An experimental assessment of the saturated transverse permeability of Non Crimp New Concept (NC2) multiaxial fabrics.

Over the past few years some manufacturing processes involving resin impregnation in dry preforms prior to cure, and more specifically resin infusion across the fabric thickness (the so-called Resin Infusion Processes) have been developed. In these increasingly used processes, the transverse permeability of the fabric controls both manufacturing cycles and dimensions, and consequently the mechanical properties of the final composites. A big effort has been realized to obtain reliable experimental techniques for measuring the transverse permeability. Since the distinction between saturated and effective permeabilities is still being discussed, and the flow-front is hardly defined in such small dimensions (of the order of 1 mm), our measurements on some so-called Non-Crimped New Concept (NC2) are carried out for saturated flow, i.e., the fiber network is completely impregnated right from the onset of the experiment. In our case [1], these measures rely on the measurements of the pressure drop induced by the flow of a controlled fluid across the fabric, easily converted into transverse permeability through Darcy's law. One of the main results of these measurements is that the low NC2 transverse permeability depends on the face of the fabric receiving the fluid. This original behavior may, in turn, be translated into manufacturing guidelines to achieve optimal processing configuration. An attempt to relate this differential to the stitching hole surface is proposed which appears to explain some minor phenomena. On the contrary, the 3D shape of the stitching hole reconstruction from polishings could yield some appropriate explanation

Numerical and experimental analyses of resin infusion manufacturing processes of composite materials

Liquid resin infusion (LRI) processes are promising manufacturing routes to produce large, thick, or complex structural parts. They are based on the resin flow induced, across its thickness, by a pressure applied onto a preform/resin stacking. However, both thickness and fiber volume fraction of the final piece are not well controlled since they result from complex mechanisms which drive the transient mechanical equilibrium leading to the final geometrical configuration. In order to optimize both design and manufacturing parameters, but also to monitor the LRI process, an isothermal numerical model has been developed which describes the mechanical interaction between the deformations of the porous medium and the resin flow during infusion.1, 2 With this numerical model, it is possible to investigate the LRI process of classical industrial part shapes. To validate the numerical model, first in 2D, and to improve the knowledge of the LRI process, this study details a comparison between numerical simulations and an experimental study of a plate infusion test carried out by LRI process under industrial conditions. From the numerical prediction, the filling time, the resin mass and the thickness of the preform can be determined. On another hand, the resin flow and the preform response can be monitored by experimental methods during the filling stage. One key issue of this research study is to highlight the changes in major process parameters during the resin infusion stage, such as the temperature of the preform and resin, and the variations of both thickness and fiber volume fraction of the preform. Moreover, this numerical/experimental approach is the best way to improve our knowledge on the resin infusion processes, and finally, to develop simulation tools for the design of advanced composite parts

Influence of the stitching density on the transverse permeability of Non-Crimped New Concept (NC2) multiaxial reinforcements : measurements and predictions

International audienceNew manufacturing processes arise for polymer-based composites which involve resin infusion through dry pre-forms. Modelling approaches of these processes require to assess new physical characteristics of the materials. In this paper, the transverse permeability of new multiaxial stitched materials, referred to as NC2, is investigated. First, in the framework of Darcy's flows, this permeability is assessed for various biaxial NC2 using a specific device. Through this approach it is shown that the transverse permeability depends strongly on the stitching density. Then, the results from a simplified FE study carried out at the blanket scale are shown to correlate quite well the experimental measurements and evidences established in the first part

Etude mécanique des articles de contention et de leurs effets sur la jambe humaine. Mechanical investigation of compression stockings and of their effects on the human leg.

