STP775

    Fractographic Studies of Graphite/Epoxy Fatigue Specimens

    Published: Jan 1982


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    Abstract

    Techniques have been developed for determining fracture directions and locating fracture origins for graphite/epoxy (Gr/EP) laminates that fail by overload. These techniques have used the scanning electron microscope (SEM) to identify failed epoxy component topographic features (hackles) that characterize overload failures. Now, the hackle interpretation technique is used to trace hackles back to fracture origin locations on the fracture surfaces of tensile failed Gr/Ep test coupons and structures.

    Recently, these SEM studies have been expanded to include fatigue tested cross-plied Gr/Ep specimens. Patterns of arrest marks (striations) have been associated with tension-compression fatigue crack propagation for some Gr/Ep test specimens. The striation features are distinctly different in appearance from hackles; therefore, they present a promising topographic feature to differentiate tension-compression fractures from overload fractures in Gr/Ep composites. Visual, nondestructive testing, and SEM techniques that were used to identify the striation topographic features are described. Progress to date is presented on attempts to correlate observed striation patterns with fatigue damage growth in Gr/Ep test specimens.

    Keywords:

    composite materials, fatigue, fracture (materials), fractography, failure analysis, graphite/epoxy, hackles, striations


    Author Information:

    Morris, GE
    Unit chief and engineer, Materials and Physics Laboratories, McDonnell Aircraft Co., McDonnell Douglas Corp., St. Louis, Mo.

    Hetter, CM
    Unit chief and engineer, Materials and Physics Laboratories, McDonnell Aircraft Co., McDonnell Douglas Corp., St. Louis, Mo.


    Paper ID: STP34319S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP34319S


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