2017 Vol. 37, No. 3
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On ballistic trajectory of rigid projectile normal penetration based on a meso-scopic concrete model
2017, 37(3): 377-386.
doi: 10.11883/1001-1455(2017)03-0377-10
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Abstract:
To study the effect of the concrete's mesoscopic factors on the deflection of the rigid projectile's ballistic trajectory, we established a 3-D mesoscopic model for the concrete based on the idea of randomly distributed aggregates, analyzed the causes and possible contributing factors of the ballistic trajectory deflection of the rigid projectile penetrating into a concrete target, and examined quantitatively the influence of the mesoscopic factors of the concrete. The results show that the mesoscopic concrete model is able to reflect the typical physical phenomena of a projectile's normal penetration, that the mesoscopic factors have significant effect on the deflection of the ballistic trajectory as the rigid projectile is penetrating into the mesoscopic concrete, and that there exists a characteristic ratio of the projectile's diameter to the largest possible diameter of the aggregate.
To study the effect of the concrete's mesoscopic factors on the deflection of the rigid projectile's ballistic trajectory, we established a 3-D mesoscopic model for the concrete based on the idea of randomly distributed aggregates, analyzed the causes and possible contributing factors of the ballistic trajectory deflection of the rigid projectile penetrating into a concrete target, and examined quantitatively the influence of the mesoscopic factors of the concrete. The results show that the mesoscopic concrete model is able to reflect the typical physical phenomena of a projectile's normal penetration, that the mesoscopic factors have significant effect on the deflection of the ballistic trajectory as the rigid projectile is penetrating into the mesoscopic concrete, and that there exists a characteristic ratio of the projectile's diameter to the largest possible diameter of the aggregate.
2017, 37(3): 387-395.
doi: 10.11883/1001-1455(2017)03-0387-09
Abstract:
An analytical model is established to study the flexible crashworthy device which is developed independently in China. The model is composed of a distributed springs linking and supporting two hexagonal-shape box-beam structures that encircle the bridge pier. The governing equation together with adequate boundary conditions and initial conditions is deduced for the outer beam under dynamic impact loading. This governing equation is solved by the method of Laplace transform and the numerical inverse Laplace transform to get the dynamic response of the outer beam. The influence of the equivalent bending stiffness on the dynamic response of the outer beam is analyzed, and the critical equivalent bending stiffness is obtained. When the equivalent bending stiffness of the outer beam is more than the critical value, the beam can be considered as a rigid one under impact load.
An analytical model is established to study the flexible crashworthy device which is developed independently in China. The model is composed of a distributed springs linking and supporting two hexagonal-shape box-beam structures that encircle the bridge pier. The governing equation together with adequate boundary conditions and initial conditions is deduced for the outer beam under dynamic impact loading. This governing equation is solved by the method of Laplace transform and the numerical inverse Laplace transform to get the dynamic response of the outer beam. The influence of the equivalent bending stiffness on the dynamic response of the outer beam is analyzed, and the critical equivalent bending stiffness is obtained. When the equivalent bending stiffness of the outer beam is more than the critical value, the beam can be considered as a rigid one under impact load.
2017, 37(3): 396-404.
doi: 10.11883/1001-1455(2017)03-0396-09
Abstract:
The blast mitigation behavior of a density-graded cellular sacrificial cladding is investigated by using a nonlinear plastic shock model and a cell-based finite element model. Based on a rate-independent, rigid-plastic hardening idealization, a theoretical approach is applied to analyze the propagation of shock wave in density-graded cellular rods subjected to blast loading. The influences of the intensity of blast load, the cover mass and the density gradient parameter of the cellular material on the critical thickness, which is the minimum thickness of the core layer when the energy of explosion is fully absorbed, are investigated. A design guide of density-gradient is provided which considers the critical thickness of the cellular core as well as the peak stress at the support end. The validity of the anti-blast analysis of the graded cellular sacrificial cladding based on the nonlinear plastic shock model is verified by using cell-based finite element models.
The blast mitigation behavior of a density-graded cellular sacrificial cladding is investigated by using a nonlinear plastic shock model and a cell-based finite element model. Based on a rate-independent, rigid-plastic hardening idealization, a theoretical approach is applied to analyze the propagation of shock wave in density-graded cellular rods subjected to blast loading. The influences of the intensity of blast load, the cover mass and the density gradient parameter of the cellular material on the critical thickness, which is the minimum thickness of the core layer when the energy of explosion is fully absorbed, are investigated. A design guide of density-gradient is provided which considers the critical thickness of the cellular core as well as the peak stress at the support end. The validity of the anti-blast analysis of the graded cellular sacrificial cladding based on the nonlinear plastic shock model is verified by using cell-based finite element models.
2017, 37(3): 405-414.
doi: 10.11883/1001-1455(2017)03-0405-10
Abstract:
Experiments on reactive powder concrete-filled steel tube (RPC-FST) specimens after exposure to high temperature were performed by using a split Hopkinson pressure bar (SHPB) apparatus, and the influences of strain rate effects and temperature effects on the dynamic behaviors of RPC-FST were investigated. Test results show that the RPC-FST specimens after exposure to high temperature have excellent impact-resistance, ductility and integrity. The strain rate effects of the RPC-FST specimens are weaker than those of the RPC specimens under impact loading. The peak stress of the RPC-FST specimens increases as the temperature increases, and the deformation capability and impact-resistance increase. The dynamic increase factor (DIF) increases as the temperature increases. It means that the strain rate effects of RPC-FST become more obvious after exposure to high temperature.
Experiments on reactive powder concrete-filled steel tube (RPC-FST) specimens after exposure to high temperature were performed by using a split Hopkinson pressure bar (SHPB) apparatus, and the influences of strain rate effects and temperature effects on the dynamic behaviors of RPC-FST were investigated. Test results show that the RPC-FST specimens after exposure to high temperature have excellent impact-resistance, ductility and integrity. The strain rate effects of the RPC-FST specimens are weaker than those of the RPC specimens under impact loading. The peak stress of the RPC-FST specimens increases as the temperature increases, and the deformation capability and impact-resistance increase. The dynamic increase factor (DIF) increases as the temperature increases. It means that the strain rate effects of RPC-FST become more obvious after exposure to high temperature.
