Integrated in-situ experimental and crystal plasticity finite element investigation on grain-scale localized damage and fatigue prediction of forged Ti-6Al-4V alloy

Understanding the material properties and fatigue behavior of titanium alloys at the microscale is essential for improving the reliability of aerospace and mechanical components. In this study, an in-situ tensile experiment was conducted on Ti-6Al-4V alloy, combined with scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) characterization, revealing the grain deformation, the evolution of grain orientation, and the accumulation of dislocation density during the tensile process. The material constitutive parameters of Ti-6Al-4V were calibrated for the crystal plasticity finite element method (CPFEM) framework. A realistic grain-scale model was then established based on the experimentally obtained microstructure, and cyclic loading simulations were performed to evaluate the local deformation and stress evolution. Using a damage-based criterion, the initiation and progression of microstructural damage within grains were quantified and visualized through damage contour diagrams. The results indicate that damage localization can be classified into two main types: within small grains whose basal planes are approximately perpendicular to the tensile direction, and at the triple-grain junctions of larger grains with basal planes approximately parallel to the tensile direction. Based on these localization characteristics, a gradient-based correction method is proposed, in which the maximum damage value is averaged over a critical radius to account for local gradients. The method was validated against low-cycle fatigue tests, demonstrating high accuracy in fatigue life prediction. The outcomes of this study provide valuable insights into fatigue damage mechanisms at the microstructural level of titanium alloys.