Thèse soutenue

Contribution à l'étude de l'interaction contraintes-diffusion dans les polymères
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Auteur / Autrice : Anne-Lise Durier
Direction : Pierre Gilormini
Type : Thèse de doctorat
Discipline(s) : Mécanique et matériaux
Date : Soutenance en 2008
Etablissement(s) : Paris, ENSAM

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The goal of this thesis held at the Laboratoire d'Ingénierie des Matériaux (LIM) was to study swelling polymers in humid environments, and was then extended to the diffusion of other fluids. Unfree swelling in a solvent (whatever its nature) induces stresses which modify the amount of water at saturation. We study in the present work the case of diffusion in composites loaded with equiaxial fillers (aluminium particles or glass spheres). These fillers, by not absorbing water, disrupt the polymer matrix swelling and induce stresses that have the water mass uptake decrease. The first experimental step of this work consisted in elaborating ideal and well characterised epoxy-amine networks, and determing their diffusion law, swelling and sorption isotherms function of the environmental moisture. Then implement to the composites with different volume fractions. The second modelling part of this work develops a new couplig model between stress and diffusion, via the swelling coefficient and allows us to compute water concentration profiles, stress and strain profiles in a pure resin, and also the mean water concentration and pressure induced by swelling in a composite matrix. It follows that if the polymer matrix has a Henry sorption isotherm, then the composite has a Langmuir one. One has also adapted the model to Langmuir based matrixes. The drawback of the sorption tests in humid environments is, with the considered systemes, tha the swelling coefficients and concentrations even at saturation are low, and thus make difficult to measure the stress impact. In order to solve this problem, we ran further diffusion experiments in heavier organic solvants. But swelling coefficients and concentration get so high that the polymer matrix crosses the glass transition.