The influence of yield stress on fracture of NaCl crystals

The critical force for crack initiation in NaCl crystals is measured as a function of yield stress (τy). Dislocation slip bands generated at the crack tip are observed. For τy > 1.5 MN/m2, the crack extends without generating dislocations. For τy < 1.5 MN/m2, dislocation slip bands are introduced on {110} planes obliquely backward from the crack tip, and the degree of the local plastic deformation is insensitive to the yield stress. With decreasing yield stress, the critical force for crack extention becomes smaller.