Transverse and longitudinal coefficient of thermal expansion of carbon fibers at high temperatures (300-2500 K)

The transverse and longitudinal coefficients of thermal expansion (CTE) of carbon fibers are important parameters in C/C composites behaviour. In this study, the measurements of CTE are presented at very high temperatures (up to 2500 K). Experimental validations are first realised on isotropic metallic (tungsten) fiber. Then, measurements are performed on four carbon fibers (rayon-based, PAN-based and pitch-based). The results show that the mean transverse CTE varies from 5 × 10⁻⁶ K⁻¹ to 10 × 10⁻⁶ K⁻¹ and the longitudinal one from 1.6 × 10⁻⁶ K⁻¹ to 2.1 × 10⁻⁶ K⁻¹ depending on the fiber structural properties. For that, the relationships between the structural properties and the heat treatment temperature of the carbon fibers are discussed in relation to thermal expansion behaviour. A calculation of the ratio between the transverse and the longitudinal measured CTE as a function of the temperature allows us to classify fibers from the most isotropic to the most anisotropic in relation with the structural properties measured at room temperature.