Creep-fatigue life prediction of single crystal turbine blade with the influence of stress relaxation

The creep-fatigue life prediction method for the single crystal turbine blade of commercial aircraft engine with the influence of stress relaxation was established. Based on the thermal-elastic-creep finite element method analysis, the uniaxial iso-strain relaxation model with the multiaxiality adjustment factor was used to simulate the stress relaxation history in whole life. The stress-low-limit was set to the primary stress. The creep strain was modeled with the combined time hardening implicit creep equation. The fatigue damage was calculated by using damage-based rainflow counting algorithms and Morrow equation. The time-divided linear damage cumulative hypothesis based on Robinson rule was used to calculate the creep damage in whole life. The creep-fatigue life was predicted when the total damage reached the critical damage, which was set to 0.5 based on the creep-fatigue data of the single crystal material. Finally the creep-fatigue life calculated considering the stress relaxation is 45.6 times of the life without the stress relaxation. To predict the blade life with both the reliability and economy, the finite element method analysis could be performed in n cycles and then the stress history in 2n cycles could be predicted by using the method established hereto.