Cyclic viscoplastic analysis for steam generator material of Indian fast breeder reactor

Creep-fatigue interaction behavior of grade 91 steel at 823 K has been studied. Creep component has been introduced with hold times 1, 10, and 30 minutes in tension and compression in continuous strain cycling. Fatigue life reduced due to application of hold and reduction was found to be more in compressive hold. The effect of various factors such as mean stress, stress relaxation, oxidation, microstructure, and inelastic strain accumulation on significant reduction in fatigue life in compression hold has been investigated. The oxidation has been observed as the key parameter that caused significant fatigue life reduction in compressive hold as compared with tensile hold. Chaboche unified viscoplasticity model has been used to understand the material's cyclic elasto-viscoplastic behavior. The simulation results were in agreement with the experimental results. Fatigue lives under creep-fatigue condition were estimated using frequency-modified strain energy damage function method and linear damage summation method. Frequency-modified strain energy damage function method under estimated the fatigue lives whereas linear damage summation method overestimated the lives.