Modeling of dual cylinder wind-up extensional rheometers

Polymer extensional flow is the one of the most important deformation in polymer processing. It is the dominant deformation in melt-spinning, bottle-blowing, and roll-coating. Because the molecular structure of the polymeric system strongly influences the extension viscosity, extensional flow measurements are useful for polymer characterization. The Sentmanat extensional Rheometer[1] is an new testing platform for the study of polymers and elastomers in extensional flow. This technique employs a dual wind-up drum technique to perform an uni-axial extensional deformation during experiments. This miniature unit requires small amount of material and has been designed in such a manner that it can be used for polymer melt and soft elastomers characterization over a very wide range of temperatures and kinematic deformations and rates. In order to validate the reliability of this testing platform a finite element technique based on a Lagrangian kinematics description of the 3D time-dependent flow of K-BKZ type fluids [2] is used to simulate extension flow of both cylindrical and strip shaped sample in the SER. Here the purpose is to discuss the potential deviations from ideal uni-axial deformation, based on theoretical ideal configurations. Our simulation can setup a theoretical based 'safe' geometry range of samples for SER experiments. Furthermore, the simulations are able to capture flow instabilities in stress relaxation, which have been experimentally observed [4]. References: [1] M.L. Sentmanat, Rheol Acta, 43:657--669, 2004. [2] J.M.R. Marín, H.K.Rasmussen, J. Non-Newtonian Fluid Mech, 156 (3) , p. 177-188. [3] K.Y, J.M.R. Marín, H.K.Rasmussen, O.Hassager, J. Non-Newtonian Fluid Mech, 165 (1) , p. 14-23. [4] Y.Wang, P.Boukany, S.Wang, X.Wang, Physical Review Letters, 99, 237801 (2007). *The title of this submission has been modified to remove the name of a commercial product or company to bring the title into compliance with SOR policy.