2007 Vol. 27, No. 3
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2007, 27(3): 193-197.
doi: 10.11883/1001-1455(2007)03-0193-05
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Abstract:
Using a gas gun, a set of plate impact experiments were performed for 20 steel by measuring the rear free-surface velocity profiles with a velocity interferometer system for any reflector (VISAR). Experiments were arranged by adjusting the thicknesses of flyer and sample to change the tensile strain rate, in order to investigate the effect of the tensile strain rate on the spall strength. The maximum tensile strain rate approximately reaches 106 s-1, and approachs to the value determined by the laser irradiation. Compared with laser irradiation, the thin flyer technique is easy to satisfy the one-dimensional strain condition for spall fracture. The measured results show that an apparent increase of spall strength with tensile strain rate is evidenced, and 70% increase of spall strength is determined in the present tensile strain rate range of 104~106 s-1. Based on the numerical simulation results, the influence of the loading conditions on the spall strength was discussed.
Using a gas gun, a set of plate impact experiments were performed for 20 steel by measuring the rear free-surface velocity profiles with a velocity interferometer system for any reflector (VISAR). Experiments were arranged by adjusting the thicknesses of flyer and sample to change the tensile strain rate, in order to investigate the effect of the tensile strain rate on the spall strength. The maximum tensile strain rate approximately reaches 106 s-1, and approachs to the value determined by the laser irradiation. Compared with laser irradiation, the thin flyer technique is easy to satisfy the one-dimensional strain condition for spall fracture. The measured results show that an apparent increase of spall strength with tensile strain rate is evidenced, and 70% increase of spall strength is determined in the present tensile strain rate range of 104~106 s-1. Based on the numerical simulation results, the influence of the loading conditions on the spall strength was discussed.
2007, 27(3): 198-223.
doi: 10.11883/1001-1455(2007)03-0198-06
Abstract:
Some instability analyses were carried out according to the experimental results of primary breakup of symmetrical spray of water and anhydrous-ethanol.It is shown that the process of primary breakup can be divided into two stages in the experimental condition: the first stage is the nonlinear development of liquid instability and the stretch of spike to form a jet caused by inertia force and resistance force of air; the second stage is the process of breakup to liquid bead cluster caused by jet instability. The analyzed result of droplet average diameter of primary breakup is approximate to the experimental result. According to the analyses, it is a necessity that the droplet average diameter of anhydrous-ethanol is smaller than one of water because the surface tension of anhydrous-ethanol is only one-third of the counterpart of water.
Some instability analyses were carried out according to the experimental results of primary breakup of symmetrical spray of water and anhydrous-ethanol.It is shown that the process of primary breakup can be divided into two stages in the experimental condition: the first stage is the nonlinear development of liquid instability and the stretch of spike to form a jet caused by inertia force and resistance force of air; the second stage is the process of breakup to liquid bead cluster caused by jet instability. The analyzed result of droplet average diameter of primary breakup is approximate to the experimental result. According to the analyses, it is a necessity that the droplet average diameter of anhydrous-ethanol is smaller than one of water because the surface tension of anhydrous-ethanol is only one-third of the counterpart of water.
2007, 27(3): 204-209.
doi: 10.11883/1001-1455(2007)03-0204-06
Abstract:
Based on the two-dimensional axisymmetric Euler equations coupling with chemical reactions, the phenomena of implosion wave in the inertia medium and interaction of the implosion flame with shock in the hydrogen-air mixture were numerically studied by using wave propagation algorithm with monotonized centered (MC) limiter in the cylindrical tube with two open ends. In the inertia medium the simulations show that toroidal shocks implode and reflect at the axis of symmetry of the cylindrical tube. Every implosion can form a Mach stem that propagates towards the previous Mach stems, which enhances shock but decreases in the whole because of absence of energy. In the hydrogen-air mixture the calculated results show that shock induced by combustion repeatedly interacts with implosion flame in the cylindrical tube, which leads to the fact that frequency and intensity of Mach stems at the axis of the cylindrical tube are higher than these in the inertia medium. Simultaneously, repeated shock-flame interactions cause instability and distortion of the flame, and then form the shape of collapsing flame front.