2017, 37(3): 415-421.
doi: 10.11883/1001-1455(2017)03-0415-07
Abstract:
In this work we used the laser velocity interferometry for measuring particle velocities and the wedge-shaped test explosive to study the structure of the chemical reaction zone of JBO-9021, a new insensitive high explosive (80 weight% TATB explosive, 15 weight% HMX explosive, 5 weight% binder). We conducted an experiment to achieve the in-situ particle velocity histories of a thin aluminium film between the test explosive and the LiF window that were introduced to obtain the particle velocities at different positions in the wedge-shaped test explosive after detonation. The CJ point of the particle velocity histories for JBO-9021 were derived from a second time derivative of the velocity history of particles from which we successfully obtained the chemical reaction structure, including the chemical reaction duration and the chemical reaction zone length. The results show that the chemical reaction duration of JBO-9021 is (238±13) ns and the chemical reaction zone length of JBO-9021 is about (1.52±0.09) mm. Additionally, they also show that the CJ point obtained from a second time derivative of the particle velocity histories is effective.
In this work we used the laser velocity interferometry for measuring particle velocities and the wedge-shaped test explosive to study the structure of the chemical reaction zone of JBO-9021, a new insensitive high explosive (80 weight% TATB explosive, 15 weight% HMX explosive, 5 weight% binder). We conducted an experiment to achieve the in-situ particle velocity histories of a thin aluminium film between the test explosive and the LiF window that were introduced to obtain the particle velocities at different positions in the wedge-shaped test explosive after detonation. The CJ point of the particle velocity histories for JBO-9021 were derived from a second time derivative of the velocity history of particles from which we successfully obtained the chemical reaction structure, including the chemical reaction duration and the chemical reaction zone length. The results show that the chemical reaction duration of JBO-9021 is (238±13) ns and the chemical reaction zone length of JBO-9021 is about (1.52±0.09) mm. Additionally, they also show that the CJ point obtained from a second time derivative of the particle velocity histories is effective.
2017, 37(3): 422-430.
doi: 10.11883/1001-1455(2017)03-0422-09
Abstract:
Magnetohydrodynamics equations are adopted to simulate the process of spherical heavy gas explosion. Meanwhile, in order to ensure the divergence of magnetic field is zero in each step, we use the CTU+CT algorithm which is derived by 12-solve CTU algorithm. The results clearly show the process of spherical heavy gas physical explosion with the influence of magnetic field. In the non-ideal case, the droplet-like structure appears on the interface of the gas cluster. With the gas cluster being compressed, the instabilities are being restrained in the end. As can be seen from the results, resistance and ambipolar diffusion effect will hinder the influence of magnetic field on gas cluster, at the same time, the ambipolar diffusion effect will increase the scope of the magnetic pressure.
Magnetohydrodynamics equations are adopted to simulate the process of spherical heavy gas explosion. Meanwhile, in order to ensure the divergence of magnetic field is zero in each step, we use the CTU+CT algorithm which is derived by 12-solve CTU algorithm. The results clearly show the process of spherical heavy gas physical explosion with the influence of magnetic field. In the non-ideal case, the droplet-like structure appears on the interface of the gas cluster. With the gas cluster being compressed, the instabilities are being restrained in the end. As can be seen from the results, resistance and ambipolar diffusion effect will hinder the influence of magnetic field on gas cluster, at the same time, the ambipolar diffusion effect will increase the scope of the magnetic pressure.
2017, 37(3): 431-438.
doi: 10.11883/1001-1455(2017)03-0431-08
Abstract:
Based on the Euler beam theory, the dynamic buckling of the functionally graded beam subjected to thermal shock was investigated in the Hamilton system. The material properties of the functionally graded beam were assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The transient temperature fields were solved analytically using the Laplace transform and power series method. It was shown that the dynamic buckling problem can be reduced to a zero-eigenvalue problem in the symplectic space, the buckling loading and the buckling mode of the FGM beam correspond to the generalized eigenvalue and eigen solution. The buckling mode and the buckling thermal axial forces can be obtained through bifurcation condition, and the buckling temperature rise of the FGM beam can be obtained by inverse solution. In this research, the solution process for dynamic buckling of the FGM beam subjected to thermal shock using the symplectic method were given, and the effects of the material constitution, geometric parameters and the parameters of thermal shock load on the critical temperature were discussed.
Based on the Euler beam theory, the dynamic buckling of the functionally graded beam subjected to thermal shock was investigated in the Hamilton system. The material properties of the functionally graded beam were assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The transient temperature fields were solved analytically using the Laplace transform and power series method. It was shown that the dynamic buckling problem can be reduced to a zero-eigenvalue problem in the symplectic space, the buckling loading and the buckling mode of the FGM beam correspond to the generalized eigenvalue and eigen solution. The buckling mode and the buckling thermal axial forces can be obtained through bifurcation condition, and the buckling temperature rise of the FGM beam can be obtained by inverse solution. In this research, the solution process for dynamic buckling of the FGM beam subjected to thermal shock using the symplectic method were given, and the effects of the material constitution, geometric parameters and the parameters of thermal shock load on the critical temperature were discussed.
2017, 37(3): 439-446.
doi: 10.11883/1001-1455(2017)03-0439-08
Abstract:
Experimental studies of the slender body's underwater movement were conducted using high-speed camera. Based on the results from the experiment, we examined the characteristics of the cavitation and ballistic of the slender body moving underwater. The experimental results show that the slender body's underwater movement is accompanied with a supercavity, and the slender body's movement and rotation occur in the supercavity except for the contact between the slender body's head and the supercavity wall and the supercavity wall is transparent and smooth except for its tail. The impact between the tail of the slender body and the supercavity wall results from the slender body's rotation in the supercavity, called the tail slap, which serves to stabilize the slender body's movement in the supercavity as a result form the initial perturbation of the flow field. The cavity evolution, closure and shedding were discussed in detail. Series of different flow mechanisms and the relationship between ballistic characteristics and cavity morphology were also analyzed with different initial velocities. The slender body has different accelerations with different initial velocities and the effect of the drag reduction using super cavitation is influenced by factors such as cavity length, diameter and aspect ratio, etc. The initial perturbation angle affects the variation of the angle between the slender body and the cavity axis.
