Microstructurally-sensitive fatigue crack nucleation in a Zircaloy-4 alloy

Microstructurally-sensitive fatigue crack nucleation and subsequently short crack growth were observed at an edge-notch in a textured Zircaloy-4 sample with the c-axis aligned perpendicular to the viewing surface. To understand the competition between the main crack and the secondary crack nucleation at the edge-notch root, a combined experimental and computational investigation was conducted to analyse various micro-scale mechanical quantities, including local strain, local stress, GND density, and stored energy density. A computational crystal plasticity finite element simulation that incorporated grain morphology, crystallographic orientation, and loading conditions was found to have good agreement with experimental results from the three-point bend fatigue test. The results showed that both the main crack and secondary crack nucleation sites had the highest magnitudes of local stored energy density, indicating that this factor was both necessary and sufficient for crack nucleation.