2008 Vol. 28, No. 6
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2008, 28(6): 481-487.
doi: 10.11883/1001-1455(2008)06-0481-07
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Abstract:
Tests were performed to investigate the influence of detonation driving on terminal ballistic effects of tungsten spheres. The experimental results show that (1) tungsten spheres are slightly deformed and damaged as a result of the high shock pulse during detonation, the average mass loss of tungsten spheres with a diameter of 6.0 mm and 7.5 mm is 8.4%; (2) for ideal tungsten spheres, the attenuation coefficient of velocity is constant, the air drag coefficient is a linear function of initial velocity, whereas for tungsten spheres formed by a warhead, the attenuation coefficient of velocity is not constant, the air drag coefficient is a linear function of flight velocity; (3) the deformation and damage of tungsten spheres exerts a obvious influence on the perforation thickness, for tungsten spheres with a diameter of 7.5 mm, experiments and calculations confirm a 35%-reduction in ballistic limit perforation thickness.
Tests were performed to investigate the influence of detonation driving on terminal ballistic effects of tungsten spheres. The experimental results show that (1) tungsten spheres are slightly deformed and damaged as a result of the high shock pulse during detonation, the average mass loss of tungsten spheres with a diameter of 6.0 mm and 7.5 mm is 8.4%; (2) for ideal tungsten spheres, the attenuation coefficient of velocity is constant, the air drag coefficient is a linear function of initial velocity, whereas for tungsten spheres formed by a warhead, the attenuation coefficient of velocity is not constant, the air drag coefficient is a linear function of flight velocity; (3) the deformation and damage of tungsten spheres exerts a obvious influence on the perforation thickness, for tungsten spheres with a diameter of 7.5 mm, experiments and calculations confirm a 35%-reduction in ballistic limit perforation thickness.
2008, 28(6): 488-493.
doi: 10.11883/1001-1455(2008)06-0488-06
Abstract:
Shock response of plastic bonded explosives were simulated at the grain scale using the discrete element method. The mesoscopic structures of explosives were created based on the Voronoi tessellation. Through simulations on explosives with and without a pore inside, the important impact of mesoscopic structure on the formation and distribution of hot spots was demonstrated. In these sample calculations, it is found that the temperature localization is mainly due to visco-plastic deformation whereas the mechanisms of friction and bulk viscosity can be ignored.
Shock response of plastic bonded explosives were simulated at the grain scale using the discrete element method. The mesoscopic structures of explosives were created based on the Voronoi tessellation. Through simulations on explosives with and without a pore inside, the important impact of mesoscopic structure on the formation and distribution of hot spots was demonstrated. In these sample calculations, it is found that the temperature localization is mainly due to visco-plastic deformation whereas the mechanisms of friction and bulk viscosity can be ignored.
2008, 28(6): 494-502.
doi: 10.11883/1001-1455(2008)06-0494-09
Abstract:
Effects of cell micro-topology on the in-plane dynamic crushing properties of honeycombs were numerically studied. The dynamic crushing of the honeycombs filled with the differently micro-arranged cells was discussed in case of these cells with the same side length and thickness. The full-scale deformation of the specimen and the micro-structure dynamic evolution were given. Influences of the cell micro-arrangements on the energy absorption mechanism of the honeycombs were clarified. Results show that except for the basic structural parameters (e.g. side length and thickness) of the cells, the cell shape and its arrangement pattern are important to determine the dynamic responses of honeycombs. Due to the structural stability of triangular cells, the honeycombs with triangular cells display stronger energy absorption ability than those with square cells. Stagger arrangement of the cells yields to more uniform deformation and stable plateau stresses. Owing to the variation of the micro-topology, the honeycombs with the staggerly-arranged cells reveal particular necking phenomena during the in-plane crushing.
Effects of cell micro-topology on the in-plane dynamic crushing properties of honeycombs were numerically studied. The dynamic crushing of the honeycombs filled with the differently micro-arranged cells was discussed in case of these cells with the same side length and thickness. The full-scale deformation of the specimen and the micro-structure dynamic evolution were given. Influences of the cell micro-arrangements on the energy absorption mechanism of the honeycombs were clarified. Results show that except for the basic structural parameters (e.g. side length and thickness) of the cells, the cell shape and its arrangement pattern are important to determine the dynamic responses of honeycombs. Due to the structural stability of triangular cells, the honeycombs with triangular cells display stronger energy absorption ability than those with square cells. Stagger arrangement of the cells yields to more uniform deformation and stable plateau stresses. Owing to the variation of the micro-topology, the honeycombs with the staggerly-arranged cells reveal particular necking phenomena during the in-plane crushing.
