This study conducted a three-dimensional crack propagation simulation based on a nonlocal algorithm of P91 steel under fatigue and creep–fatigue loading. A damage-coupled inelastic constitutive model incorporating fatigue and creep damage parameters into a Chaboche-type viscoplastic law was implemented in commercial finite element software. The nonlocal algorithm mitigates damage localization near a crack tip by averaging the damage parameter within a characteristic domain, thereby enabling a stable crack growth simulation without excessive propagation rates. Finite element analyses were performed for two configurations: (i) a cylindrical bar with a circumferential notch and (ii) a plate containing a semi-elliptical surface crack. For the notched bar, the predicted fatigue and creep–fatigue lives, hysteresis loops, and stress relaxation behavior showed good agreement with experimental results, thereby validating the developed approach. Crack growth simulations of the semi-elliptical surface crack revealed three propagation stages and showed that creep damage accelerated crack penetration through the plate thickness under strain-hold conditions. Furthermore, the evolution of the crack aspect ratio indicated that the semi-elliptical crack tended to become semi-circular during cyclic loading, which was consistent with well-known experimental observations. These findings confirm that the nonlocal algorithm combined with the damage-coupled constitutive model provides an effective framework for simulating three-dimensional fatigue and creep–fatigue crack growth in high-temperature components.
MOTOKI et al. (Thu,) studied this question.