Modélisation à l'échelle mésoscopique de la géométrie de renforts de composites tissés

Les simulations numériques à l'échelle de la pièce sont un puissant outil pour prédire la faisabilité de ces pièces. Pour alimenter ces simulations, il est nécessaire de disposer d'un modèle géométrique 3D le plus précis possible de la cellule élémentaire du renfort. Le but de cette étude est donc de développer un préprocesseur cohérent automatisé de modélisation de géométries complexes telles que celles des renforts de type interlock

Virtual mechanical testing of a complex 3D woven fabric: a unified simulation methodology for deformation mechanics of textile structures during tension, shear and draping

The most common method of modelling the behaviour of fibrous materials such as yarns and woven fabrics, is to treat them as continuous solids. The fibrous behaviour is then taken into account by appropriate constitutive laws. These constitutive laws are however very difficult to develop due to the complex behaviour (non-linearity, large displacements, anisotropy, crushing, …). Here, we show a more viable simulation methodology which allows for the virtual testing of fibrous materials. In this method, yarns are modelled as a bundle of (virtual) fibres which can realign themselves. Hence, the fibrous behaviour is taken into account in a very natural manner. The methodology is applied to study the mechanical behaviour of a complex 3D woven fabric under tensile and shear loadings. This allows for the virtual determination of tensile and shearing properties of the fabric without the need to produce or test the actual fabric. Especially in the case of 3D woven fabrics, where production and testing can be costly and time-consuming, virtual testing can result in large cost-savings. Furthermore, the proposed method is very versatile and we show that it can also be used for weaving, stitching and draping simulations when high detail is required

Consistent 3D geometrical model of fabric elementary cell. Application to a meshing preprocessor for 3D finite element analysis

International audienceMany different methods can be used to obtain a composite part. Among them, several require the forming of a dry fabric before the resin is injected. The mechanical properties of the obtained part depend to a large extent on the mechanical behavior of the dry fabric. Experimental methods are efficient to identify this behavior, but they need to be complemented with numerical approaches. Among the numerical approaches, 3D finite element simulation is very interesting but requires an accurate 3D mesh of the fabric elementary cell. In this paper, we are proposing a new consistent 3D geometrical model of 2D fabrics. Experimental observations using different optical processes have been performed in order to determine real yarn geometry in different cases of yarn structure and weaving. The analysis of these results helps us define the accurate generic 3D model of a yarn shape when it is weaved. Using this model of a yarn, a consistent 3D geometrical model of 2D fabrics is presented. One particularity of this model is that it ensures a realistic contact surface between yarns without interpenetration for all types of weaving. The section shape varies along the trajectory, so that the influence of contact between yarns on their cross section shape can be taken into account. This model can be easily identified using three to seven parameters measured on a real fabric. A meshing preprocessor based on this geometrical model is then developed. It substantially reduces the time needed to obtain an accurate hexahedral mesh of the elementary cell of a fabric. This is an important point for the 3D finite element simulation of fabrics, which is a powerful method to investigate their mechanical behavior. Examples of shear and biaxial extension are presented to show the efficiency of the whole simulation chain

Modélisation mésoscopique pour le comportement bi-axial et la mise en forme des renforts de composites tissés

ORLEANS-BU Sciences (452342104) / SudocSudocFranceF

A BEHAVIOUR MODEL OF TEXTILE STRUCTURES: DEVELOPMENT, IDENTIFICATION AND IMPLEMENTATION.

