Oxidation-resistant carbon-carbon materials have tensile, compressive, and flexural strengths of approximately 300 MPa. Low impact energies (150 in ibs/in) cause interlaminar delamination in carbon-carbon composites, but even high-speed impacts (above 700 in ibs/in) only open cavities, with no catastrophic failure observed. These results demonstrate the following characteristics of carbon-carbon composites:
Carbon-carbon materials made from PAN-based carbon fibers exhibit high flexural and compressive strengths, high fracture strains, excellent high-temperature properties, and good impact resistance. Thermal conductivity increases with the measurement temperature, but the inherent thermal conductivity is low. Carbon-carbon materials made from pitch-based carbon fibers exhibit high tensile strength, low compressive and flexural strengths, and low fracture strains. They exhibit high modulus in tension, compression, and flexure, excellent high-temperature properties, good impact resistance, and a slightly higher bulk density.
These differences in properties are likely due almost entirely to the unique characteristics of carbon fibers. Pitch-based carbon-carbon composites exhibit lower fracture strains. Carbon-carbon composites are composed of carbon fibers and a carbon matrix, but the carbon matrix exhibits a lower fracture strain than the carbon fibers. Fracture in carbon-carbon composites is initially initiated by the carbon matrix, ultimately leading to fiber breakage. The strain from the carbon matrix to the carbon fiber fracture is related to the interfacial adhesion between the carbon fibers and the matrix.
Carbon-carbon composites with lower fracture strains exhibit stronger adhesion, indicating that their failure is strongly influenced by the fracture of the carbon matrix. To ensure overshoot resistance to deformation, higher fracture strains are desirable. Future research and development efforts for carbon-carbon composites made from pitch-based carbon fibers should focus on increasing their fracture strains. This includes research into surface treatment techniques for the carbon fibers, while also considering controlling the interfacial adhesion between the carbon fibers and the matrix.