Atomic-scale insights into spallation of monocrystalline tantalum: pulse duration and peak stress effects via molecular dynamics

The fracture behavior of materials under dynamic loading exhibits fundamentally distinct characteristics compared to quasi-static loading. This study employs large-scale molecular dynamics (MD) simulations to investigate stress history effects on spall behavior of monocrystal tantalum (Ta), a model body-centered cubic (BCC) metal. By systematically modulating tensile stress history (pulse duration: 1-8 ps; peak stress: 10.3-97.1 GPa) while maintaining invariant compression history, we elucidate the atomic-scale interplay between stress evolution and void evolution. Key findings reveal that heterogeneous stress distributions arising from intrinsic defects govern preferential void nucleation at localized stress concentrations. Peak stress dominates damage initiation, enhancing void nucleation and growth rates. Pulse duration primarily influences damage accumulation through extended void coalescence, increasing final damage ratio. A critical threshold of peak stress (71.2 GPa) emerges, above which spall strength becomes independent of peak stress due to premature stress equilibrium between rarefaction wave convergence and void-mediated relaxation. Below this threshold, spall strength decreases with peak stress reduction as insufficient rarefaction wave causes premature stress decay. These results establish a relationship between loading parameters and damage progression while validating the stress competition theory at atomic resolution. The identified threshold behavior and microstructure-dependent nucleation mechanisms provide fundamental insights for predictive modeling of dynamic fracture in BCC metals.