Strong crack blunting by shear-coupled migration of grain boundaries in nanocrystalline materials

A theoretical model is proposed to illustrate the effect of shear-coupled migration of grain boundaries on the emission of lattice dislocations from a semi-infinite crack tip in nanocrystalline materials. The results obtained show that the shear-coupled migration process is able to considerably enhance the capability of the crack to emit dislocations, thus leading to strong crack blunting. Moreover, the combination of grain boundary migration and dislocation emission can serve as an effective toughening mechanism in nanocrystalline materials.