Assessment of three-dimensional crack growth in ductile layered material systems

Abstract

Fatigue crack growth in three-dimensions may follow complex patterns that depend on the local and global conditions of the material around the crack front. In layered material systems, crack growth may be enhanced or delayed over portions of the crack front as the latter approaches a dissimilar layer. Three-dimensional elasto-plastic finite element analyses were developed for the study of the effects of dissimilar layers ahead of the crack front on the crack driving force (crack tip opening displacement) and crack growth; the simulation of the latter was based on previous experimental data obtained from a fatigued specimen with identical tri-layer architecture. The efficiency of the model under elastic conditions was first assessed by comparison of its predictions with an exact analytical solution. Crack growth in the top layer was simulated up to a depth of around 95% of its thickness. The modelling was based on a re-meshing scheme and was applied to bi-layer and tri-layer architectures subjected to three-point bending. The crack front was positioned as close as possible to the dissimilar layer so that shielding and anti-shielding effects would be clearly observed. These three-dimensional simulations revealed that such effects are less intense than those predicted by previous 2D analyses that assumed through-width cracks.