Abstract
Hydrogen embrittlement alters defect activity, interfacial cohesion, and fracture processes in structural metals, yet predictive links between hydrogen–defect interactions and fracture toughness remain limited. The role of crack-tip constraint under hydrogen exposure is particularly unclear due to the coupled effects of mechanical fields, hydrogen transport, and competing embrittlement mechanisms. Here we develop H-CGM+, a mechanism-informed, void-based predictive framework that integrates hydrogen-enhanced localized plasticity (HELP), hydrogen-enhanced strain-induced vacancy formation (HESIV), and hydrogen-enhanced decohesion (HEDE), together with strain-dependent hydrogen trapping. A central advance is the introduction of a hydrogen-enhanced void nucleation (HEVN) mechanism, which links HELP and HESIV and provides a physically grounded description of hydrogen-suppressed ductile fracture. The framework captures the competition between ductile and brittle fracture modes under hydrogen within a unified formulation. Systematic analyses using a generic BCC material dataset show that increased crack-tip constraint continues to reduce fracture toughness, consistent with behavior in air, within the current mechanistic description. However, the model does not reproduce the emerging, yet not well-established, trend in which hydrogen may reverse this relationship. These results demonstrate both the predictive capability and current limitations of H-CGM+ and provide insights relevant to the design and integrity assessment of hydrogen infrastructure and structural components, highlighting key knowledge gaps and the need for targeted experimental and theoretical studies to advance predictive modeling of hydrogen-assisted fracture.