Thermal stresses and effective properties calculated for fiber composites using actual cylindrically-anisotropic properties of interfacial carbon coating

Thermal stresses in composites composed of fiber (Nicalon™ or carbon fiber), pyrolytic-carbon coating and matrix (SiC) were calculated by the use of the actual properties of carbon coating, which are elastically and thermally cylindrically-anisotropic (transversely-isotropic about radial direction). They were compared with calculations with other anisotropies for the coating, including an often assumed anisotropy which is transversely-isotropic about fiber axis. It was shown that the differences in radial and hoop stresses between the actual and assumed ones could be significant. In addition, effective moduli and CTEs of a composite fiber (fiber/carbon-coating) and those of a composite matrix (carbon-coating/matrix) were derived and used to interpret the resulted thermal stresses.