the SCS have very clear grain boundaries, which are typical dynamic recrystallization grains. It can conclude that the shape of the specimen has a great influence on the microscopic morphologies and microstructures of ASB. The cylindrical specimen is in a typical compressive stress state, while the hat-shaped specimen and SCS are in complicated stress dominated by shear. The temperature rise int the ASB of the cylindrical specimen is much lower than the austenite transformation temperature, while it is higher than the melting point of martensite in the hat-shaped specimen and SCS, leading to local melting and microstructural change.
2023, 43(4): 043201.
doi: 10.11883/bzycj-2022-0431
Abstract:
When the projectile passes through the gas-liquid interface, the sudden change of density may cause a violent impact load and do untold damage to it. It seriously affects the working effect of the projectile. In order to reduce the water entry load of the projectile, based on Rabbi’s idea of load reduction, a kind of structure of projectile with front body was proposed. The S-ALE (structured arbitrary Lagrange-Euler) algorithm and the fluid-structure coupling method with penalty function were used to simulate the shape of the cavitation wall and the projectile motion state, which is coincident by comparing with those of experiments. The validity of the numerical method is verified. Furthermore, the influence of the water entry angle of front body, the dimensionless water entry time interval parameter between main projectile and front body, the size of front body, the initial water entry velocity of main projectile and front body on impact load were researched by numerical simulation. The simulation results show that the front body will impact the main projectile when they both entering water vertically, which increases the impact load due to the collision of them. When the front body enters the water obliquely and the main projectile still enters the water vertically, the collision between main projectile and front body could be avoided and a good load reduction effect is obtained. The maximum load reduction ratio is up to 90%. The dimensionless time interval parameter range for obtaining a good load reduction effect is from 0.8 to 0.9. Within this range, variation laws of the water entry load of main projectile with the size of the front body and the initial velocity of entering water were discussed in detail. The effect of load reduction increases with the increase of the size of the front body and the initial water entry velocity.
When the projectile passes through the gas-liquid interface, the sudden change of density may cause a violent impact load and do untold damage to it. It seriously affects the working effect of the projectile. In order to reduce the water entry load of the projectile, based on Rabbi’s idea of load reduction, a kind of structure of projectile with front body was proposed. The S-ALE (structured arbitrary Lagrange-Euler) algorithm and the fluid-structure coupling method with penalty function were used to simulate the shape of the cavitation wall and the projectile motion state, which is coincident by comparing with those of experiments. The validity of the numerical method is verified. Furthermore, the influence of the water entry angle of front body, the dimensionless water entry time interval parameter between main projectile and front body, the size of front body, the initial water entry velocity of main projectile and front body on impact load were researched by numerical simulation. The simulation results show that the front body will impact the main projectile when they both entering water vertically, which increases the impact load due to the collision of them. When the front body enters the water obliquely and the main projectile still enters the water vertically, the collision between main projectile and front body could be avoided and a good load reduction effect is obtained. The maximum load reduction ratio is up to 90%. The dimensionless time interval parameter range for obtaining a good load reduction effect is from 0.8 to 0.9. Within this range, variation laws of the water entry load of main projectile with the size of the front body and the initial velocity of entering water were discussed in detail. The effect of load reduction increases with the increase of the size of the front body and the initial water entry velocity.
2023, 43(4): 044101.
doi: 10.11883/bzycj-2022-0210
Abstract:
When the conventional split Hopkinson pressure bar (SHPB) experimental method is used to realize large deformation of the specimen at a low strain rate, it is often necessary to employ an ultra-long compression bar system. However, the high cost of machining long bars and occupying large laboratory space limits the application and generalization of this technique. In this paper, a direct impact Hopkinson pressure bar double loading experimental technique is proposed. The stress wave in the transmission bar is reflected by the quasi-rigid wall at the end of the transmission bar to realize the double loading of the specimen. The influence of the size of the quasi-rigid mass on the double loading is further analyzed. The two-point wave separation method is used to separate and calculate the superimposed stress wave effectively, and the long duration loading of 1.2 ms is realized in the pressure bar system with a total length of 4 m, and the strain rate curve and stress-strain relationship of the specimen are obtained accurately. The finite element model of both direct-impact double loading and ultra-long Hopkinson bars are established. Numerical results indicate that this experimental technique can effectively achieve double loading of the specimen. Comparing the simulation results of direct-impact double loading Hopkinson bar with those of ultra-long Hopkinson bars, it is evident that the stress-strain relationships obtained by the two experimental devices are completely consistent. For direct-impact double loading Hopkinson bar, the stress-strain relationship calculated by the two-point wave separation technique is the same as that obtained by direct extraction method. Then, an experimental device of direct impact double-loading Hopkinson pressure bar has been set up, including a strike bar, a transmission bar and a rigid block. In addition, the dynamic compression experiment of aluminum alloy was carried out using this device, and the large deformation dynamic mechanical properties of aluminum alloy were tested under the strain rate of 102 s−1.
