Role of a Shear Planar Mesodefect in Nucleation of Crack at Grains Junction Due to Athermal Grain Boundary Sliding

We consider the conditions for microcrack nucleation in a grain junction due to athermal sliding along the grain boundary, containing a strain-induced shear-type planar mesodefect. The dependences of critical external stress of microcrack nucleation on the mesodefect length, its strength and the threshold stress of athermal sliding are obtained. It is shown that the presence of the mesodefect at the grain boundary can lead to a significant decrease of the crack nucleation stress in comparison with the case of pure grain boundary sliding. It is concluded that the induced athermal grain boundary sliding, carried out by the motion of the glissile components of dislocations, accumulating at the grain boundaries during intragranular plastic deformation, can be considered as one of the possible mechanisms for microcracks nucleation in materials with fragmented structure.