A composite of carbon fiber in a graphite (carbon) matrix, also known as "Carbon Fiber Reinforced Carbon". Properties given for 50% fiber content. As with any fiber-reinforced composite, mechanical properties vary substantially with fiber content.
E. Yesuda et al. (editors), Carbon Alloys: Novel Concepts to Develop Carbon Science and Technology, 2003 (link).
John D. Buckley and Dan D. Edie, Carbon-Carbon Materials and Composites, 1994 (link).