Characteristics of short fatigue crack growth in the vicinity of a low angle grain boundary

The influence on the crack growth behaviour of a short edge crack under fatigue due to different configurations of a nearby located low angle grain boundary is investigated under quasi-static and plane strain conditions. The geometry is modelled by distributed dislocation dipole elements in a boundary element method approach, and the plasticity is described by discrete dislocations, located along specific slip planes in the material. The crack is assumed to grow in a single shear mechanism due to nucleation, glide and annihilation of dislocations in the material. It was found that both the nature of the dislocations in the grain boundary, the distances between them and the placement of the dislocations in the grain boundary with respect to preferred slip plane directions strongly influenced the growth behaviour. It was found that, a boundary consisting of dislocations with Burgers vector pointing inwards into the material attracted the dislocations in the plastic zone. This resulted in lower growth rates as compared with a boundary consisting of dislocations having a Burgers vector pointing outwards of the material.