A model of extrusions and intrusions in fatigued metals I. Point-defect production and the growth of extrusions

Abstract

Based on recent experimental observations a realistic model of the evolution of the surface profile of persistent slip bands (PSBs) in fatigued metals is proposed. An essential feature of the model is the production of vacancies by the annihilation of edge dislocations which, combined with irreversible slip processes, leads to an elongation of the PSB parallel to the active slip vector. It is shown that a net extrusion forms rather rapidly. The growth processes and their dependence on temperature are discussed in detail. It is proposed that cracks initiate at the surface steps at the PSB–matrix interface and, at a later stage, also at the notch-peak profile from the random slip processes.