Nucleation of partial dislocations at a crack was analyzed based a multiscale model that incorporates atomic information into continuum-mechanics approach. The crack and the slip plane as the extension of the crack were modelled as a surface of displacement discontinuities embedded in an elastic medium. The atomic potential between the adjacent atomic layers along the slip plane was assumed to be the generalized stacking fault energy, which was obtained based on atomic calculations. The relative displacements along the slip plane, corresponding to the configurations of partial dislocations and stacking faults, were solved through the variational boundary integral method. The energetics of partial dislocation nucleation at the crack in face-centered cubic metals (Al, Cu) were comparatively studied for their distinctive difference in the intrinsic stacking fault energy. Compared with nucleation of perfect dislocations in previous studies, several new features have emerged. Among them, the critical stress and activation energy for nucleation of partial dislocations were markedly lowered. Depending on the value of stacking fault energy and crack configuration, the saddle-point configurations of partial dislocations could be vastly different in terms of the nucleation sequence and the size of the stacking fault. These findings have significant implication for identifying the fundamental dislocation and grain-boundary-mediated deformation mechanisms, which may account for the limiting strength and the high strain rate sensitivity of nanostructured metals.

Nucleation of Partial Dislocations at a Crack and its Implication on Deformation Mechanisms of Nanostructured Metals. G.Liu, G.Xu: Journal of the Mechanics and Physics of Solids, 2009, 57[7], 1078-92