Gaseous hydrogen substantially reduces fracture properties such as threshold stress intensity factor and crack growth resistance in the precipitation-hardened martensitic stainless steel investigated in this study. Fatigue crack propagation tests were performed on CT specimens under different atmospheres (hydrogen pressures from 0.09 to 40 MPa) on the Hycomat test bench, at the Pprime Institute in Poitiers, France. A strongly enhanced crack growth regime was identified at high hydrogen pressure and low-frequency loading. Crack growth rates obtained at a constant load under same pressure levels suggest that a combination of tensile stresses above a threshold (KIscc) and fatigue cycles contribute to the hydrogen embrittlement at the crack tip.

These experimental results were compared to the finite element simulation results obtained by a recently developed cohesive zone model at the crack tip. A specifically developed traction-separation law which is suitable to describe the gradual degradation of cohesive stresses under monotonic and cyclic loadings, and which is furthermore sensitive to the hydrogen concentration was used. The effects of the different testing conditions, in terms of loading frequency and hydrogen pressure, on the modeling results are discussed. It was shown that the model qualitatively predicts the detrimental influence of gaseous hydrogen on the crack growth rates.

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