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Hypothesis The temperature dependence of the static contact angle could a priori be predicted by using surface tension partitioning. An original model based on the transition state theory is also introduced. This model considers thermocapillary fluctuations on the droplet surface near the triple line and the self-affine pinning of this triple line against a solid substrate modeled with a pseudo-periodic distribution of adsorption sites. Experiments The temperature dependence of the static contact angle was studied for a representative range of liquids with different polarities and on a wide array of solid substrates for temperatures ranging from 25 to 240 °C. Atomic force microscopy (AFM) was also used to quantify the surface roughness of the solid substrates. Findings Whereas the surface tension partitioning failed to bring consistent results above room temperature, the transition state model proved very useful, thereby opening a way to yield predictive contact angle values with temperature variations. The introduction of a topological dimension in the equations yields a unified model that covers normal wetting (perfectly bonded liquids on smooth surfaces) but also the onset of Cassie-Baxter and Wenzel states on real surfaces. Moreover, the model encompasses the transition to complete wetting.

International audience; This work consists in an experimental investigation of forced dynamic wetting of molten polymers on cellulosic substrates and an estimation of models describing this dynamic. A previous work of Pucci et al. (2018) showed that for totally wetting liquids (as paraffin oils), temperature-induced variations in dynamic wetting are included into the capillary number (Ca) and then a master curve of dynamic contact angle (θ d) as a function of Ca can be obtained. The hydrodynamic theory (HDT) correctly describes the dynamic wetting for Ca > 2 · 10 −3. For lower Ca, a change in the dynamic wetting behavior was observed. Here, partially wetting liquids (polyethylene glycols, a.k.a. PEGs) at different molecular weight (Mn) were used at temperatures above their melting point to investigate the dynamic wetting behavior on cellulosic substrates for a large range of Ca. It was found that the dynamic curves of θ d vs. Ca depend on Mn. Moreover, the HDT correctly describes the experimental measurements for Ca > 2 · 10 −3. Below this threshold the dynamic contact angle decreases toward the static one. A linear correlation between parameters obtained fitting the HDT and the molecular weight of polymer was found. The prediction of dynamic wetting for low Ca (Ca < 2 · 10 −3) with the molecular kinetic theory (MKT) was also evaluated and discussed.

International audience; Flax fibres are a promising reinforcement in the development of biocomposites and are finding new applications in transport structures. However, there is a perceived problem with plant fibres related to the variability of the properties of these natural materials. This paper describes the factors which affect variability, from plant growth conditions to fibre sampling and testing. A large number of test results are presented (characterization of elementary fibres, bundles, assemblies of bundles, and unidirectional composites), and it is shown that provided fibre supply is carefully controlled, characterization procedures are appropriate, and manufacturing processes are optimal then excellent composite properties can be achieved with low variability.

International audience; The aim of this study was to set an experimental protocol in order to identify key parameters in wetting dynamics during liquid composite manufacturing. To validate the procedure, model materials were studied : cellulose films as substrates,and paraffins and polyethylene glycols as liquids. The experimental procedure consisted of characterizing the substrates interms of morphology and surface chemistry, showing that, as a first approximation, it was possible to consider substrates as model surfaces without physico-chemical defects. The characterization of liquids as a function of temperature and molar mass was then performed, considering an additional issue : the molten state of polymers. Temperature conditions and molar mass were then considered in wetting and dewetting dynamic. The results were well described by the hydrodynamic approach for a range of capillary numbers. Using these models, physical parameters were estimated, explaining the influence of temperature and polymer chain lengths on wetting dynamics.; Ce travail a pour objectif de calibrer un protocole de mesure permettant d’identifier les paramètres clés dans les phénomènes de dynamique de mouillage lors de la mise en oeuvre de composites. Pour valider la procédure, des matériaux modèles ont été étudiés : des films cellulosiques en tant que substrats, et des paraffines et polyéthylène glycols comme liquides.La procédure expérimentale a consisté à caractériser le substrat en termes de morphologie et de chimie de surface, en montrant qu’en première approximation on peut s’affranchir des hétérogénéités de surface. La caractérisation de liquides en fonction de la température et en fonction de la masse molaire a été ensuite analysée en prenant en compte l’état fondu des polymères. Les conditions de température et de masse molaire ont été ensuite considérées en dynamique de mouillage et de mouillage. Les résultats ont bien été décrit par l’approche hydrodynamique pour un certain intervalle de valeur du nombre capillaire. Sur la base de ces modèles, des paramètres physiques ont été estimés, en précisant l’influence de la température et des longueurs de chaine de polymères sur la dynamique de mouillage.

We described an experimental technique, which can be used to measure simultaneously the three principal permeabilities of fiber reinforcement made of short or long fibers. This original technique utilizes the X-Ray radioscopy for detecting the position of the liquid front inside of the preform. An analysis of the different experimental results allowed us to measure, explain and justify the influence of the various parameters related to the flow conditions, the mold geometry and the reinforcement material structure. The experimental study proves that this technique is not limited by high anisotropy factors. We obtain good agreement between results of this visualization technique and numerical simulation of the resin flow.

International audience; This experimental work addresses the mechanical behavior of weaven UD glass fiber-thermoplastic composites designed for layered materials to be used in the automotive industry. The investigation was implemented in terms of the formulation of the PA66-based thermoplastic resins, the architecture of the fibrous reinforcement (warp spacer) and the glass fiber content. Longitudinal and transverse tensile tests results demonstrate the excellent mechanical behavior of these composites, which correlates with the rheological/permeability properties and wettability behaviour. © 2016 Author(s).

International audience; The biosourced Polyamide 11 (PA11) is envisaged as a matrix in structural ecocomposites in combination with long flax fibers. Herein we compare the thermal, rheological, physical, mechanical and hydrothermal behavior of PA11 available as film or powder. These data are used for choosing between the two forms of the PA11 and to determine the temperature, holding time and pressure ranges suited for the elaboration of biocomposites by induction heating. © Lavoisier 2016.

