2007 Vol. 27, No. 2
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2007, 27(2): 97-102.
doi: 10.11883/1001-1455(2007)02-0097-06
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Abstract:
The deformation characteristics of copper tube with guard ring under two head-on collision detonation waves were experimentally researched. High-speed frame photography, pulsed X-ray radiography and VISAR interferometer were employed to record the expanding process, radius history and velocity history of the copper tube with guard ring. Experimental results show that guard ring can postpone the collision region shell to rupture. The jet-shaped protuberance was found on collision region of copper tube with guard ring. The jet-shaped protuberance consisted of mass ejection from free surface of copper tube and air shock. The DYNA3D code was utilized to simulate the expanding process of copper tube with guard ring. The calculated results and the experimental results are coincident. The LS-DYNA3D code was used to analyze the influence of guard rings fillet on deformation characteristics of metal tube.
The deformation characteristics of copper tube with guard ring under two head-on collision detonation waves were experimentally researched. High-speed frame photography, pulsed X-ray radiography and VISAR interferometer were employed to record the expanding process, radius history and velocity history of the copper tube with guard ring. Experimental results show that guard ring can postpone the collision region shell to rupture. The jet-shaped protuberance was found on collision region of copper tube with guard ring. The jet-shaped protuberance consisted of mass ejection from free surface of copper tube and air shock. The DYNA3D code was utilized to simulate the expanding process of copper tube with guard ring. The calculated results and the experimental results are coincident. The LS-DYNA3D code was used to analyze the influence of guard rings fillet on deformation characteristics of metal tube.
2007, 27(2): 103-108.
doi: 10.11883/1001-1455(2007)02-0103-06
Abstract:
Light gas gun plate impact experiments were conducted on a FeMnNi alloy and phase transition and spallation occurred. Transition pressure of this alloy obtained in the experiments (6.3~6.9 GPa) is much lower than that of pure iron (13 GPa), which demonstrats that the addition of Mn and Ni may lower the transition pressure strongly. Observation of the recovered samples shows that multiple spallations and shallow spallation may occur in the sample when the pressure is higher than the transition pressure of this alloy. Experimental results indicate that the spallation strength of this alloy doesnt increase distintly after phase transition.
Light gas gun plate impact experiments were conducted on a FeMnNi alloy and phase transition and spallation occurred. Transition pressure of this alloy obtained in the experiments (6.3~6.9 GPa) is much lower than that of pure iron (13 GPa), which demonstrats that the addition of Mn and Ni may lower the transition pressure strongly. Observation of the recovered samples shows that multiple spallations and shallow spallation may occur in the sample when the pressure is higher than the transition pressure of this alloy. Experimental results indicate that the spallation strength of this alloy doesnt increase distintly after phase transition.
2007, 27(2): 109-115.
doi: 10.11883/1001-1455(2007)02-0109-07
Abstract:
Molecular dynamics (MD) method was used to simulate the structure and properties of HMX-based four components composite material, the other components were TATB, F2311(binder) and paraffin (desensitized agent). Similarly, MD was used to simulate 3 HMX-based two components explosives (HMX/TATB, HMX/F2311and HMX/paraffin) to investigate the effects of components on base explosive. To make further elucidation of mechanism and effect of desensitized agent, the first principle of quantum chemistry, DFT were used to calculate the supermolecular system, HMX/paraffin. Furthermore, the detonation heat and velocity of them were computed according to theoretical formulas. Results show the elasticities of composite materials are increased and the effect of binder is largest in three additives on mechanical properties of HMX. Additives can decrease the detonation heat and velocity of base explosive more or less. It is found that the interaction of desensitized agent and HMX is rather weak so electronic structure factor is not the main cause of desensitization of PBX. Therefore, in the theoretical design of PBX, the complicated effects of components should be taken into account.
