Evaluation of threshold stress intensity factor of hydrogen embrittlement cracking by indentation testing

The present study investigated hydrogen embrittlement (HE) cracking upon indentation of high-strength steel. When an indentation test was applied to high-strength steel that included absorbed hydrogen, radial cracks initiated and propagated at the corners of the indentation impression, whereas the as-received steel with no hydrogen absorption exhibited no cracking. In addition, the length of the hydrogen-induced indentation cracks was found to be dependent on the hydrogen content in the steel. A combined experimental and computational investigation was conducted for a mechanistic study of Vickers indentation cracking caused by hydrogen embrittlement. Crack propagation was simulated based on a cohesive zone model in the finite element method and the stress intensity factor for the crack was evaluated. It was found that the simulated crack initiates at loading, and then propagates upon unloading. The value of the stress intensity factor at the indentation crack was in agreement with the threshold resistance to crack propagation for HE cracking (threshold stress intensity factor, KISCC). This suggests that the length of the cracks can be used to evaluate the susceptibility of the steel to HE cracking.