Aeronautical and automobile industries are more and more interested in integrating fabric-reinforced composite structures in their designs, because of their high performance/mass ratio. Several processes can be used to manufacture composite parts, such as the Resin Transfer Molding manufacturing process (RTM). During the shape forming step, fibrous reinforcements undergo different mechanical loads such as, for instance, out of plane compression, in plane torsion, bending, shear, tension, etc. These loadings induce strains and sometimes damage to the fabric. Therefore, the mechanical properties of the final parts are drastically impacted by the shaping step. Hence, in order to improve the quality of these composite parts, the mechanical behaviour of the fibrous reinforcements during the forming step must be anticipated and understood. Fabrics are made up of yarns containing hundreds to thousands of fibers. They might be studied from three different scales: macroscopic scale (the fabric), mesoscopic scale (the yarn) and microscopic one (the fiber). The microscopic scale allows to associate to each fiber a homogeneous isotropic behaviour, however, at this scale, the geometric position and the contact of thousands of fibers must be identified. This modeling, therefore, remains complicated and computationally expensive. On the other hand, the macroscopic scale would not allow predicting the defaults induced in the scales below. In fact, the entanglement and the interlacement of yarns could not be taken into account at this level. Therefore, the mesoscopic scale can be considered as a good compromise between reality and complexity. The aim of the present study is to formulate a mesoscopic constitutive law from the microscopic structure of a fiber yarn. Consequently, friction between fibers, their rearrangement and their geometric position in the yarn will be taken into account in the mechanical behaviour. A Representative Elementary Volume (REV) of a hundred fibers is submitted to different loadings and the mechanical response is analyzed. The resulting data will allow understanding the deformation mechanisms at the microscopic scale. A constitutive law can consequently be proposed for the mesoscopic scale. The study was initiated by elementary test cases in order to define an efficient simulation strategy, in terms of finite elements type, finite elements solver (Abaqus/implicit or Abaqus/explicit), contact behaviour and boundary conditions. Concerning the finite elements type, fibers are modeled by 3D beam elements for two main reasons: providing a reasonable simulation time (few hours for a few hundred fibers are targeted) and accounting for the fiber aspect ratio (from 150 to 400). Therefore, more simulations and test cases were analyzed in order to check whether the beam elements are adequate for the main aims of this study. Furthermore, the compaction of a parallel fiber network was simulated, results confirmed that a correct implementation and parameterization of the Abaqus/explicit finite elements solver leads to a reasonable accuracy/calculation time ratio. For this type of problems, and among the tasks performed to validate the implementation, test cases were studied to ensure quasistatic simulations and reduce the response instability. The contact behavior of beam elements has been established based on the Hertz contact theory and the comparison with 3D elements. Finally, the simulation strategy will be validated by means of geometric observations on a real compacted fibrous network

inter-ply friction effect on the forming result of multi-layered composite

International audienceDuring forming, defects can occur and have to be taken into account because they can significantly affect the mechanical performance of the part. This experimental study shows the type and number of defects is a function of the punch geometry, the process parameters, the orientation of the fabric with respect to the punch and the inter-ply friction. Inter-ply friction has a huge effect on the quality of the preform when inter-ply sliding occurs. This inter-ply Friction leads to several overhanging yarn shocks that generate high tangential forces, which inhibit the relative sliding of plies

Etude de déformabilité de tresses en cours de préformage pour la fabrication de composite par le procédé RTM

