STP945

    Alterations in Crack-Tip Deformation During Variable-Amplitude Fatigue Crack Growth

    Published: Jan 1988


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    Abstract

    Fatigue crack growth rate changes caused by single overloads and an overload followed by an underload have been studied in the high-strength aluminum alloy 7091. Crack-tip plasticity parameters were measured at each step in the loading sequence using the stereoimaging technique. Effective stress-intensity factor was measured with high resolution immediately at the crack tip both before an overload and during the subsequent growth rate retardation period. Crack-tip opening displacement and strain were altered in the same way as growth rate following the overload/underload events, and similitude with respect to crack-tip plasticity was preserved during the growth retardation period. Effective stress-intensity factor was found to correlate well with crack growth rate. Strains within the plastic zone were converted to stress at each step in load change. These stresses were then summed to determine the zone of residual stress caused by the overload. The region of compressive residual stress ahead of the crack tip was found to increase with overload severity but was limited to yield stress in magnitude. An underload shrank the spatial extent of the residual stresses caused by the overload.

    Keywords:

    fatigue crack growth, variable amplitude loading, similitude, crack-tip plasticity, plastic zone size, crack tip opening displacement, aluminum alloy, overload, crack closure, effective stress-intensity factor, strain


    Author Information:

    Davidson, DL
    Institute scientist, staff scientist, Southwest Research Institute, San Antonio, TX

    Hudak, SJ
    Institute scientist, staff scientist, Southwest Research Institute, San Antonio, TX


    Paper ID: STP23284S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP23284S


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