A CONSTITUTIVE EQUATION FOR A NON-NEWTONIAN LIQUID

The K-BKZ constitutive equation for non-Newtonian liquids usually uses as invariants the coefficients of the characteristic equation of a certain finite strain tensor. We show that the use of the roots of this equation, the squares of the principal stretches, is more efficient. We use a product of the linear relaxation spectrum and a simple sum of powers of the principal stretches as the "energy function" in the K-BKZ theory. The predictions of this theory agree with Meissner's data to a good approximation over many decades.