Based on the two-dimensional axisymmetric Euler equations coupling with chemical reactions, the phenomena of implosion wave in the inertia medium and interaction of the implosion flame with shock in the hydrogen-air mixture were numerically studied by using wave propagation algorithm with monotonized centered (MC) limiter in the cylindrical tube with two open ends. In the inertia medium the simulations show that toroidal shocks implode and reflect at the axis of symmetry of the cylindrical tube. Every implosion can form a Mach stem that propagates towards the previous Mach stems, which enhances shock but decreases in the whole because of absence of energy. In the hydrogen-air mixture the calculated results show that shock induced by combustion repeatedly interacts with implosion flame in the cylindrical tube, which leads to the fact that frequency and intensity of Mach stems at the axis of the cylindrical tube are higher than these in the inertia medium. Simultaneously, repeated shock-flame interactions cause instability and distortion of the flame, and then form the shape of collapsing flame front.
2007, 27(3): 210-216.
doi: 10.11883/1001-1455(2007)03-0210-07
Abstract:
By using Instron 1342 testing system and an improved SHPB technique, PP/PA blends were tested at a wide range of strain rates from 10-4 up to 103 s-1 and at a temperature range of 25~80 ℃. Their mechanical responses are shown to be sensitive both to the strain rate and temperature. Based on the experimental data of 113 blends at a wide range of strain rates from 10-4 up to 103 s-1 and at a temperature range of 25~80 ℃, it is shown that the mechanical behavior of this PP/PA blends can be described with ZWT thermoviscoelastic constitutive equation. The corresponding thermoviscoelastic parameters for 113 blends were obtained. The predicted theoretical results coincide quite well with the experimental data. The experimental results also reveal the time-temperature equivalence relation for PP/PA blends. Raising the temperature is equivalent to the increasing of time (the decreasing of strain rate). Conversely, decreasing the temperature is equivalent to the decreasing of time (the increasing of strain rate). Through introducing a dimensionless parameter Z=(d/dt)0exp(A/kT)/E, two characteristic parameters: strain rate=(d/dt) and temperature T are put together to this unified parameter Z. From experimental results, A/k was fitted, A/k=8.595 ℃, and a unified curve characterizing the-time temperature equivalence relation was obtained.
By using Instron 1342 testing system and an improved SHPB technique, PP/PA blends were tested at a wide range of strain rates from 10-4 up to 103 s-1 and at a temperature range of 25~80 ℃. Their mechanical responses are shown to be sensitive both to the strain rate and temperature. Based on the experimental data of 113 blends at a wide range of strain rates from 10-4 up to 103 s-1 and at a temperature range of 25~80 ℃, it is shown that the mechanical behavior of this PP/PA blends can be described with ZWT thermoviscoelastic constitutive equation. The corresponding thermoviscoelastic parameters for 113 blends were obtained. The predicted theoretical results coincide quite well with the experimental data. The experimental results also reveal the time-temperature equivalence relation for PP/PA blends. Raising the temperature is equivalent to the increasing of time (the decreasing of strain rate). Conversely, decreasing the temperature is equivalent to the decreasing of time (the increasing of strain rate). Through introducing a dimensionless parameter Z=(d/dt)0exp(A/kT)/E, two characteristic parameters: strain rate=(d/dt) and temperature T are put together to this unified parameter Z. From experimental results, A/k was fitted, A/k=8.595 ℃, and a unified curve characterizing the-time temperature equivalence relation was obtained.
