The determination of the mechanical properties of fabrics in biaxial tension and in-plane shearing is made from 3D finite element analyses of the unit woven cell. Compared to experimental tests these virtual tests have several advantages. They can easily be carried out for sets of varied parameters, they provide local information inside the woven material and above all they can be performed on woven materials that have not yet been manufactured. The 3D computations are not classical analyses because the yarns are made up of several thousands of fibres and their mechanical behaviour is very special. Several specific aspects of the analysis are detailed, especially the use of a hypoelastic law based on an objective derivative using the rotation of the fibre which allows a strict evolution of the directions of orthotropy according to the fibre direction. Examples of analyses are presented in biaxial tension and in-plane shear for woven reinforcements and in the case of the biaxial tension of a knitted fabric. The results obtained are in good agreement with experimental results.

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The modelling of dry knitted reinforcements for structural composite parts at the mesoscopic scale is essential to establish simulation tools related to shaping processes. Deformation modes of such structures are linked to the textile's manufacturing process, resulting in an anisotropic heterogeneous structure. This observation leads us to build an accurate 3D parametric geometric model of a jersey knit. Based on this geometric model, a finite element model is generated, allowing the analysis of the biaxial tensile mode of the elementary cell. In order to update the constitutive behavior, two formulations are implemented in the code Abaqus/Explicit and take into account a yarn's compaction law and the evolution of the constitutive axes as large deformations occur. Finally, a comparison between the results of the two formulations and an experimental test is proposed. RÉSUMÉ. La modélisation des renforts tricotés secs pour les pièces composites structurales à l'échelle mésoscopique est essentielle pour établir des outils de simulation des procédés de mise en forme. Les modes de déformation de telles structures sont liés au procédé de fabrication du textile, qui est une structure hétérogène anisotrope. Cette observation nous conduit à construire un modèle géométrique 3D paramétré suffisamment précis pour décrire un tricot à mailles cueillies de type jersey. Basé sur ce modèle géométrique, un modèle éléments finis, permettant de simuler le mode de tension biaxiale de la cellule élémentaire, est généré. Afin d'actualiser le tenseur de comportement, deux formulations sont implémentées dans le code Abaqus/Explicit et tiennent compte de l'écrasement des mèches et de l'évolution des axes constitutifs en grandes transformations. Enfin, une comparaison des résultats provenant des deux formulations avec un essai expérimental est proposée.