STP972

    A Constant ΔG Test for Measuring Mode I Interlaminar Fatigue Crack Growth Rates

    Published: Jan 1988


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    Abstract

    A method for measuring Mode I interlaminar fatigue crack growth rates under constant strain energy release rate conditions is described and results are presented for two graphite fiber composite materials. The test consists of a uniform width and thickness DCB specimen which is loaded in series with a linear elastic spring in order to provide optimum control of ΔG. Tests are run under displacement control, and delamination extension is determined by monitoring changes in compliance. A nonlinear elastic relationship between load and displacement was required due to a nonlinear material response caused by fiber bridging. Fatigue crack growth rates were observed to decline by as much as a factor of ten over a distance of less than 5 mm although this varied depending on material, lay-up, and temperature. The fatigue crack growth behavior is compared with delamination extension under quasi-static loading and noticeable differences explained in terms of the micromechanisms responsible.

    Keywords:

    delamination, interlaminar fatigue, strain energy release rate, crack growth rate, fiber bridging, Mode I, graphite/epoxy, thermoplastic, temperature, composite material


    Author Information:

    Russell, AJ
    Defence scientist and group leader, Defence Research Establishment Pacific, Victoria, British Columbia

    Street, KN
    Defence scientist and group leader, Defence Research Establishment Pacific, Victoria, British Columbia


    Paper ID: STP26140S

    Committee/Subcommittee: D30.02

    DOI: 10.1520/STP26140S


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