STP945: The Effect of Loading History on Closure Behavior in Rene' 95

    Zawada, LP
    Materials engineer and senior scientist, AFWAL/MLLN, Wright-Patterson Air Force Base, OH

    Nicholas, T
    Materials engineer and senior scientist, AFWAL/MLLN, Wright-Patterson Air Force Base, OH

    Pages: 14    Published: Jan 1988


    Abstract

    Experimental observations of closure in fatigue crack growth as a function of loading history are presented for a high-strength nickel-base superalloy, Rene' 95, at 649°C. Fatigue crack propagation (FCP) tests were conducted under either constant load amplitude (increasing ΔK) or under threshold load shedding (decreasing ΔK) test conditions. Closure loads were determined from load-offset displacement traces that were recorded with the aid of a crack mouth opening displacement extensometer. Plots of Kcl versus Kmax revealed that Kcl remained constant for both the constant load and decreasing load FCG tests, indicating that Kcl was not a consequence of the loading history. Similar plots for side-grooved specimens and smooth specimens revealed identical behavior, thus ruling out plasticity-induced closure as the operating closure mechanism.

    Keywords:

    crack closure, crack growth mechanisms, elevated temperature, nickel-base superalloy, fatigue crack propagation, fracture mechanics, oxidation, threshold


    Paper ID: STP23242S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP23242S


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