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 establish-ing 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 su-peralloys 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 vali-dated 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 phenom-enon 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.