Fatigue Crack Growth Modeling: Effect of the Stress State on Fatigue Enhanced by Microvoid Damage

In this work, the plastic work computed at the crack tip was used in a node release criterion to predict fatigue crack growth (FCG) in an AA6082-T6 alloy. Distinct finite elements and boundary conditions were employed to achieve different stress states in the specimen. The numerical model was employed to predict the FCG rates in both constant and variable amplitude loadings. The obtained results show that the models considering both plane strain and plane stress states provide reasonable predictions of the experimental data, both in terms of the slope of da/dN- $\mathrm{\Delta K}$ curves and the transient behavior induced by overloads. The 3D model with plane stress conditions can simulate the intermediate stress state that shall occur in the physical specimen. The best predictions, both in constant and variable amplitude loading conditions, were obtained with this 3D model. Nevertheless, the higher FCG obtained with the increase in the specimen's thickness could not be observed with the employed numerical models. This trend should be related to more complex interactions between the surface and the interior regions of the crack tip that can only be captured with more complex 3D models that describe the entire thickness of the specimens.