Abstract
Fatigue crack propagation (FCP) rates were obtained by R-constant (ASTM E647) and K max-constant test methods for a spectrum of R-ratios and K max values on the Ni-base alloy Nicrofer 5219 Nb (annealed) and AI 7075-T7351. Furthermore, non-propagation conditions ΔK th as a limit for the FCP regime, were determined for these materials. The partitioning point K op dividing ΔK into ΔK eff had been experimentally determined for Nicrofer 5219 Nb (annealed) and Al 7475-T7351 [1]. The K op was expressed as a polynomial equation of R-ratio and K max. These K op data were applied to the FCP data of Nicrofer 5219 Nb (annealed) and Al 7075-T7351. It is shown that the ΔK eff concept is a unique and complete description of FCP. Even the wedging action of the wake zone associated with a fatigue crack, which frequently occurs when testing at low R-ratios, is easily accounted for by the ΔK eff concept.
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