Effect of dislocation-GB interactions on crack blunting in nanocrystalline materials

A theoretical model of crack blunting has been developed by considering the interactions between dislocations and grain boundaries in nanocrystalline materials. Dislocations emitted from cracks are stopped at or/and penetrated through grain boundaries, which depends on the total force acting on the dislocations as well as the energy barrier of the grain boundaries. The energy barrier for dislocation penetration is highly sensitive to the residual Burgers vector's magnitude. The maximum number of dislocations emitted from a crack and the number of dislocations penetrated through the grain boundary are calculated. It is demonstrated that crack blunting depends significantly on both grain size and grain boundary misorientation, and the values of critical stress intensity factors calculated by considering the interactions between dislocations and grain boundaries are much larger than those of dislocations stopped at grain boundaries.