Void Growth in Single and Bicrystalline Metals: Atomistic Calculations

Abstract

MD simulations in monocrystalline and bicrystalline copper were carried out with LAMMPS to reveal void growth mechanisms. The specimens were subjected to both tensile uniaxial and hydrostatic strains; the results confirm that the emission of (shear) loops is the primary mechanism of void growth. However, these shear loops develop along two slip planes (and not one, as previously thought), in a heretofore unidentified mechanism of cooperative growth. The emission of dislocations from voids is the first stage, and their reaction and interaction is the second stage. These loops, forming initially on different {111} planes, join at the intersection, the Burgers vector of the dislocations being parallel to the intersection of two {111} planes: a (110) direction. Thus, the two dislocations cancel at the intersection and a biplanar shear loop is formed. The expansion of the loops and their cross slip leads to the severely work hardened layer surrounding a growing void. Calculations were carried out on voids with different sizes, and a size dependence of the stress response to emitted dislocations was observed, in disagreement with the Gurson model[l] which is scale independent. Calculations were also carried out for a void at the interface between two grains.

Finite-temperature non-equilibrium quasi-continuum analysis of nanovoid growth in copper at low and high strain rates

“…The resulting nanovoids subsequently grow by the emission of discrete lattice dislocations through a variety of intricate dislocation reaction paths (Marian et al, 2004(Marian et al, , 2005Meyers et al, 2009). At extremely high strain rates, nanovoid growth can be effectively simulated using molecular dynamics (Belak, 2002;Seppälä et al, 2004;Dávila et al, 2005;Traiviratana et al, 2007;Rudd, 2009;Bringa et al, 2010b;Lubarda, 2011;Tsuru and Shibutani, 2007). These studies reveal, among other useful insights, that nanovoids indeed cavitate upon the attainment of a critical stress or strain through the emission of shear and/or prismatic dislocation loops, resulting in irreversible void growth.…”