When the conventional split Hopkinson pressure bar (SHPB) experimental method is used to realize large deformation of the specimen at a low strain rate, it is often necessary to employ an ultra-long compression bar system. However, the high cost of machining long bars and occupying large laboratory space limits the application and generalization of this technique. In this paper, a direct impact Hopkinson pressure bar double loading experimental technique is proposed. The stress wave in the transmission bar is reflected by the quasi-rigid wall at the end of the transmission bar to realize the double loading of the specimen. The influence of the size of the quasi-rigid mass on the double loading is further analyzed. The two-point wave separation method is used to separate and calculate the superimposed stress wave effectively, and the long duration loading of 1.2 ms is realized in the pressure bar system with a total length of 4 m, and the strain rate curve and stress-strain relationship of the specimen are obtained accurately. The finite element model of both direct-impact double loading and ultra-long Hopkinson bars are established. Numerical results indicate that this experimental technique can effectively achieve double loading of the specimen. Comparing the simulation results of direct-impact double loading Hopkinson bar with those of ultra-long Hopkinson bars, it is evident that the stress-strain relationships obtained by the two experimental devices are completely consistent. For direct-impact double loading Hopkinson bar, the stress-strain relationship calculated by the two-point wave separation technique is the same as that obtained by direct extraction method. Then, an experimental device of direct impact double-loading Hopkinson pressure bar has been set up, including a strike bar, a transmission bar and a rigid block. In addition, the dynamic compression experiment of aluminum alloy was carried out using this device, and the large deformation dynamic mechanical properties of aluminum alloy were tested under the strain rate of 102 s−1.
2023, 43(4): 044201.
doi: 10.11883/bzycj-2022-0116
Abstract:
The calculation of the break of ship hull caused by underwater close-range non-contact explosion is a complex process, involving many factors such as the hull frame, weapon charge, explosion distance and orientation, etc., so empirical formulas are usually used in engineering design. If the ship is attacked by a directional warhead, it is usually assumed that the damage surface is approximately perpendicular to the damage axis, and the explosion process instantaneously meets the basic condition on approximate energy conservation, then the calculation method is proposed according to the assumption that the initial kinetic energy of the explosion shock wave is equally transmitted to the plastic deformation energy of the structure in the explosion action area. Considering the effect of the equivalent thickness of the hull shell-plate attached with stiffeners on the resistance to shock wave damage, and using the fundamental principle that cracking of the shell plate will take place when the ultimate strain of the hull plate under the action of explosion shock wave exceeds the dynamic ultimate strain of the plate, the calculation flow of the two-step iterative method is designed, and a simple and easy-to-use iterative calculation table is given. 768 sets of data are calculated for the damage of hull shell-plates with the typical thicknesses of 6 mm and 8 mm under the action of four typical charge equivalent shock waves, with an explosion distance within 11 m, acting on a compartment with 5-20 m span. By introducing the plane fitting equation, the applicability criterion of the calculation method is given by judging the similarity analysis of the section plane, and the valid range of the calculation parameters is discussed to ensure that the two-step iteration method can objectively reflect the actual damage effect of the underwater short-range non-contact explosion. Combined with the calculation results of empirical formulas and the measured data of damaged ships, the method is verified. The practice shows that the two-step iterative method is easy for engineering practice and has good accuracy.
