Investigation of the Membrane Behavior of UD-NCF in Macroscopic Forming Simulations

Unidirectional non-crimp fabrics (UD-NCF) provide an exceptionally high lightweight potentialcompared to other dry fabrics. However, their defect-free formability is limited compared towoven or biaxial fabrics due to their susceptibility to draping effects like wrinkling, gapping andfiber waviness. To predict these local effects and the global forming behavior efficiently, macroscopicmodelling approaches require the consideration of the mesoscopic material structure. A very detailedmacroscopic approach was proposed by Schirmaier et al. [1] and its prediction accuracy validatedwith qualitative and quantitative comparisons to component forming results. However, the approachcouples several deformation modes and therefore requires a very high number of inversely determinedmaterial parameters. In the present work a new macroscopic forming model for the membrane behaviorof UD-NCF is introduced based on superimposed shear, transverse tensile and perpendicular to thecarbon fiber tows oriented compressive strains. The model is parametrized with experimental resultsof different off-axis-tension-tests (OATs) (30°, 45° and 60°) and compared to the model proposed bySchirmaier et al. [1]. The results of the new membrane model agree well with the experimental andsimulative results in large areas, while utilizing a significantly reduced number of material parameters.However, some limitations are identified due to the reduced complexity of the model

Investigation of the compaction behavior of uni- and bidirectional non-crimp fabrics

The through-thickness compaction behavior of engineering textiles significantly influences the resulting component properties during liquid composite molding processes (LCM). It determines the final fiber volume content and thus the necessary press force, the permeability as well as the final mechanical properties. In the present work, the behavior of a uni- and bidirectional carbon fiber non-crimp fabric (UD- & Biax-NCF) with the same fiber type and areal density of fibers in the respective main reinforcement directions is tested in a punch-to-plate setup. Thereby, the influence of the relative fiber orientation at the interfaces of a layup as well as the number of plies is investigated. A combined influence of roving nesting and superposition of stitching patterns is observed. This results in a common influence of decreasing resistance to compaction for higher numbers of layers, while the relative orientation of the interfaces in a layup is only significant for the Biax-NCF

Simulation of 3D interlock composite preforming

The ply to ply interlock fabric preform enables to manufacture, by R.T.M. process, thick composite parts that are resistant to delamination and cracking. Numerical simulation of interlock reinforcement forming allows to determine conditions for feasibility of the process and above all to know the position of fibres in the final composite part. For this forming simulation, specific hexahedral finite elements made of seg- ment yarns are proposed. Position of each yarn segment within the element is taken into account. This avoids determination of a homogenized equivalent continuous law that would be very difficult consider- ing the complexity of the weaving. Transverse properties of fabric are taken into account within a hyp- oelastic constitutive law. A set of 3D interlock fabric forming simulations shows the efficiency of the proposed approach

Tension locking in finite-element analyses of textile composite reinforcement deformation

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A unit-cell mesoscale modelling of biaxial non-crimp-fabric based on a hyperelastic approach

Understanding the mechanical properties of carbon fiber reinforcements is necessary for the simulation of forming processes. A unit-cell mesoscopic model provides a tool to implement virtual material characterizations which can be served as an input for macroscopic modelling, avoiding complex experimental tests and significantly reducing calculation time. Meanwhile, the occurrence of some local defects during the forming process, such as the gapping, would be easier to be detected through a mesoscopic approach. In this research, a novel mesoscale model for biaxial non-crimp fabric is developed based on the geometry measured from the results of X-ray tomography. A hyperelastic constitutive law is applied to the fiber yarns which are considered as a continuous medium. One type of unit-cell model is chosen and validated through a comparison with experimental tests and its in-plane shear behavior is studied

Simulation à l'échelle mésoscopique de la mise en forme de renforts de composites tissés

