A low-cycle fatigue life model of nickel-based single crystal superalloys under multiaxial stress state

Abstract

The low-cycle fatigue (LCF) behavior of smooth and notched specimens of nickel-based single-crystal superalloys DD3 was studied at 620 °C. Based on experimental results and finite element analysis results, a low-cycle fatigue life model has been proposed for the nickel-based single-crystal superalloys under multiaxial stress states. In the model the mean stress effect has been considered. The LCF life model is based on the crystallographic theory. The LCF life is a power function of maximum resolved shear stress of the activated slip systems. Further, the mean stress effects are taken into consideration. The LCF model parameters can be obtained from smooth round specimens at different stress levels. The LCF life model has first been validated for another smooth round specimens. Six further notched round specimens (U-type and V-type notches) have been studied to validate the LCF life model. Next, the parameters obtained from the two smooth round specimens mentioned above have been applied. Good agreement has been obtained with experimental results. The results are supported further by the SEM check on the fracture surfaces. The deformation mechanisms of nickel-based single-crystal superalloys DD3 under multiaxial stress state were discussed briefly.