Molecular dynamics (MD) method was used to simulate the structure and properties of HMX-based four components composite material, the other components were TATB, F2311(binder) and paraffin (desensitized agent). Similarly, MD was used to simulate 3 HMX-based two components explosives (HMX/TATB, HMX/F2311and HMX/paraffin) to investigate the effects of components on base explosive. To make further elucidation of mechanism and effect of desensitized agent, the first principle of quantum chemistry, DFT were used to calculate the supermolecular system, HMX/paraffin. Furthermore, the detonation heat and velocity of them were computed according to theoretical formulas. Results show the elasticities of composite materials are increased and the effect of binder is largest in three additives on mechanical properties of HMX. Additives can decrease the detonation heat and velocity of base explosive more or less. It is found that the interaction of desensitized agent and HMX is rather weak so electronic structure factor is not the main cause of desensitization of PBX. Therefore, in the theoretical design of PBX, the complicated effects of components should be taken into account.
2007, 27(2): 116-120.
doi: 10.11883/1001-1455(2007)02-0116-05
Abstract:
The nonlinear dynamic buckling for laminated composite shallow spherical shells, which include transverse shear deformation, under the action of explosive impact was investigated. By means of the basic equations of nonlinear buckling for laminated composite shallow spherical shells,and adding the transverse inertia term and introducing the explosive load of R.H.Cole theory, the nonlinear dynamic governing equation for laminated composite shallow spherical shells subjected to explosive impact load was gained.The nonlinear dynamic responsive equation was obtained by Galerkin method and solved by Runge-Kutta method. Budiansky-Roth motion criterion expressed by peak displacement was employed to determine the critical explosive impact buckling load. The effects of geometric parameters on dynamic buckling of laminated composite shallow spherical shells were discussed. Numerical results show feasibility of the Galerkin Method.
The nonlinear dynamic buckling for laminated composite shallow spherical shells, which include transverse shear deformation, under the action of explosive impact was investigated. By means of the basic equations of nonlinear buckling for laminated composite shallow spherical shells,and adding the transverse inertia term and introducing the explosive load of R.H.Cole theory, the nonlinear dynamic governing equation for laminated composite shallow spherical shells subjected to explosive impact load was gained.The nonlinear dynamic responsive equation was obtained by Galerkin method and solved by Runge-Kutta method. Budiansky-Roth motion criterion expressed by peak displacement was employed to determine the critical explosive impact buckling load. The effects of geometric parameters on dynamic buckling of laminated composite shallow spherical shells were discussed. Numerical results show feasibility of the Galerkin Method.
2007, 27(2): 121-125.
doi: 10.11883/1001-1455(2007)02-0121-05
Abstract:
Dynamic compressive tests on cubic specimens were carried out on the servo-hydraulic static-dynamic testing machine designed and manufactured at the Dalian University of Technology, China. The confining pressure was kept constant at four levels and the strain rate varied from 10-5 s-1 to 10-2 s-1. Variation of strength and deformation of concrete with strain rate and confining pressure was investigated systematically. Based on the tests results a strength formula was proposed for the dynamic failure of concrete with one-dimensional confining pressure, which will contribute to the seismic analysis of large-scale concrete structures such as dams, the offshore concrete oil platforms etc.
Dynamic compressive tests on cubic specimens were carried out on the servo-hydraulic static-dynamic testing machine designed and manufactured at the Dalian University of Technology, China. The confining pressure was kept constant at four levels and the strain rate varied from 10-5 s-1 to 10-2 s-1. Variation of strength and deformation of concrete with strain rate and confining pressure was investigated systematically. Based on the tests results a strength formula was proposed for the dynamic failure of concrete with one-dimensional confining pressure, which will contribute to the seismic analysis of large-scale concrete structures such as dams, the offshore concrete oil platforms etc.
2007, 27(2): 126-130.
doi: 10.11883/1001-1455(2007)02-0126-05
Abstract:
By use of explicit dynamics finite element method, the elastic-plastic dynamic postbuckling of bars subjected to axial high-velocity impact was studied. In order to initiate the buckling mode, the bar was given a small initial imperfection in the form of half of a sine wave near the impacted end. Results obtained in the present study agree well with the experimental data in the reference. As the axial compressive waves propagate forward, it is found that the initial buckling deflection with one half-wave, occurring near the impacted end, quickly develops into the higher postbuckling mode with several half-waves. The present investigation reveals the mechanism of growth and spread of buckling deformation in the bar and the interaction between the axial stress wave and the buckling deformation in impact process.
