Plasticity effects and crack-closure modeling of small fatigue cracks were used on a Ti-6Al-4V alloy to calculate fatigue lives under various constant-amplitude loading conditions (negative to positive stress ratios, R) on notched and un-notched specimens. Fatigue test data came from a high-cycle-fatigue study by the U.S. Air Force and a metallic materials properties handbook. A crack-closure model with a cyclic-plastic-zone-corrected effective stress-intensity factor range and equivalent-initial-flaw-sizes (EIFS) were used to calculate fatigue lives using only crack-growth-rate data. For un-notched specimens, EIFS values were 25-μm; while for notched specimens, the EIFS values ranged from 6 to 12 μm for positive stress ratios and 25-μm for R = −1 loading. Calculated fatigue lives under a wide-range of constant-amplitude loading conditions agreed fairly well with the test data from low- to high-cycle fatigue conditions.
Fatigue-Life Prediction Method Based on Small-Crack Theory in an Engine Material
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Newman, J. C., Jr., and Annigeri, B. S. (December 28, 2011). "Fatigue-Life Prediction Method Based on Small-Crack Theory in an Engine Material." ASME. J. Eng. Gas Turbines Power. March 2012; 134(3): 032501. https://doi.org/10.1115/1.4004261
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