Dislocation-free zone model of fracture: The effect of transgranular microcrack nucleated from a grain-boundary ledge

Abstract

The effects of transgranular microcrack nucleated from a grain-boundary ledge on a dislocation-free zone model of fracture are investigated by a continuous dislocation modeling method. The dislocation distribution functions to simulate the crack and plastic zone, the number of dislocations in the crack and plastic zone, the stress field, and stress intensity factor at the crack tip are obtained. If the Burgers vector of dislocations composing the grain-boundary ledge has the same sign as that of the plastic zone dislocations, all the dislocation distributions that simulate the crack and plastic zone, the number of dislocations in the crack and plastic zone, the stress field in the dislocation-free zone, the stress intensity factor at the crack tip, the dislocation-free zone size, and the plastic zone size increase with an increasing number of grain-boundary ledge dislocations, but the applied stress σ to accumulate the plastic zone dislocations decreases with an increasing number of grain-boundary ledge dislocations. The effects of transgranular microcrack nucleated from a grain-boundary ledge on a fracture without a dislocation-free zone are also considered. 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.