Finite difference modelling for understanding the hydrogen assisted cracking in virtual slow strain rate tensile tests

Different hydrogen-induced cracking patterns have been observed on two construction steels belonging to the same strength grade for mooring offshore structures, when tested in a Slow Strain Rate Tensile test (SSRT) condition. A scenario is hypothesized, in which this behaviour arises from differences in hydrogen trapping capacity between the two steels. A novel finite difference modelling approach is proposed to assess the plausibility of this hypothesis. The model is designed to resemble the effect of the diffusible and the trapped hydrogen in the nucleation and growth of cracks during SSRT, and consequently in life service. The effect of different hydrogen trapping capacities has been simulated employing the proposed stress-diffusion-strength model. A higher content in traps led to fewer cracks; while the absence of traps led to a higher number of cracks. These results fit with the hypothesis, as variations in trapping capacity lead to variations in the number of cracks.