Analyse multi-échelle de la fissuration des élastomères chargés – AMUFISE

Sparing our natural resources is very important for tyre industry, on both the society side and the economical side. Optimal design - lighter tyres but even safer and with longer life – is a real challenge that can only be addressed with a thorough understanding of crack growth mechanisms. In the specific case of filled elastomers, representing most of the tyre composition, fatigue crack growth approach is very empirical and potential progress on material design is limited. We want to open new areas of innovation and optimization of filled elastomers, by developing a new understanding approach of the damaging phenomena in the crack tip area (from using new experimental and simulation techniques to predicting tools for guiding new material design). This way, we hope to understand the first order effects of micro-structural parameters on intrinsic crack growth resistance properties. Today, influencing mechanisms are rather poorly understood and much discussed. Among other difficulties is the key issue of coupling various phenomena at different scales: large strain constitutive law, including softening and self-heating, mechanical and thermal fields evolution through geometric modification of the crack tip, and so on … Our project consists in a multi-scale approach linking the physico-chemical scale (material structure, from a few nanometers to some micrometers), the crack tip scale (hundreds of micrometers) and the scale of the structure (a few centimeters). This approach must link physico-chemics, physical damage and continuum mechanics. It includes proposing a new constitutive law for filled elastomers, taking into account its fatigue evolution, and a damaging model at the crack tip based on the understanding of local mechanisms. These models shall be included in a finite element crack simulation. Digital image correlation technique will be used for comparing experimental displacement fields near the crack tip with simulated fields. Then simulation shall be upgraded, in several experimental/simulation loops. The first model difficulties lie in the fact that it is compulsory to have a good coherence between the small scale field and the far field at the scale of the whole structure. The project is also very ambitious in trying to put together several aspects which are individually poorly mastered in the case of filled elastomers. On one hand, physico-chemical damage origin at the crack tip is still unknown, partly because measurements are very tricky near this crack tip. On the other hand, constitutive laws for filled elastomers are difficult to measure and to simulate, due to high non linearities and to their strong sensitivity to loading history. Finally, existing damage simulation principles, developed for other materials, and displacement field measurements, by digital image correlation, have both never been applied to elastomers. Thus, the global project approach mixes several analysis scales (from micro-stuctural physico-chemics of the material to continuum mechanics). Each of these analysis hits strong difficulties and their coupling is in itself very tricky. Common work between so many specialists joining their expertises together on the same problem and on the same experimental setup has yet never been tried. We think that complementarity of gathered expertises is the only way to reach significant progress in understanding crack propagation in filled elastomers and in identifying innovative tracks for proposing more resistant materials.