Cohesive zone based axisymmetric modelling of hydrogen-assisted cracking in a circumferentially notched tensile specimen

The paper presents an axisymmetric finite element model to study hydrogen-assisted cracking (HAC) in a circumferentially notched tensile (CNT) specimen of a high-strength steel. The model includes an axisymmetric 2-D stress analysis coupled with an axisymmetric 1-D hydrogen diffusion analysis. Crack initiation is handled through cohesive elements whose strength is adjusted depending on the local hydrogen concentration. The model successfully predicted the critical SIFs of tempered AISI 4340 under different hydrogen charging conditions in rising displacement tests. Furthermore, the model is able to simulate of typical delayed failure of specimens under HAC conditions in constant load tests. Reported HAC of three different microstructures of AISI 4340 was simulated under rising displacement condition, and the respective model parameters were then also used to simulate crack initiation in the same microstructures under constant load condition. Closeness of critical SIFs from both the simulations indicates that the model parameters calibrated through slow strain rate tests are transferable to constant load situations. Moreover, it is shown that the present 2-D analysis, while being computationally advantageous, is an acceptable alternative of a 3-D model reported earlier.