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.