In Liquid Composite Molding (LCM) processes the saturation of the reinforcement by the resin may induce the creation of porosity in the preform affecting the final properties of the composite. The purpose of this work concerns the development of an experimental protocol and the associated modeling to identify the dynamic saturation curve during filling by taking advantage of sharp contrasts of thermal properties existing between dry and fully-saturated reinforcement. To identify saturation, several injections were performed with a laboratory RTM mold for which thermal design allows accurate control of heat transfer. Several heat flux sensors were used to identify the saturation curve. Sensitivity analysis proves the feasibility of the method. The results are compared with a conductometric method with good agreement. Evolution of residual voids identified for several flow rates are also consistent with those expected according to the capillary number.

Numerical simulations on confined bubble trains formed by cross-flowing streams are carried out with the numerical code THETIS which is based on the Volume of Fluid (VOF) method and has been developed for two phase flow studies and especially for a gas-liquid system. The surface tension force, which needs particular attention in order to determine the shape of the interface accurately, is computed using the Continuum Surface Force model (CSF). Through the coupling of a VOF-PLIC technique (Piecewise-Linear Interface Calculation) and a smoothing function of adjustable thickness, the Smooth Volume of Fluid technique (SVOF) is intended to capture accurately strong interface distortion, rupture or reconnection with large density and viscosity contrasts between phases. This approach is extended by using the regular VOF-PLIC technique, while applying a smoothing procedure affecting both physical characteristics averaging and surface tension modeling. The front-capturing strategy is extended to gas injection. We begin by introducing the main physical phenomena occurring during bubble formation in microfluidic systems. Then, an experimental study performed in a cylindrical T-junction for different wetting behaviors is presented. For the wetting configuration, Cartesian 2D numerical simulations concerning the gas-liquid bubble production performed in a T-junction with rectangular, planar cross sections are shown and compared with experimental measurements. Finally, the results obtained of bubble break-up mechanism, shape, transport and pressure drop along the channel will be presented, discussed and compared to some experimental and numerical outcomes given in the literature.

Usual testing methods developed for synthetic fibre bundles or slivers do not suit for plant fibres which exhibit specific characteristics. This paper reports damage investigation in flax fibre slivers (collection of disentangled and aligned fibre bundles more or less bonded by bark residues or other tissues) especially prepared for uniaxial tension testing using a new methodology and a dedicated device. The analysis of the acoustic emission data by using clustering methodology allowed categorizing three populations of damage mechanisms. Identification of the damage mechanisms was made by correlation of the tensile loading curves with acoustic emission data and by optical observations. Different damage parameters defined from the mechanical data (released elastic energy) were compared with those from acoustic data (energy of the hits). The results showed that the extension of damage vs. deformation can be expressed by using either of these two data sets.

International audience; Composite materials are heterogeneous materials which consist of a matrix reinforced by fibers. One of the most promising manufacturing processes are Liquid Composite Moulding (LCM) in which a stationary fibrous preform is impregnated by a liquid. It is essential to monitor two key-steps in order to ensure high quality composite parts: the mould-filling stage, during which the liquid resin flows through the fibrous preform and the solidification. Two examples related to these issues are detailed here, the common point being the use of the same sensor to identify the different properties. In a first part, an experimental device has been designed to quantify the saturation profile of a preform. This set-up consists of a mould with heat flux sensors and an injection device reproducing the actual forming process. The saturation curve can be obtained by exploiting the wall heat fluxes. In a second part, this study emphasizes the use of the same heat flux sensors to monitor the consolidation phase. Indeed heat transfer and temperature during the forming process are strongly coupled with the phase change through the variation of thermal properties. These methods clearly open up new perspectives regarding the online control of composite manufacturing processes at an industrial scale.

Since flax is the most promising plant for the reinforcement of polymer-based composites in structural applications, we have chosen to investigate its hygrothermal characteristics which can be useful for the understanding of the behaviour of other plant fibres. The flax fibres were exposed to different hygrothermal conditions: in an oven at various controlled temperatures (–40 to 140℃) and measured relative humidity, in a climate chamber at 50% relative humidity for define temperatures between 25℃ and 85℃, or different determined aging conditions. The correlation of these hygrothermal conditions to the evolution of the mechanical properties gives evidence of the prominent influence of water over temperature on the microstructural changes of flax fibres. The mechanical parameters drastically decrease in usually prescribed hygrothermal aging conditions for organic matrix composite materials, the strength being particularly sensitive to the presence of water. These evolutions were correlated to the fibre microstructure modifications induced by water absorption as revealed by electron microscopy analyses. These findings could be useful for understanding the behaviour of polymer matrix biocomposites in severe hygrothermal conditions.

International audience; This paper presents a large flax fibres varieties intercomparison with the aim of studying the dependence of the mechanical properties (tensile strength, ultimate strain and Young's modulus) on the variety. Thus, a Student's test analysis permits to dissociate the effects of the statistical variations within a large samples population and the effects of the species on the fibres mechanical properties. Results evidenced no significant influence of the variety on the fibres mechanical properties. Experiments show that this can be explained by a similar biochemical composition whatever the species considered, in particular the proportion of cellulose which is the reinforcing phase of the flax fibre. In addition, the cellulose crystallinity rate is the same for all the varieties. Weibull statistical analysis permits to highlight that the flax fibre is as reliable as some synthetic fibre, opening the way to its use as reinforcement in structural composite materials. Furthermore, this analysis evidenced that only one kind of defects involves the fibre breaking. Thus, X-ray tomography permits to experimentally define this type of defects which are cavities, of about 10 m long, constituting the preferential zone of crack initiation leading to the fibre breaking. Therefore, the dispersion of the fibre mechanical properties seems to be due to the number and size of the defects located in the cell walls and also to the usual determination method of the fibre diameter. Finally, it appears that the choice of the cropped variety must be mainly determined by the pedoclimatic conditions and the yields rather than by the expected mechanical properties. The improvement of the cultivation and scutching processes could be the key of the increase of the fibres mechanical properties by limiting the creation of structural defects.

