A constitutive analysis of stress overshoot for polymer melts under startup shear flow

Abstract

Predicting a transient stress overshoot for polymer melts under startup shear flow is challenging. In recent, the classical White-Metzner (WM) constitutive equation of nonlinear viscoelastic fluids was potentially extended. For viscoelastic material functions, the minus ratio of the second normal stress difference to the first normal stress difference (−N2/N1) is important in characterizing a fluid's elasticity related to molecular structures and molecular weight distribution. Using the extended WM model to analyze a dramatic change in stress overshoot with respect to the −N2/N1 ratio at high Weissenberg numbers would be significant. As a validation, numerical predictions of shear stress growth coefficient at different shear rates are in good agreement with experimental data.