Numerical analysis of the fully-coupled continuum cohesive modeling on the hydrogen-assisted degradation behavior in high-strength steel

To predict brittle fracture in high-strength steels, this study introduces a methodology for analyzing hydrogen-assisted degradation. The proposed approach considers the fully coupled problems of deformation-hydrogen diffusion and cohesive zone modeling. The analysis of hydrogen diffusion assumes that trapped and lattice hydrogen remain in a equilibrium state while accounting for the relationships between the increase in trap sites and plastic strain. The diffusion model simulates hydrogen diffusion in the small scale yielding (SSY) configuration at a crack tip. The simulation results reveal that hydrogen diffusion follows the hydrostatic stress distribution around the crack tip region. Additionally, the plastic strain near this area leads to an increased number of trap sites. Notably, the simulations indicate that lattice hydrogen is the dominant source of embrittlement when a sufficient amount of hydrogen atoms dissolve into the steel, as compared to trapped hydrogen. The hydrogen-assisted degradation evolution is studied by investigating the influence of hydrogen in a cohesive zone modeling (CZM) with a trapezoidal traction separation law (TSL), based on Hydrogen-Enhanced DEcohesion (HEDE) framework. The fully computational framework is utilized to simulate the hydrogen-charged fracture toughness test in a (CT) specimen made of 30CrMo high strength steel. It is demonstrated that the load bearing capacity of the specimen decreases with an increase in the initial hydrogen concentration. Furthermore, the study examines the evolution of the initial crack time with varying initial hydrogen concentrations. The initial hydrogen concentrations are estimated to match the maximum loads observed in the experimental load-displacement curves based on computational framework. The computational CTOD-R curves for hydrogen generally follow the experimental data, the marginally elevated computational CTOD values to underestimate the embrittling in hydrogen-contaminated steel. Overall, the present study proves the capability of this numerical technique to reproduce experimental findings related to hydrogen-assisted fracture. [Display omitted] •A numerical study on predicting hydrogen-assisted degradation in steel is proposed.•HEDE is modeled by reducing the cohesive strength owing to hydrogen concentration.•The specimen's load-bearing capacity reduces with increasing hydrogen concentration.•The computational CTOD-R curves generally follow the experimental data.