By use of explicit dynamics finite element method, the elastic-plastic dynamic postbuckling of bars subjected to axial high-velocity impact was studied. In order to initiate the buckling mode, the bar was given a small initial imperfection in the form of half of a sine wave near the impacted end. Results obtained in the present study agree well with the experimental data in the reference. As the axial compressive waves propagate forward, it is found that the initial buckling deflection with one half-wave, occurring near the impacted end, quickly develops into the higher postbuckling mode with several half-waves. The present investigation reveals the mechanism of growth and spread of buckling deformation in the bar and the interaction between the axial stress wave and the buckling deformation in impact process.
2007, 27(2): 131-135.
doi: 10.11883/1001-1455(2007)02-0131-05
Abstract:
In the FEM analysis of structure response under dynamic loading such as high velocity impact, the failure parameter is a important aspect of material behavior. With split Hopkinson tension bar tests and static material test at various stress states and temperatures, the effects of high strain rate, elevated temperature and stress triaxiality on the fracture behavior of 45 steel were studied. The Johnson-Cook damage fracture model parameters were exprimentally determined. The parameters were validated by comparison between the Taylor experiments and the simulations. The consistency between the experimental observation and numerical simulation indicates that the obtained parameters can describe the failure behavior of 45 steel under high speed deformation.
In the FEM analysis of structure response under dynamic loading such as high velocity impact, the failure parameter is a important aspect of material behavior. With split Hopkinson tension bar tests and static material test at various stress states and temperatures, the effects of high strain rate, elevated temperature and stress triaxiality on the fracture behavior of 45 steel were studied. The Johnson-Cook damage fracture model parameters were exprimentally determined. The parameters were validated by comparison between the Taylor experiments and the simulations. The consistency between the experimental observation and numerical simulation indicates that the obtained parameters can describe the failure behavior of 45 steel under high speed deformation.
2007, 27(2): 136-142.
doi: 10.11883/1001-1455(2007)02-0136-07
Abstract:
By means of finite element method the blast wave stress propagation and stress distribution in the wall rocks damaged by initial tunneling excavation were numerically analyzed. The damage evolution of rocks subjected to the wave stress was evaluated upon the employment of JHC constitutive model and damage variable D of rock element. It is shown that the influence of initial damage existing in wall rocks on properties of wave stress propagation, affecting domain and distribution depends on the extents of initial damage. The initially existing damage has apparently affected on wave stress propagation and stress distribution as long as its quantity exceeds a threshold value. It turns out that there exists an effective acting span Lp by which the blast wave stress influences on th initially damaged rock as long as a certain volume of explosive remains. Within this domain, the rock damage induced by blast wave stress increases with the increment of initial damage of rocks. Beyond this area scaled by Lp, the accumulated residual inelastic strains and residual tensile stresses in the damaged elements seem to be capable of balancing the compression wave stress resulted from the later explosion, and therefore, prevent the elements from being over damaged. This mechanism seems to dissipate the blast wave stress action and vibration energy. The reason for this phenomenon and mechanism was interpreted. In addition, the relationship between the effective acting span of wave stress and the initial damage in terms of equivalent stress was derived.
By means of finite element method the blast wave stress propagation and stress distribution in the wall rocks damaged by initial tunneling excavation were numerically analyzed. The damage evolution of rocks subjected to the wave stress was evaluated upon the employment of JHC constitutive model and damage variable D of rock element. It is shown that the influence of initial damage existing in wall rocks on properties of wave stress propagation, affecting domain and distribution depends on the extents of initial damage. The initially existing damage has apparently affected on wave stress propagation and stress distribution as long as its quantity exceeds a threshold value. It turns out that there exists an effective acting span Lp by which the blast wave stress influences on th initially damaged rock as long as a certain volume of explosive remains. Within this domain, the rock damage induced by blast wave stress increases with the increment of initial damage of rocks. Beyond this area scaled by Lp, the accumulated residual inelastic strains and residual tensile stresses in the damaged elements seem to be capable of balancing the compression wave stress resulted from the later explosion, and therefore, prevent the elements from being over damaged. This mechanism seems to dissipate the blast wave stress action and vibration energy. The reason for this phenomenon and mechanism was interpreted. In addition, the relationship between the effective acting span of wave stress and the initial damage in terms of equivalent stress was derived.
