Tensile Strength of Carbon–Carbon Composites: I – Effect of C–C Density

Abstract

The tensile fracture stress and strain of carbon fiber-reinforced carbon matrix composites (C–Cs) were examined as functions of the bulk density. When the density increased, the interfacial strength of the C–Cs monotonically increased, and the tensile fracture strain decreased. In contrast, the tensile fracture stress was improved and degraded in the regions of density lower and higher than 1.6 g/cm3, respectively. Two tensile fracture mechanisms of the examined C–Cs were identified with the transition at the density of 1.6 g/cm3. In the low-density region, load transfer capability across fiber–matrix interfaces was shown to have an important role, and in the high-density region, stress concentrations at matrix-crack tips were presumed to be a major factor for the tensile fracture of C–Cs. This suggests that the most important interfacial property for tensile fracture is not interfacial sliding but debonding stress.