An atomistic investigation into the nature of near threshold fatigue crack growth in aluminum alloys

•Coupled atomistic–discrete dislocation modeling is used to study fatigue crack growth.•The growth threshold increases with an increase in homogeneous dislocation glide resistance.•The presence of dislocations near the crack tip promotes a change in crack growth direction.•Three mechanisms of fatigue crack propagation are observed, depending on dislocation glide resistance.

Despite decades of study, the atomic-scale mechanisms of fatigue crack growth remain elusive. Here we use the coupled atomistic–discrete dislocation method, a multiscale simulation method, to examine the influence of dislocation glide resistance on near-threshold fatigue crack growth in an aluminum alloy. The simulations indicate that the threshold increases with an increase in dislocation glide resistance, and that a transition in the crack growth direction can occur when dislocation nucleation is inhibited by other nucleated dislocations. Three main mechanisms of fatigue crack propagation are observed: cleavage along the primary slip plane, crack extension by dislocation emission, and crack extension by opening along lattice defects.