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In this work, we examine the relationships between the microstructure and the mechanical properties of glass fiber–reinforced polyamide 6,6 composite materials ( V f = 54%). These materials made by thermocompression incorporate different grades of high fluidity polyamide-based polymers and two types of quasi-UD glass fiber reinforcement. One is a classic commercial fabric, while the other specially designed and manufactured incorporates weaker tex glass yarns (the spacer) to increase the planar permeability of the preform. The effects of the viscosity of the polymers and their composition on the wettability of the reinforcements were analyzed by scanning electron microscopy observations of the microstructure. The respective influences of the polymers and the spacer on the mechanical performance were determined by uniaxial tensile and compression tests in the directions parallel and transverse to the warp yarns. Not only does the spacer enhance permeability but it also improves physical and mechanical properties: tensile longitudinal Young’s modulus increased from 38.2 GPa to 42.9 GPa (13% growth), tensile strength increased from 618.9 MPa to 697 MPa (3% growth), and decrease in ultimate strain from 1.8% to 1.7% (5% reduction). The correlation of these results with the damage observed post mortem confirms those acquired from analyses of the microstructure of composites and the rheological behaviors of polymers.

Hypothesis Computer fluid dynamics simulations of dynamic wetting are often performed using a slip model on the substrate. In previous studies, the generalized Navier boundary condition (GNBC) has shown promising results and could help clear the gap between molecular and continuum scales, but lacks quantitative comparisons to experiments. We seek to investigate the dependence between the contact-line velocity and the slip length in a GNBC, by confronting numerical simulations to experimental data. Experiments The physical properties of a molten polymer (polyethylene glycol) were assessed thoroughly. Its dynamic contact angle on a cellulosic substrate was measured carefully using the Wilhelmy method. The experiment was reproduced in a finite elements model using a GNBC. It was repeated for capillary numbers between 10−6 and 10−1, and slip lengths ranging from 1 μm to 1 mm. Findings A realistic value of the slip length was selected by matching the dynamic contact angles issued from numerical simulations and their experimental counterparts. The slip length behavior as a function of contact line velocity displayed a clear transition. The model also reproduced a dynamic wetting transition between frictional and viscous dissipations, which seems to be linked to an increasing difference between microscopic and macroscopic contact angles.

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; All-cellulose nanocomposites reinforced by cellulose nanocrystals (CNC) were produced using a solvent consisting of 1-butyl-3-methylimidazolium chloride and dimethyl sulfoxide. Microcrystalline cellulose (MCC) was pre-dissolved at high temperature in the solvent. Freeze-dried CNC were then added to the slurry at room temperature, thereby avoiding complete CNC dissolution. Solid all-cellulose composite films were obtained by film casting, solvent exchange and drying. The MCC to CNC ratio was kept constant while the solvent content was incremented. The short-range and long-range cellulose–cellulose interactions in the solid materials were respectively assessed by Fourier-transform infrared spectroscopy and X-ray diffraction. The CNC used in this work contained both cellulose I and cellulose II. The cellulose concentration in the mixture drastically changed the overall crystallinity as well as the cellulose I to cellulose II ratio in the ACC. Cellulose II was formed by recrystallisation of the dissolved fractions. These fractions include the pre-dissolved MCC and the cellulose II portion of the CNC. Cocrystallisation with the cellulose I CNC acting as a template was also evidenced. This phenomenon was controlled by the initial solvent content. The correlation between the hygromechanical properties and the nanostructure features of the ACC was investigated by humidity-controlled dynamic mechanical analysis (RH-DMA). The introduction of the cocrystallisation and percolation concepts provided a thorough explanation for the humidity dependency of the storage modulus.

