Abnormal stress rebound after dynamic void coalescence in metallic glasses

Abstract

Understanding the microscopic mechanism of void coalescence is essential for evaluating the accumulation of dynamic damage in structural materials. However, experimental characterization of such a transient process remains extremely challenging. Here, the spatial arrangement of pre-existing voids and the influence of strain rate on dynamic void coalescence in a prototypical metallic glass (MG) are systematically investigated by molecular dynamics under conditions of uniaxial (1D) and triaxial (3D) tensile loading. It is found that, under 1D loading, the void arrangement affects only the stress-strain response, without impacting the growth and coalescence rate of the voids. However, under 3D dynamic loading, temperature around the voids undergoes a significant decrease after void coalescence. From the perspective of atomic packing, the number of mechanically stable <0,0,12,0> atomic Voronoi polyhedra recovers as strain rate goes up. As a result, material experiences abnormal stress rebound after void coalescence due to the unexpected microstructural hardening effect, which is absent in crystalline metals. Meanwhile, the stress rebound strength can be controlled by adjusting void characteristics or material parameters. This unusual stress rebound might find applications for metallic materials under extreme conditions.