MULTISTAGE FATIGUE MODELING FOR THREE WROUGHT ALUMINUM ALLOYS

Three structural, wrought-aluminum alloys are chosen to evaluate and compare fatigue behaviors and mechanisms using a mechanistic multistage fatigue modeling method. Solution treated, age-harden 2xxx, precipitation hardened 6xxx, and solution heat treated, precipitation hardened 7xxx Al alloys comprise some distinct yet similar microstructural features. Among the alloys, fatigue damage nucleates/incubates due to the accumulation of plastic deformation in multiple crystallographic slip systems at microscale inhomogeneities, primarily inclusion particles. The physically motivated mechanistic Multi Stage Fatigue (MSF) model is implemented on the three alloys to evaluate the fatigue lives in the high cycle fatigue regime. Preliminary MSF models for the three alloys were developed based on simple and available static, cyclic, limited fatigue behaviors, and the micromechanism for fatigue damage initiation. Detailed micromechanical simulations are conducted on the micromechanism of fatigue damage incubation, which is essential for high fidelity high-cycle multistage fatigue model development.