Mechanism-Based LCF Lifetime Assessment Under the Influence of Hydrogen

In this study, the effect of temperature on hydrogen embrittlement on Alloy 718 was investigated. The findings revealed significant hydrogen embrittlement, heavily dependent on the specific testing conditions. This underscores the need for comprehensive material testing under anticipated service conditions to ensure long-term reliability and safety. To address the challenge of extensive testing requirements, a predictive model for the low cycle fatigue regime under various operating conditions is proposed. This model focuses on short micro-crack growth to determine the cycles until technical crack initiation, accounting for the influence of hydrogen. It is based on calculating the cyclic crack tip opening displacement (ΔCTOD). The model incorporates key factors such as temperature, pressure, and frequency. To validate the model, it is compared with results from the low cycle fatigue tests conducted on hollow specimens of alloy 718. This comparison aims to refine the model and enhance its predictive capabilities. By employing predictive models for lifetime assessment, future testing efforts can be significantly reduced, thereby facilitating the transition to a safe hydrogen infrastructure. This approach not only enhances efficiency but also supports the development of reliable systems necessary for the widespread adoption of hydrogen as a clean energy source.