Void Growth in BCC Metals Simulated with Molecular Dynamics using the Finnis-Sinclair Potential

TL;DR

This study uses molecular dynamics with Finnis-Sinclair potentials to investigate void growth mechanisms in bcc metals at high strain rates, revealing transitions from twinning to dislocation flow and differences from fcc metals.

Contribution

It provides detailed atomic-level insights into void growth and plasticity mechanisms in bcc metals under high strain rates, using large-scale MD simulations.

Findings

Transition from twinning to dislocation flow with decreasing strain rate

Identification of dislocation loops as key plasticity features during void growth

Differences in void growth mechanisms between bcc and fcc metals

Abstract

The process of fracture in ductile metals involves the nucleation, growth, and linking of voids. This process takes place both at the low rates involved in typical engineering applications and at the high rates associated with dynamic fracture processes such as spallation. Here we study the growth of a void in a single crystal at high rates using molecular dynamics (MD) based on Finnis-Sinclair interatomic potentials for the body-centred cubic (bcc) metals V, Nb, Mo, Ta, and W. The use of the Finnis-Sinclair potential enables the study of plasticity associated with void growth at the atomic level at room temperature and strain rates from 10^9/s down to 10^6/s and systems as large as 128 million atoms. The atomistic systems are observed to undergo a transition from twinning at the higher end of this range to dislocation flow at the lower end. We analyze the simulations for the specific mechanisms of plasticity associated with void growth as dislocation loops are punched out to accommodate the growing void. We also analyse the process of nucleation and growth of voids in simulations of nanocrystalline Ta expanding at different strain rates. We comment on differences in the plasticity associated with void growth in the bcc metals compared to earlier studies in face-centred cubic (fcc) metals.