Near-tip behavior of ductile, steady-state crack growth in a hydrogen charged material

This study examines the influence of increased dislocation velocity due to hydrogen on the steady-state behavior of a crack propagating under quasi-static conditions in elastic-plastic, matched, over-matched, and under-matched weld materials. Finite element analyses in a small-scale yield setting with plane strain conditions resolve the near-tip fields under the remotely applied K _I - T displacement fields. The constitutive model incorporates hydrogen induced dilation and softening effects on the inelastic behavior of the ductile material representative of a pressure vessel steel. Near the crack tip, the hydrogen concentration, triaxiality, and plastic strain depend on the remote loading, the extent of material softening, and the initial concentration of hydrogen in the weld and base metal. A simple measure of damage along the uncracked ligament predicts higher values of ductile void growth in the presence of hydrogen and implies lower resistance to crack advancement.