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.