Modeling of the Slow Crack Growth Caused by Internal Hydrogen in Metals

Hydrogen-induced slow crack growth exhibits, in general, three distinct stages of crack growth kinetics, and stages I and II are controlled by hydrogen diffusion. A model that describes the kinetics of crack growth caused by internal hydrogen (in stages I and II) is proposed on the basis of the linear elastic fracture mechanics, stress-induced hydrogen diffusion theory and hydrogen-enhanced decohesion mechanism for hydrogen-induced cracking. The model predicts the crack growth rate da/dt for both stages I and II as a function of the stress intensity factor K_I and the initial level of hydrogen concentration. Some experimental data reported in the literature are used to validate the model and good agreement is obtained.