STP1169: Experimental Studies on Material Damping Characteristics of Carbon-Carbon Composites

    Vaidya, UK
    Graduate student, associate professor, and assistant professor, Auburn University, Auburn, AL

    Raju, PK
    Graduate student, associate professor, and assistant professor, Auburn University, Auburn, AL

    Kowbel, W
    Graduate student, associate professor, and assistant professor, Auburn University, Auburn, AL

    Pages: 12    Published: Jan 1992


    Abstract

    Carbon-carbon (C/C) composites differ from conventional composites due to the presence of a “carbonized” matrix in the carbon fiber reinforcement. Carbon fibers impregnated with the resin form the composite, which then goes through a complex carbonization and graphitization process before it forms a C/C composite. In going through these processes, not only do the mechanical properties of the composite vary, but also its material damping. The damping property is a critical factor in controlling vibrations of structures made from these composites. The motivation for this study was to relate the vibration-based parameters to the microstructural changes that occur during processing of the C/C composites. The two parameters studied were the damping ratio value and the resonant frequency of the composite structure. The composite was fabricated using graphite fabric and phenolic resin as the matrix precursor (referred to as the “as-cured” stage). The composite was then subjected to a carbonization process (referred to as the carbonized stage) after which the damping ratio value was measured again. Finally, the damping ratio value of the carbonized composite was measured after subjecting it to a graphitization process (referred to as “graphitized” stage). The damping ratio value was measured on beam specimens using a modified half-power point method. The specimens were tested under a free-free support condition. The microstructure of the specimens at each of the processing stages was studied using optical microscopy. The results obtained indicate that the vibration based parameters, such as material damping and resonant frequency, are indeed sensitive to the changes in the microstructure of the composite as it is subjected to different processing cycles. The study implied that material damping can be used as a parameter to optimize the mechanical properties for the C/C composite by controlling the number of densification cycles.

    Keywords:

    carbon-carbon composites, damping ratio, resonant frequency, vibration testing, microstructure, processing cycles, material damping, internal friction, internal stress, mechanical properties


    Paper ID: STP17980S

    Committee/Subcommittee: E28.10

    DOI: 10.1520/STP17980S


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