On evaluation of fatigue crack front shapes

Abstract

Experimental studies have demonstrated that the front of fatigue cracks in plates made of the various materials are often notably curved. However, for the sake of simplicity, the crack shape front and its evolution during crack propagation are normally disregarded in the current procedures for the fatigue crack growth evaluation. It is of great practical importance to understand this phenomenon, develop modelling tools and incorporate more realistic crack front shapes into fatigue failure analysis. These modelling tools are expected to better predict failure and life-time of plate and shell components subjected to the cycling loading. In this study, the steady-state front shapes of the through-the-thickness cracks are investigated. When the size of the plastic zone is very small, the angle at which the crack front intersects the free surface is governed by the three-dimensional (3D) corner singularity or by a critical angle, which is a function of Poisson's ratio. The steady state conditions of fatigue crack propagation also require the uniform distribution of the local effective stress intensity factor range along the crack front. This parameter is evaluated numerically for different crack front shapes using 3D Finite Element Analysis (FEA). This paper presents the selected results of the numerical simulations, and a comparison between the obtained results and the outcomes of the experimental studies.