International audience; Transverse compaction of textile composite reinforcements is an important deformation mode arising during composite forming and manufacture. The mesoscopic simulations of the transverse compression of textile preforms presented in this paper are based on 3D FE models of each yarn in contact with friction with its neighbours. A hypoelastic model based on the fibre rotation depicts the mechanical behaviour of the yarn. The compression responses of several layer stacks with parallel or different orientations are computed. The numerical simulations show good agreement when compared to compaction experiments. The mesoscopic simulations can be used as virtual compression tests. In addition they determine the internal geometry of the reinforcement after compaction. The internal geometry can be used to compute the permeability of the deformed reinforcement and to calculate the homogenised mechanical properties of the final composite part."

The study of forces acting inside a fluid or at the interfaces liquid/liquid, liquid/vapour or liquid/solid is very significant to improve the understanding of the multiphase flows in microdevices designed for material science applications such as pharmaceutical of food industries to name but a few. Even if the phenomena at the interfaces between the different phases are widely investigated, they continue to have a huge interest in microfluidics. This experimental study underlines the importance of wetting on air bubbles formed by a liquid/gas cross-flowing mechanism inside a glass cylindrical T-junction device. Experiments were performed by using various liquids as continuous phase that may provide different wetting behaviours. For typically small capillary numbers of the continuous shear stream, results give rise to the significant effect of the contact angle between the liquid and solid on the bubble size. Indeed, for a partially or a non-wetting behaviour, there are discrepancies between the measured bubble lengths and those predicted by Garstecki et al.'s model given for a completely wetting liquid/liquid or gas/liquid system. This can be explained by the non-uniform displacement of the contact line at the tube wall.

International audience; This work concerns the manufacturing of a composite tube using RTM process. During the preforming stage, a woven braid is laid down and stacked on a mandrel so that reinforcement plies form conical shapes with a defined angle. An innovative experimental preforming procedure has been developed to respect the specific angle. The resin injection step has been studied both experimentally and numerically. In this work a focus is applied on the optimization of the mould geometry and on the way the resin is injected within the preform to prevent the appearance of defects such as displacement of plies and porosity. Different optimization steps are described in this work and a mould geometry is proposed for this specific application and the quality of the part obtained is discussed and analysed.

International audience; La modélisation des procédés de mise en oeuvre des matériaux composites par infusion, nécessite la prise en compte du couplage hydro-mécanique entre l'écoulement de la résine et la déformation de la préforme fibreuse. Dans ce travail nous avons intégré un modèle de formation de vides à un modèle numérique pour le traitement du couplage hydro-mécanique en milieu fibreux déformable. Ce modèle de couplage hydro-mécanique est basé sur des équations de conservation moyennées obtenues par une prise de moyenne, sur un VER (Volume Elémentaire Représentatif) déformable, des équations de conservation locales relevant de la mécanique des milieux continus (masse, quantité de mouvement). Afin de mieux contrôler ces procédés d'infusion, où les étapes d'infiltration de la résine et de la compression du renfort se déroulent simultanément, Il est important de prédire le temps d'infusion, l'évolution de l'épaisseur de la pièce et le taux de défauts. Le modèle de formation de défauts intégré ici est basé sur un modèle mathématique permettant de prédire l'évolution de la répartition et du taux volumique des défauts (micro-vides et macro-vides) dans la pièce en fonction des paramètres procédé. Nous présenterons quelques résultats de simulations d'infusion de résine par le procédé VAP (Vacuum Assisted Process). Ce procédé, qui dispose d'une membrane microporeuse perméable au gaz et constituant une barrière contre la résine (Fig. 1), permet de réduire considérablement les inclusions d'air et de gaz. Une attention particulière sera portée à l'étude et l'analyse de l'influence de la déformabilité du renfort fibreux sur les caractéristiques (porosité, taux de vide,..) de la pièce obtenue. Une étude paramétrique relative au temps d'infusion, au taux volumique de fibres et au taux de vide dans la pièce en fonction des paramètres procédé (contrainte totale, pression à l'évent) sera présentée.

We propose modeling and simulation of the void formation and the tow saturation in liquid composite molding processes. The present model addresses the void formations in the macropore between fiber tows as well as in the micropore inside fiber tows. We also consider the bubble compression and tow saturation after voids are formed at the flow front. Finally, a void migration model is considered. The present models are validated by a comparison between simulation results and experimental data. The simulation results successfully represent important features of the void physics: the correlation of void formation at the flow front with capillary number, the advantage of vacuum application at air vents to reduce the void content inside tows, and the existence of partially saturated zone behind the global flow front. The representation of mold filling patterns by a degree of saturation shows the presence of a bubbly zone behind the flow front.

International audience; This work concerns the manufacturing of a composite tube using RTM process. During the preforming stage, a woven braid is laid down and stacked on a mandrel so that reinforcement plies form conical shapes with a defined angle. An innovative experimental preforming procedure has been developed to respect the specific angle. The resin injection step has been studied both experimentally and numerically. The influence of processing parameters such as the injection pressure or the imposed flow rate on the position and the size of possible defects has been evaluated. A numerical study has been conducted to model the flow of resin within the different areas of the complex preform. Planar and through-the-thickness permeability studies were conducted experimentally as a function of the fibre volume fraction and the shear angle. Within the preform and especially along a radius of the part, variation of shear, fiber volume fraction, orientation of yarns and consequently variation of the permeability tensor must be taken into account for the simulation of the resin injection. Simulation results presenting the evolution of the flow front within the preform for different injection cases are discussed and correlated to the experimental study results previously mentioned.

cited By 4; International audience; Among the possible forming processes for structural composite parts, the Liquid Composite Moulding ones are widely used. For such kind of forming process, a resin injection phase occurs after the forming of a dry fibrous reinforcement skeleton. Several parameters can affect the quality of the manufactured part. It has been experimentally proved that the deformation of the fibrous reinforcement has a significant influence on its permeability. In order to evaluate that parameter, it is necessary to have a realistic deformed solid skeleton. During the pre-forming stage, the fibrous reinforcement can be subjected to different kind of loading: yarn tension and in-plane shear to obtain the correct part shape, but also transverse compression. The aim of this paper is to analyze the influence of that last loading mode on the global state of the solid skeleton. For that purpose, two aspects are explored. First, numerical simulations are performed at the mesoscopic scale: a finite element model of the smallest pattern of the woven textile is realized in which each yarn is modelled used 3D elements. The constitutive behaviour of the yarn must exhibit the specificities of a fibrous material. Secondly, experimental characterization of the yarn material is realized. For that, a new experimental setup is used which allow to investigate the relation between longitudinal tension and transverse compression stiffness of the yarn. This allows determining the material parameters used in the yarn constitutive equation. The other material parameters are determined using a tensile test and an in-plane shear test. X-ray tomography gives geometrical validations of the model. © 2010 Springer-Verlag France.