Experimental studies of the slender body's underwater movement were conducted using high-speed camera. Based on the results from the experiment, we examined the characteristics of the cavitation and ballistic of the slender body moving underwater. The experimental results show that the slender body's underwater movement is accompanied with a supercavity, and the slender body's movement and rotation occur in the supercavity except for the contact between the slender body's head and the supercavity wall and the supercavity wall is transparent and smooth except for its tail. The impact between the tail of the slender body and the supercavity wall results from the slender body's rotation in the supercavity, called the tail slap, which serves to stabilize the slender body's movement in the supercavity as a result form the initial perturbation of the flow field. The cavity evolution, closure and shedding were discussed in detail. Series of different flow mechanisms and the relationship between ballistic characteristics and cavity morphology were also analyzed with different initial velocities. The slender body has different accelerations with different initial velocities and the effect of the drag reduction using super cavitation is influenced by factors such as cavity length, diameter and aspect ratio, etc. The initial perturbation angle affects the variation of the angle between the slender body and the cavity axis.
2017, 37(3): 447-452.
doi: 10.11883/1001-1455(2017)03-0447-06
Abstract:
An experimental circular pipeline with a length of 2 800 mm and a diameter of 50 mm was established to study the gaseous detonation propagation. Photodiode detectors were used to obtain the flame propagation velocity and the smoke film method to get the cellular structures. Polypropylene films with the blocking rate of 1.0 were set in the pipeline to investigate the characteristics of detonation velocity and cellular structures. Gaseous mixtures of C2H2+ 2.5O2 diluted by argon in different volumes were used as experimental medium. The initial pressures varied in experiments. Results show that there are two different propagation forms after the detonation wave passes through the film obstacles, including velocity deficit and detonation failure. The propagation of gaseous detonation wave in blocked obstructions can be divided into three stages: stage of steady propagation, stage of velocity deficit or detonation failure and stage of overdriven detonation.
An experimental circular pipeline with a length of 2 800 mm and a diameter of 50 mm was established to study the gaseous detonation propagation. Photodiode detectors were used to obtain the flame propagation velocity and the smoke film method to get the cellular structures. Polypropylene films with the blocking rate of 1.0 were set in the pipeline to investigate the characteristics of detonation velocity and cellular structures. Gaseous mixtures of C2H2+ 2.5O2 diluted by argon in different volumes were used as experimental medium. The initial pressures varied in experiments. Results show that there are two different propagation forms after the detonation wave passes through the film obstacles, including velocity deficit and detonation failure. The propagation of gaseous detonation wave in blocked obstructions can be divided into three stages: stage of steady propagation, stage of velocity deficit or detonation failure and stage of overdriven detonation.
2017, 37(3): 453-458.
doi: 10.11883/1001-1455(2017)03-0453-06
Abstract:
In order to study the influence of initial conditions on methane-air mixtures explosion limits, the explosion limits of methane-air mixtures were obtained experimentally at different initial temperatures up to 200 ℃ and initial pressures up to 1.0 MPa. The experiments were performed in a closed spherical 20 dm3 vessel with an ignition electrode at the center. The results show that with the increasing of initial temperature and initial pressure, the upper explosion limit increases, but the lower explosion limit decreases, that is the explosion limit expands. At atmospheric pressure/ambient temperature, the dependences of the upper explosion limit and lower explosion limit on initial temperature and initial pressure are both linear in the experimental temperature-pressure ranges. The dependence of the upper explosion limit on initial temperature/initial pressure is influenced by the initial pressure/initial temperature, but the dependence of the lower explosion limit on those is not influenced obviously. The coupling effects of initial temperature and initial pressure on the upper explosion limit and lower explosion limit are greater than that of a single factor, especially on the upper explosion limit. Surfaces are formed to describe how the initial temperature and initial pressure influence the upper explosion limit and the lower explosion limit of methane-air mixtures.
In order to study the influence of initial conditions on methane-air mixtures explosion limits, the explosion limits of methane-air mixtures were obtained experimentally at different initial temperatures up to 200 ℃ and initial pressures up to 1.0 MPa. The experiments were performed in a closed spherical 20 dm3 vessel with an ignition electrode at the center. The results show that with the increasing of initial temperature and initial pressure, the upper explosion limit increases, but the lower explosion limit decreases, that is the explosion limit expands. At atmospheric pressure/ambient temperature, the dependences of the upper explosion limit and lower explosion limit on initial temperature and initial pressure are both linear in the experimental temperature-pressure ranges. The dependence of the upper explosion limit on initial temperature/initial pressure is influenced by the initial pressure/initial temperature, but the dependence of the lower explosion limit on those is not influenced obviously. The coupling effects of initial temperature and initial pressure on the upper explosion limit and lower explosion limit are greater than that of a single factor, especially on the upper explosion limit. Surfaces are formed to describe how the initial temperature and initial pressure influence the upper explosion limit and the lower explosion limit of methane-air mixtures.
2017, 37(3): 459-463.
doi: 10.11883/1001-1455(2017)03-0459-05
Abstract:
The γ→α phase transition of 99.8% purity cerium was investigated using the passive confined split Hopkinson pressure bar experiment under a hydrostatic pressure up to 1.7GPa and at room temperature, the relationship of the hydrostatic pressure with the volume strain covering the whole process of γ↔α phase transformation was obtained, and the hysteresis loop was observed. The results show that the γ→α phase transition is the first-order with hysteresis rather than the first-order with volume discontinuity as recognized in previous researches. The γ →α phase transition occurs under the hydrostatic pressure ranging from 0.8 GPa to 1.3 GPa, whereas the inverse phase transition occurs under the hydrostatic pressure ranging from 1.1 to 0.6 GPa. The hysteresis loop shows a gap of 0.15 GPa hydrostatic pressure between the curve of hydrostatic pressure and volume strain during the γ→α phase transition and that during the inverse phase transition. The curves of the hydrostatic pressure and volume strain during the γ↔α phase transition were linear with the bulk modulus of 4.2 GPa. The mechanism behind the γ↔α phase transition is that the hydrostatic pressure drives the conversion between the phases of γ and α, which coexist during the γ↔α phase transition. Based on the mechanism of phase transition, a tri-segment linear model was constituted to describe the response of the hydrostatic pressure and volume strain in the process of γ→α phase transition. The modeled curve is found to be in good agree with the experimental curve.
