STP972: A Constant ΔG Test for Measuring Mode I Interlaminar Fatigue Crack Growth Rates

    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

    Pages: 19    Published: Jan 1988


    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


    Paper ID: STP26140S

    Committee/Subcommittee: D30.02

    DOI: 10.1520/STP26140S


    CrossRef ASTM International is a member of CrossRef.