1 INTRODUCTION The RTM process for composite material forming consists of three stages. A dry textile reinforcement is formed (performing stage), then the resin is injected within this preform and cured to obtain the final composite part. During the first stage, the reinforcement undergoes in’plane deformations as biaxial tension, in’plane shear, compaction, bending. These deformations can be large especially in’plane shear which is essential in the case of double curved shapes. These macroscopic deformations are directly related to mesoscopic deformations of the reinforcement (at the scale of the yarns). For instance large in’plane shear of the reinforcement leads to a significant lateral crushing of the yarns. As a consequence, the macroscopic behaviour is related to its mesoscopic behaviour. Moreover the local deformations can modify the mechanical properties of the reinforcement and its permeability. The objective of this paper is to present a method for the simulation of deformations of a woven composite reinforcement representative unit cell (i.e. at mesoscopic scale). These simulations enable to determine the macroscopic mechanical behaviour at large strain of dry reinforcements. This mechanical behaviour is necessary in finite element simulations of the performing stage. Besides, knowing the deformed geometry of the woven cell enables to determine the permeability of the fibrous reinforcement via Stokes (or Stokes Brinkman) flow simulations within this deformed cell. At last the geometry of the deformed reinforcement heavily influences the mechanical behaviour of the final composite part. In particular, meso’scale damage prediction simulations require knowing this geometry. The yarn constitutive model used in the following analyses is based on a hypo’elastic approach. The behaviour of the yarn is very specific since it is made of thousands of fibers which can slide with respect to each other. Therefore the objective derivative used in the yarn hypo’elastic constitutive model has to be governed by the fiber direction. The ABSTRACT: The knowledge of the mechanical behavior of woven fabrics is necessary in many applications in particular for the simulation of textile composite forming. This mechanical behavior is very specific because of the possible motions between the fibers and the yarns. The objective of this presentation is to introduce 3D mesoscopic finite element analyses of woven reinforcement shear aimed at determining their macroscopic mechanical behavior and local results such as the deformed shape of yarns. These types of results can be used for various applications such as simulations of composite forming or fluid flow simulations inside composite preforms. Since yarns are made of thousands of fibers it is not possible to model each of them and an equivalent continuum mechanics model is developed within the hypo’elastic theory. This model has to render the fibrous nature of the yarn, which requires using specific objective rates and material properties. From a macroscopic point of view, the shear behavior computed from simulations is compared to experiments, showing a good agreement. Key words: Textile composites, Meso’macro analysis, Hypoelasticity, Fibrous material, In’plane shear. Computational determination of the mechanical behavior of textile composite reinforcement. Validation with x’ray tomography. P. Badel 1 , E. Maire 2 , E. Vidal’Sallé 1 , P. Boisse 1             ! "#$#% "! &#’($#%) ""#’ ($#%) &*++#,($#%  -./           ! 000#$#%1"1 "! #"($#%