The γ→α phase transition of 99.8% purity cerium was investigated using the passive confined split Hopkinson pressure bar experiment under a hydrostatic pressure up to 1.7GPa and at room temperature, the relationship of the hydrostatic pressure with the volume strain covering the whole process of γ↔α phase transformation was obtained, and the hysteresis loop was observed. The results show that the γ→α phase transition is the first-order with hysteresis rather than the first-order with volume discontinuity as recognized in previous researches. The γ →α phase transition occurs under the hydrostatic pressure ranging from 0.8 GPa to 1.3 GPa, whereas the inverse phase transition occurs under the hydrostatic pressure ranging from 1.1 to 0.6 GPa. The hysteresis loop shows a gap of 0.15 GPa hydrostatic pressure between the curve of hydrostatic pressure and volume strain during the γ→α phase transition and that during the inverse phase transition. The curves of the hydrostatic pressure and volume strain during the γ↔α phase transition were linear with the bulk modulus of 4.2 GPa. The mechanism behind the γ↔α phase transition is that the hydrostatic pressure drives the conversion between the phases of γ and α, which coexist during the γ↔α phase transition. Based on the mechanism of phase transition, a tri-segment linear model was constituted to describe the response of the hydrostatic pressure and volume strain in the process of γ→α phase transition. The modeled curve is found to be in good agree with the experimental curve.
2017, 37(3): 464-470.
doi: 10.11883/1001-1455(2017)03-0464-07
Abstract:
The dynamic anti-plane behavior of the radial inhomogeneous piezoelectric medium with a circular cavity under the SH-wave was investigated using the complex function theory. It was assumed that the density of the piezoelectric medium varied as a power-law function on the radial distance but the elastic parameters, the piezoelectric parameters, and the dielectric parameters all remained as constants. The wave equations of the inhomogeneous piezoelectric medium were converted to the standard Helmholtz equations by variable substitution and the analytical expression of the wave function satisfying the boundary condition was obtained. The influence of the incident angle, the frequency of incident wave and the power of the power-law function, etc. on the dynamic stress concentration factor and electric field intensity concentration factor was analyzed and compared with the existing references in the calculated example. The numerical results show that the values of the dynamic stress concentration factor and the electric field intensity concentration factor increase as the power increases with combination of certain parameters.
The dynamic anti-plane behavior of the radial inhomogeneous piezoelectric medium with a circular cavity under the SH-wave was investigated using the complex function theory. It was assumed that the density of the piezoelectric medium varied as a power-law function on the radial distance but the elastic parameters, the piezoelectric parameters, and the dielectric parameters all remained as constants. The wave equations of the inhomogeneous piezoelectric medium were converted to the standard Helmholtz equations by variable substitution and the analytical expression of the wave function satisfying the boundary condition was obtained. The influence of the incident angle, the frequency of incident wave and the power of the power-law function, etc. on the dynamic stress concentration factor and electric field intensity concentration factor was analyzed and compared with the existing references in the calculated example. The numerical results show that the values of the dynamic stress concentration factor and the electric field intensity concentration factor increase as the power increases with combination of certain parameters.
2017, 37(3): 471-478.
doi: 10.11883/1001-1455(2017)03-0471-08
Abstract:
Research on the longitudinal impact compression of an aluminum alloy ring found that an obvious stress-drop process will appear in the macro plastic hardening stage of the specimen under certain conditions. In order to reveal the mechanism of this stress-drop process, we conducted the longitudinal impact compression experiment on LY12 aluminum alloy ring specimens whose ratio of OD, ID and height was 6:3:2 using the split Hopkinson pressure bar (SHPB) under the three end face roughness conditions: lubrication, fine grinding and rough grinding. The experiment results show that the stress-drop process occurs mainly in the large strain and high strain rate loading conditions. Moreover, the results of the metallurgical analysis of the aluminum alloy ring specimens show that the formation and development of the adiabatic shear band is the intrinsic mechanism of the stress-drop process, which is a dynamic plastic instability. This study can serve as a reference for the study of the heat insulation shear band in metal materials under impact.
Research on the longitudinal impact compression of an aluminum alloy ring found that an obvious stress-drop process will appear in the macro plastic hardening stage of the specimen under certain conditions. In order to reveal the mechanism of this stress-drop process, we conducted the longitudinal impact compression experiment on LY12 aluminum alloy ring specimens whose ratio of OD, ID and height was 6:3:2 using the split Hopkinson pressure bar (SHPB) under the three end face roughness conditions: lubrication, fine grinding and rough grinding. The experiment results show that the stress-drop process occurs mainly in the large strain and high strain rate loading conditions. Moreover, the results of the metallurgical analysis of the aluminum alloy ring specimens show that the formation and development of the adiabatic shear band is the intrinsic mechanism of the stress-drop process, which is a dynamic plastic instability. This study can serve as a reference for the study of the heat insulation shear band in metal materials under impact.
2017, 37(3): 479-486.
doi: 10.11883/1001-1455(2017)03-0479-08
Abstract:
Added into the drilling fluid in a volume portion of 1% to 3%, particles are capable of striking the rock with a high velocity after erupting from the bit nozzle and breaking the rock by particle impact combined with the mechanical action of the bit nozzle, thus greatly increasing the rock breaking efficiency. Using the transient nonlinear dynamics finite element simulation software and considering the influence of water jet, we established the physical model of rock breaking by particle impact based on the smoothed particle hydrodynamics (SPH) method, investigated the influence of the particle jet's parameters on the rock breaking volume, and verified the simulation results by comparing them with those of the indoors experiment which could verify the effectiveness of the SPH simulation method. Our results show that a regulation V-shaped crater is formed by the particle jet impact; the rock breaking volume resulting from this particle jet impact is 2 to 4 times that of the volume from the water jet under identical conditions. The rock breaking volume increases over time, but in the meantime the rock breaking efficiency decreases. When the pressure of the particle jet is above 10 MPa, there is a great increase of the rock breaking efficiency. When the jet angle is above 6°, there is a quick decrease of the rock breaking efficiency.