The calculation of the break of ship hull caused by underwater close-range non-contact explosion is a complex process, involving many factors such as the hull frame, weapon charge, explosion distance and orientation, etc., so empirical formulas are usually used in engineering design. If the ship is attacked by a directional warhead, it is usually assumed that the damage surface is approximately perpendicular to the damage axis, and the explosion process instantaneously meets the basic condition on approximate energy conservation, then the calculation method is proposed according to the assumption that the initial kinetic energy of the explosion shock wave is equally transmitted to the plastic deformation energy of the structure in the explosion action area. Considering the effect of the equivalent thickness of the hull shell-plate attached with stiffeners on the resistance to shock wave damage, and using the fundamental principle that cracking of the shell plate will take place when the ultimate strain of the hull plate under the action of explosion shock wave exceeds the dynamic ultimate strain of the plate, the calculation flow of the two-step iterative method is designed, and a simple and easy-to-use iterative calculation table is given. 768 sets of data are calculated for the damage of hull shell-plates with the typical thicknesses of 6 mm and 8 mm under the action of four typical charge equivalent shock waves, with an explosion distance within 11 m, acting on a compartment with 5-20 m span. By introducing the plane fitting equation, the applicability criterion of the calculation method is given by judging the similarity analysis of the section plane, and the valid range of the calculation parameters is discussed to ensure that the two-step iteration method can objectively reflect the actual damage effect of the underwater short-range non-contact explosion. Combined with the calculation results of empirical formulas and the measured data of damaged ships, the method is verified. The practice shows that the two-step iterative method is easy for engineering practice and has good accuracy.
2023, 43(4): 044202.
doi: 10.11883/bzycj-2022-0222
Abstract:
The main challenge of numerical simulation of intense explosion is how to accurately determine the equations of state for the explosive products. The traditional equations of state are mostly empirical or semi-empirical formulas, which can just deal with ordinary explosions, but the treatment of intense explosions is of great limitation. The parameters of intense explosive products span an extremely wide range, which often exceeds the scope of empirical formula. Neural network has an excellent nonlinear fitting function and can realize the function of the equations of state. At the same time, there are a lot of state parameters of material in the sesame library, and the material parameters suitable for intense explosive products were selected as training data of neural network. The tabulated data of intensive explosive product samples were pretreated to make them better used in neural networks, then the data was adopted as training set to train the BP neural network and a one-dimensional spherical numerical code embedded with neural network equation of state was used to calculate the blast wave parameters of the explosion of fission device. In the process of neural network construction, the structure of neural network was optimized by enumeration experiment, and the structure of multi-layer neural network with a simple structure and good precision was obtained. In the process of numerical calculation, the code called the embedded neural network equations of state module, calculated the pressure of the explosive product through the density and the specific internal energy, and the flow field parameters of the whole explosive blast wave were finally obtained. The numerical results show that the calculated peak overpressure, arrival time and positive pressure duration coincide with the standard values, which proves the feasibility of the application of the neural network equation of states in the intense blast wave calculations. The results are of great significance to the numerical simulation of intense explosion.
The main challenge of numerical simulation of intense explosion is how to accurately determine the equations of state for the explosive products. The traditional equations of state are mostly empirical or semi-empirical formulas, which can just deal with ordinary explosions, but the treatment of intense explosions is of great limitation. The parameters of intense explosive products span an extremely wide range, which often exceeds the scope of empirical formula. Neural network has an excellent nonlinear fitting function and can realize the function of the equations of state. At the same time, there are a lot of state parameters of material in the sesame library, and the material parameters suitable for intense explosive products were selected as training data of neural network. The tabulated data of intensive explosive product samples were pretreated to make them better used in neural networks, then the data was adopted as training set to train the BP neural network and a one-dimensional spherical numerical code embedded with neural network equation of state was used to calculate the blast wave parameters of the explosion of fission device. In the process of neural network construction, the structure of neural network was optimized by enumeration experiment, and the structure of multi-layer neural network with a simple structure and good precision was obtained. In the process of numerical calculation, the code called the embedded neural network equations of state module, calculated the pressure of the explosive product through the density and the specific internal energy, and the flow field parameters of the whole explosive blast wave were finally obtained. The numerical results show that the calculated peak overpressure, arrival time and positive pressure duration coincide with the standard values, which proves the feasibility of the application of the neural network equation of states in the intense blast wave calculations. The results are of great significance to the numerical simulation of intense explosion.
