Effect of graphite fiber properties on microcracking due to thermal cycling of epoxy-cyanate matrix laminates

The high specific strengths and stiffness obtainable with graphite-fiber-reinforced polymer composite materials and the ability to design them with a near-zero coefficient thermal expansion provide a flexibility that is virtually unmatched for spaced structures. However, microcracks resulting from thermal cycling can lead to drastic property changes of the composites. Specimens of five composites materials are studied to determine the effects of fiber physical properties on the resulting microcrack behavior. It is found that although the maximum crack density varied with the ply lay-up angle, it did not vary much with fiber type. This behavior is best described by fitting a hyperbolic function to the microcrack density as a function of the number of thermal cycles.