The aim of this work is to underline the influence of the wetting behavior on bubble formation and transport during the impregnation of fibrous preforms for Liquid Composite Molding processes. The void prediction within the elaboration of composite material sparks off interest because it represents a significant issue to keep the expected mechanical properties of the final product. Voids or bubbles are mainly formed due to the resin flow competition inside and outside the tows. However, the experimental characterization of void formation and transport during the flow inside fibrous media remains delicate. Since the direct visualization of the liquid flow and the entrapped bubbles in a practical material is uneasy, we used model networks to study the formation of bubbles and their transport. Thus, our experimental study deals with a simple configuration of connected pores: two capillaries converging at a node perpendicularly (T-junction). We emphasized on microfluidic and millifluidic approaches where the wetting is significant during bubble formation mechanisms. For the same flow conditions, the experimental results reveal that the bubble lengths are higher for partially wetting liquids than for completely wetting ones. In a wetting case, it was demonstrated that the lubrication hypothesis can be a good approximation to describe the bubble transport in fibrous media.

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).

A simple model is used to explain the decrease of the Young’s modulus of plant fibers as the apparent diameter is increased. The assumption made in this work is that the fiber consists of a very thin but stiff outer shell, and a thicker but less stiff inner shell which defines the load bearing area. The model is favorably compared with the experimental data reported in the literature for flax, hemp and stinging nettle fibers.

Fiber-reinforced composite materials are often composed of fibers collected in bundles that are stitched together. During the impregnation of a fibrous preform by a liquid resin, the multiscale porous medium leads to an heterogenous flow front, and therefore bubbles may be created and entrapped. Indeed, for a wetting system, capillary pressure is higher inside bundle, due to the microspace between fibers, than outside the bundles that represent the macrospace, thus, inducing an overflow between both pore scales. Motivated by the prediction of bubble formation during fiber fabric infiltration for composite materials, we attempt to determine the bubble rate in imbibition through a simple model network with two connected capillaries, called “Pore Doublet Model” (PDM). Our system is composed of two parts: a first part, continuously interconnected, in which the suppling mass to the microchannel from the macrochannel occurs, and a second part connected only by nodes. To quantify the leading flow front, a theoretical model based on the supplying principle and arranged Washburn equation is proposed. This approach has been conducted for wetting liquids, Newtonian flows, incompressible fluids and pores, no inertial and gravitational forces and no dynamic contact angle. The geometrical variability (channel radius and length) and the different configuration of connections (continuous and discrete) influence the entrapped bubble rate, leading to either microbubble in the microchannel or macrobubble in the macrochannel. The outcomes can contribute to the knowledge of void formation especially during the filling of fibrous preforms and may extend the previous works on the PDM in general.

In this work, a train of confined bubbles inside a millimetric cylindrical T-junction device is studied. Calibrated bubbles need to be known precisely for multiphase phase flow applications. Experimental results of bubble formation and transport processes will be presented and discussed. For a liquid-gas flow, we will demonstrate how the wetting behaviour plays a significant role on the formation and motion of the bubble.

In this international permeability benchmark exercise, in-plane permeability data for two reinforcement fabrics, obtained using a total of 16 different experimental procedures, were compared. Although, for each procedure, the results appear consistent, different procedures result in a scatter of up to one order of magnitude in principal permeability values for each fabric at any given fibre volume fraction. The ratio of the principal permeability values varies by factors of up to 2. While experimental uncertainties and variability of the specimens affect the scatter in results for any single series of experiments, it is suspected that the main source of scatter in results from different procedures is related to human factors. Aiming at standardisation of measurement methods and interchangeability of results, "good practice" guidelines will be formulated in order to eliminate sources of scatter. (C) 2011 Elsevier Ltd. All rights reserved.

International audience; The modelling of composite manufacturing processes where hydro-mechanical coupling takes place depends on the validity of compressibility and permeability models. In this work, the computer code initially used to simulate the effect of coupled hydro-mechanical load on composite preform (Ouahbi et al. Composites Part A, 38:1646-1654, 2007) is integrated into an inverse method to predict the compaction behaviour of the reinforcements. An experimental device developed at Le Havre is used to apply hydro-mechanical loads to the preforms. Two ramps of stress are imposed to the preform and the thickness evolution is measured as a function of time. The speed of thickness reduction is not constant and varies in the range of 0.1 to 12 mm/min. The effect of compression speed upon the saturated fabrics is investigated. For a fixed fibre volume fraction, an increase in stress is observed in increasing compression speed. The experimental results are compared to the compressibility curves determined by an inverse method. The calculated curves correspond to the compressibility curves experimentally obtained with low compression speed (∼0.25 mm/min). As a consequence, this suggests that a low compression speed should be applied when investigating the compressibility behaviour of composite preform with a view of modelling resin infusion processes.

