Inelastic finite element analysis of circumferentially notched specimen by damage-coupled inelastic constitutive equation of P91 steel

P91 steel, known for its excellent creep strength and corrosion resistance, is used in key high-temperature equipment in power plants. This equipment has geometric discontinuities such as notches, where cracks will develop due to creep-fatigue loading by subjecting the equipment to start-up, continuous operation, and shutdown. Therefore, accurately predicting the crack initiation life at such notches is essential. In this study, finite element (FE) analysis was performed on circumferentially notched specimens with different radii of curvature at the notch root using finite element (FE) analysis software that implements the damage-coupled inelastic constitutive equation developed by the authors' group. To validate the FE results, they were compared with test results obtained from a creep-fatigue test we conducted. The comparison revealed that the variation of the peak stress with the number of cycles, the hysteresis loop, and the stress relaxation curve in the FE results were consistent with the test results, regardless of the shape of the radius of curvature and the hold time condition. Additionally, the creep-fatigue crack initiation and growth process obtained based on the non-localization algorithm were compared with the SEM observation results, thereby confirming that both the crack initiation and its propagation path simulated by the FE were consistent with the observed results.