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    Crack Opening Under Variable Amplitude Loads

    Published: 01 January 1989

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    Crack growth rate tests were conducted on eleven compact tension specimens of A588A steel plate to assess the ability of linear cumulative damage models to estimate fatigue life under load-time histories composed of cycles of variable amplitude and mean. Crack opening was monitored using a clip gage and through transmission ultrasonics. Crack growth rate results show that closely spaced overloads can cause acceleration; retardation occurs only if overloads are separated by many small cycles. Comparison of crack opening data to crack opening estimates based on Elber's closure model shows that the influence of crack opening on growth rate in constant-amplitude tests is less than predicted by the model, while the influence of crack opening in variable-amplitude tests is greater than predicted by the model.


    crack closure, crack propagation, fatigue (materials), loads (forces), overload, predictions, retardation, stress ratio, stress cycle, underload

    Author Information:

    Zwerneman, FJ
    Assistant professor, Oklahoma State University, Stillwater, OK

    Frank, KH
    Associate professor, University of Texas, Austin, TX

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP18843S