De nos jours, l intégration de pièces composites dans les produits intéresse de plus en plus les industriels, particulièrement dans le domaine des transports. En effet, ces matériaux présentent de nombreux avantages, notamment celui de permettre une diminution de la masse des pièces lorsqu ils sont correctement exploités. Pour concevoir ces pièces, plusieurs procédés peuvent être utilisés, parmi lesquels le RTM (Resin Transfer Molding) qui consiste en la mise en forme d un renfort sec (préformage) avant une étape d injection de résine. Cette étude concerne la première étape du procédé RTM, celle de préformage. L objectif est de mettre en œuvre une stratégie efficace conduisant à la simulation par éléments finis de la mise en forme des renforts à l échelle mésoscopique. A cette échelle, le renfort fibreux est modélisé par un enchevêtrement de mèches supposées homogènes. Plusieurs étapes sont alors nécessaires et donc étudiées ici pour atteindre cet objectif. La première consiste à créer un modèle géométrique 3D le plus réaliste possible des cellules élémentaires des renforts considérés. Elle est réalisée grâce à la mise en œuvre d une stratégie itérative basée sur deux propriétés. D une part, la cohérence, qui permet d assurer une bonne description du contact entre les mèches, c'est-à-dire, que le modèle ne contient ni vides ni interpénétrations au niveau de la zone de contact. D autre part, la variation de la forme des sections de la mèche le long de sa trajectoire qui permet de coller au mieux à la géométrie évolutive des mèches dans le renfort. Grâce à ce modèle et à une définition libre par l utilisateur de l architecture tissée, un modèle représentatif de tout type de renfort (2D, interlock) peut être obtenu. La seconde étape consiste à créer un maillage hexaédrique 3D cohérant de ces cellules élémentaires. Basé sur la géométrie obtenue à la première étape. L outil de maillage créé permet de mailler automatiquement tout type de mèche, quelle que soit sa trajectoire et la forme de ses sections. La troisième étape à franchir consiste, à partir du comportement mécanique du matériau constitutif des fibres et de la structure de la mèche, à mettre en place une loi de comportement du matériau homogène équivalent à un matériau fibreux. Basé sur les récents développements expérimentaux et numériques en matière de loi de comportement de structures fibreuses, un nouveau modèle de comportement est présenté et implémenté. Enfin, une étude des différents paramètres intervenant dans les calculs en dynamique explicite est réalisée. Ces deux derniers points permettent à la fois de faire converger rapidement les calculs et de se rapprocher de la réalité de la déformation des renforts. L ensemble de la chaîne de modélisation/simulation des renforts fibreux à l échelle mésoscopique ainsi créée est validée par comparaison d essais numériques et expérimentaux de renforts sous sollicitations simples.Nowadays, manufacturers, especially in transport, are increasingly interested in integrating composite parts into their products. These materials have, indeed, many benefits, among which allowing parts mass reduction when properly operated. In order to manufacture these parts, several methods can be used, including the RTM (Resin Transfer Molding) process which consists in forming a dry reinforcement (preform) before a resin being injected. This study deals with the first stage of the RTM process, which is the preforming step. It aims to implement an efficient strategy leading to the finite element simulation of fibrous reinforcements at mesoscopic scale. At this scale, the fibrous reinforcement is modeled by an interlacement of yarns assumed to be homogeneous and continuous. Several steps are then necessary and therefore considered here to achieve this goal. The first consists in creating a 3D geometrical model of unit cells as realistic as possible. It is achieved through the implementation of an iterative strategy based on two main properties. On the one hand, consistency, which ensures a good description of the contact between the yarns, that is to say, the model does not contain spurious spaces or interpenetrations at the contact area. On the other hand, the variation of the yarn section shape along its trajectory that enables to stick as much as possible to the evolutive shape of the yarn inside the reinforcement. Using this tool and a woven architecture freely implementable by the user, a model representative of any type of reinforcement (2D, interlock) can be obtained. The second step consists in creating a 3D consistent hexahedral mesh of these unit cells. Based on the geometrical model obtained in the first step, the meshing tool enables to mesh any type of yarn, whatever its trajectory or section shape. The third step consists in establishing a constitutive equation of the homogeneous material equivalent to a fibrous material from the mechanical behavior of the constituent material of fibers and the structure of the yarn. Based on recent experimental and numerical developments in the mechanical behavior of fibrous structures, a new constitutive law is presented and implemented. Finally, a study of the different parameters involved in the dynamic/explicit scheme is performed. These last two points allow both to a quick convergence of the calculations and approach the reality of the deformation of reinforcements. The entire chain modeling/simulation of fibrous reinforcements at mesoscopic scale created is validated by numerical and experimental comparison tests of reinforcements under simple loadings.VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

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

Full-field strain measurements in textile deformability studies

Full-field strain measurements are applied in studies of textile deformability during composite processing: (1) in testing of shear and tensile deformations of textiles (picture frame, bias and biaxial extension test) as an "optical extensometer", allowing accurate assessment of the sample deformation, which may differ significantly from the deformation applied by the testing device; (2) to study mechanisms of the textile deformation on the scale of the textile unit cell and of the individual yarns (meso- and micro-scale full-field strain measurements); (3) to measure the 3D-deformed shape and the distribution of local deformations (e.g., shear angles) of a textile reinforcement after draping, providing input data for the validation of material drape models and for the prediction of the consolidated part performance via structural finite element analysis. This paper discusses these three applications of the full-field strain measurements, providing examples of studies of deformability of woven (glass, glass/PP) and non-crimp (carbon) textile reinforcements. The authors conclude that optical full-field strain techniques are the preferable (sometimes the only) way of assuring correct deformation measurements during tensile or shear tests of textile