The formation of cracks in plastic flow. II

Abstract
The detailed mechanism by which a piled-up group of dislocations generates a crack is considered; it is suggested that a crack arises from short-range non-Hookian interactions of the dislocations at the head of the pile-up, and a model which takes some account of this is developed. The possibility of relieving the stresses round the pile-up by slip in the perfect lattice instead of by fracture is considered. Finally, it is shown that a crack can equally well be initiated by a smaller number of dislocations in each of several slip planes; this may be important in ductile materials.