International audience; Nowadays, the market demand for environmentally friendly materials is rapidly increasing. Biodegradable fibres and biodegradable polymers mainly extracted from renewable resources are expected to be a major contribution to the production of new industrial high performance biodegradable composites, partially solving the problem of waste management. At the end of its lifetime, a structural biodegradable composite can be crushed and recycled through a controlled industrial composting process. Bodros et al. [1] showed that biodegradable PLLA (L-polylactide acid)/flax fibres mat composites exhibiting specific tensile properties equivalent to glass fibre polyester composites can be manufactured by an un-optimised film stacking process. In our study, the process has been investigated more extensively. Indeed, the compaction of flax mats requires a higher load than for glass mats of similar areal weight. The transverse permeability of flax mats has also been shown to be lower than for glass mats. In both cases, this is due to a higher degree of entanglement of the flax fibres within the mat. However, the range of permeability and compressibility values of the flax mats are well within the values that allow a good through-thethickness impregnation. Flax fibres cannot sustain long exposures at the impregnation temperature of the mats by PLLA resin. Through-the-thickness impregnation of flax mats processes such as film stacking are more suitable than in-plane impregnation processes such as Resin Transfer Molding because the flow of resin is limited on short distances and allows short times of impregnation.

International audience; The compaction of composite preforms and the flow of resin through the fibrous network take place simultaneously during the Resin Film Infusion process. Therefore there is a coupled loading of the porous reinforcements. A new experimental device to impose combinations of hydraulic and mechanical loadings (Hydro-Mechanical loadings) to fibrous preforms is used to evaluate the transverse permeability in a continuous manner (under Hydro-Mechanical conditions) for a flax mat, a flax non-crimped fabric, a carbon plain weave and a glass satin weave. For a 0.5 mm/min compression speed the continuous technique gives values similar to the ''classical" technique for the four composite reinforcements of very different nature. This suggests that it is possible to use the continuous technique to evaluate the transverse permeability behaviour of fibrous reinforcements (permeability vs. fibre volume) with a time reduction of about 8-10. Increasing the compression speed gives slowly decreasing continuous transverse permeability values.

An integrated optimisation methodology is proposed to optimise the manufacturing cost as well as the structural performance and the weight of composite laminated plates manufactured by the resin transfer moulding (RTM) process. In the present approach, the fibre type, the number of fabrics, the layer stacking sequence and the fibre volume fraction are optimised to minimise the structural weight and the material cost of composite structure under the stiffness constraint and the mould filling time constraint which is a part of process cycle time. With the results obtained, it is investigated how the weight and the material cost are traded-off. The optimisation methodology suggests a guide to cost-effective material selection in the preliminary conceptual design stage.

The mechanical properties of flax fibres are analysed as a function of their biochemical and morphological characteristics. The fibres, from the Agatha variety, have been selected from either the top, the middle or the bottom of the stems. The results of each analysis are discussed according to the position of the fibre in the stem and compared among themselves. Considering a flax fibre as a natural composite, this study underlines the complexity of its structure and shows that many parameters intervene in its deformation behaviour.

International audience; The identification of the transverse properties of fabrics is becoming an important topic, as the transverse flow is significant in advanced liquid composite molding processes such as resin film infusion, vacuum assisted resin transfer molding process and compression resin transfer molding process. However, it is not easy to characterize the transverse permeability and the compressibility of preform, since the fluid flow and the mechanical response of fabrics simultaneously occur in the transverse direction. Due to the strong hydro-mechanical coupling, hence, it has been a common approach to identify the transverse properties either under the simplified assumption (uniform resin pressure in the transverse direction) or under the ideal case where the closed form solution is known. In the previous works, we developed a numerical code to simulate the resin film infusion process and an experimental device to for the measurement of transverse compressibility and permeability considering different compression conditions; either imposed force or imposed speed of compression. In this work, we characterize the material behaviors in the transverse direction by incorporating the material model into the full numerical simulation of an actual filling process. To identify the model coefficients, inverse method is applied with experimental measurements.

The manufacturing of large composite parts in the field of aeronautics is increasingly important. LCM processes (Liquid Composite Molding) are currently used. Infusion processes such as the Resin Film Infusion (RFI) are more and more used for the manufacturing of large parts. During this process, the resin flows through the fibrous medium under the stress created by a flexible membrane in the transverse direction of the reinforcement’s plane. The compaction of the preforms and the flow of resin through the fibrous network take place simultaneously. There is, therefore, a coupled loading of the porous reinforcements. In order to better control this process, it is necessary to optimize resin pressure and fabric compression by using the appropriate simulating tools. It is also necessary to clarify which laws are suitable to model the process. To this objective, a new experimental device was set up to impose hydromechanical loadings to fibrous preforms. Results analyzing the hydromechanical couplings in saturated medium with flow rate conditions and a compression control with r stress conditions are presented and discussed in this work. A model simulating infusion processes [1] has also been used to analyse the compressibility behaviour of the fibrous reinforcement by using an inverse method.

