AN EXTENDED WHITE-METZNER VISCOELASTIC FLUID MODEL BASED ON AN INTERNAL STRUCTURAL PARAMETER

A phenomenological viscoelastic model of differential type is proposed along the lines of the White-Metzner modification where, though, the model constants are functions of the invariants of an internal tensorial structural parameter. This modification arises naturally in the context of the generalized Bracket formulation and leads to a model which does not lose its evolutionarity and satisfies the entropy production inequality. A power-law dependence of the relaxation time on the trace of the tensorial internal parameter is shown to produce reasonable predictions, including a finite zero shear rate viscosity and nonsingular behavior in extension. A multiple mode version is used in fitting experimental data obtained for polymeric melts and its predictions are compared to those of the Phan-Thien and Tanner model.