Polycrystal deformation in a discrete dislocation dynamics framework

Grain boundaries (GBs) typically play an important role in obstructing the glide of dislocations in polycrystalline materials, giving rise to the classic Hall–Petch effect. Molecular dynamics simulations of the deformation of nanocrystalline materials demonstrate that GBs do much more. We extend the now classical discrete dislocation dynamics (DDD) simulation approach to account for GB sliding and the absorption, emission and transmission of lattice dislocations at GBs. This is done in a framework in which GB dislocations are nucleated and migrate along the GB in a manner that is an extension of the DDD formalism. We demonstrate that incorporation of a dislocation picture of GB dynamics allows all of these effects to competitively relax localized stress fields (such as from dislocation pileups) and act synergistically to modify the mechanical response of polycrystals—well beyond GBs simply blocking dislocation slip.