International audience; The demand for composite parts is constantly increasing particularly in the aeronautic industry. The infusion process has been developed to be a cost-effective technique for the fabrication of large and complex composite structures. This process has been identified as an alternative to the resin transfer moulding (RTM) as well as the conventional autoclave prepreg technique. Unlike in the RTM process, a strong hydro-mechanical coupling between resin flow and reinforcement deformation takes place in infusion processes. In this work, a numerical model to simulate the hydro-mechanical coupling in infusion processes is proposed. Based on this model, a numerical code was developed. A new experimental device for hydro-mechanical coupling was developed and a validation of the hydro-mechanical model was carried out by comparing our experimental and numerical results. In every case, a good agreement was observed. The numerical code was applied to simulate the infusion process by calculating the maximum height infused by the resin, the final height of the part and the infusion time.

The tensile mechanical properties of flax fibres from the Hermes variety are estimated according to their diameter and their location in the stems. The large scattering of these properties is ascribed to the variation of the fibre size along its longitudinal axis, as revealed by SEM observations. The higher values of the mechanical properties for the fibres issued from the middle of the stems are associated with the chemical composition of their cell walls. The mechanical properties of unidirectional flax fibre/epoxy matrix composites are studied as a function of their fibre content. The properties of the composites are lower than those expected from single fibre characteristics.

International audience

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International audience; The microstructure of a unidirectional glass-fiber composite material is described seeking especially for the influence of the stitching perpendicular to the reinforcement. Serial cuts are performed through the composite and the microstructure is quantified using global parameters and linear morphological analysis. A key result is that the stitching induces variations in fibers spacing within the yarns and in the matrix volume between the yarns. This can affect noticeably the flow of the resin during the manufacturing process and also the mechanical properties of the composite.

International audience; A methodology for studying the implications of taking into account manufacturing at early design stages is presented. It is applied to a rectangular laminate made by RTM and compression (RTCM). The plate is designed for injection time, maximum mold pressure, stiffness and buckling. Semi-analytical, numerically inexpensive models of the processes and structure enable a thorough investigation of the couplings between process and structure by comparing four design formulations: in decoupled problems, either the process or the structure is optimized; then, the process is optimized with targetted low or high structural performance. A globalized Nelder-Mead optimization algorithm is used. The rigour of the method and the relative simplicity of the application case provide a clear description of how maximum mold pressures, injection times and final structures properties are traded-off.

The existence of void type defects in composite laminates manufactured using the liquid composite molding process alters the mechanical characteristics of the final product. The object of this paper is to present a procedure to simulate mold filling and to incorporate void formation. The model is composed of a unique combination of robust and accurate numerical algorithms for solving the transport equation. The saturation ratio is a macroscopic entity yet it is clearly the consequence of microscopic phenomena and especially of air entrapment within tows, hence the presence of micropores. In the model, the source term is dependent on the capillary number and is related to the micro–macro scale effects with the dual-porosity. The unsaturated flow and transport model was applied to a problem and was found to produce accurate, mass conserving solutions when compared to experimental results in void content.

The void defects present in composite parts are due to air entrapped during the injection process. We propose to use electrical conductivity measurements of the liquid to detect these defects. The saturation rate of the resin is measured as a function of time. Thanks to several sensors, placed along the mould, we are able to plot the resin front profile evolution versus the position. This method is a step forward in our knowledge of the parameter range for which no void is observed at the end of the injection.

In order to simulate the resin flow occurring in a reinforcement during manufacture of composite materials by resin transfer moulding (RTM); the numerical codes need data such as the permeability, K, of the reinforcement. In the case of thick parts (e.g. a few centimetres thick), the spatial components of the permeability can be deduced from experimental kinetics if we are able to visualise the resin path in the reinforcement opaque bulk. Here we describe the original technique we used to achieve this aim and we demonstrate the results of X-ray spectrography for the determination of the kinetics of spatial flows through a porous medium. We then propose a mathematical approach in order to treat our experimental results and calculate the values of K. Finally, examples of simulations are compared to the corresponding experimental observations. These simulations are obtained from two numerical codes based on the finite-differences technique with curvilinear meshes and finite elements with control volumes, respectively.

La modelisation de l'injection de resine sur renfort telle qu'elle intervient dans les procedes SRIM ou RTM pour l'obtention de materiaux composites a matrice polymere, passe par la connaissance d'un parametre determinant qui est la permeabilite du renfort. Jusqu'a present la fabrication de pieces en materiaux composites etait restreinte a des produits minces pour lesquels la permeabilite des renforts utilises pouvait etre atteinte par un suivi cinetique de l'ecoulement superficiel. Notre travail est concerne par la modelisation de la fabrication de pieces epaisses en materiaux composites. Dans ce cas il est necessaire de pouvoir determiner la permeabilite du renfort dans la dimension parallele a son epaisseur. Cela necessite donc de pouvoir suivre l'ecoulement du fluide (resine) dans le volume du renfort (tissu ou mat de fibres de verre). Pour ce faire l'opacite de ce milieu entraine quelques difficultes que nous avons surmontees en faisant appel a la radioscopie X pour suivre l'avancee du front de matiere dans l'epaisseur du renfort. Nous decrivons le dispositif experimental que nous avons mis en œuvre. Compte tenu de l'originalite de la technique utilisee, nous proposons un modele analytique adapte a l'exploitation d'un suivi de front tridimensionnel.