2007, 27(3): 217-222.
doi: 10.11883/1001-1455(2007)03-0217-06
Abstract:
Impact tests of a new kind of pavement material for concrete bridge deck, steel fiber reinforced and polymer modified concrete (SFRPMC), were carried out by using a large cross-section SHPB system. The impact behaviors of the new material were compared with those of plain concrete and steel fiber reinforced concrete under the same basic mixture ratio. After tests, the destructive behaviors of the three materials were observed and their stress and strain relations at different strain rates were measured. The sensitivities of strain rate of three materials were compared. The mechanism of influences of steel fiber and polymer additions on the dynamic mechanical behavior of concrete was analyzed. Results show that SFRPMC has good impact properties, and it is one of the ideal pavement materials.
Impact tests of a new kind of pavement material for concrete bridge deck, steel fiber reinforced and polymer modified concrete (SFRPMC), were carried out by using a large cross-section SHPB system. The impact behaviors of the new material were compared with those of plain concrete and steel fiber reinforced concrete under the same basic mixture ratio. After tests, the destructive behaviors of the three materials were observed and their stress and strain relations at different strain rates were measured. The sensitivities of strain rate of three materials were compared. The mechanism of influences of steel fiber and polymer additions on the dynamic mechanical behavior of concrete was analyzed. Results show that SFRPMC has good impact properties, and it is one of the ideal pavement materials.
2007, 27(3): 223-229.
doi: 10.11883/1001-1455(2007)03-0223-07
Abstract:
An investigation into the energy absorption behaviors of axially splitting thin-walled metal tubes with polygonal sections was carried out. Curl radius and crushing forces were theoretically calculated for the system under quasi-static load. Numerical solution of the energy dissipating system was obtained by LS-DYNA finite element method and compared with the theoretical results.Influences of die semi-angle, wall thickness and edge number on energy absorption of the structure were discussed by analyzing tearing energy, plastic deformation energy and frictional energy.
An investigation into the energy absorption behaviors of axially splitting thin-walled metal tubes with polygonal sections was carried out. Curl radius and crushing forces were theoretically calculated for the system under quasi-static load. Numerical solution of the energy dissipating system was obtained by LS-DYNA finite element method and compared with the theoretical results.Influences of die semi-angle, wall thickness and edge number on energy absorption of the structure were discussed by analyzing tearing energy, plastic deformation energy and frictional energy.
2007, 27(3): 230-235.
doi: 10.11883/1001-1455(2007)03-0230-06
Abstract:
Using the loading technique of electrical explosion of metallic foil driving the polyester film flyer to produce short-duration pulse shock wave, the shock initiation characteristics of a TATB/HMX based explosive were studied according to the DRM (delayed Robbins-Monro) test procedure. Both the shock initiation thresholds under the condition of 50% initiation probability and the minimum initiation thresholds under the condition of 100% initiation probability were obtained. And by means of the diagnostic technique of optical fibre probe, optical-electrical converter, and digital oscillograph and the method of cylindrical wedges of explosive material, the run distance to detonation was measured as a function of initial shock pressure in the studied explosive , and the effect of pulse duration on the initiation and growth to detonation characteristics was considered. The results in the form of Pop plots were presented.
Using the loading technique of electrical explosion of metallic foil driving the polyester film flyer to produce short-duration pulse shock wave, the shock initiation characteristics of a TATB/HMX based explosive were studied according to the DRM (delayed Robbins-Monro) test procedure. Both the shock initiation thresholds under the condition of 50% initiation probability and the minimum initiation thresholds under the condition of 100% initiation probability were obtained. And by means of the diagnostic technique of optical fibre probe, optical-electrical converter, and digital oscillograph and the method of cylindrical wedges of explosive material, the run distance to detonation was measured as a function of initial shock pressure in the studied explosive , and the effect of pulse duration on the initiation and growth to detonation characteristics was considered. The results in the form of Pop plots were presented.
