Damage parameter determination and life modeling for high temperature fatigue of single crystals

High temperature fatigue damage is a major factor causing the failure of single crystal turbine blades. The influence mechanisms of crystal orientation, strain range, mean strain and dwell time on the high temperature fatigue damage of nickel-based single crystal superalloys are studied respectively with the results of low cycle fatigue and creep-fatigue tests on DD6 standard specimens under different testing conditions and with viscoplastic stress-strain analysis based on slip systems. Furthermore, the slip system with the max slip shear strain is utilized as the critical slip system where the max Schmid stress, max slip shear strain rate, cyclic Schmid stress ratio and slip shear strain range are selected as the damage parameters, and a new cyclic damage accumulation (CDA) model based on critical plane is proposed. The results indicate that the predicted high temperature fatigue life of DD6 with the proposed CDA model based on critical plane is basically within a factor three of the experimental life.