An Exact Transient Study of Dislocation Emission and its Effects on Dynamic Fracture Initiation

Abstract

Closed-form transient solutions for the micromechanical process of screw dislocation emission from a stationary crack which is subjected to SH-wave diffraction are presented. The dislocations are allowed to leave the crack edge in arbitrary directions, either singly or in pairs. Imposition of an emission criterion that is both based on the dislocation force concept and is similar to criteria applied to quasi-static emission studies allows expressions for the instants of dislocation emission and arrest and the distance traveled by the dislocation to be obtained. These expressions are studied for their dependence on parameters such as emission direction and speed, and several distinctive dynamic effects are observed. A standard fracture criterion is then imposed, and conditions for determining whether fracture will precede or follow emission are established in terms of real time. Finally, some estimates for the orders of magnitudes of the parameters involved in this micromechanical process are given.