Influence of the matrix microstructure on the mechanical properties of CVI-infiltrated carbon fiber felts Original Research Article

The correlation between the matrix microstructure and the mechanical properties of CVI-infiltrated carbon fiber felts was studied by optical microscopy, scanning electron microscopy, and three-point bending tests. The results of these investigations show a correlation between (a) the content of highly textured pyrocarbon in the matrix and the quasi-ductile fracture behavior of the samples and (b) the thickness of the low textured pyrocarbon layers beneath the fibers and the measured flexural strengths. Fractographic investigations using SEM showed that toughness increase results from multiple crack deflections at the interface between numerous ‘sublayers’ forming the highly textured pyrocarbon. The increase of flexural strength could be explained by a thicker, so called ‘virtual’ fiber.