Low cycle fatigue lifetime and deformation behaviour prediction of nickel-based single crystal superalloy considering thickness debit effect

Through stress-controlled low cycle fatigue (LCF) experiments, LCF performances for thickness debit effect of nickel-based single crystal superalloy DD6 with [0 0 1] orientation are investigated. Based on scanning electron microscope (SEM) observation, the formation mechanism of thickness debit effect and the damage mechanism under LCF loads are revealed. Then, considering the thickness debit effect of nickel-based single crystal superalloy DD6, an improved slip-based damage model is developed. Predicted LCF lifetimes are mainly within a scatter band of factor 2, and the predicted laws between LCF lifetimes and wall-thicknesses are in good agreement with the experimental data, which verifies the rationality and accuracy of the thickness-sensitive LCF damage model established in this paper. Furthermore, a damage-coupled crystallographic constitutive model reflecting thickness debit effect is developed. For DD6 specimens with different wall-thicknesses, the predicted results of the stress-controlled LCF deformation behaviours including the whole-lifetime ratcheting behaviours show good agreement with the experimental data.