Dislocation and grain-boundary processes contributed significantly to plastic behaviour in polycrystalline metals, but a full understanding of the interaction between these processes and their influence on plastic response has yet to be achieved. The coupled atomistic discrete-dislocation method was used to study edge dislocation pile-ups interacting with a Σ11-<113> symmetric tilt boundary in Al at zero temperature under various loading conditions. Nucleation of grain-boundary dislocations at the dislocation/grain-boundary intersection was the dominant mechanism of deformation. Dislocation pile-ups modify both the stress state and the residual defects at the intersection, the latter due to multiple dislocation absorption into the boundary, and so change the local grain-boundary/dislocation interaction phenomena as compared with cases with a single dislocation. The deformation was irreversible upon unloading and reverse loading if multiple lattice dislocations absorb into the boundary and damage in the form of micro-voids and loss of crystalline structure accumulates around the intersection. Based upon these results, the criteria for dislocation transmission formulated by Lee, Robertson and Birnbaum were extended to include the influences of grain-boundary normal stress, shear stress on the leading pile-up dislocation and minimization of step height at the intersection. Two possible yield loci for the onset of grain-boundary dislocation nucleation versus compressive stress and relevant shear stresses were derived from the simulations. These results, and similar studies on other boundaries and dislocation characters, guide the formulation of continuum constitutive behaviours for use in discrete-dislocation or strain-gradient plasticity modelling.

Multiscale Modelling of Dislocation/Grain-Boundary Interactions - I. Edge Dislocations Impinging on Σ11 (113) Tilt Boundary in Al. M.P.Dewald, W.A.Curtin: Modelling and Simulation in Materials Science and Engineering, 2007, 15[1], S193-215