Prediction of Creep Fatigue Interaction for Turbine Engine Components

Of particular consideration under VAATE I will be future requirements for long range strike aircraft. The sustained high mach usage requirements for the long range strike aircraft necessitate up to 10 times the requirement of F119. OEMs have indicated that in some cases the current fleet was flown hotter than expected and life was reduced on the order of 10 to 1. VEXTEC successfully demonstrated the potential for predicting creep-fatigue interaction based on bolt hole specimens. A significant difference was predicted for pure fatigue without creep, fatigue with global creep effects but no localized creep effects, and fatigue with both global and local creep consideration. The Phase I demonstration predicting valley dwell and peak dwell missions correlated with OEM experience. Phase I research consisted of damage nucleation and propagation (ie: transgranular verses intergranular effects), cyclic damage accumulation, cycle verses time dependence, and the availability of physics-based modeling approaches. Building on the Phase I work, the Phase II will develop a comprehensive methodology for predicting creep effects on fatigue life prediction for complex missions. This methodology will also consider environmental effects, such as embrittlement due to oxidation.