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    STP1060

    Influences of Crack Closure and Load History on Near-Threshold Crack Growth Behavior in Surface Flaws

    Published: 01 January 1990


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    Abstract

    Fatigue crack growth threshold tests are conducted on a high-strength titanium alloy using a surface flaw specimen geometry. A laser interferometer is used to monitor crack-mouth opening displacements, from which compliance determined crack length is computed. Four types of loading history involving both increasing-and decreasing-ΔK are used to reach a threshold condition. Two of the test conditions maintain constant Kmax under computer control. Crack closure is obtained from the load-displacement plots and used to determine an effective stress-intensity range, ΔKeff. Results from all four test types indicate that a single value of an effective stress-intensity range is obtained which is independent of stress ratio, R, or load history. Crack growth rate data in the near-threshold regime, on the other hand, appear to have a dependence on R even when ΔKeff is used as a correlating parameter.

    Keywords:

    fatigue crack growth, threshold, surface flaw, crack closure, effective stress intensity


    Author Information:

    Jira, JR
    Materials research engineer and senior scientist, Wright Research and Development Center, Materials Laboratory (MLLN), Wright-Patterson Air Force Base, OH

    Nagy, DA
    Graduate student, Air Force Institute of Technology, Wright-Patterson Air Force Base, OH

    Nicholas, T
    Materials research engineer and senior scientist, Wright Research and Development Center, Materials Laboratory (MLLN), Wright-Patterson Air Force Base, OH


    Committee/Subcommittee: E08.03

    DOI: 10.1520/STP23440S