Molecular dynamics simulations were used to evaluate the primary interface dislocation sources and to estimate both the free enthalpy of activation and the critical emission stress associated with the interfacial dislocation emission mechanism. Simulations were performed on Cu in order to study the tensile failure of a planar Σ5 {210} 53.1° interface and an interface with the same misorientation that contained a ledge. Simulations revealed that grain-boundary ledges were more favourable as dislocation sources than were planar regions of the interface and that their role was not limited to that of simple dislocation donors. The parameters extracted from the simulations were used in a 2-phase composite mesoscopic model for nanocrystalline deformation that included the effects of both dislocation emission and dislocation absorption mechanisms. A self-consistent approach based upon the Eshelby solution for grains as ellipsoidal inclusions was augmented by the introduction of stress concentration into the constitutive law of the matrix phase to account for more realistic grain boundary effects. Model simulations suggested that stress concentration was required in the standard continuum theory in order to activate the coupled grain boundary dislocation emission and absorption mechanisms when activation energy of the dislocation source was determined from atomistic calculation on grain boundaries without consideration of impurities or other extrinsic defects.

Dislocation Nucleation from Bicrystal Interfaces and Grain Boundary Ledges - Relationship to Nanocrystalline Deformation. L.Capolungo, D.E.Spearot, M.Cherkaoui, D.L.McDowell, J.Qu, K.I.Jacob: Journal of the Mechanics and Physics of Solids, 2007, 55[11], 2300-27