Three dimensional analysis of the interaction between a crack and a dislocation loop

In this paper is calculated the stress intensity factor induced by a dislocation loop emitted at a crack tip in a three dimensional system. The numerical calculations, performed at experimentally studied configurations, indicate that a growing dislocation loop induces a shielding effect and that this effect is imposed by the loop portion closest to the emission point. On the other hand, sections far from the crack tip have an anti-shielding effect. This conclusion is contrary to the one derived from a two-dimensional approach. It must be pointed out that a dislocation loop with a Burgers vector parallel to the crack plane can induce a mode I shielding. Examples are presented for both the stress intensity factors distribution along the crack tip and the evolution of their maximum and average values with the loop radius. (C) 1998 Acta Metallurgica Inc.