Grain size dependent fracture toughness of nanocrystalline materials

A theoretical model is suggested which describes the combined effects of intergrain sliding and emission of edge dislocations from crack tip on the toughness of nanocrystalline (nc) materials. In the framework of the model, stress concentration near crack tip initiates intergrain sliding and it leads to generation of edge dislocations at triple junctions of grain boundaries (GBs); besides, stress concentration at crack tip initiates edge dislocations, which are stopped at the opposite GBs. Both these two deformation mechanisms result in blunting of cracks. The dependence of critical crack intensity factors on grain size was analyzed, it was demonstrated that the two deformation mechanisms lead to an increase of critical crack intensity factors nearly by two times than that in the dislocation free case.