2008, 28(6): 503-506.
doi: 10.11883/1001-1455(2008)06-0503-04
Abstract:
VISAR and X-ray were adopted and the FeMnNi alloy specimens were subjected to the shock pressure far beyond the induced phase transition pressure. Abnormal spalling behaviors were observed in the FeMnNi alloy specimens under symmetric and same thickness impact. These abnormal spalling behaviors were analyzed by the interaction among plastic wave, phase transition wave, release fan wave and rarefaction shock wave induced by reverse phase transition. Results show that phase transition and reverse phase transition occur in FeMnNi alloy, and the rarefaction shock wave induced by reverse phase transition is a main factor to result in the abnormal spalling phenomenon.
VISAR and X-ray were adopted and the FeMnNi alloy specimens were subjected to the shock pressure far beyond the induced phase transition pressure. Abnormal spalling behaviors were observed in the FeMnNi alloy specimens under symmetric and same thickness impact. These abnormal spalling behaviors were analyzed by the interaction among plastic wave, phase transition wave, release fan wave and rarefaction shock wave induced by reverse phase transition. Results show that phase transition and reverse phase transition occur in FeMnNi alloy, and the rarefaction shock wave induced by reverse phase transition is a main factor to result in the abnormal spalling phenomenon.
2008, 28(6): 507-514.
doi: 10.11883/1001-1455(2008)06-0507-08
Abstract:
Dynamic time history analysis of ground motion with vertical fault fracture zones of different widths and shear wave velocities under Rayleigh wave was carried out by using the Rayleigh wave input method based on the viscous-spring artificial boundary. Influence of vertical fault fracture zones with various widths and shear wave velocities on the spreading of Rayleigh wave and ground motion was investigated. The results show variations of fault width and shear wave velocity have little effect in the mediate and far field on the incident side. Peak displacement response of the fault corner and the ground nearby on the incident side enlarges greatly with the increase of fault width or with the decrease of shear wave velocity of the fault. While in the mediate and far field on the other side, peak horizontal and vertical absolute displacements decrease gradually with the increase of fault width or with the decrease of shear wave velocity of the fault, and the horizontal displacement peak has a slighly decrease than that of vertical displacement peak. The results indicate the weak fault fracture zone weakens the Rayleigh wave and with the increase of fault width or with the decrease of shear wave velocity of the fault the weakening effect tends to be enhanced.
Dynamic time history analysis of ground motion with vertical fault fracture zones of different widths and shear wave velocities under Rayleigh wave was carried out by using the Rayleigh wave input method based on the viscous-spring artificial boundary. Influence of vertical fault fracture zones with various widths and shear wave velocities on the spreading of Rayleigh wave and ground motion was investigated. The results show variations of fault width and shear wave velocity have little effect in the mediate and far field on the incident side. Peak displacement response of the fault corner and the ground nearby on the incident side enlarges greatly with the increase of fault width or with the decrease of shear wave velocity of the fault. While in the mediate and far field on the other side, peak horizontal and vertical absolute displacements decrease gradually with the increase of fault width or with the decrease of shear wave velocity of the fault, and the horizontal displacement peak has a slighly decrease than that of vertical displacement peak. The results indicate the weak fault fracture zone weakens the Rayleigh wave and with the increase of fault width or with the decrease of shear wave velocity of the fault the weakening effect tends to be enhanced.
2008, 28(6): 515-520.
doi: 10.11883/1001-1455(2008)06-0515-06
Abstract:
The preliminary mesoscale simulation was done for the hot spot formation of plastic bonded explosives(PBX) under shock loading with the combined method of the finite element and discrete element methods. The explosive crystals and binder are simulated using FEM and DEM, respectively. Simulated results indicate that hot spots focus on the binder region between crystals. The important factor of hot spot formation is the shock interaction between crystals and binder, the temperature of HMX is lower than that of binder, and the periphery temperature is higher than the inner temperature in HMX crystals.
The preliminary mesoscale simulation was done for the hot spot formation of plastic bonded explosives(PBX) under shock loading with the combined method of the finite element and discrete element methods. The explosive crystals and binder are simulated using FEM and DEM, respectively. Simulated results indicate that hot spots focus on the binder region between crystals. The important factor of hot spot formation is the shock interaction between crystals and binder, the temperature of HMX is lower than that of binder, and the periphery temperature is higher than the inner temperature in HMX crystals.
