Multiaxial mechanical behavior and service performance modeling of FGH95 superalloy: An integrated elastoplastic approach

Multiaxial fatigue behavior is a key concern in the engineering design of high-performance structural materials. In this study, a novel energy-based fatigue criterion is developed to predict the fatigue life and crack initiation behavior of FGH95 superalloy under multiaxial loading conditions. The proposed model incorporates both normal and shear strain energy contributions, with a stress-path-dependent weighting factor to account for the relative influence of different damage modes. A finite element framework was established using a user-defined UMAT based on the Ohno-Wang cyclic plasticity model, enabling accurate simulation of stress–strain evolution. To validate the model, multiaxial fatigue tests were conducted using a specially designed cruciform specimen at elevated temperatures. Finally, numerical predictions of crack initiation angles and fatigue life were compared with experimental observations, demonstrating strong agreement and verifying the robustness of the model. This study provides a unified framework for energy-based fatigue assessment and contributes to the understanding of multiaxial damage mechanisms in nickel-based superalloys.