2007, 27(3): 236-239.
doi: 10.11883/1001-1455(2007)03-0236-04
Abstract:
A new reaction model was proposed by thinking of the excitation process and slow reaction in the detonation process of insensitive high explosives (IHE). This reaction model can be used in coarse mesh as compared with other reaction model. In the mesh of 50 cells per centimeter, the calculated results of the free velocity of tantalum and aluminum flyers driven by IHE are according with the experiment data. This model was applied to calculate the process of IHE driving LiF. In the mesh of 50 cells pre centimeter. The calculated result of the interface between LiF and IHE is according with the experimental data. When the mesh size is smaller, the error between them is smaller. It indicates that this new model can describe the process of driven flyers by IHE in coarse mesh, and it can be used in practical works.
A new reaction model was proposed by thinking of the excitation process and slow reaction in the detonation process of insensitive high explosives (IHE). This reaction model can be used in coarse mesh as compared with other reaction model. In the mesh of 50 cells per centimeter, the calculated results of the free velocity of tantalum and aluminum flyers driven by IHE are according with the experiment data. This model was applied to calculate the process of IHE driving LiF. In the mesh of 50 cells pre centimeter. The calculated result of the interface between LiF and IHE is according with the experimental data. When the mesh size is smaller, the error between them is smaller. It indicates that this new model can describe the process of driven flyers by IHE in coarse mesh, and it can be used in practical works.
2007, 27(3): 240-245.
doi: 10.11883/1001-1455(2007)03-0240-06
Abstract:
Numerical simulations of non-spherical projectiles hypervelocity impact on single bumper shield at normal angles were carried out using the SPH (smoothed particle hydrodynamics) technique of AUTODYN hydro-codes. The results of 2D and 3D simulation were given. Effects of projectile aspect ratios with different shapes and impact orientations, etc. on characteristics of debris cloud and module-wall damage sizes produced by hypervelocity impact on shield configuration were investigated with the same mass and velocity. Simulation results were compared with the characteristic of debris cloud and module-wall damage sizes created by spherical projectiles. It is shown that a projectile has a larger aspect ratio, it has a higher perforation capability; debris cloud shapes, mass distribution, fragmentation degree and perforation capability created by non-spherical projectiles are different with various impact orientations.
Numerical simulations of non-spherical projectiles hypervelocity impact on single bumper shield at normal angles were carried out using the SPH (smoothed particle hydrodynamics) technique of AUTODYN hydro-codes. The results of 2D and 3D simulation were given. Effects of projectile aspect ratios with different shapes and impact orientations, etc. on characteristics of debris cloud and module-wall damage sizes produced by hypervelocity impact on shield configuration were investigated with the same mass and velocity. Simulation results were compared with the characteristic of debris cloud and module-wall damage sizes created by spherical projectiles. It is shown that a projectile has a larger aspect ratio, it has a higher perforation capability; debris cloud shapes, mass distribution, fragmentation degree and perforation capability created by non-spherical projectiles are different with various impact orientations.
2007, 27(3): 246-250.
doi: 10.11883/1001-1455(2007)03-0246-05
Abstract:
In order to describe the adiabatic shearing localization of the projectile that impacts to concrete, the model of adiabatic shearing localization for projectile that impacts to concrete was proposed according to the results of one-dimensional analysis and it was incorporated in the numerical calculations. To describe the nonlinear deformation and fracture characteristics of the concrete and to keep the projectile-concrete interface clearness, the concrete was divided into smooth particles and computed by SPH method but the projectile was divided into finite elements and computed by finite element method. It is shown that the domains of adiabatic shearing localization in the projectile from the computations using the presented model are in agreement with the experimental results.
In order to describe the adiabatic shearing localization of the projectile that impacts to concrete, the model of adiabatic shearing localization for projectile that impacts to concrete was proposed according to the results of one-dimensional analysis and it was incorporated in the numerical calculations. To describe the nonlinear deformation and fracture characteristics of the concrete and to keep the projectile-concrete interface clearness, the concrete was divided into smooth particles and computed by SPH method but the projectile was divided into finite elements and computed by finite element method. It is shown that the domains of adiabatic shearing localization in the projectile from the computations using the presented model are in agreement with the experimental results.
