Elastic modulus and thermal expansion rate of a CFRP heated in inert gas environments

A chopped carbon cloth impregnated with a phenol resin that is compressed under an elevated temperature is termed the chopped CFRP. Thermal and mechanical properties of the chopped CFRP are nearly isotropic. Heated CFRP is carbonized because the internal resin undergoes thermal decomposition. Due to this thermochemical reaction, cavities in the form of minute cracks developed inside the chopped CFRP. Once these cavities are formed, the interior of the chopped CFRP exhibits non-linear stress-strain characteristics. The elastic modulus and thermal expansion rate of the CFRP in this state have not been described analytically in detail till date. In this study, the formation of these cavities due to thermal decomposition was assumed to damage the interior of the CFRP. Based on this assumption, the elastic modulus and thermal expansion rate of the chopped CFRP in the nonlinear region were analyzed by using either a damage multiplier or the reaction rate. The results of this analysis were in good agreement with the measured values. Therefore, this approach of analyzing the elastic modulus and thermal expansion rate of the chopped CFRP is appropriate.