4. Curvilinear Fatigue Crack Growth Under Out-of-Phase Loading Conditions

Methods for predictive modeling and simulation of crack branching and curvilinear crack paths under cyclic out-of-phase loading conditions have been developed and implemented in a custom finite element code CRACK3D. 3D mixed-mode stress intensity factors (SIFs) for fatigue crack growth simulations with curved crack paths and curved crack fronts are determined using the 3D virtual crack closure technique (3D VCCT) and a locally structured re-meshing approach in which the local region immediately surrounding a moving crack front is automatically re-meshed with a structured mesh pattern to facilitate the 3D VCCT and maintain its accuracy. The prediction of the crack growth direction is achieved using the maximum circumferential stress criterion. Fatigue crack growth events under out-of-phase loading conditions in cruciform aluminum specimens with a central hole and an edge crack at the hole are simulated. Simulation predictions of crack branching angles and the curvilinear paths of the branched cracks agree well with experimental measurements.