Thermal and isothermal low cycle fatigue of MANET I and II

Structural components of a DEMO-blanket are subjected during service to alternating thermal and mechanical stresses as a consequence of the pulsed reactor operation. Of particular concern is the fatigue endurance of martensitic steels like MANET under cyclic strains and stresses produced by these temperature changes. In order to design such structures, operating under combined mechanical and thermal cycling, fatigue life has to be calculated with reasonable accuracy. This paper proposes a description of thermal and isothermal mechanical low-cycle fatigue of MANET I and II steels using a single damage model, including plastic strain, temperature and strain rate as variables. This model presents notable advantages for the designer. As it corresponds to a single and continuous 'fatigue strength surface', it enables a reliable interpolation to be made throughout the studied domain of strains and temperatures, and allows for a reasonable extrapolation out of this domain, provided that no different metallurgical phenomena occur. (orig.)