Effectiveness and necessity of physics-based crystalline plasticity finite element method in analyzing fatigue crack behavior with strain localization

Strain localization (SL) in metals manifests in various forms, including dislocation slip bands, Portevin-Le Chatelier (PLC) bands, dislocation pile-ups at grain boundaries, and shear bands. These phenomena contribute to strain hardening and softening, significantly influencing crack behavior. Although a physics-based crystal plasticity finite element method (CPFEM) model incorporating SL can simulate these localized deformation mechanisms, its suitability and accuracy in predicting stress and strain distribution around the crack tip remain uncertain. Furthermore, the necessity of employing CPFEM over the conventional elastic-plastic finite element method (EPFEM) for fatigue crack behavior prediction remains a subject of investigation. To address this, we analyzed the plastic strain distribution around the notch tip using a physics-based CPFEM model incorporating SL, complemented by an in situ tensile test on a notched specimen. The role of CPFEM in fatigue crack behavior prediction is evaluated by comparing its strain distribution results with those obtained from EPFEM around the notch tip. The findings indicate that the physics-based CPFEM model incorporating SL reliably predicts plastic strain distribution around the notch tip. Moreover, the model successfully captures SL phenomena arising from dislocation slip, PLC effects, shear band formation, and grain boundary interactions. Additionally, CPFEM is essential for accurately predicting damage accumulation fatigue crack propagation (DA-FCP).