High temperature deformation and damage behavior of RAFM steels under low cycle fatigue loading: Experiments and modeling

Structural materials of fusion reactors are subjected to complex creep–fatigue loading and high irradiation doses. Correct modeling of their deterioration is a precondition of a sufficiently reliable lifetime prediction procedure. In the continuum mechanics approach selected for lifetime prediction of RAFM steels under creep–fatigue conditions, the inelastic strain rate modified (ISRM) damage model is coupled with a modified viscoplastic deformation model taking into account the complex non-saturating cyclic softening of RAFM steels. The resulting coupled model is a powerful prediction tool, which can be applied to arbitrary creep–fatigue loading provided that the material, temperature and possibly irradiation dose-dependent parameters of the model have been determined. Therefore, a fitting procedure has been developed for the parameters identification on the base of deformation and lifetime data from strain-controlled low cycle fatigue (LCF) tests without and with hold time as well as creep tests. The coupled deformation-damage model has been applied to F82H mod and EUROFER 97 in the reference (unirradiated) state under isothermal cyclic loading at 450, 550 and 650 °C. The comparisons between model and experiment show that the observed lifetimes in the LCF tests could be fairly well calculated even for the tests with hold time, which were not considered for the identification of the damage model parameters.