STP797: A Four-Point Shear Test for Graphite/Epoxy Composites

    Browning, CE
    Materials Research Engineer, Materials Laboratory, Air Force Wright Aeronautical Laboratories, Wright-Patterson Air Force Base, Ohio

    Abrams, FL
    Materials Research Engineer, Materials Laboratory, Air Force Wright Aeronautical Laboratories, Wright-Patterson Air Force Base, Ohio

    Whitney, JM
    Materials Research Engineer, Materials Laboratory, Air Force Wright Aeronautical Laboratories, Wright-Patterson Air Force Base, Ohio

    Pages: 21    Published: Jan 1983


    Abstract

    The consistent inability of the short-beam shear (SBS) test to yield the desired interlaminar shear failure mode in thin-beam specimens of graphite/epoxy has led to the development of an alternative test method, the four-point shear (FPS) test. In the course of this developmental effort, four different shear specimens were investigated: a thin-beam 16-ply SBS specimen, a thick-beam 50-ply SBS specimen, a thin-beam 16-ply FPS specimen, and a slightly thicker 24-ply FPS specimen. All specimens were tested to failure, the resulting data were statistically analyzed, and the fractured surfaces were examined with a scanning electron microscope (SEM). The 16-ply SBS specimen never produced an interlaminar shear failure and therefore was considered unacceptable. The thick 50-ply SBS specimen consistently produced shear failure modes and corresponding failure surfaces and a very narrow data distribution. However, the thick-beam specimen is not an attractive alternative, since it poses cost and fabrication difficulties inherent to thick composites. The FPS specimen was found to be an effective alternative to the thin-beam SBS specimen. It consistently produced interlaminar shear failure modes and corresponding failure surfaces and a reasonable data distribution. In addition, the FPS specimen retains the attractive features of the thin-beam SBS specimen, being small, thin, easily machined, and employing a simplified test method. Therefore the FPS test warrants serious consideration as an alternative to the thin-beam SBS test.

    Keywords:

    composite materials, four-point shear test, short-beam shear test, interlaminar shear failure mode, graphite/epoxy, lognormal distribution, fractograph


    Paper ID: STP28539S

    Committee/Subcommittee: D30.04

    DOI: 10.1520/STP28539S


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