2008, 28(6): 521-526.
doi: 10.11883/1001-1455(2008)06-0521-06
Abstract:
Considering that the target is an intrinsic friction medium, the cavity-expansion approximation and dynamic equations of the medium near the cavity of penetration are used to calculate the resistance of the rigid warhead. The influence of the target with a free surface on penetration is taken into account and the oblique penetration process is divided into three phases. According to the above work, the formula to compute stress on the projectile surface is deduced and a new analytical solution to oblique penetration depth of the rigid projectile into the target is obtained. The solution is identical with the BLZ formula in form and the calculation results also fit well. The solution provides the theoretical explain for the BLZ formula.
Considering that the target is an intrinsic friction medium, the cavity-expansion approximation and dynamic equations of the medium near the cavity of penetration are used to calculate the resistance of the rigid warhead. The influence of the target with a free surface on penetration is taken into account and the oblique penetration process is divided into three phases. According to the above work, the formula to compute stress on the projectile surface is deduced and a new analytical solution to oblique penetration depth of the rigid projectile into the target is obtained. The solution is identical with the BLZ formula in form and the calculation results also fit well. The solution provides the theoretical explain for the BLZ formula.
2008, 28(6): 527-531.
doi: 10.11883/1001-1455(2008)06-0527-05
Abstract:
Stress-strain curves of 0Cr17Mn5Ni4Mo3Al,at three Strain rates of 300,1 000,2 700 s-1 and four temperatures of 25,300,500,700 ℃ were experimentally obtained by using the split Hopkinson pressure bar equipped with a temperature controller.And the quasi-static experiment (0.000 5 s-1) was done in the material test system at three temperatures of 25,300,500 ℃.Experimental results show that the flow stress decreases with temperature but increases with strain and strain rate.The traditional Johnson-Cook model was modified considering the thermal softening caused by the impact adiabatic process. The modified Johnson-Cook model is in good agreement with the experimental results.
Stress-strain curves of 0Cr17Mn5Ni4Mo3Al,at three Strain rates of 300,1 000,2 700 s-1 and four temperatures of 25,300,500,700 ℃ were experimentally obtained by using the split Hopkinson pressure bar equipped with a temperature controller.And the quasi-static experiment (0.000 5 s-1) was done in the material test system at three temperatures of 25,300,500 ℃.Experimental results show that the flow stress decreases with temperature but increases with strain and strain rate.The traditional Johnson-Cook model was modified considering the thermal softening caused by the impact adiabatic process. The modified Johnson-Cook model is in good agreement with the experimental results.
2008, 28(6): 532-538.
doi: 10.11883/1001-1455(2008)06-0532-07
Abstract:
Reactive powder concrete (RPC) with a compressive strength of 200MPa was prepared by substitution of ultra-fine industrial waste powders for 60% cement by weight. The dynamic mechanical behaviour of RPC with different fiber volume fraction was researched on repeated compressive impact in four kinds of impact modes with the split Hopkinson pressure bar. Standard strength of repeated impact was defined. The effects of impact times, impact modes and fiber volume fraction on the properties of RPC subjected to repeated impact were explored. Results show that the ability of repeated impact resistance of RPC is increases with fiber volume fraction. With the increase of impact times, the damage of material increases and the standard strength decreases. With the change of impact modes, the damage of material on the first impact and the reduction rates of the peak stresses on the second and third impact increase.
Reactive powder concrete (RPC) with a compressive strength of 200MPa was prepared by substitution of ultra-fine industrial waste powders for 60% cement by weight. The dynamic mechanical behaviour of RPC with different fiber volume fraction was researched on repeated compressive impact in four kinds of impact modes with the split Hopkinson pressure bar. Standard strength of repeated impact was defined. The effects of impact times, impact modes and fiber volume fraction on the properties of RPC subjected to repeated impact were explored. Results show that the ability of repeated impact resistance of RPC is increases with fiber volume fraction. With the increase of impact times, the damage of material increases and the standard strength decreases. With the change of impact modes, the damage of material on the first impact and the reduction rates of the peak stresses on the second and third impact increase.
2008, 28(6): 539-543.
doi: 10.11883/1001-1455(2008)06-0539-05
Abstract:
According to an aquarium test, an experimental method was proposed to measure shock waves in the near field of an underwater explosion. The axial scanning photographs were obtained and analyzed digitally. The shock front pressure along the axle of the charge was gained from the scanning trace of shock wave by using the Rankine-Hugoniot relation, and was extrapolated to the initial pressure of shock wave. The axial pressure damping of the cylindrical TNT charges in the near field was computed by the code LS-DYNA, and the initial pressure of shock wave was measured by manganin gauges. The experimental result is consistent with the theoretical calculation, and the near-field axial pressure damping of the cylindrical TNT charges follows an exponential function.
