Closure of microcracks during unloading and the formation of reverse dislocations

Abstract

During unloading, local closure of the crack is followed by the emission of the first pair of reverse dislocations. The formation of an area of local contact during unloading occurs with a “bang”; the critical SIF of the external loads at this moment coincides with the value of the overall SIF of the field of the primary “sessile” dislocations. There is always a free gap between the crack tip and the area of local contact. External loads acting in the crack plane and not resulting in a stress concentration at the crack front play an important role in the emission of reverse dislocations (in particular, they may block their departure from the S-structure).