Tensile properties of 4D braided carbon/carbon composites produced from carbon fiber bundles and carbon rods

4D preforms woven with carbon fiber bundles and carbon rods were densified by repeated pitch impregnation, carbonization and high temperature treatment to obtain 4D-C/C composites. The tensile properties were investigated at room temperature when tension was applied in the carbon rod direction (Z direction). The strain and stress under tensile load were measured, and the surface morphologies of specimens after tensile failure were observed by scanning electron microscopy. Results indicate that the tensile strengths of the composite were controlled by interfacial shear strength between the carbon rod and the carbon matrix. The carbon rods were pulled out entirely from matrix after tensile failure, indicating that the material was not sufficiently reinforced by the carbon rods. Numerous micro-cracks were found on the surface of specimens after tensile failure. These were perpendicular to the load direction and equally spaced by a distance of about 2mm. The damage model of 4D-C/C is similar to that of 1D-C/C.