Void collapse and subsequent spallation in Cu50Zr50 metallic glass under shock loading by molecular dynamics simulations

Void evolution at the microscopic scale is an important part of the shock response of porous metallic glasses (MGs). Here, large-scale molecular dynamics simulations are used to investigate the shock loading of Cu50Zr50 MG, including thermodynamic quantities, shock-induced void collapse, and spall behavior. The results show that the shear transformation zone nucleation and growth around the void is the main plastic deformation mechanism for the shock-induced void collapse in MGs. The stress around the void is analyzed to reveal the evolution of the void shape and the relationship between the critical stress for the void collapse and the Hugoniot elastic limit stress. A model is proposed to predict the void collapse time in MGs. Softening occurs at around the location of the void after the void collapse due to a local temperature increase. Consequently, spallation is colocated with the high temperature region, rather than at the position associated with maximum tensile stress. Void growth and nucleation of tension transformation zones compete with each other as the shock intensity increases. At a high strain rate, the Cu50Zr50 MG shows more brittle fracture behavior with a larger number of voids and smaller average void size.