Anisotropic debris cloud formation after hypervelocity impact into rolled magnesium alloy plates

Abstract

Magnesium (Mg) alloys are attractive structural materials because of their high specific properties. However, their behavior under impact is complicated due to their anisotropic, hexagonal, close packed crystal structure and coupled deformation mechanisms of twinning and dislocation slip. Here we investigate the breakout and fragmentation of rolled AZ31B Mg alloy plates by the hypervelocity impact of spherical projectiles, using time-resolved and quantitative diagnostics. We find that the impact, subsequent penetration, and rupture of the rolled plate are followed in many cases by the development of a debris cloud that is not isotropic. We have quantified the degree of this asymmetry by employing multiple high-speed cameras, mounted along orthogonal directions, relative to the penetration axis of the projectile. A series of impact tests with velocities ranging from 1.2 to 3.6 km/s revealed that the formation and overall shape of the debris cloud were dependent on the projectile material and magnitude of the impact velocity. These salient features have also been captured in simulations of the impact event by incorporation of a simple anisotropic description of the material strength while retaining an isotropic model for material failure. Agreement between the experiments and model predictions suggests that the anisotropic strength response of Mg is primarily responsible for most of the observed anisotropy in the debris cloud formation, especially for impacts up to 3.0 km/s.