Recent advances in carbon-carbon substrate technology at NASA. Langley Research Center

A comparison of specific strengths of candidate high-temperature materials as a function of temperature is shown. From this comparison, it is apparent why there is an interest in carbon-carbon composites for applications as a strong, light-weight thermal protection system (TPS), or as hot structure, for applications above 2500 F. The lower bound of the carbon-carbon band is representative of the tensile strength of cross-ply Advanced Carbon-Carbon (ACC). The upper bound represents capabilities of various experimental carbon-carbon composites. Thin carbon-carbon composites, such as would be used as TPS panels or hot aero-structure, are usually constructed of layups of 2-D fabrics of carbon-fiber yarns (tows). Although the in-plane strengths of these composites can be very attractive, a major problem area is low interlaminar strength. The low interlaminar strength is the result of a relatively weak carbon matrix and poor interaction between the fibers and matrix. The purpose of this paper is to discuss strategies being employed to improve the interlaminar strengths of the materials at the upper bound of the carbon-carbon band, and to present some recent encouraging results. The emphasis of these strategies is to improve interlaminar shear and tensile strengths while maintaining, or even improving, the inplane properties.