According to an aquarium test, an experimental method was proposed to measure shock waves in the near field of an underwater explosion. The axial scanning photographs were obtained and analyzed digitally. The shock front pressure along the axle of the charge was gained from the scanning trace of shock wave by using the Rankine-Hugoniot relation, and was extrapolated to the initial pressure of shock wave. The axial pressure damping of the cylindrical TNT charges in the near field was computed by the code LS-DYNA, and the initial pressure of shock wave was measured by manganin gauges. The experimental result is consistent with the theoretical calculation, and the near-field axial pressure damping of the cylindrical TNT charges follows an exponential function.
2008, 28(6): 544-551.
doi: 10.11883/1001-1455(2008)06-0544-08
Abstract:
In the experiments, two types of holed-cracked flattened Brazilian disc specimens were adopted, one was geometrically similar with the diameters of 42, 80, 122 mm and 155 mm respectively, the other was a one-size specimen geometry with an identical 80-mm diameter and varying crack lengths. The discs were diametrically impacted by the split Hopkinson pressure bar, and the strain waves and typical failure patterns of the specimens were given. It is concluded that the rock dynamic fracture toughness increases with the increasing diameter size for the geometrically similar specimens; however, it increases and then decreases with the increasing crack lengths for the specimens of the identical 80-mm diameter. The size effect of rock dynamic fracture toughness is caused by the fracture process zone length l and incubation time . To reduce the size effect, a method to determine the rock dynamic fracture toughness was proposed by averaging the integration of dynamic stress intensity factor distribution in the spatio-temporal domain.
In the experiments, two types of holed-cracked flattened Brazilian disc specimens were adopted, one was geometrically similar with the diameters of 42, 80, 122 mm and 155 mm respectively, the other was a one-size specimen geometry with an identical 80-mm diameter and varying crack lengths. The discs were diametrically impacted by the split Hopkinson pressure bar, and the strain waves and typical failure patterns of the specimens were given. It is concluded that the rock dynamic fracture toughness increases with the increasing diameter size for the geometrically similar specimens; however, it increases and then decreases with the increasing crack lengths for the specimens of the identical 80-mm diameter. The size effect of rock dynamic fracture toughness is caused by the fracture process zone length l and incubation time . To reduce the size effect, a method to determine the rock dynamic fracture toughness was proposed by averaging the integration of dynamic stress intensity factor distribution in the spatio-temporal domain.
2008, 28(6): 552-556.
doi: 10.11883/1001-1455(2008)06-0552-05
Abstract:
Scattering of flexural waves by multiple cutouts and dynamic stress concentration in the thin plates were investigated in terms of the complex variable function method and multi-polar coordinates. The expressions of function approach sequences and condition boundary for the general solution to this problem were proposed by deducing the bending motion equations of the plates. It was solved as a series of infinite algebraic equations by expanding the orthogonal functions. The dynamic moment factors of the plates with three circular cutouts were numerically presented, and the influences of paces between circular cutouts and wave number on dynamic stress distribution were analyzed.
Scattering of flexural waves by multiple cutouts and dynamic stress concentration in the thin plates were investigated in terms of the complex variable function method and multi-polar coordinates. The expressions of function approach sequences and condition boundary for the general solution to this problem were proposed by deducing the bending motion equations of the plates. It was solved as a series of infinite algebraic equations by expanding the orthogonal functions. The dynamic moment factors of the plates with three circular cutouts were numerically presented, and the influences of paces between circular cutouts and wave number on dynamic stress distribution were analyzed.
2008, 28(6): 557-560.
doi: 10.11883/1001-1455(2008)06-0557-04
Abstract:
Using mild detonating fuse(MDF) impulse simulating the X-ray blow-off impulse in studying the structural response of cylindrical shells, it is needed to measure the distribution characteristics of MDF impulse. According to the optimized results， an array of MDFs is arranged around a cylindrical shell, the MDF impulses at several angles around the circumference of the cylindrical shell are measured. The measured impulses indicate that a nearly cosine distributed impulse around the circumference can be obtained by designing the space between the MDF strands and the standoff distance from the strands to the shell.
