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

The correlation between the matrix microstructure and the mechanical
properties of CV1-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.