An energy-based low-cycle fatigue life evaluation method considering anisotropy of single crystal superalloys

The crystal orientation significantly affects the low-cycle fatigue (LCF) properties of single crystal (SC) superalloys. However, the orientation-dependent LCF life model with precise mechanisms and strong applicability is still lacking. This investigation aims at establishing an energy-based LCF life evaluation method that could consider the orientation effect. First, the influencing factors of anisotropy were identified through the literature review. Secondly, the multiaxial formula of the Ramberg-Osgood (R–O) equation was established to describe the anisotropic cyclic deformation characteristics. Furthermore, the strain energy density of SC superalloys was determined based on this equation, and the effective strain energy density was introduced to account for the effect of orientation. Finally, the energy-based method was validated by its application to several SC superalloys. Results showed that the crystallographic orientation with a lower Young's modulus usually exhibits better LCF resistance. This phenomenon could be attributed to the different values of strain energy density dissipated in one cycle. The multiaxial R–O relationship could capture the anisotropic cyclic deformation response of DD6. Compared with the classical methods, the energy-based model is favored by its precise mechanism and strong applicability. And it also exhibited better prediction accuracy. Most data points of different crystallographic orientations lay within the ±3 error band.