EUROFER 97, reduced activation ferritic martensitic (RAFM) steel, is a candidate as structural material for plasma facing components of future fusion reactors where it will be subjected to complex thermo-mechanical loading and high irradiation doses. Correct modeling of its deterioration under these loading conditions is a precondition of a sufficiently reliable lifetime prediction procedure. Therefore a coupled deformation damage model taking into account its complex non-saturating cyclic softening has been developed and successfully applied to describe its creep-fatigue behavior under isothermal cyclic loading.
The model has been implemented in the finite element code ABAQUS allowing best estimation of the mechanical behavior of real structures built from EUROFER 97. For verification the implementation has been applied to thermo-mechanical fatigue tests performed on tube specimens. Previous evaluation of these tests showed that thermo-mechanical fatigue loading leads to remarkably reduced lifetime in comparison to isothermal fatigue loading with the same mechanical strain range. In this evaluation changes in the stress range as well as actual test conditions, e.g. temperature gradients, were not considered. However, when applying the coupled deformation damage model changes in stresses between isothermal and thermo-mechanical loadings will be a priori taken into account. Even though the simulations have provided a better description and thus a modified evaluation for the thermo-mechanical tests considered they showed at the same time the lack in describing partial phenomena among others the reduced softening observed in this type of tests. Consequently, further modifications of the deformation constitutive equations are required in order to predict the lifetime correctly. These results underline once more the complexity in modeling the thermo-mechanical material behavior and the need of comprehensive research in this area.