STP907

    Fatigue Failure Mechanisms in Unidirectional Composites

    Published: Jan 1986


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    Abstract

    The tension fatigue behavior of unidirectional composites has been studied using model composites where bundles of E-glass and T300 graphite fibers were combined with ductile and brittle epoxies. Model specimens allowed one to monitor and identify the basic failure mechanisms which are difficult to detect in real composite coupons. Fatigue failure modes and the sequence of damage accumulation depended on the stress level. Matrix microcracks between fibers normal to the applied load were subcritical failure mechanisms which occurred early during fatigue in both glass and graphite bundles. In graphite fiber bundle, they were initiated at the interface along the fibers and were rather isolated. These microcracks were not deleterious in that they neither triggered fiber failures nor grew bridging the fibers. At medium and high cyclic stresses, degradation of the glass as well as the graphite bundle in the form of fiber failures was observed. In glass specimens, extensive interfacial failure and matrix cracking followed while in graphite bundles matrix cracking occurred close to the zones of accumulation of fiber breaks. At low stress levels, only matrix microcracking and few scattered fiber failures were seen.

    Keywords:

    unidirectional composites, glass/epoxy, graphite/epoxy, fatigue failure mechanisms, failure modes, damage accumulation, fiber bundles


    Author Information:

    Lorenzo, L
    Research assistant and professor, Center for Composites Research, Washington University, St. Louis, MO

    Hahn, HT
    Research assistant and professor, Center for Composites Research, Washington University, St. Louis, MO


    Paper ID: STP19988S

    Committee/Subcommittee: D30.04

    DOI: 10.1520/STP19988S


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