2007, 27(2): 143-150.
doi: 10.11883/1001-1455(2007)02-0143-08
Abstract:
Acceleration of the shock generated by normal reflection of gaseous detonation wave was experimentally, numerically and theoretically investigated. The pizeo-electric transducers were employed to obtain the pressure history at the specific port. Based on two-dimensional reactive Euler equations and detailed chemical reaction model, numerical simulation was performed. The 2nd additive semi-implicit Runge-Kutta method and 5th order WENO scheme were respectively used to discretize the time and space terms. The numerical pressure history at the specific port was also obtained. Based on detonation theory and shock dynamics, the complicated wave evolution involved in the process of gaseous detonation reflection was analyzed and the velocity of reflected shock was obtained. The results show that numerical simulation and theoretical analysis qualitatively reproduce and explain the experimental phenomena. After gaseous detonation reflects on the right wall, the right-traveling rarefaction waves accelerate the reflected shock. The reason is that the shock Mach number increases and the gas flow velocity ahead of the shock decreases even though the acoustic velocity ahead of the shock decreases. Possibly due to the left unreacted or partly reacted mixture behind gaseous detonation wave, the reflected shock accelerates at low initial pressure more than at high initial pressure.
Acceleration of the shock generated by normal reflection of gaseous detonation wave was experimentally, numerically and theoretically investigated. The pizeo-electric transducers were employed to obtain the pressure history at the specific port. Based on two-dimensional reactive Euler equations and detailed chemical reaction model, numerical simulation was performed. The 2nd additive semi-implicit Runge-Kutta method and 5th order WENO scheme were respectively used to discretize the time and space terms. The numerical pressure history at the specific port was also obtained. Based on detonation theory and shock dynamics, the complicated wave evolution involved in the process of gaseous detonation reflection was analyzed and the velocity of reflected shock was obtained. The results show that numerical simulation and theoretical analysis qualitatively reproduce and explain the experimental phenomena. After gaseous detonation reflects on the right wall, the right-traveling rarefaction waves accelerate the reflected shock. The reason is that the shock Mach number increases and the gas flow velocity ahead of the shock decreases even though the acoustic velocity ahead of the shock decreases. Possibly due to the left unreacted or partly reacted mixture behind gaseous detonation wave, the reflected shock accelerates at low initial pressure more than at high initial pressure.
2007, 27(2): 151-158.
doi: 10.11883/1001-1455(2007)02-0151-08
Abstract:
The failure mode of ship structure attacked by typical semi-armour-piercing missile in target practice experiment was analyzed. The characters of internal explosion load and the failure mode of gross panel of the cabin were studied by numerical simulation. Results show that the explosion loads and the failure modes of the gross panel under explosion inside a cabin have many differences from under explosion in an open area; the dynamic response of the gross panel under explosion inside a cabin can not be simulated under explosion in an open area; the explosion loads acting on the gross panel inside a cabin, include reflected shock wave, converged shock wave on the corner, and the quasi-static pressure. Intensities of converged shock wave on the corners of two gross panels and three gross panels are 5 and 12 times larger than that of the reflected shock wave respectively. The gross panels of a cabin have 4 failure modes, under internal explosion loads, in which mode Ⅲ and Ⅳ are most frequent. The stiffeners of the panels placed on the blast side can enhance the local damage, but can weaken the converged shock wave on the corner, and decrease the tearing damage on the corner.
