This effect was investigated for the case of a transgranular micro-crack which nucleated from a grain-boundary ledge. The dislocation distribution functions which were required in order 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 energy barrier to dislocation emission from the crack tip) were obtained. It was found that, if the Burgers vectors of the dislocations which comprised the grain boundary ledge had the same sign as that of plastic zone dislocations, the dislocation distributions which simulated 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, increased with increasing number of grain boundary ledge dislocations. However, they increased with decreasing grain size. Each side of the grain boundary ledge dislocations had differing effects upon the dislocation-free zone size, plastic zone size, and the applied stress that was required in order to accumulate plastic zone dislocations. The stress intensity factor at the crack tip increased with increasing dislocation-free zone size. When there was no dislocation-free zone ahead of the crack tip, the stress intensity factor was equal to zero; regardless of whether grain boundary ledge dislocations existed.

S.T.Shiue: Journal of Applied Physics, 1996, 79[8], 3975-83