Thermal Expansion Coefficients of Commingled Carbon Fiber/Poly(ether-ether-ketone) Composites

Thermal expansion coefficients (CTE) of commingled composites manufactured from commingled yams composed of carbon fibers (CF) and PEEK [poly(ether-ether-ketone)] filaments were measured and compared with those of CF/ PEEK prepreg composites. All specimens showed stable and non-scattered CTE data as a result of the thermal treatment or the repeating measurement on the same specimen. This procedure was necessary to obtain reproducible data. The unidirectional (U-D) commingled composite exhibited lower longitudinal CTE than the U-D prepreg composite, and showed a remarkable decrease of CTE at around Tg of PEEK resin. The CTE of the warp direction in 2-dimensional (2-D) commingled composite, that showed lower CTE than the weft direction due to the higher warp density, was found to be almost similar to that of 2-D prepreg (cross-ply) composite. Assuming the temperature dependence of CTE of the carbon fiber itself, theoretical predictions of CTEs of the U-D commingled and the 2-D prepreg composites were obtained in good agreement with experimental results.