Added into the drilling fluid in a volume portion of 1% to 3%, particles are capable of striking the rock with a high velocity after erupting from the bit nozzle and breaking the rock by particle impact combined with the mechanical action of the bit nozzle, thus greatly increasing the rock breaking efficiency. Using the transient nonlinear dynamics finite element simulation software and considering the influence of water jet, we established the physical model of rock breaking by particle impact based on the smoothed particle hydrodynamics (SPH) method, investigated the influence of the particle jet's parameters on the rock breaking volume, and verified the simulation results by comparing them with those of the indoors experiment which could verify the effectiveness of the SPH simulation method. Our results show that a regulation V-shaped crater is formed by the particle jet impact; the rock breaking volume resulting from this particle jet impact is 2 to 4 times that of the volume from the water jet under identical conditions. The rock breaking volume increases over time, but in the meantime the rock breaking efficiency decreases. When the pressure of the particle jet is above 10 MPa, there is a great increase of the rock breaking efficiency. When the jet angle is above 6°, there is a quick decrease of the rock breaking efficiency.
2017, 37(3): 487-495.
doi: 10.11883/1001-1455(2017)03-0487-09
Abstract:
Intensive shock loading can lead to obvious stress concentration at the corner of a doorframe and jeopardize the safety of a doorframe wall and even the whole protective structure where it is installed. To solve this problem, we proposed to install a weak layer between the doorframe and the lining to reduce the excessive tensile stress, based on the cantilever beam theory that takes into account the shear deformation. The results show that, as the constraint stiffness of the beam end can influence the structure's failure mode and distribution of the internal force, lowering the constraint stiffness of the beam end can reduce the peak value of the internal force and delay the failure time of the structure. Using the finite element method, we analyzed the influence of the weak layer on the dynamic response and the failure mode of the doorframe. The results show that the weak layer can effectively reduce the stress of the doorframe's corner and the damaging effect of the doorframe wall structure so that the resistance of the doorframe can be improved.
Intensive shock loading can lead to obvious stress concentration at the corner of a doorframe and jeopardize the safety of a doorframe wall and even the whole protective structure where it is installed. To solve this problem, we proposed to install a weak layer between the doorframe and the lining to reduce the excessive tensile stress, based on the cantilever beam theory that takes into account the shear deformation. The results show that, as the constraint stiffness of the beam end can influence the structure's failure mode and distribution of the internal force, lowering the constraint stiffness of the beam end can reduce the peak value of the internal force and delay the failure time of the structure. Using the finite element method, we analyzed the influence of the weak layer on the dynamic response and the failure mode of the doorframe. The results show that the weak layer can effectively reduce the stress of the doorframe's corner and the damaging effect of the doorframe wall structure so that the resistance of the doorframe can be improved.
2017, 37(3): 496-501.
doi: 10.11883/1001-1455(2017)03-0496-06
Abstract:
A 20-liter nearly-spherical container was employed to examine the influence of initial ignition energy, ignition delay time and zirconium dust concentration on the characteristics of zirconium dust cloud explosion. The experimental results indicate that the maximum explosion pressure of zirconium dust cloud increases as the initial ignition energy increases, however, with the increase of ignition delay time, the maximum explosion pressure of the dust cloud increases at first and decreases thereafter. At the same time, there exists an optimal ignition delay time. In addition, with the increase of dust concentration, the maxmum explosion pressure of the dust cloud increases at first and decreases thereafter as well. Finally, there exists an optimal dust concentration, and the lower explosion limit of zirconium dust cloud is 18 to 20 g/m3.
A 20-liter nearly-spherical container was employed to examine the influence of initial ignition energy, ignition delay time and zirconium dust concentration on the characteristics of zirconium dust cloud explosion. The experimental results indicate that the maximum explosion pressure of zirconium dust cloud increases as the initial ignition energy increases, however, with the increase of ignition delay time, the maximum explosion pressure of the dust cloud increases at first and decreases thereafter. At the same time, there exists an optimal ignition delay time. In addition, with the increase of dust concentration, the maxmum explosion pressure of the dust cloud increases at first and decreases thereafter as well. Finally, there exists an optimal dust concentration, and the lower explosion limit of zirconium dust cloud is 18 to 20 g/m3.
2017, 37(3): 502-509.
doi: 10.11883/1001-1455(2017)03-0502-08
Abstract:
In view of the underground powerhouse excavation work by blasting at the Baihetan Hydropower Station Project, in order to reduce the blasting-involved damage to the rock mass, numerical simulation and field test were carried out to analyze the influence of the initiation delay time and the distance between later detonated holes on the blasting and the cracking with time sequence controlled pre-splitting blasting, and the reasonable delay time and the optimum distance between post-detonated holes were obtained. The results show that when the hole diameter is 42 mm and the distance between the pre-detonated holes is 35 cm, the reasonable initiation delay time is 75~100 μs, and the optimum distance between the post-detonated holes is 70cm, with joint consideration of the blasting energy's utilization ratio and blasting effect. It is found that time sequence controlled pre-splitting blasting, used scientifically, is a safe and efficient method to excavate the rock mass close to the underground powerhouse wall, which can reduce the load of blasting, cut down on the explosives used, and limit the blasting-involved damage to rock mass.
