The stress intensity factor which was produced by a dislocation loop that was emitted at a crack tip in a 3-dimensional system was calculated. Numerical calculations, that were based upon experimentally studied configurations, indicated that a growing dislocation loop introduced a shielding effect. This effect was imposed by the loop portion closest to the emission point. On the other hand, sections far away from the crack tip had an anti-shielding effect. This conclusion was contrary to that drawn from a 2-dimensional approach. It was pointed out that a dislocation loop with a Burgers vector parallel to the crack plane could introduce mode-I shielding. Examples were presented for the stress intensity factor distribution along the crack tip, and for the evolution of their maximum and average values as a function of loop radius.

Three-Dimensional Analysis of the Interaction between a Crack and a Dislocation Loop M.A.L.De Oliveira, G.Michot: Acta Materialia, 1998, 46[4], 1371-83