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Reference : UMR5223-PAUSOT-001
Workplace : VILLEURBANNE
Date of publication : Monday, November 15, 2021
Scientific Responsible name : Paul Sotta
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 February 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
The proposed PhD is part of a collaborative project (acronym WEEL) between Laboratoire de Tribologie et Dynamique des Systèmes (LTDS), Ingénierie des Matériaux Polymères (IMP) and Solvay Silica company, funded by the French National Agency for Research (ANR). The project aims at bringing new insights in the fundamental understanding of the abrasion wear mechanisms of reinforced elastomers that will set the basis for future improvement in the prediction of durability of such materials, and in particular car or truck tires. Understanding abrasion wear remains an unsolved scientific challenge, that we propose to tackle by combining, for the first time, (i) proper wear experiments and (ii) advanced experimental and numerical investigation of the in-operando stress/strain field at a sliding interface. Indeed, our main research hypothesis is that the latter mechanical fields are the true local driving forces responsible for wear evolution. Our strategy will thus include:
1. well-defined reinforced elastomer samples representative of tire tread compounds manufactured at Solvay Silica labs, with a number of formulations and process parameters corresponding to specific dynamic and mechanical properties.
2. use of a home-made wear test device to characterize the wear properties of those samples, including the evolutions of their shape and of the local wear patterns (ridges, rolls,…);
3. use of a recent, cutting-edge opto-mechanical device to analyse the contact stress/strain state and dynamics, at different stages of the wear evolution;
4. development of an improved, comprehensive model of wear of reinforced elastomers incorporating the local contact conditions.
Therefore, the proposed PhD work will consist in performing wear measurements of samples in kinematic conditions relevant for tire durability, with thousands of cycles on an abrading surface, using our specifically designed laboratory tribometer. The physico-chemical structure of the samples will be characterized by various techniques (DSC, TGA, FTIR, time-domain proton NMR). The objective of the PhD is to establish a full mapping of the obtained wear patterns and wear rates as a function of experimental conditions (pressure, temperature, number of cycles, duty cycle of the wear cycle, etc), for a set of well-chosen representative materials. The amount of wear debris present in the contact is another parameter with major impact on the wear process. Wear debris will be collected and analyzed in terms of size distribution and physico-chemical structure, in order to elucidate local fracture and/or physico-chemical mechanisms associated to wear.
Wear tests will be performed at Laboratoire de Tribologie et Dynamique des Systèmes (LTDS, CNRS-Ecole Centrale de Lyon, Ecully) and sample characterization at laboratory Ingénierie des Matériaux Polymères (IMP, CNRS-INSA Lyon), both located very near to Lyon. The PhD shall involve close contact and collaborative work with other partners, specifically with other PhD or postdoc fellows and with the industrial company Solvay Silica, also located close to Lyon.
The PhD will be co-supervised by Paul Sotta, CNRS senior Researcher (Directeur de Recherches), polymer physicist specialist in process/structure/properties relationships in elastomers and solid polymers, and by Jean-Luc Loubet, CNRS senior Researcher (Directeur de Recherches), expert in Material Science, mechanical engineering, contact mechanics and tribology. Both Researchers have already collaborated extensively, as well as with the Solvay Silica Company, on the wear of elastomer.
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