Model Based Fatigue Life Prediction for AA 7075-T651

VEXTEC's fatigue simulation capability predicts the fatigue life of components based on the microstructural material properties of the alloy rather than using large empirical datasets. Current industry standard methods determine fatigue life based on time consuming and expensive physical component testing. VEXTEC's component fatigue model is unique because it uses intrinsic material properties and very limited testing to accurately predict fatigue durability. The model simulates the microstructure of the material using probabilistic material properties such as grain size, grain boundary stress intensity factor, Poisson's ratio, particle size and particle density. The simulation then predicts the number of cycles to complete each stage of fatigue damage: crack nucleation, short crack growth and long crack growth. In a validation case, the fatigue model was created for a common aircraft alloy, aluminum 7075-T651, using material properties and a limited set of smooth bar fatigue test points. This same fatigue model accurately predicted the fatigue life for a flat plate in bending and a 2-hole specimen in complex mission. Physical fatigue testing validated the fatigue predictions. VEXTEC can use this algorithm to model the fatigue durability of aircraft components. Accurate health management algorithms for component fatigue can be developed through modeling rather than extensive and expensive testing. PHM systems will benefit from a widely applicable model that accurately predicts structural reliability.