Meccanica (2008) 43: 327–337 DOI 10.1007/s11012-007-9097-z Experimental identiﬁcation of viscoelastic properties of rubber compounds by means of torsional rheometry Herbert W. Müllner · Andreas Jäger · Elisabeth G. Aigner · Josef Eberhardsteiner Received: 28 September 2007 / Accepted: 18 October 2007 / Published online: 29 November 2007 © Springer Science+Business Media B.V. 2007 Abstract Rheological models are used for the de- scription of viscoelastic properties. Such investiga- tions are mostly based on experiments with a torsional rheometer, i.e. a Rubber Process Analyzer. The re- sults of such experiments are storage and loss mod- ulus, which depend on the applied angular frequency. The investigations were performed with rubber com- pounds used in industry, with different crystallization degrees of the used EPDM basic polymer as well as different ﬁller degrees. Moreover, the inﬂuence of melt temperature on these dynamic moduli is considered. For the rheological description of the investigated rub- ber compounds three different viscoelastic models are used. After derivation of the corresponding relation- ships for each of the spring-dashpot models the ap- plication for rubber compounds was investigated. The best agreement between experiment and model predic- tion was achieved by a nonlinear viscoelastic model. With such a model the inﬂuence of different crystal- lization and ﬁller degrees on the viscoelastic material properties can be covered. Keywords Rheology · Viscoelasticity · RPA · Huet model · Mechanics of ﬂuids H.W. Müllner ( ) · A. Jäger · E.G. Aigner · J. Eberhardsteiner Institute for Mechanics of Materials and Structures, Vienna University of Technology, Karlsplatz 13, 1040 Vienna, Austria e-mail: Herbert.Muellner@tuwien.ac.at 1 Introduction The design of injection heads for the extrusion of rub- ber proﬁles is exclusively based on empirical knowl- edge of the non-linear viscoelastic ﬂow behavior of elastomers. Thus, the injection heads were designed for the employed rubber compound, where the geome- try of the sealing proﬁle is obtained by empirical adap- tation of the extrusion die. This adaptation process is mainly inﬂuenced by the swelling of rubber after extrusion. This process con- sists of several steps. Disadvantages of the current pro- duction process are the non-reproducible process tech- nology and the time-consuming design of dies, which affects the production capacity. The was a strong mo- tivation for a research project devoted to characteriza- tion of the die swell properties of rubber compounds. The research work was jointly carried out with Sem- perit Technische Produkte Ges.m.b.H., who provided the material and the experimental equipment. An important task of the constitutive material char- acterization is the determination of viscoelastic prop- erties which are required for the description of arbi- trary parts of the tools for production of rubber pro- ﬁles. Until now, torsional rheometry is one of the most important methods for the determination of such prop- erties of plastics. In many cases this method is also used for rubber compounds. For the performance of numerical simulations of injection heads and other ex- trusion applications knowledge of viscoelastic mater- ial parameters is required. The latter are coupled with