Volker Schippl

Hydrogen can substantially increase the material degradation under cyclic loading. During short fatigue crack growth, which is often the dominating stage during crack propagation, the crack growth rate is highly influenced by microstructural characteristics such as grain boundaries, the formation of slip bands and the local concentration of hydrogen at the crack tip. To address the problem of prediciting the short crack growth behavior, a multi‐physics approach is presented accounting for these interacting influences.

The experimentally observed short fatigue crack growth rate of an uncharged specimen tested in air is compared with results obtained from specimens tested in 10 MPa hydrogen atmosphere and specimens previously charged with hydrogen. To further discuss the hydrogen related short propagation mechanisms, a simulation approach for predicting short fatigue crack growth is presented. The boundary element method is used for calculating stresses and displacements in an anisotropic elastic solid. The hydrogen concentration is assumed to be homogeneously distributed in the microstructure. Based on this modelling approach, it could be concluded that hydrogen leads to an increasing short fatigue crack growth rate due to increasing irreversible deformation processes at the crack tip and also promotes grain boundary cracking in specimens tested in 10 MPa hydrogen atmosphere.

In the present study, the influence of hydrogen on the fatigue behavior of the high strength martensitic stainless steel X3CrNiMo13-4 and the metastable austenitic stainless steels X2Crni19-11 with various nickel contents was examined in the low and high cycle fatigue regime. The focus of the investigations were the changes in the mechanisms of short crack propagation. Experiments in laboratory air with uncharged and precharged specimen and uncharged specimen in pressurized hydrogen were carried out. The aim of the ongoing investigation was to determine and quantitatively describe the predominant processes of hydrogen embrittlement and their influence on the short fatigue crack morphology and crack growth rate. In addition, simulations were carried out on the short fatigue crack growth, in order to develop a detailed insight into the hydrogen embrittlement mechanisms relevant for cyclic loading conditions. It was found that a lower nickel content and a higher martensite content of the samples led to a higher susceptibility to hydrogen embrittlement. In addition, crack propagation and crack path could be simulated well with the simulation model.