Innovative Capability to Quantify Fatigue Damage and Assessment of Endurance Limit in Spectrum Load Histories

Flight-critical components in aircraft and helicopters experience complex service and loading conditions comprising of spectrum (variable amplitude) loading during their lifetime. Due to complex interaction of several life-limiting factors during spectrum loading, particularly, multiple fatigue damage mechanisms and microstructure sensitivity, development of analytical models to accurately predict fatigue damage and service life of the material/component in spectrum loading has been difficult. Additionally, highly conservative recommendations for component inspection and retirement schedule are subsequently adopted. In this effort, QuesTek proposes to combine its expertise in microstructure-sensitive fatigue modeling with Professor James Newman's expertise in fatigue crack growth and FASTRAN software development, to apply an innovative modeling scheme to accurately predict fatigue damage and service life during spectrum loading histories. The modeling strategies will be based on the mechanisms of small/short crack growth, with consideration of relevant microstructure features, during low amplitude cycles integrated with the well-established long crack growth law. The models will be integrated into FASTRAN to enable rapid transition into Navy applications. QuesTek intends to demonstrate the feasibility of this approach in Phase I through modeling and validation against existing data, and further refine and improve the analytical models utilizing a combined experimentation and numerical simulations in Phase II.