STP969: Threshold and Nonpropagation of Fatigue Cracks Under Service Loading

    Castro, DE
    Graduate student, and branch head, Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt (DFVLR), Köln,

    Marci, G
    Graduate student, and branch head, Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt (DFVLR), Köln,

    Munz, D
    Professor, University of Karlsruhe, Karlsruhe,

    Pages: 12    Published: Jan 1988


    Abstract

    New testing conditions for determination of fatigue threshold and a new interpretation of this parameter make it amenable to general fatigue life design. To distinguish between the terms, the conditions for nonpropagating fatigue cracks were called the fatigue tolerance range and denoted as ΔKT. The conditions for nonpropagating fatigue cracks were investigated on Inconel 617 alloy in the range of Kmax between 10 to 50 MPa m1/2 under four different types of fatigue loading conditions. It was found that ΔKT decreases with increasing Kmax. Furthermore, ΔKT decreases with increasing prior amplitude, ΔKpr, up to a certain amplitude, ΔKs, at which the effect of prior amplitudes reaches saturation. For Inconel 617 alloy, ΔKs is between 5 and 7 MPa m1/2 at Kmax = 10 MPa m1/2 and approximately 5 MPa m1/2 at Kmax = 35 MPa m1/2. The test result on saturation behavior at Kmax = 10 MPa m1/2 suggests an influence of closure on the effects of prior amplitudes. The results are explained by differing damage states in the near region of the crack front introduced by Kmax and ΔK of the prior fatigue cycles.

    Keywords:

    fatigue threshold, fatigue tolerance range, closure, spectrum loading, history effects, fatigue process zone, life prediction, fracture mechanics


    Paper ID: STP33108S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP33108S


    CrossRef ASTM International is a member of CrossRef.