The present work is a contribution to the thermoplastic composites manufacturing by a non-reactive Liquid Composite Molding process for the automotive industry. The thesis was carried out by the « ANR TAPAS » project (Thermoplastic Process for Automotive Composite Structure) and was focused on the elaboration of continious-fiber reinforced composites plates injected with a high-fluidity polyamide 6,6 (PA 6,6) by the Resin Transfer Molding process. The first goal was focused on increasing injection rates through the study of the in-plane permeability of unidirectional (UD) glass fiber fabrics with high mechanical modulus (HM). Experiments and modelling results showed that the permeability of these UD has been enhanced by modifying specific structural parameters of their architecture. The analytical model developped and used is based on a flow distribution according two differents scales of porosity : in and inter-yarns. The second part of the work was focused on the understanding of phenomenas that take place at the interface created between glass fiber and the matrix during the impregnation step. The wettability and adhesion of molten PA 6,6 dropped on a glass substrate is studied at different processing temperature. The last part introduce the thermoplastic composite plates elaborated by RTM-TP process. The optimum operating conditions as well as preforms saturation and mechanical properties are also studied and discussed., ALes travaux présentés sont une contribution à l’élaboration de composites à matrices thermoplastiques (TP) par un procédé de type Liquid Composite Molding non réactif pour l’industrie automobile. La thèse a été effectuée dans le cadre du projet ANR TAPAS (ThermoplAstic Process for Automotive composite Structure) et s’est focalisée sur la mise en œuvre de plaques composites en renfort continu injectées avec des matrices polyamides 6,6 (PA 6,6) de hautes fluidités par Resin Transfer Molding. Le premier objectif est porté sur l’optimisation des cadences d’injection à travers l’étude de la perméabilité de préformes unidirectionnelles (UD) en fibres de verre et à hauts modules mécaniques. L’architecture de ces UD a ainsi été modifiée de manière à faciliter les écoulements. La perméabilité des différents tissus a pu être évaluée par un couplage entre des mesures expérimentales et une modélisation analytique basée sur un raisonnement à deux échelles de pores : l’écoulement intra et inter-torons. Le deuxième objectif sur lequel les travaux de thèse se sont concentrés s’est reposé sur la maitrise de l’état d’imprégnation par le bais d’une étude complète sur les phénomènes qui se déroulent à l’interface entre la fibre et la matrice à haute température. Plusieurs viscosités et formulations du PA 6,6 ainsi qu’un traitement appliqué sur le verre ont pu être caractérisés et discutés en termes de mouillabilité et d’adhésion. Enfin, la dernière partie du manuscrit présente les résultats obtenus sur les plaques mises en œuvre par RTM-TP en injection in-plane. Les conditions optimales de fonctionnement ainsi que les aspects de saturation, de santé matière et des propriétés mécaniques sont ensuite présentés et discutés.

The impregnation of fabrics, which are double-scale fibrous media that are commonly used to reinforce composite materials, remains to this day a relatively poorly controlled process. The increasing use of natural, bio-based fibres which present specific features, such as their sensitivity to humidity, accentuates the need for a better understanding of the involved phenomena. This thesis explores the importance of the double pore scale of the fabric, often ignored by the models despite its influence on most of the processes involved. The pore morphology was characterized by quantitative image analysis, while the microstructure of the fibrous preforms could also be extracted from numerical simulations of their mechanical behavior. An intensive focus was then made on the influence of capillarity within the tows. A detailed study of wetting dynamics allowed the identification of a transition between two modes of dissipation, depending on the contact-line velocity, which may also be observed at a macroscopic scale in infiltration processes. The modeling of a double-scale porous medium's permeability, associated with the derivation of the capillary pressure in a dynamic regime, finally lead to the formulation of a model, which describes the impregnation kinetics of a unidirectional medium for a specific flow regime.; L'imprégnation de tissus, préformes fibreuses à double échelle couramment utilisées pour renforcer des composites, reste aujourd'hui un processus mal maîtrisé. Le recours croissant à des fibres naturelles d'origine végétales, qui présentent des spécificités comme leur sensibilité à l'humidité, accentue la nécessité d'une meilleure compréhension des phénomènes mis en jeu. Cette thèse a permis de mettre en avant l'importance de la double échelle de pores au sein des tissus, souvent ignorée par les modèles alors qu'elle influence la plupart des phénomènes rencontrés. La morphologie des pores a été caractérisée par analyse d'image quantitative, et la microstructure des préformes fibreuses a pu être extraite de simulations numériques de leur comportement mécanique. Une attention particulière a ensuite été portée sur l'influence de la capillarité au sein des mèches. L'étude détaillée de la dynamique du mouillage a permis d'identifier une transition dans les modes de dissipation, liée à la vitesse de la ligne triple, et que l'on retrouve à une échelle macroscopique lors de l'infiltration. La modélisation de la perméabilité d'un milieu à double échelle, associée à une détermination de la pression capillaire en régime dynamique, a finalement mené à l'établissement d'un modèle décrivant l'imprégnation d'un milieu unidirectionnel pour un régime spécifique d'écoulement.

The present work investigates the potential of flax shives for the production of nanocelluloses. Two methods were investigated in order to produce cellulose nanocrystals (CNC) and cellulose nanofibers (CNF). The CNC production was conducted in two steps: a bleaching step and an exposure to an HCl vapour. Rietveld analysis of the diffractograms and 13C NMR proved that the shape of the crystallites wasn’t affected by the hydrolysis despite a slight co-crystallisation along the hydrophilic faces. FTIR spectroscopy demonstrated ample dependence of the ratio of deuterium-labelled sites with temperature. This ratio depends on the substrate topology. The « native » continuous microfibril topology implies pores that can trap water. In contrast, a discrete rod-like topology cannot trap water: the hydrophilic faces that were “stabilized” by co-crystallisation are unable to trap water. Drying hysteresis is usually observed after an isotopic re-exchange experiment: the labelled polymer chains co-crystallize and some of them become inaccessible to re-exchange. This hysteresis wasn’t observed after hydrolysis. The production of CNF was performed with an ultrafine grinder after swelling. Four swelling agents were selected after an initial screening involving more than 40 different liquids. Optical microscopy and SEM demonstrated the intrinsic difficulty of producing CNF from such a lignin-rich substrate without any pre-treatment. The combination of ultrafine grinding and swelling was however capable of reducing the sample crystallinity to a large extent. FTIR demonstrated that a lignin-rich phase could be produced using this mechanical process.; Ce travail a porté sur la production de nanocristaux de cellulose (NCC) et de nanofibres de cellulose (NFC) à partir d’anas de lin.La production de NCC a été réalisée par hydrolyse acide avec de l’HCl gazeux après blanchiment. L’analyse des résultats de DRX et RMN montrent que la forme des cristallites reste inchangée après l’hydrolyse malgré une faible co-cristallisation le long des faces hydrophiles. La spectroscopie IR en température après un échange isotopique montre que le ratio de matériau marqué évolue avec la température de manière différente selon qu’il s’agit d’anas blanchis ou de NCC. Avant hydrolyse, des pores dans lesquels de l’eau est piégée sont mis en évidence. Cette nature de pore est absente des NCC. Lors d’un séchage, une partie des chaînes peut co-cristalliser et piéger une partie des groupements hydroxyles deutéres ; ce piégeage n’est plus mesurable une fois le matériau hydrolysé. Ces résultats montrent une meilleure stabilité des NCC lors de cycles de séchage/humidification.Afin de produire des NFC, une défibrillation mécanique a été réalisée sans délignification préalable et après un gonflement des anas dans des liquides gonflants. La caractérisation microscopique a démontré que la production de suspensions de NFC sans prétraitement supplémentaire des anas n’était pas viable. La DRX prouve néanmoins que les agents gonflants combinés à la défibrillation peuvent diminuer de manière importante la cristallinité du matériau. La spectroscopie IR a démontré que le matériau était séparé en deux phases à l’issue du traitement, et l’une des phases est significativement plus riche en lignine.

