Numerical Predictions of Transient and Steady Rheometric Functions of Polyethylene Melts through a Spectral Tensorial Constitutive Equation

PEIROTTI, MARTA BEATRIZ; OTTONE, MARIEL LORENA; DEIBER, JULIO ALCIDES

MECANICA COMPUTACIONAL

Año: 2006 vol. XXV p. 3 - 20

At present, one can find in the literature a high number of constitutive equations in order to quantify, with varying precision, the stress tensor of viscoelastic materials through rheometric measurements. These equations may be basically classified as integral and differential models. Also, these models may be expressed through the addition of several stress modes by using a spectrum of relaxation times, which is obtained from linear viscoelastic properties of materials, tested in the mechanical spectrometer. Therefore, the choice of a tensorial constitutive equation to predict computationally complex flow kinematics in the processing operations of materials is a rather difficult task with this wide menu. This undesired situation occurs mainly when one needs a rather complete set of rheometric functions characterizing the material under consideration. In this work we explore the capability of the spectral Phan-Thien and Tanner model to characterize transient and steady shear and elongational rheometric functions of linear and branched, and low and high density polyethylene melts, involving different microstructures. For these specific purposes, precise numerical programs are carried out to consider different mechanical histories involving experimental data already reported in the literature. A discussion concerning the prediction quality of the rheological model proposed is presented and some physical aspects involving requirements for further research are provided.