THE MECHANISM OF FIBER MATRIX INTERACTIONS IN CARBON CARBON COMPOSITES

The condition of the carbon fiber surface is of great importance in determing the mechanical properties of a carbon-carbon (CC) composite. The presence of functional groups on the fiber surface and roughness of the surface control to a great extent the tensile strength, fracture toughness and interlaminar shear strength. A compromise has to be made between a weak interfacial bond which improves fracture toughness by the debonding and fiber pull-out mechanism, but results in a low tensile strength and a strong interfacial bonding which leads to a catastrophic failure. Thus fiber-matric interactions have to be studied in order to determine the correlation between the conditions of the carbon fiber surface and the mechanical properties of C-C composites. This paper demonstrates the use of surface treatments and de-treatments to optimize the mechanical properties of C-C composites. Oxygen plasma and nitric acid treatments were used to introduce the surface functional groups and to alter the surface morphology. An argon plasma de-treatment was used to reduce the surface functionality. A correlation between the carbon surface modifications and the mechanical properties of C-C composites is discussed with the emphasis on the fundamental understanding of the fiber-matrix interactions. © 1990.