Effects of hydrogen on steady, ductile crack growth: Computational studies

This paper describes studies of the near tip fields and the effects on void growth rates for a steadily advancing crack through a ductile metal in the presence of hydrogen, under plane-strain and quasi-static conditions. The computational model determines directly the deformation history of a steadily propagating crack without the need for a priori (transient) analysis that considers blunting of the pre-existing stationary crack and subsequent growth through the associated initial plastic zone. The present approach enables straightforward investigation over a range of geometric constraint configurations encountered in test specimens and structural components by application of a far field KI-TKI-T loading. The ductile crack propagation simulated in these studies represents that observed in a high-solubility model material, where the diffusion rate can sustain equilibrium of the hydrogen concentration ahead of the steadily propagating crack tip. The constitutive model accounts for the influence of hydrogen on the elastic–plastic regimes of material response at the continuum level, e.g. hydrogen-induced material softening. The model reflects the amount of hydrogen in the material under stress and the intensity of hydrogen-induced softening in the material. The hydrogen influenced, crack front fields serve as input to an exponential-based characterization of void growth rates which provides qualitative estimates for the impact of hydrogen on tearing resistance curves. The analyses suggest significantly higher void growth rates exist in a hydrogen-charged material than in a hydrogen free material, with a corresponding reduction in tearing resistance in the presence of hydrogen regardless of the level of imposed constraint.