Dependence of Ductile and Brittle Response on Initial Energy Dissipation Mechanism at Crack Tip

Abstract

The criteria which determine the initial energy dissipation mechanism that is activated at or near a crack tip are derived. The possible mechanisms considered are cleavage, crack tip dislocation nucleation and also Frank-Read source activation near the tip. The criteria can be succinctly expressed in graphical form. It is suggested that a change in the initial energy dissipation mechanism may determine the conditions under which the brittle to ductile transition occurs. The criteria compare favourably to several experiments in the literature which address the competition between the various energy dissipation mechanisms.