A RECURSIVE MODEL FOR RHEOTENS TESTS

An iterative model is described to predict isothermal and nonisotherma l elongation of an extruded filament at a given force. The principle o f the model allows a quite simple description of Rheotens tests with m uch flexibility regarding the shape of the elongational viscosity func tion, including true viscoelastic flow and thermal boundary conditions . The algorithm is compact and computing time on a PC is short. The ap plication of an integral K-BKZ constitutive equation to predict Rheote ns curves of the well characterized LDPE Melt I is demonstrated and th e influence of the slope of the transient viscosity in the strain-hard ening regime is discussed. A simple approximation to take into account the prehistory of the material in the die based on purely elongationa l strains is proposed which includes the irreversibility assumption of the damping function (Wagner model). Predicted Rheotens curves are co mpared with experimental results. (C) 1997 The Society of Rheology.