International audienceThis paper presents a synthesis of different studies willing to bring a scientific insight into leg compression, which is the process of applying external compression forces onto the human leg with stockings or socks, for enhancing the venous flow. It seems obvious that the pressure distribution on the leg affects the blood flow in the veins. However, the pressure distribution that leads to the optimal blood flow is not trivial, and it is different with regard to the application: medical treatment or recovering after an effort in sports. In order to improve the scientific knowledge about this topic, a numerical 2D model was set up for computing stress fields inside the leg, accounting for the actual material properties of both the compression stocking and of the leg biological tissues. Suitable identification methods, based either on model updating from digital image correlation (for the compression stockings), or on image warping and model updating from MRI scans (for the internal leg tissues), were developed for retrieving these material properties. ===================================================Ce papier est une synthèse de différentes études apportant un regard scientifique sur la contention qui consiste à exercer des pressions sur la jambe humaine au moyen de chaussettes ou de bas afin de faciliter le reflux veineux. Il paraît évident que la répartition des pressions sur la jambe affecte le débit sanguin dans les veines. Néanmoins, la répartition conduisant à un débit veineux optimal est non triviale, et diffère en fonction de l'application : traitement médical ou récupération chez les sportifs. Afin d'améliorer les connaissances à ce sujet, un modèle numérique 2D a été mis en place pour calculer les champs de contraintes dans la jambe en prenant en compte le comportement mécanique réel des articles de contention et des tissus de la jambe. Des méthodes d'identification appropriées, basées soit sur le recalage de modèle et la corrélation d'images numériques (pour les articles de contention), soit sur le recalage de modèle par mise en correspondance locale non linéaire d'images fournies par l'IRM (pour les tissus internes de la jambe), ont été développées pour identifier ces paramètres de comportement

Mechanical investigation of compression stockings and of their effects on the human leg. Étude mécanique des articles de contention et de leurs effets sur la jambe humaine.

Ce papier est une synthèse de différentes études apportant un regard scientifique sur la contention qui consiste à exercer des pressions sur la jambe humaine au moyen de chaussettes ou de bas afin de faciliter le reflux veineux. Il paraît évident que la répartition des pressions sur la jambe affecte le débit sanguin dans les veines. Néanmoins, la répartition conduisant à un débit veineux optimal est non triviale, et diffère en fonction de l'application : traitement médical ou récupération chez les sportifs. Afin d'améliorer les connaissances à ce sujet, un modèle numérique 2D a été mis en place pour calculer les champs de contraintes dans la jambe en prenant en compte le comportement mécanique réel des articles de contention et des tissus de la jambe. Des méthodes d'identification appropriées, basées soit sur le recalage de modèle et la corrélation d'images numériques (pour les articles de contention), soit sur le recalage de modèle par mise en correspondance locale non linéaire d'images fournies par l'IRM (pour les tissus internes de la jambe), ont été développées pour identifier ces paramètres de comportement. This paper presents a synthesis of different studies willing to bring a scientific insight into leg compression, which is the process of applying external compression forces onto the human leg with stockings or socks, for enhancing the venous flow. It seems obvious that the pressure distribution on the leg affects the blood flow in the veins. However, the pressure distribution that leads to the optimal blood flow is not trivial, and it is different with regard to the application: medical treatment or recovering after an effort in sports. In order to improve the scientific knowledge about this topic, a numerical 2D model was set up for computing stress fields inside the leg, accounting for the actual material properties of both the compression stocking and of the leg biological tissues. Suitable identification methods, based either on model updating from digital image correlation (for the compression stockings), or on image warping and model updating from MRI scans (for the internal leg tissues), were developed for retrieving these material properties

Mise en œuvre, instrumentation, validation et modélisation d'un système d'injection RTM pour la fabrication de structures composites de hautes performances

Les matériaux composites ont connu ces dernières années une forte croissance, croissance aujourd'hui renforcée par les nouvelles normes européenne visant à diminuer les émissions CO2 d'ici 2020. La réalisation de pièces complexes peut poser de nombreuses problématiques de fabrication comme la formation de zones sèches, ou la création de distorsions géométriques. Les origines de ces problématiques sont souvent liées à un manque de connaissance et de maîtrise des phases d'imprégnation des renforts et de cuisson du matériau. L'amélioration de la robustesse des procédés nécessite d'avoir une connaissance fine des phénomènes physiques qui ont lieu lors de l'élaboration. Dans cette perspective, les procédés d'élaboration de matériaux composites ont été étudiés à travers la mise en place d'un démonstrateur de laboratoire dans le cadre du projet LCM Smart. Ce pilote d'injection a permis de valider des solutions d'instrumentation, à partir de capteurs innovants (OFS) développés en partenariat avec le laboratoire d'optique Hubert Curien.L'application de cette instrumentation dans le cadre du suivi du procédé RTM a démontré les capacités des OFS pour le suivi des caractéristiques physiques de la pièce (le front d'écoulement, la température, les déformations résiduelles et le degré de cuisson). La comparaison des caractéristiques mesurées avec des simulations numériques effectuées en collaboration avec ESI, a montré une bonne corrélation.Enfin, l'instrumentation a permis de mettre en évidence l intérêt d un outillage composite en HexTool pour la réduction des contraintes résiduelles liées à l'interaction outil/pièce.A significant growth in production and consumption of composite materials can be seen recently; growth reinforced by the new European standards, aimed at reducing CO2 emissions by the year 2020.The producing of complex parts can cause many difficulties for manufacturing because of their geometries and / or their constituents (using of various materials). For example, dry zones or geometric distortion formation. The origins of these difficulties are often related to a lack of knowledge and control of the reinforcement's impregnation phases and material curing.Improving the robustness of the processes demands a detailed knowledge of physical phenomena that occur during the producing. For this, we studied the composite materials production through the implementation of a laboratory demonstrator in the project LCM Smart. This pilot injection was used to validate instrumentation solutions, from innovative sensors (OFS) developed in partnership with the optical laboratory Hubert Curien. The application of this instrumentation in the context of RTM process monitoring in the development of simple parts has demonstrated the capabilities of OFS to control physical characteristics of the part (the flow front, temperature, residual strain and curing degree). The comparison of the measured characteristics with numerical simulations carried out in collaboration with ESI showed a good correlation.Finally, instrumentation has demonstrated the capacity of composite tool made by HexTool to minimize the residual stresses due to the tool/part interaction.ST ETIENNE-ENS des Mines (422182304) / SudocSudocFranceF