2023, 43(4): 045101.
doi: 10.11883/bzycj-2022-0346
Abstract:
Accurately evaluating the damage and failure of concrete shield subjected to combination of penetration and explosion of warheads can provide an important reference for the design of protective structures. Firstly, based on the frame of Karagozian & Case (K&C) model, a newly dynamic-damage constitutive model was established. The hydrostatic pressure, Lode angle, strain rate, and damage were all considered in strength surface. The tension and compression damages were described separately with a continued transition. Besides, the contribution of shear deformation and hydrostatic compression were also considered. Then, the combined penetration and explosion test of 105-mm-caliber projectile on the semi-infinite concrete target was conducted. The corresponding numerical simulation was conducted to verify the accuracy of the constitutive model, the parameters, and the finite element analysis approach in describing the dynamic resistance of concrete. Furthermore, by conducting the numerical simulations of the existing prefabricated hole charge explosion test on the finite concrete plane, the accuracy of the established constitutive model, parameters, and finite element analysis approach in describing the damage evolution and cracking behavior of concrete was validated. Finally, the perforation limit and scabbing limit of normal strength concrete subjected to the combination of penetration and explosion of three typical warheads at sound velocity were determined. The results show that, the perforation limits of the SDB, WDU-43/B, and BLU-109/B warheads are 1.4, 3.4 and 3.8 m, respectively. The scabbing limit are 3.6, 6.3 and 8.3 m, respectively. Due to the differences of the explosive mass in warheads, the ratios of perforation limit and scabbing limit under combined penetration and explosion to the depth of penetration are not constant. The corresponding ratio ranges are 1.49−2.13 and 2.90−4.66, respectively.
Accurately evaluating the damage and failure of concrete shield subjected to combination of penetration and explosion of warheads can provide an important reference for the design of protective structures. Firstly, based on the frame of Karagozian & Case (K&C) model, a newly dynamic-damage constitutive model was established. The hydrostatic pressure, Lode angle, strain rate, and damage were all considered in strength surface. The tension and compression damages were described separately with a continued transition. Besides, the contribution of shear deformation and hydrostatic compression were also considered. Then, the combined penetration and explosion test of 105-mm-caliber projectile on the semi-infinite concrete target was conducted. The corresponding numerical simulation was conducted to verify the accuracy of the constitutive model, the parameters, and the finite element analysis approach in describing the dynamic resistance of concrete. Furthermore, by conducting the numerical simulations of the existing prefabricated hole charge explosion test on the finite concrete plane, the accuracy of the established constitutive model, parameters, and finite element analysis approach in describing the damage evolution and cracking behavior of concrete was validated. Finally, the perforation limit and scabbing limit of normal strength concrete subjected to the combination of penetration and explosion of three typical warheads at sound velocity were determined. The results show that, the perforation limits of the SDB, WDU-43/B, and BLU-109/B warheads are 1.4, 3.4 and 3.8 m, respectively. The scabbing limit are 3.6, 6.3 and 8.3 m, respectively. Due to the differences of the explosive mass in warheads, the ratios of perforation limit and scabbing limit under combined penetration and explosion to the depth of penetration are not constant. The corresponding ratio ranges are 1.49−2.13 and 2.90−4.66, respectively.
2023, 43(4): 045401.
doi: 10.11883/bzycj-2022-0120
Abstract:
In order to control and prevent the safety risks caused by volatile gases during the storage and transportation of crude oil, the explosion limit of the ternary flammable gas mixture composed of volatile light hydrocarbons including CH4, C3H8 and C2H4 in crude oil was experimentally investigated in a 20 L spherical explosive device. The experiment was carried out at 20 °C and 0.1 MPa, and the method of partial pressure was used to distribute the gases. Taking the rise of pressure over 5% as the criterion for explosion, each group of the experiments was repeated three times. Methods for predicting the explosion limit of the ternary flammable gas mixture based on Le Chatelier’s law and the model of one-dimensional laminar premixed flame in Chemkin are proposed, and the reliability of these two methods is verified by the experiment. The results show that the explosion limit of the ternary flammable gas mixture is always within the explosion limit of these three pure components, which tends to approach the explosion limit of a certain pure component with its increase. The influence of the three pure components on the upper explosion limit is more pronounced than on the lower explosion limit, and the effect of C2H4 on the upper explosion limit is particularly obvious compared with the other two pure components. Both methods of prediction are highly consistent with the experimental regularity. The prediction of the lower explosion limit by Le Chatelier’s law is relatively accurate. However, the deviation of the upper explosion limit increases with the raise of C2H4 due to its special characteristics of combustion, and the deviation decreases significantly after the correction of Le Chatelier’s law. Although the prediction of the lower explosion limit by Chemkin, which predicts the lower explosion limit by calculating the laminar burning velocity near the lower explosion limit, desplays a certain deviation, it is within the allowable range of experimental deviations. Therefore, it can be used as a new method to predict the lower explosion limit of the ternary flammable gas mixtures, but the model of one-dimensional laminar premixed flame is not suitable for the prediction on the upper explosion limit.
