Dynamic Emission of Dislocations From a Moving Crack

The emission of dislocations from a propagating crack in the mode II or III situations is studied by computer simulation. While the crack is moving the steady state number of dislocations is smaller than the saturation number which could be emitted from a stationary crack and such a steady state number decreases with increasing crack velocity. The effect on the emission process of the applied stress, the lattice friction for dislocation motion and the critical stress intensity factor for dislocation emission is studied. The results include also the plastic zone size, the dislocation distribution, the dislocation-free zone, and the instantaneous crack velocity. The average crack velocity does not depend on the applied stress but depends only on the critical stress intensity factor for dislocation emission. When such a factor is zero as assumed in some theories, the crack does not move at all.