Effect of pore shape on steady plastic shockwaves and collapse dynamics in porous metals

Abstract

Porous materials offer the possibility to optimize shock wave mitigation by monitoring, with additive manufacturing, the pore configuration (volume fraction, shape and spatial distribution of voids). Therefore, it is of interest to uncover the relationship between void configuration and shock wave response. In this paper we develop an analysis of planar plastic shock waves generated in porous aluminum by the impact of a projectile. Methodology and results can be easily extended to other materials. We focus specially on the relationship between shock-width and void-shape for given impact velocity and fixed initial volume fraction and spatial distribution of voids. We consider a Finite Element modeling of a periodic material with axisymmetric configuration. Each unit cell contains a spheroidal void with symmetry axis aligned along the impact direction. It is shown that the shock width is significantly affected by the process of void collapse. This process appears to be quite different for flat (oblate) and elongated (prolate) voids. For both types of voids, we analyze how the process and the speed of void closure are affected by the void aspect ratio, and we demonstrate that the shock width is increased by slowing down the speed of void collapse. Effects of the void aspect ratio on the void closure speed and on the shock-width are quantified. We explain why the slowest void closure and the largest shock width are obtained for spherical voids.