The effect of the cylindrically orthotropic morphology known to exist in graphite fibers on the effective properties of a composite material was studied using the composite cylinder assemblage model. The cylindrical orthotropy of the fibers was found to have no effect on the properties of a composite with purely orthotropic fibers. For fibers with a transversely isotropic core both the size of the core and the morphology of the sheath were found to have an effect on the composite properties.

The stress states resulting in the composite cylinder for axial, radial, axial shear, and thermal loads were examined. Singular stresses were observed to occur at r=0 in some fibers in some load conditions. The presence of a transversely isotropic core, which must exist in a real fiber, removed this singularity.

The strength of the composite cylinder was found to depend on uÌ ber morphology. The size of the transversely isotropic core within the uÌ ber also affected the strength. The strength of the uÌ ber increased with increasing transversely isotropic core size in some instances. In general, for axial loading failure is expected to be caused by fiber breakage. For radial, axial shear, and thermal loading the failure mode is uÌ ber splitting.