Fibrous composites have very specific mechanical behaviours due to their compositions. They exhibit not only the strain in the fibre direction but also the shear caused by the relative movement of weft and warp during the deformation. To address these behaviours, in this paper, a constitutive model has been proposed for the simulation of fabric shaping process, which is based on a meso-macro approach. The strain energy by tension is considered in the field of large strain, and the shear behaviour is also taken into account. The bias-test experiment is employed to characterize the shear behaviour. The model is implemented in the user subroutine ‘Vuel’ of Abaqus/Explicit and it is applicable either to four nodes or to three nodes element. A set of elementary tests and a simulation of bias-test have been performed to validate this approach. Finally, a composite forming of real part is simulated with this method. In the simulation results, we can observe the winkle that takes place in the experiment test which corresponds well to the experimental.

Textile composites become more and more popular in aeronautic industries, due to their high performances. In this work, based on the model shown in the paper [9], a solid-shell element is used to simulate the woven composite forming. Comparing with other shell elements, a distinctive advantage of solid-shell elements is that the complication on handing finite rotations does not exist. Accounting the specific mechanical behaviors of woven composite material, the tensile, in-plane shear, bending and compressive energies are taken into account depending on the fiber direction, and then the total strain energy is computed to be the sum of those energies. The necessary material data for the simulation come from standard tensile, compressive and bias test experiments. Some forming simulations are performed with this method, and we can observe the wrinkles that exhibit the influence of bending stiffness. The results show the efficiency of the approach.

The topic of this paper concerns void defects. We introduce a model to describe the macroscopic resin flow considering the compression of residual air in the preform. A microscopic flow model is also developed to account for the microvoid formation due to the variation of resin velocity at the flow front. According to these mathematical models, a numerical simulation code was developed to perform a combined macro and micro flow analysis with the saturation of the medium. The results of these simulations are compared with experimental results obtained by the laboratory device. We present the real-time measurement of the void content evolutions during the injection, using an original sensor. Our technique is based on the electrical conductivity of the injected liquid. After the material and method presentation, some results obtained during injection are shown. The developed analysis technique and the numerical simulation code can be used for obtaining the optimal processing conditions and design parameters in manufacturing of composites by Liquid Composite Molding (LCM) processes.

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; 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.

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.

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.

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

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 thermoforming of continuous fiber reinforced thermoplastic (CFRTP) composite panels generally involves significant in-plane shear deformation. In the present work, the in-plane shear behavior of woven thermoplastic composites (Carbon/Polyphenylene Sulfide) over a range of processing temperatures is studied by bias-test experiments at different velocities. The experimental data of force versus displacement and force versus shear strain are presented for different extension velocities and temperatures. A thermo-visco-elastic model for numerical simulations of woven thermoplastic composite forming is proposed considering the influences of temperature and of strain rate. We applied a large displacement three-dimensional cohesive element with eight nodes which has been used for crack analysis in fracture mechanics by other authors, to investigate the inter-ply shear mechanism of woven thermoplastic composites. Applying three-dimensional cohesive elements, multi-plies forming simulations are performed to show inter-ply slip behaviors at different temperatures. The proposed models can be useful to predict from the properties of reinforcement and resin the intra/inter-ply shear behaviors of woven thermoplastic composites at high temperatures if experimental characterization of composite laminate behaviors is difficult to conduct.

International audience; It is an important topic to measure the through-thickness permeability of fiber reinforcements as the resin flow in the thickness direction is widely employed in many composites manufacturing techniques. Continuous techniques for the permeability measurement by simultaneous fabric compaction and liquid flow have been recently proposed as an alternative way to the tedious and laborious conventional permeability measurement techniques. In spite of their efficiencies, these continuous techniques have some limits if the fabric compaction speed or flow rate is relatively great. To address this issue, a new equation for the permeability estimation is proposed. Parametric studies are performed to investigate the influences of the experimental conditions on the validity of the continuous technique. A dimensionless number is proposed as a measure of the relative error of the continuous technique.