Effects of Compressive Loads on Spectrum Fatigue Crack Growth Rate

    Published: Jan 1980

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    A procedure, which allows flight-simulation profiles to be applied under stress intensity factor control, was used to study effects of compressive-compressive load cycles on spectrum fatigue crack growth rate. This approach eliminates the maximum stress-intensity factor, Kmax, and its associated plastic-zone size as a variable within a given test, and allows a small amount of crack growth representing instantaneous conditions in conventional load control tests. Tests were performed on center-cracked 7075-T651 aluminum alloy specimens subjected to typical flight-spectra, simulating both transport and bomber airplanes. The results indicated that the number of compressive-compressive cycles has little effect on spectrum-crack-growth rate and that essentially the same results were produced by a single compressive load. It was also found that the crack growth rate was relatively insensitive to the magnitude of the compressive load. A saturated condition was reached at a fairly low load level. The sequence of overload-comprensive load was also evaluated. For low stress intensity factor, the crack growth rate obtained was slightly higher when the application of compressive loads preceded an overload. However, the opposite occurred when the stress intensity factor was larger.


    crack-growth rate, spectrum load, retarding, aluminum alloy, fatigue (materials), crack propagation

    Author Information:

    Hsu, TM
    Aircraft Development Engineers-Specialists, Lockheed-Georgia Company Marietta, Ga.

    McGee, WM
    Aircraft Development Engineers-Specialists, Lockheed-Georgia Company Marietta, Ga.

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP27483S

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