Abstract
C/C composites utilize only 30〜40% of fiber strength, resulting in lower composite strength compared with that of CFRPs, which utilize almost 100% of the fiber strength. Previous study revealed that the bundle C/C composites, which were reinforced by one carbon fiber bundle, showed almost the same level of the fiber strength utilization (fiber efficiency) with that of the cross-ply laminate, indicating that the strength controlling factors of the C/C composites be in the bundles. In the present paper, therefore, strength controlling factors in the bundle was examined. At first, fracture appearance and microstructure before tensile test were observed. Results showed that fracture of the bundle C/C composite was dominated by that of the sub-bundles in the bundle C/C composites, indicating tensile properties of the sub-bundles is essential to understand tensile behavior of C/C composites. For this purpose, model composites with various numbers of fibers were fabricated and tested in tension. It was shown that tensile strength of the model composites was almost 100% fiber efficiency when the number of fiber was small. The tensile strength of the model composites, however, decreased with the number of fibers, and showed the same level with the bundle composites when the number of fibers was more than 20. It was also suggested that such difference was mainly due to the difference in the fiber/matrix inter facial properties.
