Crack dislocation interactions in ionic crystals with rock-salt structure

The modification of the local stress intensity factor due to dislocations near a crack tip has been analysed using 2–D and 3–D potential function methods. Observations of dislocation configurations in ionic crystals with a rock–salt structure have also been made using the etch–pit technique, photoelasticity and high–voltage electron microscopy (HVEM). In thick crystals, hinge–type structures of slip bands were formed along {100} planes ahead of a {100} crack, while in thin crystals dislocation structures corresponding to the 45°–shear–type plastic zone were commonly observed. Based on the observed geometry of the crack tip dislocations, interactions between a crack and dislocations were calculated, and it was found that mode I shielding was induced by the dislocations in both structures.