A localizing gradient damage model for hydrogen-assisted cracking

Hydrogen-assisted cracking remains a critical threat to the durability and safety of metallic structures, arising from the interaction of diffusible hydrogen with the microstructure, which weakens interatomic cohesion and promotes premature fracture. This work presents a novel chemo-mechanical modeling framework that integrates material deformation, stress-assisted hydrogen diffusion, and hydrogen-induced degradation of mechanical properties. A localizing gradient damage enhancement is employed to regularize softening responses and produce sharply localized damage zones that correspond to macroscopic cracks, thereby eliminating the spurious effects typically observed in conventional gradient damage models. The approach delivers physically consistent, mesh-objective crack propagation and seamless integration into standard finite element workflows without requiring predefined crack paths or cohesive interfaces. The framework is implemented using a staggered solution strategy to ensure stable convergence even in nonlinear regimes and is validated through three representative case studies: a cracked plate under hydrogen charging, compact tension testing subjected to internal hydrogen-assisted cracking, and single-edge notch tension tests in sour environments. The simulations reproduce key experimental trends and accurately capture the interplay among hydrogen transport, stress fields, and damage localization. Owing to its predictive capability, numerical robustness, and ease of implementation, the proposed method provides a practical computational tool for assessing hydrogen-induced fracture and structural integrity in hydrogen-rich environments.