STP1074: Closure Measurements via a Generalized Threshold Concept

    Marci, G
    Branch Head, Graduate Student, and Senior Research Engineer, Institute for Materials Research, DFVLR, German Aerospace Research Establishment,

    Castro, DE
    Branch Head, Graduate Student, and Senior Research Engineer, Institute for Materials Research, DFVLR, German Aerospace Research Establishment,

    Bachmann, V
    Branch Head, Graduate Student, and Senior Research Engineer, Institute for Materials Research, DFVLR, German Aerospace Research Establishment,

    Pages: 18    Published: Jan 1990


    Abstract

    Fatigue thresholds have been determined for Inconel 617 and Ti-6Al-4V that are unaffected by any closure phenomenon. These results show that a nonpropagation condition exists between Kop and Kmax of unique amplitude ΔKT which is unaffected by the position between Kop and Kmax. This experimental fact opens up the possibility of measuring the dividing point Kop (fixing the ΔKeff) based on a propagation/nonpropagation criterion. Three such test methods are proposed. Results of these measurements are compared with Kop determinations via load-displacement curves made in parallel on Inconel 617. Comparison of both results show that they contradict each other.

    It is concluded that the two different experimental procedures determine and characterize two independent phenomena affecting the fatigue crack growth process differently. Characterizing the two different phenomena by Kop is incorrect.

    Keywords:

    fatigue threshold, closure, effective stress intensity range, test methods, R, -dependence, fatigue crack growth curves


    Paper ID: STP19014S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP19014S


    CrossRef ASTM International is a member of CrossRef.