Effective Thermal Conductivity and Thermal Contact Conductance of Graphite Fiber Composites

Abstract

The transverse and longitudinal effective thermal conductivity and contact conductance of discontinuous and misoriented graphite fiber-reinforced composites has been studied over a range of temperatures (20-200°C) and pressures (172-1720 kPa). Three different fiber types (DKE X, DKA X, and K22XX) and three fiber volume fractions (55, 65, and 75%) in a cyanate ester matrix were studied. The addition of fibers to the matrix resulted in an increase in effective thermal conductivity, but appears to level off at fiber volume fractions of 65%. Furthermore, the effective thermal conductivity in the longitudinal direction was significantly greater than in the transverse direction and was more dependent on temperature. These data were used to develop an equation relating the thermal contact conductance to the harmonic mean thermal conductivity of the fiber and matrix material, fiber volume fraction, sample thickness, and microhardness