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Etude de vieillissement d’un silicone de type VMQ sous contrainte mécanique

Abstract : During their in-service use (up to 11 years) for mechanical blocking and damping function at room temperature, VMQ silicone O-rings showed high CS values, indicating a decrease in their elastic properties. The aim of the thesis was, on the one hand, to try to determine the factors influencing the changes in CS and the corresponding mechanisms and, on the other hand, to estimate the lifetime of the seals under real conditions in an industrial site. Firstly, CS was measured after accelerated ageing tests under compression with variation of time (up to 2 years), temperature (from 30 to 160°C), compression and shear ratios, oxygen (from 0 to 99,9 %) and humidity quantities (from 5 to 100% RH) and the presence or not of PP. Based on the principle of the time-temperature equivalence, the different CS isotherms obtained were used to determine the shift factor obeying an Arrhenius law in order to plot the different master curves. The hypotheses of mechanisms (entanglement of the dangling chains and chain ends, oxidative cross-linking and hydrolysis followed by recombinations) to explain the behaviour of the silicone in CS were discussed in terms of structure-property relationships thanks to a physicochemical (DSC, FTIR, equilibrium swelling and solid state NMR) and mechanical (IRHD microhardness and DMA) analytical approach. It clearly appears that humidity plays a key rôle during the ageing of silicones.
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Submitted on : Thursday, June 16, 2022 - 9:36:19 AM
Last modification on : Saturday, August 6, 2022 - 3:07:12 AM

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  • HAL Id : tel-03696550, version 1

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Haoua Brahami. Etude de vieillissement d’un silicone de type VMQ sous contrainte mécanique. Mécanique des matériaux [physics.class-ph]. HESAM Université, 2022. Français. ⟨NNT : 2022HESAE033⟩. ⟨tel-03696550⟩

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