In view of the underground powerhouse excavation work by blasting at the Baihetan Hydropower Station Project, in order to reduce the blasting-involved damage to the rock mass, numerical simulation and field test were carried out to analyze the influence of the initiation delay time and the distance between later detonated holes on the blasting and the cracking with time sequence controlled pre-splitting blasting, and the reasonable delay time and the optimum distance between post-detonated holes were obtained. The results show that when the hole diameter is 42 mm and the distance between the pre-detonated holes is 35 cm, the reasonable initiation delay time is 75~100 μs, and the optimum distance between the post-detonated holes is 70cm, with joint consideration of the blasting energy's utilization ratio and blasting effect. It is found that time sequence controlled pre-splitting blasting, used scientifically, is a safe and efficient method to excavate the rock mass close to the underground powerhouse wall, which can reduce the load of blasting, cut down on the explosives used, and limit the blasting-involved damage to rock mass.
2017, 37(3): 510-519.
doi: 10.11883/1001-1455(2017)03-0510-10
Abstract:
To study the mechanism behind the penetration resistance capability of the ceramic/fluid cabin composite structure, numerical simulation was carried out using LS-DYNA to represent the structure's failure process and modes under the impact of the projectile, and results were obtained that agree well with those from the experiment. The results show that the shockwave generated at the impact point of the structure propagated forward spherically, and bounced and oscillated back and forth in the structure. Cavity was generated in the water and constantly grew, and there was an area of high pressure in front of the projectile when the projectile was moving in the water. The projectile mainly exhibited coarse and erosive damage, and the damage mainly occurred in the process of the projectile penetrating the ceramic and the front plate at low velocities and in the water at high velocities, eventually forming approximately bake-shaped serious deformation. The front and back plates mainly suffered local failure and overall deformation, while petal-shaped cracking occurred in the back plate under high-velocity impact.
To study the mechanism behind the penetration resistance capability of the ceramic/fluid cabin composite structure, numerical simulation was carried out using LS-DYNA to represent the structure's failure process and modes under the impact of the projectile, and results were obtained that agree well with those from the experiment. The results show that the shockwave generated at the impact point of the structure propagated forward spherically, and bounced and oscillated back and forth in the structure. Cavity was generated in the water and constantly grew, and there was an area of high pressure in front of the projectile when the projectile was moving in the water. The projectile mainly exhibited coarse and erosive damage, and the damage mainly occurred in the process of the projectile penetrating the ceramic and the front plate at low velocities and in the water at high velocities, eventually forming approximately bake-shaped serious deformation. The front and back plates mainly suffered local failure and overall deformation, while petal-shaped cracking occurred in the back plate under high-velocity impact.
2017, 37(3): 520-527.
doi: 10.11883/1001-1455(2017)03-0520-08
Abstract:
The behavior of one-dimensional elastic waves at a unilateral frictional contact piezoelectric material interface was studied theoretically in this thesis. When the incident wave is strong enough, the contact interface will separate or slip in local interface areas and non-linearity (boundary non-linearity) will pose as a serious problem, and high harmonics will be generated due to this non-linearity, thus not only causing difficulties in mathematics but giving rise to some new phenomena in physics. In this paper one-dimensional problems were discussed in details using the Fourier analysis, and the mix-boundary value problems with unknown regions were converted to a set of non-linear algebraic equations for a one-dimensional case. An iterative method was developed to determine the extent and location of the separation, slip and stick regions which vary with the external mechanical-electrical loads. The interface tractions, relative slip velocities and the amplitudes of the reflected and refracted high harmonics due to the boundary non-linearity were calculated. Their variation with the applied mechanical-electrical loads was discussed. It was found that, due to the mechanical-electrical coupling, the non-linearity of mechanical parameters would induce the non-linearity of electrical parameters, and the applied electrical fields would influence the interface states by changing the mechanical loads. The present research may enrich the wave theory of piezoelectricity and facilitate its practical application. For instance, we could evaluate the contact state and modulate an interface by detecting the mechanical or electrical information carried by high harmonics.
The behavior of one-dimensional elastic waves at a unilateral frictional contact piezoelectric material interface was studied theoretically in this thesis. When the incident wave is strong enough, the contact interface will separate or slip in local interface areas and non-linearity (boundary non-linearity) will pose as a serious problem, and high harmonics will be generated due to this non-linearity, thus not only causing difficulties in mathematics but giving rise to some new phenomena in physics. In this paper one-dimensional problems were discussed in details using the Fourier analysis, and the mix-boundary value problems with unknown regions were converted to a set of non-linear algebraic equations for a one-dimensional case. An iterative method was developed to determine the extent and location of the separation, slip and stick regions which vary with the external mechanical-electrical loads. The interface tractions, relative slip velocities and the amplitudes of the reflected and refracted high harmonics due to the boundary non-linearity were calculated. Their variation with the applied mechanical-electrical loads was discussed. It was found that, due to the mechanical-electrical coupling, the non-linearity of mechanical parameters would induce the non-linearity of electrical parameters, and the applied electrical fields would influence the interface states by changing the mechanical loads. The present research may enrich the wave theory of piezoelectricity and facilitate its practical application. For instance, we could evaluate the contact state and modulate an interface by detecting the mechanical or electrical information carried by high harmonics.
2017, 37(3): 528-535.
doi: 10.11883/1001-1455(2017)03-0528-08
Abstract:
In order to improve the large deformation problem within the Lagrangian domain, a CEL method with the capability of mapping Lagrangian materials to the Eulerian domain was presented. The contact problem in the Eulerian-Lagrangian overlapping region was converted to the multi-materials problem in the Eulerian region. The construction of the CEL method was also simplified. The method was verified by the calculation of two experiments (a steel bullet impacting an aluminous plate experiment and a structure response to the blast wave experiment). It is found that the numerical results agree well with the experimental data.
In order to improve the large deformation problem within the Lagrangian domain, a CEL method with the capability of mapping Lagrangian materials to the Eulerian domain was presented. The contact problem in the Eulerian-Lagrangian overlapping region was converted to the multi-materials problem in the Eulerian region. The construction of the CEL method was also simplified. The method was verified by the calculation of two experiments (a steel bullet impacting an aluminous plate experiment and a structure response to the blast wave experiment). It is found that the numerical results agree well with the experimental data.
