Objective:  

Definition, characterization and mechanism-based modeling of the limiting states of damage associated with the onset of high-cycle fatigue (HCF) failure in Ti- and Ni-base alloys for propulsion systems.  

It is intended that the program will provide the scientific basis for new comprehensive life-prediction and maintenance schemes for the high-cycle fatigue of critical components in turbine engines 

Scientific/technical approaches:  

• systematic characterization of HCF thresholds for large and small cracks at high frequencies to determine “worst-case” thresholds 
• definition and modeling of the role of high cycle fatigue/low/cycle fatigue interactions, foreign object damage (FOD) 
• development of mechanism-based models for fretting fatigue 
• characterization of damage by in situ techniques

Accomplishments:  

established lower bound HCF threshold stress intensities for onset of naturally-initiated small crack growth and cracking from FOD sites in Ti-6Al-4V 

developed new life-prediction methodology for fretting fatigue (termed Crack Analogue Method) relevant to aircraft engine components 

developed a 3-D finite-element method for simulating cyclic frictional contact problems (termed Contact Fatigue Simulator) relevant to fretting 

developed new theoretical model for fretting of coated surfaces