Comportement hygroscopique et couplage hygromécanique dans les composites lin / époxy : approche expérimentale multi-échelle et modélisation.

Abstract : Flax fibre reinforcements are nowadays an alternative able to compete with conventional synthetic fibres since they are ecological, economic and have interesting mechanical properties. However, their major drawback is their potentially significant water absorption which affects their mechanical properties. This research project proposes to study the hygroscopic behaviour and hygro-mechanical coupling in flax / epoxy composites. This study is based on a multi-scale experimental approach. A modelling of visco-elasto-plastic behaviour taking into account the hygro-mechanical coupling within flax /epoxy composites is established. The diffusion kinetics in composites were modelled by a Fick law. However, the diffusion kinetics in epoxy were modelled by a Langmuir law. The hygro-expansion coefficients of the composites and the elementary yarns that constitute the fabric reinforcement were determined experimentally. A study of the influence of conditioning until saturation at different relative humidities on the mechanical behaviour in the three main directions of the laminates was conducted. This study showed the existence of an optimal water content for which the mechanical properties are maximum. The emergence of a two-linear-region behaviour was pointed out and attributed to the presence of local heterogeneities within the fabric reinforcement. Creep / recovery and stress relaxation tests were exploited in order to develop a visco-elastoplastic model with consideration of the hygro-mechanical coupling. This model offers good predictive capabilities and could be used to predict the behaviour of flax fibres reinforced composite structures in humid atmospheres.
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Marwa Abida. Comportement hygroscopique et couplage hygromécanique dans les composites lin / époxy : approche expérimentale multi-échelle et modélisation.. Mécanique [physics.med-ph]. Normandie Université; École nationale d'ingénieurs de Sfax (Tunisie), 2018. Français. ⟨NNT : 2018NORMC281⟩. ⟨tel-02289074⟩

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