In a previous experimental study, it was observed that the break-through process of a cleavage front across a high-angle grain boundary could be highly non-uniform. While the central part of the boundary could be cleaved quite smoothly, the rest parts must be sheared apart. The trapping effect of grain boundary shearing was analyzed in considerable detail here. Before the shearing was completed, the crack flanks were locally pinned together and a bridging stress must be provided. The bridging stress has a negative contribution to the local stress intensity at the cleavage front segment that penetrates across the grain boundary, and thus the crack growth driving force must be increased. A closed-form equation was derived to relate the overall fracture resistance to the fracture mode through an energy analysis.

Resistance to Cleavage Cracking and Subsequent Shearing of High-Angle Grain Boundary. W.Lu, J.Chen, S.S.Chakravarthula, Y.Qiao: Engineering Fracture Mechanics, 2010, 77[5], 768-75