Using mild detonating fuse(MDF) impulse simulating the X-ray blow-off impulse in studying the structural response of cylindrical shells, it is needed to measure the distribution characteristics of MDF impulse. According to the optimized results， an array of MDFs is arranged around a cylindrical shell, the MDF impulses at several angles around the circumference of the cylindrical shell are measured. The measured impulses indicate that a nearly cosine distributed impulse around the circumference can be obtained by designing the space between the MDF strands and the standoff distance from the strands to the shell.
2008, 28(6): 561-564.
doi: 10.11883/1001-1455(2008)06-0561-04
Abstract:
The behavior of quasi-brittle materials like cement mortar depends on the level of confinement. In order to study the dynamic behavior of cement mortar under active confinement, An device which fits the split Hopkinson bar loading was developed, and it provides the lateral confining pressure upper to 30 MPa. The axial stress-strain curves under various level of confinement and strain rate were derived according to the experiment. It shows that the strength and ductility increase significantly because of confinement, and finally turn into plasticity, also it is strain rate sensitive.
The behavior of quasi-brittle materials like cement mortar depends on the level of confinement. In order to study the dynamic behavior of cement mortar under active confinement, An device which fits the split Hopkinson bar loading was developed, and it provides the lateral confining pressure upper to 30 MPa. The axial stress-strain curves under various level of confinement and strain rate were derived according to the experiment. It shows that the strength and ductility increase significantly because of confinement, and finally turn into plasticity, also it is strain rate sensitive.
2008, 28(6): 565-571.
doi: 10.11883/1001-1455(2008)06-0565-07
Abstract:
Aimed at the stability analysis of layered rock slope affected by the erosion, impulse, and compaction of the weak intercalation caused by blasting, and applied on the theory that blasting gas is isoentropy adiabatic expansion in the lamination cracks and charge hole, the quasi-static mechanical model for the lamination of weak intercalation in layered rock slope was established during the deep-hole blasting. The explicit expressions of the quasi-static pressure in the blasting cavum and the critical lamination length of the weak intercalation were deduced. Through the study on the raise effect of the rock mass caused by the blasting gas wedging into the weak intercalation, the quantitative relationship between the stability factor of the latency slip and the parameters of charge, the mechanics parameters of the rock and the geometry size of the slope was obtained. The blasting dynamic stability of the two typical layered rock slopes was analyzed by using the quasi-static mechanical model presented in this paper. Analyzed results are in agreement with the engineering practice.
Aimed at the stability analysis of layered rock slope affected by the erosion, impulse, and compaction of the weak intercalation caused by blasting, and applied on the theory that blasting gas is isoentropy adiabatic expansion in the lamination cracks and charge hole, the quasi-static mechanical model for the lamination of weak intercalation in layered rock slope was established during the deep-hole blasting. The explicit expressions of the quasi-static pressure in the blasting cavum and the critical lamination length of the weak intercalation were deduced. Through the study on the raise effect of the rock mass caused by the blasting gas wedging into the weak intercalation, the quantitative relationship between the stability factor of the latency slip and the parameters of charge, the mechanics parameters of the rock and the geometry size of the slope was obtained. The blasting dynamic stability of the two typical layered rock slopes was analyzed by using the quasi-static mechanical model presented in this paper. Analyzed results are in agreement with the engineering practice.
2008, 28(6): 572-576.
doi: 10.11883/1001-1455(2008)06-0572-05
Abstract:
Dynamics of bubble oscillation formed during underwater explosions were studied in a water tank. The expansion and collapse of the bubble pictures created by the explosion of the short length-diameter ratio(1.05) PETN were captured by a high-speed camera. The geometry of the bubble is approximately spherical. The radius and period of oscillation of the bubble increment with the charge weight. The position of the bubble is almost constant during its expansion, but when the bubble is growing smaller, the bubble rises more distinctly. The contract velocity in the bottom of bubble is faster than that of the up surface caused by the influence of gravity; a water jet was formed at the last stages of the bubble collapse.
Dynamics of bubble oscillation formed during underwater explosions were studied in a water tank. The expansion and collapse of the bubble pictures created by the explosion of the short length-diameter ratio(1.05) PETN were captured by a high-speed camera. The geometry of the bubble is approximately spherical. The radius and period of oscillation of the bubble increment with the charge weight. The position of the bubble is almost constant during its expansion, but when the bubble is growing smaller, the bubble rises more distinctly. The contract velocity in the bottom of bubble is faster than that of the up surface caused by the influence of gravity; a water jet was formed at the last stages of the bubble collapse.
