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    The Effect of Graphite Fiber Properties on Microcracking Due to Thermal Cycling of Epoxy-Cyanate Matrix Laminates

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    Graphite-fiber-reinforced polymer composite materials have become prime candidates for space structures. The high specific strengths and stiffnesses obtainable with these materials and the ability to design them with a near-zero coefficient of thermal expansion provide a flexibility that is virtually unmatched. However, microcracks resulting from thermal cycling can lead to drastic property changes of the composites. Specimens of five composite materials, each with the same epoxy-cyanate blend matrix and reinforced with different graphite fibers, were subjected to a simulated spacecraft thermal cycling environment to determine the effects of fiber physical properties on the resulting microcrack behavior. The lay-up for each material was [0/45/90/-45]s with a nominal ply thickness of 0.0125 cm (0.005 in). The specimens were cycled between -157°C (-250°F) and +121°C (+250°F) up to 500 times. They were examined at a magnification of ×400 at different thermal cycle intervals for microcracks. It was found that although the maximum crack density varied with the ply lay-up angle, it did not vary much with fiber type. However, the fiber type had a strong influence on the rate of microcrack development. This behavior was found to be best described by fitting a hyperbolic function to the microcrack density as a function of the number of thermal cycles.


    epoxy-cyanate blend, graphite fibers, microcracking, polymer matrix composites, space structures, thermal cycling

    Author Information:

    Knouff, BJ
    Ph.D. candidate, University of Cincinnati, Cincinnati, OH

    Tompkins, SS
    Senior researcher, NASA Langley Research Center, Hampton, VA

    Jayaraman, N
    Professor, University of Cincinnati, Cincinnati, OH

    Committee/Subcommittee: D30.05

    DOI: 10.1520/STP14019S