Abstract
Fatigue crack propagation (FCP) rates were obtained by R-constant (ASTM E647) and Kmax-constant test methods for a spectrum of R-ratios and Kmax values on the Ni-base alloy Nicrofer 5219 Nb (annealed) and AI 7075-T7351. Furthermore, non-propagation conditions ΔKth as a limit for the FCP regime, were determined for these materials. The partitioning point Kop dividing ΔK into ΔKeff had been experimentally determined for Nicrofer 5219 Nb (annealed) and Al 7475-T7351 [1]. The Kop was expressed as a polynomial equation of R-ratio and Kmax. These Kop data were applied to the FCP data of Nicrofer 5219 Nb (annealed) and Al 7075-T7351. It is shown that the ΔKeff 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 ΔKeff concept.
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