Principles for the design of components exposed to pressurized hydrogen taking into account material-related damage mechanisms

• Applicants: Professor Dr.-Ing. Tobias Melz; Professor Dr.-Ing. Matthias Oechsner
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins ; Coating and Surface Technology
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 271741688

Scarcities of resources as well as latest developments in the international automotive industry underline a growing importance of hydrogen as a future energy source and fuel.Its application requires the development and qualification of new materials and consideration of the influence of hydrogen in the design process of components exposed to hydrogen.Basic characterisations of the material behaviour of steels under exposure to pressurized hydrogen or electrolytic loading have been subject of numerous studies. The planned research project focuses on the design of cyclically loaded components exposed to pressurized hydrogen taking into account material properties. Emphasis will be put on the application of local strain concepts as well as the transfer concept for cyclic data, the highly stressed material volume. Last mentioned concept will be enhanced regarding a hydrogen permeation volume in dependence of the strain amplitude and local strain distribution.The local concept bases on the assumption that local processes and material behaviour at critical locations are determinant for the initiation of fatigue cracks and therefore fatigue life, irrespective of the complexity of component geometry.While minor influences of stress gradients and testing frequencies are assumed for the application in air, they have to be expected for hydrogen exposure.In order to quantify influencing parameters strain- and force-controlled fatigue tests will be carried out in air and under pressurized hydrogen at 50 bar at different testing frequencies with notched and unnotched specimens.The influence of static and dynamic mechanical loading on the diffusion and trapping behaviour at selected load levels will be characterised under strain- and force-control in electrochemical permeation tests and be compared to the unloaded condition. Moreover, the determination of the permeation current density over time allows an assessment of hydrogen activity in dependence of time and applied load.In order to gain information regarding the potential threat of hydrogen embrittlement due the effective content of hydrogen TDS/hot carrier gas extraction measurements will be carried out after completion of the fatigue and permeation tests for each strain and force level.Extensive significance of the research results is ensured by the selection of two steels with austenitic and ferritic microstructure that reveal significant differences in their trapping and diffusion behaviour.Based on the research results application limitations of the local concept as well as the transfer concept of the highly stressed material volume for the design of components exposed to hydrogen will be pointed out and essential adaptations of the concepts as well as the experimental parameter determination be deduced.

• DFG Programme: Research Grants