Molecular dynamics simulation of spall behavior of amorphous/crystalline composites under shock loading

Abstract

The industrial application of metallic glass (MG) is greatly limited due to its poor ductility and susceptibility to catastrophic fracture. The mechanical properties of MG can be effectively improved by adding crystal phases to make amorphous/crystalline composites. Meanwhile, spallation is a typical form of dynamic failure of materials under shock loading. However, the spall behavior of amorphous /crystalline composites has been rarely studied. In this work, the shock induced spallation process of Cu50Zr50/copper (Cu) composite materials was investigated through molecular dynamics (MD) simulations. It is found that stress waves transmit and reflect at interface due to the mismatch of acoustic impedance. Besides, MG is “softer” than the single crystal Cu from the perspective of stress wave propagation. By changing the loading direction, it was found that classical spall is more likely to occur in the Cu phase, while micro-spall is more likely to occur in the MG phase. However, as the loading velocity increases, the spall form in the Cu phase will also transform into micro-spall. The spall strength and strain rate through acoustic approximation and MD simulations were also obtained. Finally, it was observed that the tensile stress superposition region caused by interface reflection waves may form new danger points where spallation may initiate, thereby resulting in complex spall phenomena in composite materials. The conclusions obtained reveal the characteristics of the spall phenomenon in Cu50Zr50/Cu composite materials, which is beneficial to further understanding the spall mechanism and providing guidance for designing amorphous/crystalline composite materials under shock loading.