Experimental study of the strengthening effect: A novel fatigue life prediction method for variable amplitude loads

Abstract The strengthening effect of low‐amplitude loading at elevated temperatures was investigated experimentally. A powder metallurgy nickel‐based superalloy FGH96 was preloaded with different cycle numbers and stress levels, and the residual fatigue life was tested under subsequent high‐amplitude loads. The results show that when the number of preloading cycles is in a specific range, the residual fatigue life is higher than that of the virgin specimen under the same load. A novel damage accumulation model was proposed to incorporate the strengthening effect into the life prediction framework. The proposed model was validated using experimental results for various materials in the literature. The mechanism of the strengthening effect of FGH96 was discussed based on electron backscatter diffraction (EBSD) analysis.