Effect of grain boundary ledge on the dislocation-free zone model of fracture: Transgranular microcrack nucleated from a grain boundary ledge

The effect of grain boundary ledge on the dislocation-free zone model of fracture is investigated in the case of a transgranular microcrack nucleated from a grain boundary ledge. The dislocation distribution functions to simulate the crack and plastic zone, the numbers of dislocations in the crack and plastic zone, the stress field, and the stress intensity factor at the crack tip (or the energy barrier for the dislocation emission from the crack tip) are obtained. If the Burgers vector of dislocations comprising the grain boundary ledge has the same sign as that of plastic zone dislocations, the dislocation distributions to simulate the plastic zone, the number of dislocations in the plastic zone, the stress field in the dislocation-free zone, and the stress intensity factor at the crack tip increase with increasing number of grain boundary ledge dislocations, but increase with decreasing grain size. Both sides of the grain boundary ledge dislocations have different effects on the dislocation-free zone size, plastic zone size, and the applied stress to accumulate the plastic zone dislocations. The stress intensity factor at the crack tip increases with increasing dislocation-free zone size. When there is no dislocation-free zone in front of the crack tip, the stress intensity factor is zero regardless of whether the grain boundary ledge dislocations exist.