Finite element modeling of hydrogen instantaneous trapping in porosities

The competition between instantaneous hydrogen trapping on dislocations and in voids is studied in the context of continuum mechanics and ductile damage (Gurson-Tvergaard-Needleman model) by finite element simulations. The numerical model is applied to a small-scale yielding configuration from the literature, in two hydrogen loading cases, corresponding to gaseous and cathodic environments, and two initial configurations (saturated and hydrogen-free), representing two limiting situations for the tests. For low initial concentrations, the presence of voids does not significantly modify the distribution of lattice hydrogen or hydrogen trapped on dislocations at the end of mechanical loading. For initial concentrations representing cathodic loading, the concentration of hydrogen trapped by dislocations is negligible compared to other concentrations. The impact of voids on the lattice hydrogen concentration, however, is very significant at the end of mechanical loading, and its value ahead of the crack tip is very low. In all cases, the total hydrogen concentration increases significantly due to trapping in the voids. • An extension of the hydrogen transport equation is proposed. • This extension includes instantaneous trapping in voids. • Void density increases with time due to plasticity. • The competition between trapping in void and on dislocation is highlighted. • The higher the hydrogen concentration, the greater the effect of trapping in the voids.