Experimental study and numerical simulation of projectile obliquely penetrating into concrete target
2017, 37(3): 536-543.
doi: 10.11883/1001-1455(2017)03-0536-08
Abstract:
The ballistic characteristics of the projectile obliquely penetrating into the concrete target were investigated, with such data as the penetration depth, crater depth and diameter, deflection angle obtained via the experiments and simulation calculation. The results from simulation agree well with those from the experiments. The results show that the oblique angle has great influence on the crater zone. The greater the oblique angle, the greater the projectile's deflection; the greater the impact velocity, the less the influence of the ballistic deflection angle; and the ricochet occurs when the oblique angle increases to a certain degree. Thus the relationship was identified between the ricochet angle and the oblique angle and the penetration velocity.
The ballistic characteristics of the projectile obliquely penetrating into the concrete target were investigated, with such data as the penetration depth, crater depth and diameter, deflection angle obtained via the experiments and simulation calculation. The results from simulation agree well with those from the experiments. The results show that the oblique angle has great influence on the crater zone. The greater the oblique angle, the greater the projectile's deflection; the greater the impact velocity, the less the influence of the ballistic deflection angle; and the ricochet occurs when the oblique angle increases to a certain degree. Thus the relationship was identified between the ricochet angle and the oblique angle and the penetration velocity.
2017, 37(3): 544-548.
doi: 10.11883/1001-1455(2017)03-0544-05
Abstract:
The Mach reflection occurs when two high-detonation-velocity detonating cords are arranged symmetrically on both sides of the cartridge. After the detonation the explosive's detonation waves converge and collide along the line of symmetry, multiplying the detonation pressure and forming a Munroe effect region with high pressure and high energy density when the collision angle reaches a certain value. In this paper, explosive-determination of power and brisance tests were conducted based on the theory of detonation wave collision and reflection. The results from the test of the explosive-determination of power show that the detonation wave collision can improve the efficiency of the explosive energy utilization, and those from the test of the brisance show that the symmetrical initiation of the detonation can change its distribution in a particular direction. The geometrical relationship of the experimental results with the incidence angle of the detonation wave shows that, when the initiating explosive velocity is above 1.15 times that of the main charge, the detonation wave collision will produce a certain degree of Munroe effect.
The Mach reflection occurs when two high-detonation-velocity detonating cords are arranged symmetrically on both sides of the cartridge. After the detonation the explosive's detonation waves converge and collide along the line of symmetry, multiplying the detonation pressure and forming a Munroe effect region with high pressure and high energy density when the collision angle reaches a certain value. In this paper, explosive-determination of power and brisance tests were conducted based on the theory of detonation wave collision and reflection. The results from the test of the explosive-determination of power show that the detonation wave collision can improve the efficiency of the explosive energy utilization, and those from the test of the brisance show that the symmetrical initiation of the detonation can change its distribution in a particular direction. The geometrical relationship of the experimental results with the incidence angle of the detonation wave shows that, when the initiating explosive velocity is above 1.15 times that of the main charge, the detonation wave collision will produce a certain degree of Munroe effect.
2017, 37(3): 549-553.
doi: 10.11883/1001-1455(2017)03-0549-05
Abstract:
A radiation hydrodynamics model was established to analyse the pulse irradiation characteristic of thermal radiation in intense explosion and its dependence on explosion yield. Based on the splitting method, the temperature gradient was set as the indicator for the dynamic regional division to achieve highly efficient parallel calculation, on the basis of which the thermal radiation evolutions in intense explosion at different yields were calculated. The results show that the intensity of thermal radiation at different times exhibits a two-pulse pattern. The intensity extremums and extremum times vary with the change of the explosion yields. The minimum time and second maximum time of the thermal radiation are proportional to the power of the explosion yields. The radiant power history exhibits similar results with the thermal radiation intensity. However, the extremum times may differ due to the dependence of the fireball radius on the explosion yield.
A radiation hydrodynamics model was established to analyse the pulse irradiation characteristic of thermal radiation in intense explosion and its dependence on explosion yield. Based on the splitting method, the temperature gradient was set as the indicator for the dynamic regional division to achieve highly efficient parallel calculation, on the basis of which the thermal radiation evolutions in intense explosion at different yields were calculated. The results show that the intensity of thermal radiation at different times exhibits a two-pulse pattern. The intensity extremums and extremum times vary with the change of the explosion yields. The minimum time and second maximum time of the thermal radiation are proportional to the power of the explosion yields. The radiant power history exhibits similar results with the thermal radiation intensity. However, the extremum times may differ due to the dependence of the fireball radius on the explosion yield.
2017, 37(3): 554-559.
doi: 10.11883/1001-1455(2017)03-0554-06
Abstract:
A failure criterion considering multiaxial stress state was proposed based on the thin plate damage testing. According to the evaluation of the stress state variation and damage level of the cracking and non-cracking areas, the following conclusions can be reached: (1) the petaling phenomenon of the thin plate used for naval ships can be forecasted effectively by the proposed failure criterion; (2) the petaling procedure can be divided into three distinct stages consisting of butterfly depressing, central area cracking, and petal processing; (3) the stress states of the cracking area and the non-cracking area are complicated, and the stress state's influence on the damage characteristics should be considered in predicting the petaling crevasse; (4) during the petaling, the central area will sink homogeneously, the cracking will result in large local deformation, and the petal cusps' curve will lead to a secondary damage to the petal roots.
A failure criterion considering multiaxial stress state was proposed based on the thin plate damage testing. According to the evaluation of the stress state variation and damage level of the cracking and non-cracking areas, the following conclusions can be reached: (1) the petaling phenomenon of the thin plate used for naval ships can be forecasted effectively by the proposed failure criterion; (2) the petaling procedure can be divided into three distinct stages consisting of butterfly depressing, central area cracking, and petal processing; (3) the stress states of the cracking area and the non-cracking area are complicated, and the stress state's influence on the damage characteristics should be considered in predicting the petaling crevasse; (4) during the petaling, the central area will sink homogeneously, the cracking will result in large local deformation, and the petal cusps' curve will lead to a secondary damage to the petal roots.
