Deformation and damage of RAFM steels under thermo-mechanical loading: A challenge for constitutive equations

A coupled deformation damage model recently developed for reduced activation ferritic martensitic (RAFM) steels and implemented in the finite element code ABAQUS was used to simulate thermo-mechanical fatigue tests performed on EUROFER 97 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, but changes in the stress range as well as actual test conditions, e.g. temperature gradients, were not considered. However, by applying the coupled deformation damage model, changes in stresses between isothermal and thermal loadings were taken into account. Results showed a local mechanical strain range that was greater than that obtained experimentally. However, the lifetime due to the calculated fatigue load was still higher than that was found experimentally. Some geometric nonlinear deformation instabilities are suggested, but must be verified.