The XYZ 3-dimensional thermal conductivities of the C/C up to 2000 °C were measured by a laser flash method. Carbon fiberreinforced carbon composites (C/C) were generally developed for aerospace missions due to their excellent thermal resistivity at ultrahigh temperature. C/C must endure harsh environments such as thousands of degrees Celsius without degradation of its mechanical properties. To solve this problem, among the passive thermal protection system, we suggest a method of conducting more heat through the mono-axial direction, which resulted in ease of the thermal rise in the heat receiving part. For example, the X-43A flight applied unbalanced C/C (UCC) with different carbon fiber orientation ratios according to the XY direction in the leading edge part. To investigate the difference in thermal conductivity between unbalanced C/C (UCC) and balanced C/C (BCC), unbalanced and balanced preforms were prepared by a needle punching process, and then they were densified by pitch infiltration and a carbonization process. We compared and analyzed the effects of unbalanced C/C(UCC) and balanced C/C (BCC) structures on the thermal conductivity. We also designed the “rule of mixtures” equation for calculating thermal conductivities of each C/C using reported data of carbon fiber and graphite matrix. Our calculations of thermal conductivity ratio match the ratio of real data.

    Abstract
    1 Introduction
    2 Experimental procedure
        2.1 Materials preparation
        2.2 Tests and analysis
    3 Results and discussion
        3.1 UCC and BCC structures
        3.2 Microstructure of UCC and BCC
        3.3 Crystal structure of UCC and BCC
        3.4 Tensile strength
        3.5 Evaluation of thermal conductivities
        3.6 Calculation of thermal conductivities
    4 Conclusion
    Acknowledgements 
    References

• Jungmin Lee(Agency for Defense Development)
• Hyung Ik Lee(Agency for Defense Development)
• Jong Gyu Paik(Agency for Defense Development)