2017, 37(3): 560-565.
doi: 10.11883/1001-1455(2017)03-0560-06
Abstract:
An explosive diode was designed according to the principle of explosive logic components. This paper studied thorough experiment of the internal structure of the components to identify the length of extinction channel and flame-proof structure as key parameters. The flame-proof structure adopted the layered charges of different density including an excitation device, 1st charge of PETN, 2nd charge of PETN. Connecting the A-end and B-end to the detonating cord, changing the size of the extinction channel, ensuring the parameter of the layered charge to conduct the experiment of detonation reliability and explosion-proof safety, the results show that the detonation signal can detonate the B-end detonating cord, satisfying the reliability function while passing through the extinction channel of 10 mm to 35 mm by inputting from the A-end. While the detonation signal input from the B-end was not able to detonate the A-end detonating cord to meet the flame-proof function across the flame-proof structure and extinction channel when the length of the extinction channel is 15 to 35 mm. The result indicates the length of the extinction channel amongst 15 mm to 35 mm and the layered charge of different densities can be selected as the design standard of the blasting network to make the denotation signals transmit in one direction in the network, thus increasing the security of the network.
An explosive diode was designed according to the principle of explosive logic components. This paper studied thorough experiment of the internal structure of the components to identify the length of extinction channel and flame-proof structure as key parameters. The flame-proof structure adopted the layered charges of different density including an excitation device, 1st charge of PETN, 2nd charge of PETN. Connecting the A-end and B-end to the detonating cord, changing the size of the extinction channel, ensuring the parameter of the layered charge to conduct the experiment of detonation reliability and explosion-proof safety, the results show that the detonation signal can detonate the B-end detonating cord, satisfying the reliability function while passing through the extinction channel of 10 mm to 35 mm by inputting from the A-end. While the detonation signal input from the B-end was not able to detonate the A-end detonating cord to meet the flame-proof function across the flame-proof structure and extinction channel when the length of the extinction channel is 15 to 35 mm. The result indicates the length of the extinction channel amongst 15 mm to 35 mm and the layered charge of different densities can be selected as the design standard of the blasting network to make the denotation signals transmit in one direction in the network, thus increasing the security of the network.
2017, 37(3): 566-570.
doi: 10.11883/1001-1455(2017)03-0566-05
Abstract:
To assess the coal dust explosive power, we used the dimensional analysis mathematical method to model the prediction of the energyreleased from coal dust explosion. The basic dimensions selected are those of the distance, the mass and the time, of coal dust explosion's flame propagation. The selected output dimensions are those of explosive energy, the air density and the barometric pressure. According to the dimensional analysis Π theorem, we established the energy prediction model with unknown parameters and undetermined parameters, a model that is universally applicable. By carrying out a small-scale coal dust explosion experimental design, we determined the model parameters, and obtained the average maximum flame length of ten times of coal dust explosion, the average maximum flame time, and the released energy. The undetermined parameter was calculated as 0.467. It follows that the prediction model for coal dust explosive energy and its qualification were obtained. Based on our rationality analysis of this model, the experimental measured flame length of 15 different times of coal dust explosion was used to test the power exponent relationship. The test result verifies the completeness of the selected dimensions and the scientific rationality of the prediction model. Using fewer variable parameters, this model simplifies calculations and will provide important reference for explosion hazard assessment.
To assess the coal dust explosive power, we used the dimensional analysis mathematical method to model the prediction of the energyreleased from coal dust explosion. The basic dimensions selected are those of the distance, the mass and the time, of coal dust explosion's flame propagation. The selected output dimensions are those of explosive energy, the air density and the barometric pressure. According to the dimensional analysis Π theorem, we established the energy prediction model with unknown parameters and undetermined parameters, a model that is universally applicable. By carrying out a small-scale coal dust explosion experimental design, we determined the model parameters, and obtained the average maximum flame length of ten times of coal dust explosion, the average maximum flame time, and the released energy. The undetermined parameter was calculated as 0.467. It follows that the prediction model for coal dust explosive energy and its qualification were obtained. Based on our rationality analysis of this model, the experimental measured flame length of 15 different times of coal dust explosion was used to test the power exponent relationship. The test result verifies the completeness of the selected dimensions and the scientific rationality of the prediction model. Using fewer variable parameters, this model simplifies calculations and will provide important reference for explosion hazard assessment.
2017, 37(3): 571-576.
doi: 10.11883/1001-1455(2017)03-0571-06
Abstract:
The artillery chamber pressure is so important a parameter for interior ballistic performance that it has to be measured repeatedly in the course of artillery development, production, acceptance, storage check. When a batch of ammunitions are measured by internal electronic pressure gauge (IEPG) and copper cylinder pressure gauge (CCPG) at the same time, the distribution of IEPG peak values is found to be much larger than that of CCPG ones. The ANSYS model of CCPG was proposed based on the CCPG working principle, and the Johnson-Cook model parameters were optimized according to the dynamic calibration data. The results shows that when discrepancy occurred with respect to the peak pressures measured respectively by IEPG and CCPG, the pressure-change-rate histories of IEPG were different, and the test pressure exerted on the CCPG model was consistent with the copper cylinder deformation obtained in the copper test. The results also show that the difference in peak pressure, captured by IEPG and CCPG in a batch of ammunition chamber pressure measurement at the same time, is due to the influence of different copper cylinder strain rates as a result of different rising rates of the chamber pressure.
The artillery chamber pressure is so important a parameter for interior ballistic performance that it has to be measured repeatedly in the course of artillery development, production, acceptance, storage check. When a batch of ammunitions are measured by internal electronic pressure gauge (IEPG) and copper cylinder pressure gauge (CCPG) at the same time, the distribution of IEPG peak values is found to be much larger than that of CCPG ones. The ANSYS model of CCPG was proposed based on the CCPG working principle, and the Johnson-Cook model parameters were optimized according to the dynamic calibration data. The results shows that when discrepancy occurred with respect to the peak pressures measured respectively by IEPG and CCPG, the pressure-change-rate histories of IEPG were different, and the test pressure exerted on the CCPG model was consistent with the copper cylinder deformation obtained in the copper test. The results also show that the difference in peak pressure, captured by IEPG and CCPG in a batch of ammunition chamber pressure measurement at the same time, is due to the influence of different copper cylinder strain rates as a result of different rising rates of the chamber pressure.
