Void growth in bcc metals simulated with molecular dynamics using the Finnis–Sinclair potential

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 10⁹/s down to 10⁶/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 analyse 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.

Keywords:

• void growth
• molecular dynamics
• Finnis–Sinclair potential
• body-centred cubic
• bcc
• dynamic fracture
• nanocrystalline tantalum

Acknowledgements

It is a pleasure to thank Jim Belak, Eira Seppälä, and Laurent Dupuy for useful discussions, as well as the earlier work on voids in fcc metals. The initial atomic configuration for the nanocrystalline simulations was provided by Streitz, Glosli, and Patel 47. Computer resources were provided by Livermore Computing through a Supercomputing Grand Challenge project. This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Notes

Note

1. Summing just the three pairs with the lowest |u _i + u _i′|² gives a variant of centrosymmetry deviation that detects the fcc dislocation cores but not the stacking faults.