Fracture anisotropy in additively manufactured SS 316L: A phase-field approach

Additively manufactured (AM) metallic components often exhibit pronounced anisotropy due to deposition-induced microstructural features, which strongly influence their deformation and fracture behavior. In this work, a coupled anisotropic phase-field fracture framework incorporating rate-independent elastoplasticity is developed to model fracture in directed energy deposited AISI 316L stainless steel, with explicit sensitivity to deposition direction. The formulation combines isotropic linear elasticity with stress-based spectral decomposition to ensure tension–compression asymmetry. Fracture anisotropy is introduced through a structural tensor embedded in the crack surface density function, while plastic deformation is described using classical J 2 plasticity with isotropic hardening. The model preserves the variational structure of the phase-field approach, with plasticity influencing fracture indirectly through the evolution of elastic strains and a crack-driving history variable. An extensive experimental campaign, including quasi-static tensile testing of specimens extracted along multiple build orientations, digital image correlation, and microstructural and fractographic analyses, is conducted to characterize anisotropic mechanical response and failure mechanisms. Numerical simulations successfully reproduce the experimentally observed orientation-dependent stress–strain behavior, crack paths, and fracture modes, demonstrating the capability of the proposed framework to capture the interplay between plasticity, anisotropy, and fracture in AM metals. The results highlight the critical role of deposition direction in governing fracture resistance and provide a robust predictive tool for failure analysis of AM structures.