Mechanism Of Micro-Void Effect On The Shock Response Of Brittle Material

In the shock wave field,it's difficult to avoid the shock damage and failure of brittle material.Experimental studies under quasi-static and shock compression show that voids can significantly increase the plasticity of brittle material,but experimental results can not directly reveal the mesoscopic evolution mechanism inside the material.The purpose of this thesis is to develop a computer simulation study to reveal the physical mechanism of how voids affect the shock response of brittle material,and to provide physical understanding of how to avoid or delay the shock failure of brittle material.The thesis chooses "Lattice-spring model" as the calculation method,establishes a shock compression model to reasonably describe the phenomena such as large shock deformation,extension of a large number of cracks and medium breaking of brittle material.According to the analysis on the collapse process of isolated void,when the shock wave sweeps the void,the shear stress concentration will appear around the void,then shear cracks begin to initiate and propagate,broken medium starts to fill the void,leading to the sample's volume shrinks at the same time.In the shocked porous brittle material,there are a large number of broken medium generated during the shear cracks propagate,they can maintain plastic deformation process through relative slippage and rotation deformation even after the voids collapse completely.By the comparison of the mesoscopic deformation features under different void-patterns we can find that,in the samples of square void-pattern and hexagon void-pattern,the voids' penetration and volume shrinkage deformation dominates,and the strain localization degree is strong.While,in the samples of random void-pattern and triangle void-pattern,shear crack long extension and slippage and rotation deformation dominates,and the degree of strain localization is weak.The calculation results of macro shock response show that,the shock wave will gradually evolve into a double-wave structure of elastic wave-deformation wave when it propagates in porous samples.The porosity determines the HEL of porous brittle material.Porosity and shock stress together determine the propagation speed of deformation wave.Although the Hugoniot curve of porous brittle material always contains three parts,which are namely linear elastic stage,collapse deformation stage and slippage and rotation deformation stage,the collapse deformation stage makes the largest contribution to macro shock plasticity when the sample is in square void-pattern.