The influence of the Poisson’s ratio and corner point singularities in three-dimensional plasticity-induced fatigue crack closure: A numerical study

In this paper three-dimensional finite element analyses of a plate with a central crack were performed to investigate whether or not the closure behaviour is influenced by the effect of corner point singularities and Poisson’s ratio. Both crack closure and corner point singularities are essentially “free surface” effects and it is difficult to look at 3D crack closure without addressing the associated stress singularity problem. These effects are studied by modifying the shape of the crack front and quantifying both stress singularity and closure level along the crack front. In the first part of this work, the power of the singularity along the crack front is assessed using a log–log regression analysis of the stresses and displacements. The thickness of the boundary layer and the stress intensity factors along the crack front were also assessed. In the second part of the paper, the closure behaviour is assessed for 3D straight crack fronts and crack fronts with a different shape, for different values of the Poisson’s ratio. This work shows that the magnitude of the stress intensity factor along the crack front is higher than the predictions for plane strain by about 5.5% for a Poisson’s ratio of 0.3. In addition, this study supports that corner point singularities do not seem to significantly influence the closure behaviour of 3D fatigue cracks.