Multi-scale studies of elastomersmaterials (in a tire tread)

Benoît SCHNELL
Ingénieur de Recherche, MICHELIN

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Abstract : A tire tread is a nanocomposite in a particular shape, which has to ensure good grip for safety without neglecting other performances such as wear or rolling resistance, the latter being actually directly related to the fuel consumption of the vehicles. It is well known that the material processing has a great impact on the properties of treads and more quantitative relationships are still under investigation. One possibility is to achieve improvements by considering the process/product as a whole, but another possible approach is to design an optimized structure for one or several properties by coupling theory / simulation / structure analysis, and then develop the process which would allow reaching the desired target. The presentation will focus on the step “design of an optimized structure”.

Several properties of the tire tread materials are mainly governed by the polymer dynamics. As the dynamic properties of a polymer melt involve a large interval of relaxation times, a multi-scale approach is necessary for its study. Thus, from atomistic simulations (Molecular Dynamics) we develop for different polymers the so-called “realistic mesoscopic interaction potentials” (usable in DPD or more general CG simulations) with an inverse iterative Boltzmann method [1], in particular deriving a method for the NPT ensemble [2]. These mesoscopic potentials allow to obtain good static properties such as the squared end-to-end vector Re2, and more generally allow to distinguish several kinds of polymer microstructures. Work is still in progress to also obtain the polymer dynamics from chemically realistic DPD simulations.

Such chemically realistic DPD simulations are used to optimize the polymer network topology through the establishment of structure-properties relationships and to better understand network’s mechanical properties or related properties, as for example the non-affinity during swelling [3]. These simulations are also used for quantitative predictions to a composite model that consists of two planar fillers of silica confining several chains of polymer, grafted or not; the effect of the confinement on the entanglements and chain dynamics will be more particularly studied, similarly to what has been done in a generic way in reference 4.

[1] Lahmar F. et al., Onset of entanglements revisited. Topological analysis, Macromolecules, 2009, 42, pp 7474 – 7484.

[2] Maurel G. et al., A multi-scale modeling strategy for the prediction of thermodynamic and mechanical properties of polymers, J. Chem. Theory Comput., 2012, 8, pp 4570-4579.

[3]  Saalwächter K. et al., Swelling Heterogeneities in end-linked model networks : a combined proton multiple-quantum NMR and computer simulation study, Macromolecules, 2004, 37, pp 8556 – 8568.

[4] Vladkov M. and Barrat J.-L., Local dynamics and primitive path analysis for a model polymer near a surface, Macromolecules, 2007, pp 3797 – 3804.

Biography : Benoît Schnell is fellow in structure-properties relationships in the Elastomers Department at Michelin, leader of tire manufacturers. His main activity is to design, due to molecular simulations, new materials which can be used in tires. He also owns a French particular degree called “l’Agrégation”, which allows to teach in particular classes dedicated to the preparation of engineer schools. Thus, he makes some interventions in such a class and also gives a course about polymer nanocomposites at the University of Clermont-Ferrand.