Three-dimensional fatigue crack closure numerical modelling: Crack growth scheme

Abstract

Numerical models based on finite element method have been employed to analyse the plasticity induced crack closure phenomenon for a long time. These numerical analyses require the development of a plastic wake. During the development of the plastic wake a transient behaviour can be observed on the numerical results. Most of these previous analyses have been performed considering bi-dimensional models. The use of three-dimensional models has been extended during last years. Nevertheless, the methodology considered has been inherited from the bi-dimensional ones. Optimising the numerical parameters involved on the development of the plastic wake is a key issue to keep the computational cost under control, particularly when a three-dimensional analysis is considered. This study presents a three-dimensional analysis of the influence of the crack growth scheme on fatigue crack closure results. This three-dimensional analysis allows to study the influence of the number of loading cycles not just on plane stress or plane strain conditions but all along the thickness. In the present work, a CT aluminium specimen has been modelled three-dimensionally and several calculations have been made in order to evaluate the influence of the number of loading cycles between node releases and after releasing the last set of nodes on fatigue crack closure results. The numerical accuracy is analysed in terms of crack closure and opening values and in terms of strain and stress fields.