Effect of high temperature carbonization on the tensile properties of integrally-braided 5D carbon/phenolic composites

The longitudinal and transverse tensile properties were tested for integrally-braided 5D carbon/phenolic composites carbonized at different temperatures in comparison to the virgin material. The tensile stress-strain curves were obtained and the principal mechanical properties (tensile strength, tensile modulus, failure strain, Poisson's ratio) were determined. A phenomenological relationship between tensile properties and carbonization temperature was established. The fracture morphology and microstructure after tension were observed to further understand the deformation and the failure mechanism. Both longitudinal and transverse tensile strength and modulus show a transition from decrease to increase with temperature rise around a certain temperature point, and the magnitude of modulus change is relatively small. The failure strain exhibits monotonic gradual decrease. The property change is supposed to be correlated with the microstructural evolution of the phenolic matrix upon carbonization at different temperatures.