The failure mode of ship structure attacked by typical semi-armour-piercing missile in target practice experiment was analyzed. The characters of internal explosion load and the failure mode of gross panel of the cabin were studied by numerical simulation. Results show that the explosion loads and the failure modes of the gross panel under explosion inside a cabin have many differences from under explosion in an open area; the dynamic response of the gross panel under explosion inside a cabin can not be simulated under explosion in an open area; the explosion loads acting on the gross panel inside a cabin, include reflected shock wave, converged shock wave on the corner, and the quasi-static pressure. Intensities of converged shock wave on the corners of two gross panels and three gross panels are 5 and 12 times larger than that of the reflected shock wave respectively. The gross panels of a cabin have 4 failure modes, under internal explosion loads, in which mode Ⅲ and Ⅳ are most frequent. The stiffeners of the panels placed on the blast side can enhance the local damage, but can weaken the converged shock wave on the corner, and decrease the tearing damage on the corner.
2007, 27(2): 159-164.
doi: 10.11883/1001-1455(2007)02-0159-06
Abstract:
Using the dynamic caustic-test system, the PMMA model transmission-type experiment of dynamic caustics was carried out to simulate the blasting process of rock with joints. Varieties of dynamic intensity factors in the crack-tip field, extensions of cracks going through the joint planes for different distances between hole and joint were analyzed especially under the condition that the initial cracks and joint planes had different separation angles. Experimental results show that the dynamic intensity factor of the crack-tip and the extension speed decrease dramatically while the cracks go through joint planes but afterwards the intensity factor increases, that when the crack goes through the joint plane, it can deviate a short distance along the joint, and then continues to develop in its initial direction with respect to the appropriate distance between hole and joint.
Using the dynamic caustic-test system, the PMMA model transmission-type experiment of dynamic caustics was carried out to simulate the blasting process of rock with joints. Varieties of dynamic intensity factors in the crack-tip field, extensions of cracks going through the joint planes for different distances between hole and joint were analyzed especially under the condition that the initial cracks and joint planes had different separation angles. Experimental results show that the dynamic intensity factor of the crack-tip and the extension speed decrease dramatically while the cracks go through joint planes but afterwards the intensity factor increases, that when the crack goes through the joint plane, it can deviate a short distance along the joint, and then continues to develop in its initial direction with respect to the appropriate distance between hole and joint.
2007, 27(2): 165-170.
doi: 10.11883/1001-1455(2007)02-0165-06
Abstract:
A general Godunov finite difference schemes-WENO schemes which had fifth-order accuracy was used to make a numerical calculation for 2-dimensional axis symmetrical laser-supported plasma flow field under laser ablated solid target and laser ablated propulsion efficiency parameters(mechanical coupling coefficient etc.) was obtained by the simulation. The models of the calculation of ionization degree of plasma and the interaction between laser beam and plasma and the simplified eos(equation of state) of plasma were considered in the simulation. Comparision of simulation and calculation results shows that the different materials of target and the laser parameters (intensity, wave length etc.) and the geometry of target are the main factors which influence the laser propulsion efficiency.
A general Godunov finite difference schemes-WENO schemes which had fifth-order accuracy was used to make a numerical calculation for 2-dimensional axis symmetrical laser-supported plasma flow field under laser ablated solid target and laser ablated propulsion efficiency parameters(mechanical coupling coefficient etc.) was obtained by the simulation. The models of the calculation of ionization degree of plasma and the interaction between laser beam and plasma and the simplified eos(equation of state) of plasma were considered in the simulation. Comparision of simulation and calculation results shows that the different materials of target and the laser parameters (intensity, wave length etc.) and the geometry of target are the main factors which influence the laser propulsion efficiency.
2007, 27(2): 171-178.
doi: 10.11883/1001-1455(2007)02-0171-08
Abstract:
The scattering of a semi-cylindrical canyon and a crack with incident SH waves was studied based on Greens function. A special Greens function which was a fundamental solution of displacement field for a half-elastic space with a semi-cylindrical canyon bearing an anti-plane harmonic line-source force at any point was proposed for the present problem. And the scattering problem of SH-wave by a half-elastic space with semi-cylindrical canyon was solved. Then, at the actual position of cracks, the existent cracks could be reverted by using Greens function and the method of crack-division. Integration for the obtained solution of the whole problem was established, and the solution of the ground surfaces displacement amplitude was concluded.
