Constitutive relationships for anisotropic viscous materials

Constitutive relationships for anisotropic materials are considered to describe the viscous flow of fiber-reinforced, thermoplastic composites during forming. The fully anisotropic and the orthotropic cases are first presented. The special case of a transversely isotropic viscous material, which is of particular interest to the deformation of assemblies of oriented fibers suspended in a viscous fluid, is then investigated and the correspondence between two approaches found in the literature on the subject is established.