Emerald Group Publishing Limited
Copyright © 2000, MCB UP Limited
Conference reports. First European Conference on Constitutive Models
Keywords: Conferences, Modelling, Rubber, Austria
First European Conference on Constitutive Models
The First European Conference on Constitutive Models for Rubber was held at the Institute of Structural Engineering, University of Applied Sciences, Vienna, Austria, 9-10 September 1999.
Despite the rather specialist title, this conference attracted 87 delegates. Not only were most European countries represented, but so also were Russia, the Middle East, North America and even Australia.
Cyberneticians and systemists were interested in this conference because of the application of modelling to materials, which for this meeting was very much concerned with rubber. The challenges to CAED researchers and implementers and to the software engineers were apparent.
Vienna was doubtless part of the attraction, and the Institute of Structural Engineering, University of Applied Sciences, proved to be an excellent venue in the leafy suburbs of northern Vienna within walking distance of vineyards. But the lecture room where all the proceedings took place remained filled until closure at 17.00 on Friday, such was the interest of the delegates. The University of Applied Sciences was originally devoted to agriculture, making it an appropriate host for a conference on the extraordinary stress-strain properties of natural rubber.
The list of sponsors gives insight into the success of the conference - being mainly providers and users of computer-aided engineering design (CAED) facilities. The utility of CAED depends on implementation of appropriate constitutive models for the materials, but it is only recently that computers and software with the capability to apply realistic models for rubber has become widely available. Research workers therefore face the challenge to develop models for rubber that can be implemented in the software packages and describe adequately those properties of engineering significance. Software engineers face the challenge of which one of the many models for rubber they should choose.
H. Menderes (MSC), presenting the first paper, gave an overview of the benefits and difficulties of finite element analysis (FEA) of elastomers. He showed the huge scope of FEA, from manufacturing (e.g. extrusion and assembly) to performance (e.g. tyre-road contact or coupled acoustic and structural analysis), available to users who are willing to generate special subroutines. The next paper of the opening session was contributed by M. KÏssner (Abacom). He pointed out that "traditional" hyperelastic models, such as Mooney-Rivlin and Ogden, give a good fit only if very comprehensive and expensive stress-strain data is available; the predictions of such models of the stress-strain behaviour in one mode of deformation from the fit obtained from a different mode can be very unrealistic. This problem has largely been overcome by "new" hyperelastic models, neglecting the second strain invariant, which "contributes little to the fit in comparison with its threat to pollute" according to KÏssner. Most delegates concurred with this view, and in a later presentation, H. Shariff (University of Arab Emirates) reinforced the point that a "sensible" constitutive model should be capable of taking data from one mode of deformation to make a reliable prediction in another mode, effectively concluding discussion on the problems of hyperelastic models. From this point, the proceedings moved on to discuss ways of modelling inelastic effects. R.W. Ogden (University of Glasgow) presented an elegant new phenomenological model for the Mullins' effect. This model provided a good 'fit for Mullins' own data, and may be extended to describe set and anisotropy. Several subsequent authors presented ways of modelling the phenomenon - known also as stress softening, or damage. A verdict on the most useful and natural model will no doubt emerge in the future once experience of their application has accumulated. The final presentation of the opening session was by S. Reese (University of Hanover) on modelling thermo-mechanical behaviour. She presented a three-dimensional model of finite strain viscoelasticity; the structure of the continuum mechanics model could be viewed as arising from a generalisation of the statistical theory of rubber elasticity to include viscoelasticity; thermo-mechanical coupling phenomena could also be incorporated in a thermodynamically consistent way. Although experimental validation was not discussed, the model was used in FEA calculations of the adiabatic temperature rises of laminated rubber bearings undergoing strain cycles, and the results shown as contour plots.
D. Besdo (University of Hanover) announced, at the closure of the meeting, that a sequel conference would be run in Hanover in 2001. This will have the status of an international rather than a European conference, since the high level of international interest had been proven in Vienna.
Hardback copies of the proceedings: Constitutive Models for Rubber, edited by: A. Dorfmann and A.H. Muhr, Published by Balkema, 1999, ISBN 90 5809 1139, are now available.