ECCMR 2011 Dublin :: Keynote speakers

Keynote speakers

Professor Emeritus Alan Gent

A. N. Gent

The University of Akron, Akron Ohio 44325-3909 U.S.A.

Chonbuk National University, Jeonju, Korea

Abstract

Elastic Instabilities in Rubber

Materials that undergo large elastic deformations can exhibit novel instabilities. Moreover, the onset of such highly non-uniform deformations has serious implications for the fatigue life and fracture resistance of rubber components. Several examples are described: development of an aneurysm on inflating a rubber tube; non-uniform stretching on inflating a spherical balloon; formation of internal cracks in rubber blocks when they are subjected to a critical amount of triaxial tension or supersaturated with a dissolved gas; wrinkling of the surface at a critical degree of compression; and the sudden formation of “knots” on twisting stretched cylindrical rods. These various deformations are analyzed in terms of the theory of large elastic deformations [1, 2] and the theoretical results are then compared with experimental measurements of the onset of unstable states [3]. Such comparisons provide new tests of the theory and, at least in principle, critical tests of the validity of proposed strain energy functions for rubber. (They also provide interesting challenges for finite element programmers.)

References

1. R. S. Rivlin, Philos. Trans. Roy. Soc. Lond. Ser. A241 (1948) 379–397.

2. O. Lopez-Pamies, M. I. Idiart, T. Nakamura, J. Mech. Phys. Solids 59

(2011) 1464-1505.

3. A. N. Gent, Internatl. J. Non-Linear Mech. 40 (2005) 165–175.

Biographical notes - Professor Emeritus Alan N. Gent

Alan N. Gent is Professor Emeritus of Polymer Physics and Polymer Engineering at The University of Akron, where he has been since 1961. He is currently a WCU Professor at Chonbuk National University, Korea. He has received many scientific awards including the Bingham Medal of the Society of Rheology, the Colwyn Medal of the Plastics and Rubber Institute, the International Research Award of the Society of Plastics Engineers, the 3M Award of the Adhesion Society, the Charles Goodyear Medal of the American Chemical Society and the Polymer Physics Prize of the American Physical Society. He received N.A.S.A.'s Public Service Medal for services rendered after the Challenger space-shuttle disaster (1986) and was elected to the U.S. National Academy of Engineering in 1991.

M. Klüppel, H. Lorenz, M. Möwes, D. Steinhauser, J. Fritzsche*

Deutsches Institut für Kautschuktechnologie e. V., Eupener Straße 33, 30519 Hannover, FRG

Abstract

The Role of Glassy-Like Polymer Bridges in Rubber Reinforcement

For a better understanding of the structure and dynamics of elastomer composites, it is convenient to study the dielectric properties of conducting carbon black filled elastomers on a broad frequency scale [1-5]. It is demonstrated that due to the heat treatment during vulcanization, a pronounced flocculation of filler particles takes place in the rubber matrix leading to a drastic modification of the dielectric spectra [2]. In particular, the percolation threshold decreases significantly and a second high frequency relaxation transition appears which is traced back to the tunneling of charge carriers over small gaps between adjacent carbon black particles. From the dielectric spectra the gap size can be evaluated which is found to decrease with increasing carbon black concentration in the range of 4-8 nm [3].

From a mechanical point of view the gaps correspond to glassy-like polymer bridges representing quite stiff filler-filler bonds which transmit the stress between adjacent particles of the filler network. By applying combined rheological and dielectric analysis it is shown that the gap size decreases during heat treatment leading to a stiffening of filler-filler bonds. This observation supports our view about the thermo-mechanical properties of filler-filler bonds which are shown to play a major role in understanding the viscoelastic properties of elastomer composites [3-5].

The thermo-mechanical response of glassy-like polymer bridges (filler-filler bonds) is also closely related to the quasistatic stress-strain properties of filled elastomers. By referring to the structural analysis of elastomer composites, a micro-mechanical model of stress softening and filler-induced hysteresis has been developed [5-8]. It is based on a tube model of rubber elasticity together with a micro-mechanical model of stress induced filler cluster breakdown. The evaluation of stress softening is obtained via a pre-strain dependent hydrodynamic amplification of the rubber matrix by a fraction of rigid filler clusters with virgin filler-filler bonds. The filler-induced hysteresis is described by a cyclic breakdown and re-aggregation of the residual fraction of softer filler clusters with already broken, damaged filler-filler bonds. The model is shown to be in fair agreement with experimental data obtained with carbon black and silica filled elastomers. In particular it is shown that the effect of temperature on the stress-strain cycles can be well described by considering an Arrhenius like activation behavior of the filler-filler bonds.

Biographical notes - Professor M. Klüppel

Manfred Klüppel is Head of the Department "Material Concepts and Modeling" at the German Institute of Rubber Technology (DIK) in Hannover and is also Associate Professor (Priv.-Doz.) in Polymer Materials at the Leibniz-University Hannover.

He received his Diploma in Physics in 1982 and his Ph.D. in theoretical Physics in 1987 from the Phillips University Marburg. From 1982 to 1988 he was scientific coworker in the group of Prof. G. Ludwig "Foundations of Physics and Mathematical Physics" at the Phillips University Marburg.

