Lightweight and flexible thermal protection systems for high temperature composite applications

Carbon fiber reinforced polymers (CFRP) are increasingly used in aerospace applications which demand lightweight and stability at elevated temperatures. This paper discusses a method of fabricating a lightweight and flexible skin layer that made of carbon nanotube (CNT)/phenolic nanocomposite and using it as a thermal protection layer (TPL) to improve the heat resistance of CFRP. The presence of TPLs in the hybrid composites resulted in a 17% decrease of through-thickness thermal conductivity. Residual flexural strength and modulus after a flame torch test were 39% and 70% respectively of the initial value, a substantial improvement over 11% and 21% of a control sample. We also discuss the effects of TPLs on the coefficient of thermal expansion (CTE) and protection mechanisms. A heat transfer model is developed using finite element analysis to understand the thermal protection mechanism of the developed TPL layer. In the model, the heat conduction equation is solved with temperature-dependent material properties of the different composite material layers. The heat flux flowing from the flame torch to the material surface is estimated through a calibration procedure that compares the predicted back surface temperature against the experimental data. The model was used to conduct a parametric study to investigate the effects of TPL layer thicknesses and volume fractions on the thermal response of the hybrid composite material. This research could lead to the scalable manufacturing of CFRPs with enhanced performance characteristic at elevated temperatures for aerospace applications.