The discrete nature of the growth and arrest of microstructurally short fatigue cracks modelled by dislocation technique

Growth of a microstructurally short edge crack in the neighbourhood of a grain boundary has been studied using a dislocation technique. Influence of the distance between the crack tip and a high-angle grain boundary was studied for 5000 load cycles. Growth rate was found to change stepwise during crack advance, both accelerating and decelerating, and finally retarding before crack arrest. Crack propagation is ruled by the competition between the shielding effect from the dislocations in the plastic zone and the stress field increase due to crack extension, and clearly shows a discrete behaviour at growth below the fatigue threshold load.