In the context of renewable energy transition and reduction of CO₂ emissions, hydrogen is gaining more and more attention in energy supply and transportation. However, cyclically loaded components in hydrogen service can exhibit hydrogen embrittlement in critical locations, which may result in a reduced component lifetime. To prevent premature failure, the mechanisms acting at macroscopic and microstructural scales must be considered in the design and material selection of such components. The characterization of candidate materials must hence include hydrogen exposure during the tests. The cyclic mechanical material behavior is usually investigated on cylindrical specimens in autoclaves under high-pressure hydrogen atmosphere. The tests in large-volume autoclaves are rather complex and expensive due to high investment costs. Furthermore, the existing test capacities are considerably limited making full material characterization of all candidate materials in a reasonable time span all but impossible. In addition, the testing temperatures are limited to around 90 °C with rare exceptions.

Currently, there are numerous efforts in industry, to operate internal combustion engines for power generation with oxyhydrogen gas, which raises the question about the possible presence of hydrogen embrittlement at higher temperatures (up to 700 °C). Since materials testing at these temperatures cannot performed in an autoclave, other test methods and specimen geometries must be developed. One promising approach is the hollow specimen technique, where the hydrogen is applied in the through-hole. At the Fraunhofer IWM, tensile tests on hollow specimens performed in conventional uniaxial fatigue testing machines show a good agreement with standard cylindrical specimens. Hence, the aim is to apply the hollow specimen technique also for cyclic fatigue tests in the low cycle fatigue (LCF) and high cycle fatigue (HCF) regime as well as at elevated temperatures.

For comparison in the LCF regime with traditional cylindrical specimen geometries, some open questions regarding the influence of the internal hydrogen pressure and the resulting circumferential stresses on the deformation behavior and, thus, the macroscopic stress-strain hysteresis remain. These questions are addressed with the numerical investigation of the hollow specimen geometry by means of the finite element method in ABAQUS. Furthermore, the influence of hydrogen on an internal circumferential crack is investigated by coupling the mechanical simulation with a subsequent mass diffusion analysis. Here, a special focus lies on the crack-length- and load-dependent relationships between plastic and diffusion zones originating in front of the crack tip.