2007, 27(3): 251-258.
doi: 10.11883/1001-1455(2007)03-0251-08
Abstract:
The downstream detonation initiation induced by interaction between the shock wave and the single rectangle obstacle interaction was simulated numerically. The upstream detonation forming and its following wave dynamics which initiated the downstream detonation waves were investigated. From the numerical results two initiation modes, which were the direct detonation diffraction and the diffraction wave reflection on the upper wall, were found out and validated by the previous experimental results. The processes of the upstream detonation transmitting downstream were analyzed by studying the influences of the incident shock Mach number, gas mixture pressure, and the tube length scale. The operating rules and governing factors of two initiation modes were concluded and the downstream detonation initiation rules were illustrated.
The downstream detonation initiation induced by interaction between the shock wave and the single rectangle obstacle interaction was simulated numerically. The upstream detonation forming and its following wave dynamics which initiated the downstream detonation waves were investigated. From the numerical results two initiation modes, which were the direct detonation diffraction and the diffraction wave reflection on the upper wall, were found out and validated by the previous experimental results. The processes of the upstream detonation transmitting downstream were analyzed by studying the influences of the incident shock Mach number, gas mixture pressure, and the tube length scale. The operating rules and governing factors of two initiation modes were concluded and the downstream detonation initiation rules were illustrated.
2007, 27(3): 259-264.
doi: 10.11883/1001-1455(2007)03-0259-07
Abstract:
The distribution of state parameters for detonation products behind the wave front, the relationship between the effective explosive volume and cylindrical charge geometry, the state equation of detonation products and the expressions of strong detonation were respectively discussed to analyse the phenomenon on a plane detonation wave changed into a convex wave induced by series-detonation of cylindrical explosives with low and high detonation velocities.The evolved process of a plane detonation wave changed into a convex wave was described by taking series-detonation of 100 mm50 mm TNT and 100 mm50 mm RC cylindrical explosives for example, and the plane area and the lagging time from the center section to the edge of the waveform were predicted. The predicted results is consistent with the measurements.
The distribution of state parameters for detonation products behind the wave front, the relationship between the effective explosive volume and cylindrical charge geometry, the state equation of detonation products and the expressions of strong detonation were respectively discussed to analyse the phenomenon on a plane detonation wave changed into a convex wave induced by series-detonation of cylindrical explosives with low and high detonation velocities.The evolved process of a plane detonation wave changed into a convex wave was described by taking series-detonation of 100 mm50 mm TNT and 100 mm50 mm RC cylindrical explosives for example, and the plane area and the lagging time from the center section to the edge of the waveform were predicted. The predicted results is consistent with the measurements.
2007, 27(3): 266-271.
doi: 10.11883/1001-1455(2007)03-0266-06
Abstract:
In order to inspect longitudinal stress-corrosion cracks of large-diameter functionally graded pipes more efficiently, guided circumferential waves in infinitely long hollow cylinders were studied by an orthogonal polynomial approach. Properties of material were assumed to vary in the direction of the thickness according to a known radial variation law. The formulation was based on linear three-dimensional elasticity. Results from homogeneous cylinders were compared with that published earlier to check up the accuracy and range of applicability of the proposed approach. The guided circumferential wave dispersion curves of graded pipes under different gradient functions were calculated, and the effect of the gradient functions on dispersion curves was shown. Finally, the guided circumferential wave dispersion curves of graded pipes under different ratios of the inner radius to thickness were calculated to observe the effect when the ratio varied on the dispersion curves.
