MEASUREMENTS OF THE THERMAL-DIFFUSIVITY TENSOR OF POLYMER-CARBON FIBER COMPOSITES BY PHOTOTHERMAL METHODS

The thermal diffusivity tensor of a polymer-carbon fiber composite wit h unidirectionally distributed fibers has been measured using a modula ted photothermal mirage device. The thermal diffusivity along the fibe rs is k(parallel to) = 6.0 +/- 0.5 mm(2).s(-1) that perpendicular to t he fibers is k(perpendicular to) = 0.35 +/- 0.05 mm(2).s(-1), and that perpendicular to the sample surface is k(z) = 0.40 +/- 0.15 mm(2).s(- 1). These results have been confirmed by independent measurements on t he sample by other laboratories using three other different phototherm al techniques. A previous claim on anomalous results found on this sam ple (k(parallel to) < k(perpendicular to) and high thermal diffusiviti es) can be explained by the inappropriate use of the frequency range. We have also found that there is not perfect thermal contact between t he fibers and the matrix, which can be characterized by the thermal co ntact resistance of R-th = (9 +/- 2) x 10(-6) m(2).K.W-1.