Development of a Physically-Based Methodology for Predicting Material Variability in Fatigue Crack Initiation and Growth Response

Abstract

Abstract : The report summarizes the results of an interdisciplinary program aimed at developing a computational methodology for treat material variability in the fatigue crack initiation and growth responses of aerospace structural alloys. In this three-year program, physics-based fatigue crack initiation and growth models were developed and integrated into a probabilistic micromechanical code for treating fatigue life variability resulting from material variations. Dubbed MicroFaVa (Micromechanical Fatigue Variability), the code is based on a set of physics-based fatigue models that predict fatigue crack initiation life, fatigue crack growth life, fatigue limit, fatigue crack growth threshold, crack size at initiation, and fracture toughness. Using microstructure information as material input, the code is capable of predicting the average behavior and the confidence limits of the crack initiation and crack growth lives of structural alloys under LCF or HCF loading. The code has been integrated and utilized with DARWIN, a probabilistic design and life-prediction code developed at Southwest Research Institute (SwRI), to treat fatigue life variability in a Ti rotor due to variation in the microstructure. The probabilistic micromechanics code has been verified and validated against two benchmark problems with known solutions, as well as comparisons against an extensive database of fatigue life and fatigue crack growth data.