In order to control and prevent the safety risks caused by volatile gases during the storage and transportation of crude oil, the explosion limit of the ternary flammable gas mixture composed of volatile light hydrocarbons including CH4, C3H8 and C2H4 in crude oil was experimentally investigated in a 20 L spherical explosive device. The experiment was carried out at 20 °C and 0.1 MPa, and the method of partial pressure was used to distribute the gases. Taking the rise of pressure over 5% as the criterion for explosion, each group of the experiments was repeated three times. Methods for predicting the explosion limit of the ternary flammable gas mixture based on Le Chatelier’s law and the model of one-dimensional laminar premixed flame in Chemkin are proposed, and the reliability of these two methods is verified by the experiment. The results show that the explosion limit of the ternary flammable gas mixture is always within the explosion limit of these three pure components, which tends to approach the explosion limit of a certain pure component with its increase. The influence of the three pure components on the upper explosion limit is more pronounced than on the lower explosion limit, and the effect of C2H4 on the upper explosion limit is particularly obvious compared with the other two pure components. Both methods of prediction are highly consistent with the experimental regularity. The prediction of the lower explosion limit by Le Chatelier’s law is relatively accurate. However, the deviation of the upper explosion limit increases with the raise of C2H4 due to its special characteristics of combustion, and the deviation decreases significantly after the correction of Le Chatelier’s law. Although the prediction of the lower explosion limit by Chemkin, which predicts the lower explosion limit by calculating the laminar burning velocity near the lower explosion limit, desplays a certain deviation, it is within the allowable range of experimental deviations. Therefore, it can be used as a new method to predict the lower explosion limit of the ternary flammable gas mixtures, but the model of one-dimensional laminar premixed flame is not suitable for the prediction on the upper explosion limit.
2023, 43(4): 045402.
doi: 10.11883/bzycj-2022-0240
Abstract:
With the rapid development of air transportation, the safe usability of aviation fuel is extremely important. However, during the storage, transportation and use of aviation fuel, it is very easy to form steam because of its good fluidity and volatility. In case of leakage, it will quickly form a flammable mixture with the air in the cabin, and combustion and explosion accidents may occur in case of fire source, while the combustion and explosion parameters of aviation fuel may vary in different compartment structures. In order to understand and grasp the hazard of aviation fuel combustion and explosion in different structural cabins, a numerical simulation study on aviation fuel vapor combustion and explosion in various structural aviation fuel cabins is conducted by using CFD (computational fluid dynamics). The results show that when the premixed deflagration of aviation fuel vapor occurs in the closed aviation fuel cabin, the pressure changes are more uniform, the flame surface is spherical diffusion, and the combustion reaction mainly occurs on the flame surface. Under the conditions of this numerical simulation, the maximum combustion and explosion pressures of aviation fuel in the closed compartment without partition and the closed compartment with incomplete partition are 0.76 MPa and 0.74 MPa, respectively; that is, the special structures such as incomplete partition in the compartment have no significant effect on the maximum pressure generated by aviation fuel combustion and explosion. The existence of special structures such as diaphragms makes the air flow vortex in the cabin, increases the fuel consumption rate, and increases the propagation speed and pressure rise rate of the flame surface. The change of temperature distribution is highly consistent with the propagation process of the flame surface, while the combustion reaction mainly occurs on the flame surface. The mass fraction of fuel in the cabin is determined by the flame surface.
