Dislocation Emission and Crack Dislocation Interactions

An understanding of the crack initiation and crack growth in metals spanning the entire spectrum of conventional and advanced has long been a major scientific challenge. It is known that dislocations are involved both in the initiation and propagation of cracks in metals and alloys. In this review, we first describe the experimental observations of dislocation emission from cracks under stress. Then the role played by these dislocations in fatigue and fracture is considered at a fundamental level by considering the interactions of crack and dislocations emitted from the crack. We obtain precise expression for the equilibrium positions of dislocations in an array ahead of crack tip. We estimate important parameters, such as plastic zone size, dislocation free zone and dislocation stress intensity factor for the analysis of crack propagation. Finally, we describe very recent novel and significant results, such as residual stresses and relatively large lattice rotations across a number of grains in front of the crack that accompanies fatigue process.

Damage Zone Size Limit During the Crack Propagation

The principal goal of this work is to limit the damage zone length during the crack propagation in brittle materials. This study is based on the determination of stress fields by varying the distance between a semi-infinite crack and a neighboring dislocation. The model suggested is a rectangular element (a dish), having a semi-infinite crack in one of its ends and a dislocation located in the vicinity of a crack-tip, subjected to a tensile stress on mode I. The problem is treated numerically using Finite Element Method.For each distance between the two cracks (semi-infinite crack and dislocation), stress fields are given. On the basis of these stress fields, a limiting damage zone length is obtained.