In order to inspect longitudinal stress-corrosion cracks of large-diameter functionally graded pipes more efficiently, guided circumferential waves in infinitely long hollow cylinders were studied by an orthogonal polynomial approach. Properties of material were assumed to vary in the direction of the thickness according to a known radial variation law. The formulation was based on linear three-dimensional elasticity. Results from homogeneous cylinders were compared with that published earlier to check up the accuracy and range of applicability of the proposed approach. The guided circumferential wave dispersion curves of graded pipes under different gradient functions were calculated, and the effect of the gradient functions on dispersion curves was shown. Finally, the guided circumferential wave dispersion curves of graded pipes under different ratios of the inner radius to thickness were calculated to observe the effect when the ratio varied on the dispersion curves.
2007, 27(3): 272-278.
doi: 10.11883/1001-1455(2007)03-0272-06
Abstract:
The formation of a normal blasting crater for the break blasting of a roadway in rock with high residual stress was investigated based on the theory of cylindrical blasting crater. The criterion on the formation of a normal blasting crater, and the parameters of stoping blasting for driving a roadway in rock with high residual stress as well, were deduced. It is concluded from investigation that the parameters of break blasting need to be modified due to the effect of residual stress, and that the higher the residual stress is, the smaller the burden and the blasthole separation are, the larger the specific charge and the number of round blastholes are. Finally, it is pointed out that high explosive can be used to decrease the rate at which the parameters of break blasting for driving a roadway change due to the effect of high residual stress.
The formation of a normal blasting crater for the break blasting of a roadway in rock with high residual stress was investigated based on the theory of cylindrical blasting crater. The criterion on the formation of a normal blasting crater, and the parameters of stoping blasting for driving a roadway in rock with high residual stress as well, were deduced. It is concluded from investigation that the parameters of break blasting need to be modified due to the effect of residual stress, and that the higher the residual stress is, the smaller the burden and the blasthole separation are, the larger the specific charge and the number of round blastholes are. Finally, it is pointed out that high explosive can be used to decrease the rate at which the parameters of break blasting for driving a roadway change due to the effect of high residual stress.
2007, 27(3): 278-282.
doi: 10.11883/1001-1455(2007)03-0278-05
Abstract:
The digital holographic theories and application in explosion were discussed. The digital hologram of micro-jet from Al flyer with a small conical hole in center under shock load was obtained, based on the questions solved about the resolving power, the dynamic blur, the safety and the accurate time delay synchronization. The micro-jet particles were reconstructed from the hologram in computer. The velocities of micro-jet particles ranged from 2.7 to 4 km/s. And their diameters were from several micrometers to tens of micrometer.
The digital holographic theories and application in explosion were discussed. The digital hologram of micro-jet from Al flyer with a small conical hole in center under shock load was obtained, based on the questions solved about the resolving power, the dynamic blur, the safety and the accurate time delay synchronization. The micro-jet particles were reconstructed from the hologram in computer. The velocities of micro-jet particles ranged from 2.7 to 4 km/s. And their diameters were from several micrometers to tens of micrometer.
2007, 27(3): 283-288.
doi: 10.11883/1001-1455(2007)03-0283-06
Abstract:
The dynamic unloading effect of initial stress in hydrostatic field in excavation process of circlar tunnel by blasting under high geostress condition was studied and the damage field was caculated.In the process of dynamic unloading, the radial stress unloaded first and then rebounded, the circum-stress concentrated. The unloading time affects the radial stress much more than the circum-stress.The shorter the unloading time is, the larger the influenced field is. The damage field induced by dynamic unloading is larger than that induced by static unloading.
The dynamic unloading effect of initial stress in hydrostatic field in excavation process of circlar tunnel by blasting under high geostress condition was studied and the damage field was caculated.In the process of dynamic unloading, the radial stress unloaded first and then rebounded, the circum-stress concentrated. The unloading time affects the radial stress much more than the circum-stress.The shorter the unloading time is, the larger the influenced field is. The damage field induced by dynamic unloading is larger than that induced by static unloading.
