Consistency Relations for Double-Step Strain Experiments

Consistency relations for double-step strain deformations are formulated and applied in the evaluation of proposed constitutive models for nonlinear viscoelastic behavior. Two important double-step deformations are used to evaluate three constitutive models: the Doi-Edwards model without the independent alignment approximation, an integral viscoanelastic model, and a strain-coupling model. Comparison of the consistency relations for the Doi-Edwards and viscoanelastic models with double-step shear stress data showed that there may be important deficiencies in these models. The shear stress data were in reasonable accord with the consistency relation for the strain-coupling constitutive equation.