Influence of voids or He bubbles on the spall damage in single crystal Al

This paper presents the effects of initial voids or He bubbles on the spall damage in single crystal Al, with molecular dynamics simulations. The time evolution of pressure and temperature profiles, as well as the corresponding microstructure, are analyzed in detail. The initial spall of the samples containing voids or He bubbles is captured at the impact velocity 0.5 km s(-1), where we find the disordered atoms' generation and confluence from the initial voids or He bubbles. This state finally induces the relaxation of tensile stress (spall impulse). At the impact velocity 1.0 km s(-1), we observe homogeneous void nucleations, whose growth can be reduced by the initial voids and the growth of He bubbles. The spall strength of samples containing voids or He bubbles reduces by 2.6 GPa from 11.8 GPa (in a perfect sample). However, when the impact velocity increases to 2.5 km s(-1), a wide voids-included disordered zone is formed, where the homogeneous void nucleations become dominant and all the samples have the same spall strength of 8.6 GPa. Here, the tensile strain rates during spall are in the range of 4.0 x 10(10)-6.0 x 10(10) s(-1).