Numerical modeling of the flax fiber morphology variability

International audienc

Fourier based methodology for simulating 2D-random shapes in heterogeneous materials

International audienc

Multiscale modelling of thermal conductivity in composite materials for cryogenic structures

International audienc

An Application of Stochastic Simulation to the Study of the Variability of Road Induced Fatigue Loads

International audienceTo adapt their products to the durability requirements, car manufacturers must possess a suitable methodology to quantify the large variety of road induced fatigue loads that vehicles' components undergo during their life. The load data acquisition process is generally based on long and costly measurement campaigns. Here an alternative load characterization methodology is proposed. It is based on stochastic modelling and simulation rather than purely on a collection of load measurements. Stochastic models, in the form of random processes, are proposed for vehicle-independent influential factors, namely road roughness and vehicle's speed. Random realizations are generated and used as inputs for multi-body simulations, describing the dynamics of any given vehicle. An arbitrarily large set of fatigue loads can therefore be obtained inexpensively, for any given elementary life situation, and subsequently, for the total life of the vehicle, using customer usage information. A study of the influence of a change in market region is performed as an illustration of the stochastic simulation methodology. For this study, existing measurements carried out by Renault within the considered market regions, are used as a source of statistical information

The effect of lignin on the reactivity of natural fibres towards molecular fluorine

International audienceIn this study, a range of natural fibres and their main components have been treated by direct fluorination using F2 gas. Fourier-Transform infrared spectroscopy, 19F solid state Nuclear Magnetic Resonance and tensiometry results underline the substitution of OH groups by fluorine atoms and thus the formation of CF covalent bonds. Fluorination induces a significant decrease in the hydrophilic properties in the case of lignocellulosic materials. The relationship between the chemical composition of the natural fibres and their reactivity during fluorination has been established. Indeed, on the one hand, the affinity for F2 is improved by the presence of lignin, leading to a better conversion of COH into CF bonds. On the other hand, a high cellulose content tends to inhibit the reaction. As a consequence, the cellulose and lignin contents of wood materials can be determined thanks to their reactivity during fluorination. However, for high-content cellulose materials, estimating the cellulose and lignin contents by this method is more difficult because of their low reactivity during fluorination. In this case, a thermal assisted fluorination is necessary to increase reactivity and thus classify samples according to their cellulose content

Estimation of road profile variability from measured vehicle responses

International audienc

Fluorination as an Effective Way to Reduce Natural Fibers Hydrophilicity

International audienceIn order to get composite materials with high mechanical properties, the quality of the interface between the fibres and the matrix has to be good enough to enable the load transfer. In the case of wood polymer composites, made of hydrophilic wood particles and of a generally non-polar polymer, the lack of natural compatibility between the constituents hinders the load transfer. Aiming at decreasing the gap of polarity between wood fibres and polymer matrices, fluorination has been applied to wood. This treatment is known to be very efficient to make more hydrophobic materials without requiring solvent or high temperature. After the optimization of the treatment parameters so as to get a high level of fluorine grafting without burning the particles, the hygroscopic and thermal behaviors of the fluorinated wood flour have been evaluated and compared to the non-treated flour. For that purpose, several analyses were carried out: FT-IR spectroscopy, 19F solid-state NMR spectroscopy, SEM, contact angle measurements, TGA. The fluorine based treatment was shown to decrease notably the capacity of the wood particles to absorb water without damaging their surfaces. Lastly, at the composite scale, the wood fluorination was shown to strongly reduce its hydrophilicity and to largely enhance its tensile and flexural properties. This is directly linked with the improvement of the compatibility between the treated (and thus, less hydrophilic) wood particles and the polymer matrix, as also proved by X-ray tomography

Caractérisation des propriétés biochimiques et hygroscopiques d’une fibre de lin

L’étude des fibres de lin comme renfort de matrice polymère a commencé au début des années 2000 et a déjà mis en évidence leur capacité à remplacer efficacement les fibres de verre. Dans cette étude, l’influence de l’eau sur le comportement mécanique des fibres végétales est mise en avant. Les premiers résultats de mesures de variation de masse de fibres conditionnées dans des atmosphères contrôlées en humidité et en température montrent que les fibres séchées récupèrent très rapidement leur teneur en eau (en quelques secondes). De plus, des essais de traction menés sur ces fibres permettent de comparer leurs propriétés mécaniques avec celles des fibres non séchées. En complément de cette étude, une estimation des teneurs en cellulose, hémicelluloses et lignines de la fibre a été réalisée