STP1059: Loading Rate Sensitivity of Open-Hole Composite Specimens in Compression

    Lubowinski, SJ
    BASF Structural Materials, Charlotte, NC

    Guynn, EG
    Texas A & M University, College Station, TX

    Elber, W
    U.S. Army Aerostructures Directorate, Hampton, VA

    Whitcomb, JD
    NASA Langley Research Center, Hampton, VA

    Pages: 20    Published: Jan 1990


    Abstract

    This paper reports the results of an experimental study on the compressive, time-dependent behavior of fiber-reinforced polymer composite laminates with open holes. The effect of loading rate on compressive strength was determined for six graphite/matrix material systems ranging from brittle epoxies to thermoplastic, at both room temperature and 104°C (220°F). Tests were conducted by loading specimens to failure using different loading rates. The slope of the strength versus elapsed-time-to-failure curve was used to rank the material's loading rate sensitivity. All of the materials had greater strength at room temperature compared to the same material at the higher temperature. All of the materials showed loading rate effects in the form of reduced failure strength for longer elapsed time to failure. When the temperature was increased to 104°C (220°F), loading rate sensitivity was less than the same material at 21°C (70°F). However, C12000/ULTEM and IM7/8551-7 were more sensitive to loading rate than the other materials at the higher temperature. AS4/APC2 laminates with 24, 32, and 48 plies and 1.59 and 6.35-mm (1/16 and 1/4-in.) diameter holes were tested. The sensitivity to loading rate was less for either increasing number of plies or larger hole size. The failure of the specimens made from brittle resins was accompanied by extensive delaminations, while the failure of the toughened systems was by shear crippling with small amounts of delaminations. Fewer delamination failures were observed at the higher temperature. A new fixture developed for this study permitted the testing of smaller specimens while producing failures typical in large panels.

    Keywords:

    polymer, composite materials, open hole, loading rate, high temperature, compression, graphite, epoxy, PEEK, APC2


    Paper ID: STP24126S

    Committee/Subcommittee: D30.04

    DOI: 10.1520/STP24126S


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