Identification des propriétés mécaniques des tissus biologiques de la jambe à partir d'images IRM.

Les tissus biologiques mous constituant le corps humain font individuellement l'objet d'études visant à déterminer leurs propriétés mécaniques. L'étude propose l'identification des propriétés mécaniques des tissus de la jambe par le couplage d'images IRM et de différents niveaux de contention comme chargement mécanique. Celui-ci peut être assimilé à une compression sur une section complète de jambe. La méthode d'identification fait intervenir d'une part le traitement des images IRM (corrélation, extraction des volumes, etc...) et d'autre part la modélisation par la méthode aux élémentsfinis combinée à un algorithme d'optimisation. On présente ici une méthodologie d'identification basée sur un protocole de mesure non-invasif in vivo

Mixed experimental and numerical approach for characterizing the biomechanical response of the human leg under elastic compression.

8 p.International audienceElastic compression is the process of applying an elastic garment around the leg, supposedly for enhancing the venous flow. However, the response of internal tissues to the external pressure is still partially unknown. In order to improve the scientific knowledge about this topic, a slice of a human leg wearing an elastic garment is modeled by the finite-element method. The elastic properties of the tissues inside the leg are identified thanks to a dedicated approach based on image processing. After calibrating the model with magnetic resonance imaging scans of a volunteer, the pressure transmitted through the internal tissues of the leg is computed. Discrepancies of more than 35% are found from one location to another, showing that the same compression garment cannot be applied for treating deficiencies of the deep venous system or deficiencies of the large superficial veins. Moreover, it is shown that the internal morphology of the human leg plays an important role. Accordingly, the approach presented in this paper may provide useful information for adapting compression garments to the specificity of each patient

Coupling multiphysics problems in transient regimes: application to liquid resin infusion process

Liquid resin infusion (LRI) process is widely considered in the aeronautics, due to its benefits (low void content and production of large parts), for high performance composite material forming. The main objective of the present work is to simulate nu- merically the LRI process, in a high performance computing framework, which consists in coupling fluid-solid mechanics. Hence, two fluid flow regimes are coupled with an ef- ficient ASGS stabilized monolithic finite element formulations: the resin flow in both a highly permeable distribution medium (Stokes) and low permeability fibrous orthotropic preforms (Darcy). Moreover, weak coupling algorithms are used along for coupling solid / fluid mechanics, solid / level-set problems and fluid / level-set problems; where the level-set method is used to capture the moving flow front and the Stokes-Darcy interface. To transfer the different physical variables between the above coupled problems, Message Passing Interface (MPI) library is chosen, to ensure the best data transfer performances

3D simulation of the matter transport by surface diffusion within a level-set context

International audienceWithin the framework of the sintering process simulation, this paper proposes a numerical strategy for the direct simulation of the matter transport by surface diffusion. A level-set method is used to describe the topological changes which arise at the free boundary of the sintering particles. The surface velocity is found to be proportional to the surface Laplacian of the curvature, that is, proportional to the fourth-order derivative of the level-set function. Consequently, both curvature and velocity must be computed carefully and with accuracy. Finally, three-dimensional simulations are shown and investigated