The development of ceramic matrix composites (CMCs) to replace certain metal components ininternal hot parts of aircraft engines is an active research field for the aeronautical industry. Theseadvanced components may be manufactured with a fluid processing called ReactiveMelt Infiltration(RMI). The densification step is the capillary rise of a molten metal such as silicon within a wovenpreform. The molten metal can react with the previously introduced ceramic powder and lead to arefractory matrix. The competition between capillary rise and the reaction between molten siliconand introduced carbon powder has to be managed. The ambition is to prevent choking off effectsand closed pores created by preferential paths. Simulations of two-phase flows at macroscopic scaleare undertaken with a homemade code developed in SAFRAN whereas simulations of two-phaseflows atmicroscopic scale were undertaken with CFD code Thétis (developed at I2M, Bordeaux). Anexperimental methodology for analysis of reactive or not reactive capillary impregnation in granularmedia is described., L’industrie aéronautique a exprimé un besoin en matériaux pour des zones fortement chargées thermiquement et mécaniquement. L’objectif est d’optimiser grâce à ces matériaux, notamment en termes de poids et de rendement, le coeur des turboréacteurs. Un procédé par voie liquide appelé «Reactive Melt infiltration» est industriellement envisagé pour fabriquer ces matériaux. La densification est tributaire de la compétition entre la montée capillaire et la réaction chimique entre le silicium liquide et la poudre préalablement introduite. Cette concurrence peut conduire à des phénomènes de «choking off» qui doivent être évités. Dans ce travail, l’approche numérique est à la fois macroscopique et microscopique. Des validations numériques, des applications dans le cadre de géométries modèles et des analyses physiques sont présentées pour les deux échelles. Les simulations d’imbibition réactive à l’échelle de la pièce sont effectués avec un outil développé au sein de SAFRAN alors que les simulations de montées capillaires dans des géométries modèles à l’échelle du pore sont réalisées avec le code de calcul Thétis (développé à l’I2M, Bordeaux). Une méthodologie expérimentale pour le suivi et l’analyse de l’imprégnation capillaire réactive d’un milieu granulaire constitué de matériaux modèles est également présentée.

The present work is a contribution to the thermoplastic composites manufacturing by a non-reactive Liquid Composite Molding process for the automotive industry.The thesis was carried out by the « ANR TAPAS » project (Thermoplastic Process for Automotive Composite Structure) and was focused on the elaboration of continious-fiber reinforced composites plates injected with a high-fluidity polyamide 6,6 (PA 6,6) by the Resin Transfer Molding process.The first goal was focused on increasing injection rates through the study of the in-plane permeability of unidirectional (UD) glass fiber fabrics with high mechanical modulus (HM). Experiments and modelling results showed that the permeability of these UD has been enhanced by modifying specific structural parameters of their architecture. The analytical model developped and used is based on a flow distribution according two differents scales of porosity : in and inter-yarns.The second part of the work was focused on the understanding of phenomenas that take place at the interface created between glass fiber and the matrix during the impregnation step. The wettability and adhesion of molten PA 6,6 dropped on a glass substrate is studied at different processing temperature. The last part introduce the thermoplastic composite plates elaborated by RTM-TP process. The optimum operating conditions as well as preforms saturation and mechanical properties are also studied and discussed.; Les travaux présentés sont une contribution à l’élaboration de composites à matrices thermoplastiques (TP) par un procédé de type Liquid Composite Molding non réactif pour l’industrie automobile.La thèse a été effectuée dans le cadre du projet ANR TAPAS (ThermoplAstic Process for Automotive composite Structure) et s’est focalisée sur la mise en œuvre de plaques composites en renfort continu injectées avec des matrices polyamides 6,6 (PA 6,6) de hautes fluidités par Resin Transfer Molding.Le premier objectif est porté sur l’optimisation des cadences d’injection à travers l’étude de la perméabilité de préformes unidirectionnelles (UD) en fibres de verre et à hauts modules mécaniques. L’architecture de ces UD a ainsi été modifiée de manière à faciliter les écoulements. La perméabilité des différents tissus a pu être évaluée par un couplage entre des mesures expérimentales et une modélisation analytique basée sur un raisonnement à deux échelles de pores : l’écoulement intra et inter-torons. Le deuxième objectif sur lequel les travaux de thèse se sont concentrés s’est reposé sur la maitrise de l’état d’imprégnation par le bais d’une étude complète sur les phénomènes qui se déroulent à l’interface entre la fibre et la matrice à haute température. Plusieurs viscosités et formulations du PA 6,6 ainsi qu’un traitement appliqué sur le verre ont pu être caractérisés et discutés en termes de mouillabilité et d’adhésion.Enfin, la dernière partie du manuscrit présente les résultats obtenus sur les plaques mises en œuvre par RTM-TP en injection in-plane. Les conditions optimales de fonctionnement ainsi que les aspects de saturation, de santé matière et des propriétés mécaniques sont ensuite présentés et discutés.