With the rapid development of air transportation, the safe usability of aviation fuel is extremely important. However, during the storage, transportation and use of aviation fuel, it is very easy to form steam because of its good fluidity and volatility. In case of leakage, it will quickly form a flammable mixture with the air in the cabin, and combustion and explosion accidents may occur in case of fire source, while the combustion and explosion parameters of aviation fuel may vary in different compartment structures. In order to understand and grasp the hazard of aviation fuel combustion and explosion in different structural cabins, a numerical simulation study on aviation fuel vapor combustion and explosion in various structural aviation fuel cabins is conducted by using CFD (computational fluid dynamics). The results show that when the premixed deflagration of aviation fuel vapor occurs in the closed aviation fuel cabin, the pressure changes are more uniform, the flame surface is spherical diffusion, and the combustion reaction mainly occurs on the flame surface. Under the conditions of this numerical simulation, the maximum combustion and explosion pressures of aviation fuel in the closed compartment without partition and the closed compartment with incomplete partition are 0.76 MPa and 0.74 MPa, respectively; that is, the special structures such as incomplete partition in the compartment have no significant effect on the maximum pressure generated by aviation fuel combustion and explosion. The existence of special structures such as diaphragms makes the air flow vortex in the cabin, increases the fuel consumption rate, and increases the propagation speed and pressure rise rate of the flame surface. The change of temperature distribution is highly consistent with the propagation process of the flame surface, while the combustion reaction mainly occurs on the flame surface. The mass fraction of fuel in the cabin is determined by the flame surface.
2023, 43(4): 045901.
doi: 10.11883/bzycj-2022-0224
Abstract:
Safety separation distance is one of the key concerns in the engineering construction and the study of hazards warehouses. In order to reduce the safety separation distance, a novel type of hazards warehouse is proposed based on the current codes and structural patterns of existing hazards warehouses. The novel warehouse is mainly composed of a shallow-buried main body, a reinforced concrete (RC) distribution slab and a heaped-up earth cover (HEC). Considering the variations of distribution slab and the strength of the main body, three scaled models of the novel hazards warehouse were built and internal explosion tests were carried out. The overpressure time histories of shock waves generated in the explosion tests were recorded and the distribution of blast debris around the warehouse were counted. According to the testing data and damage criteria of personnel subjected to shock waves, the safety separation distance of the novel hazards warehouse is plotted. Moreover, the effects of the RC distribution slab and the main body strength on shock wave propagation and debris distribution are analyzed. The results show that the novel hazards warehouse can bring about directional venting during internal explosions and effectively restrain the shock waves propagation and debris flying. The safety separation distance of shock waves has significantly directionality. Compared with the ground explosion, the safety separation distance of the novel hazards warehouse can be reduced up to 77% on both sides and the rear. In the rear direction, the safety separation distance of the novel hazards warehouse is only 50% of that of the earth-covered hazards warehouse. As the key component of the novel hazards warehouse, the RC distribution slab can reduce the safety separation distance by 30% in the rear direction. Compared with the corrugated steel main body, the RC main body can reduce the safety separation distance up to 38% in the rear direction.
Safety separation distance is one of the key concerns in the engineering construction and the study of hazards warehouses. In order to reduce the safety separation distance, a novel type of hazards warehouse is proposed based on the current codes and structural patterns of existing hazards warehouses. The novel warehouse is mainly composed of a shallow-buried main body, a reinforced concrete (RC) distribution slab and a heaped-up earth cover (HEC). Considering the variations of distribution slab and the strength of the main body, three scaled models of the novel hazards warehouse were built and internal explosion tests were carried out. The overpressure time histories of shock waves generated in the explosion tests were recorded and the distribution of blast debris around the warehouse were counted. According to the testing data and damage criteria of personnel subjected to shock waves, the safety separation distance of the novel hazards warehouse is plotted. Moreover, the effects of the RC distribution slab and the main body strength on shock wave propagation and debris distribution are analyzed. The results show that the novel hazards warehouse can bring about directional venting during internal explosions and effectively restrain the shock waves propagation and debris flying. The safety separation distance of shock waves has significantly directionality. Compared with the ground explosion, the safety separation distance of the novel hazards warehouse can be reduced up to 77% on both sides and the rear. In the rear direction, the safety separation distance of the novel hazards warehouse is only 50% of that of the earth-covered hazards warehouse. As the key component of the novel hazards warehouse, the RC distribution slab can reduce the safety separation distance by 30% in the rear direction. Compared with the corrugated steel main body, the RC main body can reduce the safety separation distance up to 38% in the rear direction.
