Numerical simulation of hydrogen induced delayed fracture of AISI4135 high strength steel using cohesive zone modeling

High strength steels are susceptible to hydrogen induced delayed fracture (HIDF). A sequential coupling calculation on HIDF of high strength steel was developed based on cohesive zone modeling (CZM) using finite element program-ABAQUS. The calculation procedure contained three steps: elastic plastic stress analysis, stress assisted transient hydrogen diffusion and cohesive stress analysis using hydrogen dependent linear traction-separation law. Using this method, the prediction of fracture time and crack initiation location of pre-charged notched bar of AISI4135 high strength steel was obtained. The effects of stress concentration factor, initial hydrogen content, and tension load were also considered. The results show: (i) predictions of the time to fracture were in good quantitative agreement with the experimental results; the hydrogen dependent cohesive zone modeling can be used in prediction of failure in actual structures; (ii) crack initiation occurs when a critical hydrogen concentration at the location of stress peak is reached by accumulation, the critical hydrogen concentration is dependent on stress concentration factor and tension load, but independent of initial hydrogen content; (iii) as one of the three parameters mentioned above decreasing, the fracture initiation time and the critical hydrogen concentration increase.