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    Evaluation of Crack Growth Gages for Service Life Tracking

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    An analysis and test program was performed to evaluate the ability of a crack growth gage to monitor crack growth damage in fatigue-critical areas of F-4C/D aircraft structure. Crack growth gages were designed and manufactured for use on the F-4 lower wing skin. The crack growth behavior of the gage and relationship of gage crack growth to potential crack growth in the wing skin were determined through analysis and test. Eight gages were bonded on the Air Force F-4C/D full-scale fatigue test article at Wright-Patterson Air Force Base. Assessments were made of (1) the capability to predict crack growth behavior of the gages mounted on the fatigue test article, (2) the ability of crack growth gage to monitor potential crack growth damage at specified control points, and (3) the impact of manufacturing, installation, and data collection procedures on the utility of the gage as a damage monitoring device. Sheet thickness was found to have a profound effect on crack growth retardation under spectrum loading in 7075-T6 aluminum.


    crack growth, crack growth gages, aircraft, fleet management, spectrum loads

    Author Information:

    Saff, CR
    Lead engineer, McDonnell Aircraft Co., McDonnell Douglas Corp., St. Louis, Mo.

    Holloway, DR
    Captainaerospace engineer, USAFAir Force Flight Dynamics Laboratory, Wright-Patterson AFB, Ohio

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP28821S