Cette thèse traite la fabrication de pièces composites par le procédé Resin Transert Molding (RTM), appliquée à des tubes de protections thermiques assemblées dans des propulseurs de systèmes d armes. Ces travaux ont pour objectif de démontrer la faisabilité d utilisation de ce procédé pour la fabrication de ces pièces complexes. C est le préformage, première étape du procédé de fabrication par RTM, qui est étudié dans le cadre de cette thèse. Cette étape est cruciale du point de vue de la faisabilité de l étape d injection qui la suit dans le procédé RTM mais aussi pour s assurer de la qualité de la pièce composite finale obtenue. L objectif des travaux de thèse est triple. Il faut tout d abord développer le protocole de fabrication répétable adapté pour garantir l obtention de préformes conformes. Ce protocole devra être viable du point de vue industriel. Pour cela, une démarche expérimentale a été mise en place. Un pilote de laboratoire puis un pilote industriel ont permis de comprendre et maitriser les phénomènes survenant en cours de préformage en faisant varier les paramètres procédé pour la fabrication de nombreux prototypes. Un modèle macroscopique prédictif de la forme globale des plis obtenus à partir des paramètres procédés a été développé à l aide des observations expérimentales. Un modèle mésoscopique, à l échelle de la maille élémentaire, a été écrit également. Il permet de prédire, à partir des données constitutives du matériau et d une géométrie de pièce, la déformation de compaction et de cisaillement, modes de sollicitations prépondérants en cours de préformage, subie par le renfort en cours de la première étape du procédé de fabrication. Ces modèles mésoscopique et macroscopique couplés permettent le développement d un outil global qui, de manière théorique et prédictive, assure la faisabilité d une pièce de géométrie connue avec un matériau connu et fournit les paramètres procédé optimum pour assurer sa fabrication future. Les phénomènes de déformation en cisaillement et compaction apparaissant sur la tresse en cours de préformage sont donc identifiés et connus. Le procédé de fabrication est optimisé et l outil prédictif permet d envisager et tester en amont un changement de matériau, de géométrie de pièce à fabriquer ou de cahier descharges industriel.This study deals with the manufacture of composite parts by the process "Resin Transert Molding" (RTM), applied to thermal protection tubes. This work aims to demonstrate the feasibility of using this method for the production of these complex parts. This study deals with the first step of the RTM process, the fiber performing. This is critical from the standpoint of the feasibility of injecting step that follows in the RTM process but also to ensure the quality of the final composite part obtained. The aim of the thesis is threefold. Must first develop the manufacturing protocol adapted to ensure repeatable obtaining preforms compliant. This protocol should be viable to the industrial point of view. For this purpose, an experimental approach was implemented. A pilot laboratory and an industrial pilot helped to understand and master the phenomena occurring during forming varying the process parameters for the production of many prototypes. A macroscopic model predictive of overall shape folds obtained from the process parameters has been developed with the experimental observations. A mesoscopic model, the scale of the unit cell was also writing. It can predict, based on the specifications of the material and part geometry, the deformation of compaction and shear stresses. These models mesoscopic and macroscopic allow the development of a global tool that, theoretically predictive and ensures the feasibility of a piece of known geometry with a known material parameters and provides the "process" to ensure its optimum manufacturing future. The phenomena of compaction and shear strain appearing on the braid during preforming are identified and known. The manufacturing process is optimized and the predictive tool allows to explore and test upstream change of material, part geometry in manufacturing or industrial specifications.ORLEANS-SCD-Bib. electronique (452349901) / SudocSudocFranceF

Characterisation of the mesoscopic and macroscopic friction behaviours of glass plain weave reinforcement

International audienceFriction at different levels of the multi-scale structure of textile reinforcements is one of the most significant phenomena in the forming of dry fabric composites. This paper investigates the effect of the test conditions on fabric/fabric and yarn/yarn friction. Friction tests were performed on a glass plain weave and its constitutive yarns, varying the pressure and velocity. The results showed that the friction behaviours at the two scales were highly sensitive to these two parameters. An increase in pressure led to a decrease in the friction coefficients until steady values were reached, while an increase in velocity led to an increase in the friction coefficients. At each scale, the frictional behaviour of the material was significantly influenced by the structural reorganisation of the lower scale

Characterisation of the mesoscopic and macroscopic friction behaviours of glass plain weave reinforcement

International audienceFriction at different levels of the multi-scale structure of textile reinforcements is one of the most significant phenomena in the forming of dry fabric composites. This paper investigates the effect of the test conditions on fabric/fabric and yarn/yarn friction. Friction tests were performed on a glass plain weave and its constitutive yarns, varying the pressure and velocity. The results showed that the friction behaviours at the two scales were highly sensitive to these two parameters. An increase in pressure led to a decrease in the friction coefficients until steady values were reached, while an increase in velocity led to an increase in the friction coefficients. At each scale, the frictional behaviour of the material was significantly influenced by the structural reorganisation of the lower scale