Since 1989 his research activities are focusing on elastomer physics and rubber technology. His research interests include polymers based functional materials, reinforcement mechanisms of elastomers by active fillers, polymer fluid dynamics and rheology, interface phenomena in polymer composites, soft matter contact mechanics and rubber friction. So far, he published more than 150 scientific papers, 2 books and 6 book chapters.

C.P.Buckley & co-authors of this paper will be D.S.A.De Focatiis and C.Prisacariu

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK

Abstract

Unravelling the Mysteries of Cyclic Deformation in Thermoplastic Elastomers

In thermoplastic elastomers (TPEs), ‘crosslinking’ is of physical origin, arising from phase separation. In many high volume products these materials offer useful rubber-like properties, but with the great advantage of cost-effective thermoplastic manufacturing routes, not open to chemically crosslinked elastomers. Their resilience in cyclic loading situations is of great practical importance, but shows considerable and poorly understood variation, depending on circumstances and on the choice of TPE. For example, sometimes the Mullins effect is clearly evident, but sometimes not. This paper aims to provide a coherent physical interpretation of the various facets of the observed cyclic response of TPEs, and its dependence on chemical and physical structure; and also the implications for constitutive modelling of these materials. In doing so, it exploits in particular the results from experimental studies of a range of model polyurethane TPEs, with well-characterised structures.

Biographical notes - Professor C. P. Buckley

Paul Buckley studied Engineering Science at the University of Oxford, graduating in 1968. He stayed in Oxford to complete a DPhil on the viscoelasticity of oriented semicrystalline polymers with Dr Gerry McCrum. He then held a NATO Research Fellowship at the CNRS Centre de Recherches sur les Macromolecules in Strasbourg, working on melting and crystallisation of polymers with Dr Andre Kovacs. He returned to Oxford as ICI Research Fellow for two years, working on nonlinear viscoelasticity of polymers, before being appointed Lecturer in Fibre Physics in the Department of Textile Technology at the University of Manchester Institute of Science and Technology in 1975. In 1980 he moved to the Department of Mechanical Engineering to become Lecturer in Polymer Engineering, to help found the UK’s first university Polymer Engineering group, and was later promoted Senior Lecturer. In 1990 Paul moved back to the University of Oxford as University Lecturer in Engineering Science, and was later promoted Reader and then Professor of Engineering Science. He has served as Chairman of the Faculty of Engineering Science at Oxford. Within this Faculty, he is a member of the Solid Mechanics and Materials Engineering Group, where his research interests span several aspects of the mechanical performance of polymer-based materials, including synthetic polymers, composites and biological tissue. Since 1990, Paul has also been a Fellow of Balliol College, Oxford. For over 20 years he has been a Fellow of the Institute of Materials Minerals and Mining, and a Fellow of the Institution of Mechanical Engineers. Paul is a co-author of the well-known text-book “Principles of Polymer Engineering” and his research has been published in over 180 book chapters, journal papers and conference papers

Shigeyuki Toki & Benjamin S. Hsiao

State University of New York at Stony Brook, USA, Jitladda Sakdapipanich, Mahidol University, Thailand

Abstract

Strain-induced Crystallization and Stress-strain Relations in Crystalizable Rubbers: Un-vulcanized, vulcanized, Un-filled and Filled Systems by Synchrotron X-ray Studies

Strain-induced crystallization (SIC) has been considered as a key factor of the superiority of vulcanized natural rubber (V-NR), however SIC is a common phenomenon in crystalizable rubbers at vulcanized state such as polyisoprene rubber (IR), polybutadiene rubber (BR), polyisobutylene(Butyl rubber (IIR)) and so on. Even in the case of filled system, carbon black and nano-clay seem to accelerate SIC. Un-vulcanized NR shows SIC too. Therefore, SIC must be a key element to show higher tensile strength and larger strain at break in crystalizable rubbers. It is still a controversial theme that SIC contributes to an upturn of stress at large strain in stress-strain relations during uni-axial deformation. In order to approach this longtime question, we have to monitor crystallization and stress buildup during stretching at the same time. Synchrotron X-ray measurements make it possible to analyze stress-strain relations and strain-induced crystallization simultaneously. I like to show how SIC is created in rubbers at different systems at different temperatures and pursue the origin of the strength of vulcanized NR.

Biographical notes – Doctor Shigeyuki Toki

Ph. D Polymer Engineering, University of Tennessee

2001- present Chemistry of State University of New York at Stony Brook

1998-2001 Polymer engineering of the university of Akron

1986-98 Tonen Chemical (subsidiary of Exxon Chemical)

1970-86 Bridgestone tire

References

1. Toki, S. et al., Polymer 41 (2000) 5423

2. Toki, S. et al., Macromolecules 35(17) 6578(2002)

3. Trabelsi S. et. al. Macromolecules 2003, 36, 7624

4. Toki, S. et al.,Polymer 44(2003) 6003

6. Toki, S. et al.,J. Polym. Sci. B,42,856 (2004)

7. Trabelsi S., et al. Macromolecules 2003, 36, 9093

8. Tosaka M. et al. Macromolecules 2004, 37, 3299

9. Toki, S. et al., Polymer 50 (2009), 2142

10. Toki, S. et al., Macromolecules 41, (2008), 2295

11. Toki, S. et al., J. Polym. Sci. B, 46, 2456 (2008)

12. Gonzalez. et al., Macromolecules 41, (2008), 2295

13. Ikeda Y, et al. Macromolecules, 2008, 41, 5876

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