Dynamic And Thermodynamic Response Of Porous Metals Under Impact

The response of porous metals to impact is a research area with increasing interest both on civil and military applications.It covers both fields of impact dynamics and porous materials,and there are a few questions worthy of further study.Constitutive relation of porous metals under impact was studied first in this work,including the Hugoniot curves of different metals with various porosities,and the Hugoniot elastic limits?HEL?of porous metals.Three calculation methods of adiabatic impact curve of porous metals were analyzed in detail,especially on the algorithm and precision.A new three-step method was proposed for the calculation of constitutive relation of porous metals under impact.The impact response of porous metal was theoretically studied in which impact was loaded by direct explosion.The parameters of initial shock wave were computed through the method of impendence matching of impact,and planar shock wave decay in porous metal was analyzed with characteristic method.The results showed that there is a lower initial shock wave in porous metal than that in relative metal with theoretical density.Shock wave decays faster in porous metal than in condensed one,and the decay ratio is more sensitive to the porosity.The impendence of base metal,the detonation feature and density of explosive,the constraint condition were also affecting the attenuation of shock wave.Based on the analyses of the deficiency of homogenous approximation of constitutive relation of porous metal and characteristic method,a critical void size was deduced which is in the range of 10^-3mm¹0^-1mm as the same level of the width of shock front.The openness of voids and connectivity between them were also analyzed,and these features greatly affect the energy absorption and buffering performance of porous metal.Numerical simulations of different void shapes were conducted with explicit dynamic software,namely LS-DYNA code.And the results showed that the shock wave attenuation performances are good for those porous metals with circle voids,while those with triangle and hexgon voids are better,and those with square voids are poor.Temperature rise of porous metal under impact was also studied,and temperature rising may be attributing to the following mechanics: plastic deformation of the base metal,friction of the void walls,gas compress in voids,and surface energy release as the voids collapse in the adiabatic impact process.Using a granular tungsten model,the void walls friction process of porous metal was studied with numerical simulation method,and the simulated results were agree with the theoretical analysis and that in literatures.Furthermore,temperature rise in the local area of friction was computed,and was compared with the metal point of tungsten under high pressure in literature,based on which a conclusion can be drawn that tungsten,with highest melt point in metals,can be locally melted in porous form under impact.The last item in this work is the discussion of mechanism of energy concentration of impact,which includes plastic work,defect produce,and phase transform,etc.as that in a condense metal,while the effects in porous metals are stronger.