Multi-scale fatigue crack growth behavior and unified XFEM-VNE predicting approach of L-PBF titanium matrix composites

This study establishes an experimental and numerical framework to elucidate fatigue crack growth and life prediction in TiC-reinforced Ti-6Al-4V composites manufactured by laser powder bed fusion. In-situ fatigue tests were conducted under stress ratios of 0 and 0.3 at room temperature to monitor real-time crack growth. Subsequently, scanning electron microscopy was used to identify the underlying fracture mechanisms. Digital image correlation, interpreted through the strain energy density criterion, shows that the crack grows in a direction corresponding to the minimum distance to the elastoplastic boundary. A numerical approach combining the extended finite element method (XFEM) with adaptive local mesh refinement and variable-node elements was developed to accurately model the crack-tip stress field without constraining the mesh to crack geometry. Localized updates around the crack tip allowed small crack increments without compromising stress intensity factor stability. Crack growth direction is predicted using the maximum tangential stress criterion, and growth rates are evaluated via Paris’ law. Validation against experiments demonstrated good agreement in stress intensity factors and crack growth rates under studied conditions, confirming the framework as a reliable tool for fatigue life prediction and structural assessment of additively manufactured titanium matrix composites.