Measurements of the thermal diffusivity tensor of polymer-carbon fiber composites by photothermal methods

The thermal diffusivity tensor of a polymer-carbon fiber composite with unidirectionally distributed fibers has been measured using a modulated photothermal mirage device. The thermal diffusivity along the fibers is k(parallel to) = 6.0 +/- 0.5 mm(2).s(-1) that perpendicular to the 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 the sample by other laboratories using three other different photothermal techniques. A previous claim on anomalous results found on this sample (k(parallel to) < k(perpendicular to) and high thermal diffusivities) can be explained by the inappropriate use of the frequency range. We have also found that there is not perfect thermal contact between the fibers and the matrix, which can be characterized by the thermal contact resistance of R-th = (9 +/- 2) x 10(-6) m(2).K.W-1.