Abstract: Carbon/carbon composite material is a new type of composite material with high temperature and friction resistance. In order to investigate the damage and failure mechanism of carbon/carbon composites under tensile load at high temperature, axial tensile test of [0]₁₆ unidirectional laminate carbon/carbon composites with anti-oxidation coating(hereinafter referred to as coating) and [0]₁₆ unidirectional laminate carbon/carbon composites without coating were carried out at 700 ℃. The fracture of corresponding test parts was observed and analyzed under SEM. The fractures of specimens were analyzed by SEM. The tensile test results show that the stress-strain curves of unidirectional carbon/carbon composites with coating at 700 ℃ are linear, and the tensile strength and elastic modulus of unidirectional carbon/carbon composites with coating at 700 ℃ are enhanced compared with room temperature. The stress-strain curves of uncoated unidirectional carbon/carbon composites at 700 ℃ are highly nonlinear and the corresponding mechanical properties decrease obviously. The results of microscopic observation show that the damage forms of unidirectional carbon/carbon composite fiber bundle with coating at 700 ℃ include tensile failure, matrix crack and fiber pulling out. Fiber bundles become thin and distributed for carbon/carbon composite without coating at 700 ℃.

Key words: carbon/carbon composites, high temperature tensile, mechanical behavior, damage mechanism, failure analysis