This aim of this work is to characterize the damage suffered by a carbon tow in textile processing methods, and more particularly during preforms weaving for composites materials. A mechanical characterization protocol on dry tow tensile test and a non-destructive method of image analysis, have been developed to quantify this damage.; Ce travail de thèse consiste à caractériser l’endommagement subi par une mèche de carbone au cours des procédés de transformation textile, et plus particulièrement au cours du tissage des préformes pour les matériaux composites. Un protocole de caractérisation mécanique sur mèche sèche, ainsi qu’une méthode non-destructive d’analyse d’images, ont été mis au point pour quantifier cet endommagement.

Transportation industries, especially aeronautics and automotive industries, are facing more than ever energy-saving issues, which imply weight reduction of structures. Within this context, composite materials appear to be appropriate candidates, due to their outstanding “strength to weight” ratio. Liquid Composite Molding (LCM) and particularly Resin Transfer Molding (RTM) are becoming increasingly important for a wide range of industrial applications involving complex structural parts. The quality of LCM products strongly depends on the impregnation of the fiber preform during the mold-filling stage. During this step, a partiallysaturated zone emerges in the flow, and induces consequently the formation of porosities, which drastically affect mechanical performances. This study presents an original approach in which heat transfers are used to quantify the saturation profile. In a first step, the effective thermal conductivity of a model composite material have been measured by several methods. A homogenization methodology based on asymptotic expansion has been performed at dual-scale in order to predict the thermal properties of the composite as a function of saturation. Several heat flux sensors and thermocouples were integrated in an experimental bench, which allows the injection of a model fluid into a textile preform. Finally, an alternative numerical approach is proposed bymodeling a multi-phase flow, proving the feasibility of identifying the relative permeabilities of each phase through thermal analysis.; Les industries du transport, en particulier les industries automobile et aéronautique, font face plus que jamais à une problématique d’économie d’énergie, qui passe nécessairement par un allègement des structures.Dans ce contexte, les matériaux composites semblent être des candidats idéaux, en raison de l’exceptionnel compromis masse/performance qu’ils présentent. Les procédés LCM (Liquid Composite Molding) et plus particulièrement RTM (Resin Transfer Molding) sont très utilisés pour produire des pièces structurelles complexes de hautes performances. La qualité des pièces ainsi produites dépend fortement de la phase d’imprégnation des renforts fibreux, durant laquelle l’écoulement de la résine induit la création d’une zone non-saturée, provoquant par conséquent la formation de porosités qui affectent les propriétés mécaniques. Les travaux présentés dans cette thèse s’attachent à détecter et à quantifier la saturation du renfort par le biais d’une analyse des transferts de chaleur. Dans un premier temps, le tenseur de conductivité thermique d’un matériau modèle a été caractérisé à l’aide d’un large panel de dispositifs expérimentaux. Une méthode d’homogénéisation a été mise en place afin de prédire les propriétés thermiques du composite en fonction de la nature des vides rencontrés. Par la suite, un banc expérimental doté d’une métrologie thermique adaptée est conçu, permettant l’imprégnation d’un renfort par un fluide modèle. L’identification de la saturation est rendue possible par un modèle simplifié d’écoulement. Enfin, une approche par modélisation diphasique est proposée, démontrant la faisabilité de l’identification des perméabilités relatives de chacune des phases par la thermique.

The aim of this work is to contribute in improving fibrous preforms impregnation for Liquid Composite Molding (LCM) processes. Theoretical and experimental investigations were focused on void that may be appearing during resin injection. Voids or bubbles are mainly formed due to the flow competition inside and outside the yarns. However, the experimental characterization of void formation and transport through the flow inside a fibrous media remains delicate. Since the direct visualization of the liquid flow and the entrapped bubbles in a practical material is uneasy, we use model networks to study the formation of bubbles and their transport. For our experimental studies, a multi-scales approach was adopted considering microfluidic and millifluidic analysis where wetting forces are significant. The obtained results show the influence of those forces on the bubble formation and transport mechanism. A simple model taking into account the interconnectivities between micropore and macropore was suggested. Several geometrical configurations and different flow regimes could be considered by the proposed model. Finally, using this simplified approach it can be possible to compare the forecast results and those obtained in the range of fibrous media impregnation and composites elaboration.; L'objectif de ce travail est de contribuer à l'amélioration des mécanismes d'imprégnation d'un renfort fibreux par une résine polymère dans les procédés de mise en œuvre de matériaux composites de type LCM (Liquid Composite Molding). Les études théoriques et expérimentales réalisées se sont focalisées sur les anomalies d'imprégnation pouvant apparaître lors des écoulements. Les défauts couramment observés sont des vides pouvant s'assimiler à des bulles et provenant, en partie, d'une compétition entre les régimes gouvernant les écoulements intra-mèche et inter-mèches. L'analyse de la formation et du transport des bulles au sein d'une structure fibreuse demeure délicate à réaliser du fait de l'architecture complexe de la préforme. Afin de s'exonérer des difficultés rencontrées lors de la visualisation au sein du renfort et pour répondre à cette problématique de vide créé, nous avons fait le choix d'étudier les mécanismes d'imprégnation ainsi que la formation et le transport de bulles dans des réseaux modèles. Une analyse multi-échelles a été adoptée pour nos expérimentations faisant appel à une approche micro et millifluidique où les forces de mouillabilité sont prépondérantes. Les résultats obtenus montrent, dans un premier temps, l'influence de ces forces dans les mécanismes de génération et de transport de bulles et permet de justifier certaines observations proposées dans ce sujet. Un modèle simple basé sur des configurations d'inter-connectivités micropore/macropore a été proposé. Ce modèle permet d'envisager différentes analyses paramétriques selon des configurations géométriques et des régimes d'écoulement variés. Sur cette base, il est possible de prendre en compte différents facteurs et de les comparer à certaines contributions de la littérature dans le domaine de l'imprégnation des milieux fibreux et de la mise en œuvre des composites.