Low-strain fatigue in 316L steel surface grains: a three dimension discrete dislocation dynamics modelling of the early cycles. Part 2: Persistent slip markings and micro-crack nucleation

Abstract

The early stages of the formation of persistent slip markings in fatigue are analysed using three-dimensional discrete dislocation dynamics modelling. Surface displacements due to slip are computed using a specific post-processing method. Fatigue simulations under various strain ranges and grain sizes have been performed. The resulting surface slip markings and their evolutions are analyzed quantitatively in terms of marking height and thickness. A detailed scheme for persistent slip marking formation and morphology is proposed in relation to the persistent slip-band dislocation arrangements present within the grain. The simulations show the crucial role of these arrangements for the extrusion–intrusion growth and localisation of slip at the band edges. Local stress concentrations inside the crystal and their relationship to damage initiation are also analysed. The results provide insights for an original micro-crack initiation scheme, combining different initiation mechanisms as described in the literature.