Dislocation modelling of fatigue cracks: An overview

The intrinsic threshold behavior of fatigue cracks and the disappearance of any cyclic plastic deformation below a threshold value can be understood by taking into account the discreteness of plasticity with recourse to discrete dislocation models. The aim of this paper is to document the progress in the discrete dislocation modelling within the past twenty years and the resulting increase in the understanding of fatigue cracks. The problems addressed are (1) the nature of the intrinsic fatigue threshold, (2) the influence of microstructure and/or of the mean stress level on the crack tip deformation and (3) the physical reason for the minimum striation spacing at small stress intensity ranges. A particular purpose of this paper is to compare the different dislocation models proposed in the literature in order to differentiate aspects of fatigue crack growth that do and do not depend on modelling and on microstructural details.