Green [8] has shown that a constitutive relation of the form
arises as a special case of an incompressible anisotropic simple fluid, where S is the stress tensor or matrix,
and V is the velocity gradient matrix at time t, all measured in a fixed rectangular cartesian coordinate system. Also, if F is the displacement gradient measured with respect to some curvilinear reference system θi, then
where R is a proper orthogonal matrix, and M and K are positive definite symmetric matrices. In addition
and