Damage evolution during spallation of Metallic Glasses under Femtosecond Laser Loading using an MD-TTM method

Metallic glass (MG) has significant potential applications in extreme environments involving ultra-high strain rate loading owing to its excellent mechanical properties. However, the dynamic tensile fracture (spallation) mechanisms of MGs under ultra-high strain rate loading remain unclear. In this paper, classical molecular dynamics simulations coupled with the two-temperature model are employed to systematically investigate the spallation of Cu₅₀Zr₅₀ metallic glass under femtosecond laser loading. Moreover, the effects of a pre-existing void at different locations on spallation damage are also studied. The results show that laser energy deposition generates a rapidly attenuating triangular stress wave, which differs fundamentally from the nearly constant-amplitude shock waves produced by conventional piston loading. With increasing laser energy density, the peak stress increases while its growth rate gradually decreases and approaches saturation. Correspondingly, the failure mode transitions from classical spallation to micro-spallation characterized by distributed void nucleation. In addition, nanoscale voids introduced at different locations only induce short-term localized perturbations and exert negligible influence on the global stress-wave structure and the overall spallation evolution. These findings provide new insights into the spallation mechanisms and defect sensitivity of metallic glasses under femtosecond laser–induced ultra-high strain rate loading.