A simple constitutive model describing the steady state shear viscosity and its prediction of the first normal stress function in shear flow

To describe the nonlinear behavior of polymer melts with few parameters, a simple three-parameter model for the shear viscosity function is proposed and applied to the polymer melt viscosity prediction as well as the first normal stress coefficient prediction using Wagner’s relationship. Its predictions were compared with experimental data. The nonlinear form of the model correlates the viscosity very well with the experimental data over many decades of shear rate. It demonstrates that a simple nonlinear term can replace the sum of the series of multiple linear spectra. From the first normal stress coefficient correlation with the experimental data, the damping constant of Wagner’s equation was obtained. Another applicability is demonstrated by the description of the elongational viscosity.