In-plane thermal conductivity in thin carbon fiber composites
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The main objective of this present work was to study the effect of fiber type, fiber angle and filler material on the inplane thermal conductivity of thin carbon fiber composites (CFC), ranging in thickness from 7 to 15 mils. Two sets of CFC samples were fabricated and tested: low thermally conductive (LTC) samples made with Hexcel AS4 PAN-based fibers (K=6.8 W/m-K) in Fiberglast epoxy resin, and high thermally conductive (HTC) samples fabricated with Mitsubishi K13C coal-pitch-based fibers (K=620 W/m-K) in cyanate ester resin. Samples were made out of woven cloths with 2-2 satin pattern and warped to obtain a range of fiber-pattern angles from 251-25 to 65/-65, plus the traditional 0/90 pattern. Samples of unidirectional tape made of Mitsubishi fiber were also fabricated using a filament winder. LTC and HTC extra samples of 0/90 angle were prepared with 10% volume fraction of graphite powder in the epoxy in order to test filler effect on overall conductivity. Measured thermal conductivity of the LTC samples was in the range of 15-20 W/m-K, and showed moderate variation with fiber angle. Three different angles were tested for these samples, and thermal conductivity was improved by roughly 15% when changing the angle. HTC samples showed thermal conductivities between 60 and 150 W/m-K, with a significant variation of thermal conductivity with angle. An improvement of 60% in the inplane's thermal conductivity was attained when the angle of the fibers relative to the heat flux direction was changed from 0/90 to 25/-2S. Unidirectional tape and eGraph's spreadershield graphite foil showed good thermal performance, while the samples with graphite powder showed that the increase in mass and thickness due to the powder overshadowed any gain in thermal performance.
