Shock response of nanoporous magnesium by molecular dynamics simulations

Shock response of nanoporous magnesium (np-Mg) is investigated by using nonequilibrium molecular dynamics simulations. Hugoniot curves of Mg are obtained and agreed well with experimental data. Two typical mechanisms of void collapse under c-axis loading are revealed: the plasticity mechanism and the internal jetting mechanism. The plasticity mechanism, which dominates under weak shock intensity, leads to transverse collapse of voids; while the internal jetting mechanism, which plays important role under higher shock intensity, leads to longitudinal filling of voids. In plasticity induced void collapse, dislocations activities on void surface are found to concentrate at positions with the incident angles being 60 degrees and 120 degrees. This is closely related to the basal slip system {0001}<<(1)over bar>2 (1) over bar0> and can be well explained from a perspective of continuum mechanics. The thermodynamic characteristics during void collapse are discussed. The energy dissipation in np-Mg is correlated to local temperature risen and stress attenuation during void collapse, which are resulted from a series of plastic activities at microcosmic (including dislocation, shear ring and fault movement, etc.). In addition, our results also discover that spall strength of np-Mg under shock loading is influenced by shock intensity and void size. In general, it will decrease with the increase of shock intensity, and large size void has a significant weakening effect while small size void has a slight enhancing effect.