The scattering of a semi-cylindrical canyon and a crack with incident SH waves was studied based on Greens function. A special Greens function which was a fundamental solution of displacement field for a half-elastic space with a semi-cylindrical canyon bearing an anti-plane harmonic line-source force at any point was proposed for the present problem. And the scattering problem of SH-wave by a half-elastic space with semi-cylindrical canyon was solved. Then, at the actual position of cracks, the existent cracks could be reverted by using Greens function and the method of crack-division. Integration for the obtained solution of the whole problem was established, and the solution of the ground surfaces displacement amplitude was concluded.
2007, 27(2): 179-184.
doi: 10.11883/1001-1455(2007)02-0179-06
Abstract:
The process of shock acted on a vibration and shock isolation system with double-stiffness was divided into two steps. In the shock action phase of a half sine wave, the response was calculated by using a double DOF model. In the free vibration phase, the response was calculated by adopting a single DOF system, the initial displacement and velocity of single DOF adopt the final value of the first phase. The property of the double-stiffness system in the shock of the half sine wave was analysed by using this method. Some conclusions were gained by being compared with the linear system. Results indicate the preferable effect of vibration and shock.
The process of shock acted on a vibration and shock isolation system with double-stiffness was divided into two steps. In the shock action phase of a half sine wave, the response was calculated by using a double DOF model. In the free vibration phase, the response was calculated by adopting a single DOF system, the initial displacement and velocity of single DOF adopt the final value of the first phase. The property of the double-stiffness system in the shock of the half sine wave was analysed by using this method. Some conclusions were gained by being compared with the linear system. Results indicate the preferable effect of vibration and shock.
2007, 27(2): 185-189.
doi: 10.11883/1001-1455(2007)02-0185-05
Abstract:
Dynamic compression tests of W-Ni-Mn alloy were performed, using cylindrical specimens 5 mm both in diameter and long with the split Hopkinson pressure bar (SHPB) technique. Both sections and fracture surfaces of specimens were observed with SEM. Connected with true stress-strain curves of specimens, it was found that adiabatic shear bands in sections of specimens appeared distinctly when specimens took place about 45% true strain. W-Ni-Mn alloy is easier to come into being adiabatic shear band(ASB) than the conventional tungsten heavy alloy, and has higher adiabatic shear sensitivity.
Dynamic compression tests of W-Ni-Mn alloy were performed, using cylindrical specimens 5 mm both in diameter and long with the split Hopkinson pressure bar (SHPB) technique. Both sections and fracture surfaces of specimens were observed with SEM. Connected with true stress-strain curves of specimens, it was found that adiabatic shear bands in sections of specimens appeared distinctly when specimens took place about 45% true strain. W-Ni-Mn alloy is easier to come into being adiabatic shear band(ASB) than the conventional tungsten heavy alloy, and has higher adiabatic shear sensitivity.
2007, 27(2): 190-192.
doi: 10.11883/1001-1455(2007)02-0190-03
Abstract:
The impact switch is a kind of inertial device that can sense impact acceleration and output on-off signal. A micro-mechanical impact switch is designed and fabricated with MEMS technology. The sensitive unit of the micro impact switch consists of a seismic mass supported with a cantilever beam. The movable mass is displaced to contact the micro electrode tip when subjected to impact acceleration. The chip size of the switch is 5 mm5 mm0.5 mm and the switch threshold is 3 000g while the response time is 84 s. It can survive ultra-high g-loads impact.
The impact switch is a kind of inertial device that can sense impact acceleration and output on-off signal. A micro-mechanical impact switch is designed and fabricated with MEMS technology. The sensitive unit of the micro impact switch consists of a seismic mass supported with a cantilever beam. The movable mass is displaced to contact the micro electrode tip when subjected to impact acceleration. The chip size of the switch is 5 mm5 mm0.5 mm and the switch threshold is 3 000g while the response time is 84 s. It can survive ultra-high g-loads impact.
