Fatigue crack growth and life predictions under variable amplitude loading for a cast and wrought aluminum alloy

Variable amplitude fatigue crack growth in the cast aluminum alloy, D357, is compared with the wrought aluminum alloy, 2024. Variable amplitude loading is applied in the form of single tensile overloads, repeated tensile overloads, and simulated flight spectra loading. Fatigue crack growth life predictions are made with the FASTRAN modified strip-yield model for both materials under each of the loading conditions and compared with experimental results. The effect of the FASTRAN constraint parameter on life predictions for each alloy is examined using three different approaches. D357 exhibited better variable amplitude fatigue crack growth resistance compared to 2024 under most of the loading conditions. FASTRAN predictions for both materials were quite good, with most predictions falling within a factor of ±2 of the experimental results.