ABSTRACT--This paper presents experimental studies on the mechanical behavior of fiber fabrics using a biaxial tensile device based on two deformable parallelograms. The crossshaped specimens are well adapted to fabrics because of their lack of shear stiffness. Tension versus deformation curves, for different strain ratios, are obtained in the case of composite woven reinforcements used in aeronautic applications. It is shown that the tensile behavior of the fabric is strongly nonlinear due to the weaving undulations and the yarn contraction, and that the phenomenon is clearly biaxial. A constitutive model is described and identified from the experimental data.The essential role played by the yarn crushing will be pointed out.KEY WORDS--Woven composite reinforcements, constitutive model of fabrics, biaxial tests, cross-shaped specimen, fabric shaping, process simulations Use of Textile ReinforcementThe use of fiber fabrics as composite reinforcements has strongly increased in some industrial fields, particularly in the automotive and aeronautical sectors)'2 Indeed, their good mechanical performances added to their low weight and their capability to deaden vibrations make them adequate materials for the transportation field. Complex shapes can be obtained by a single forming operation, which is a great advantage. Various manufacturing processes are based on this property, in particular for draping and resin transfer molding (RTM) processes, 3-6 (concerning dry fabrics) and for sh_aping thermoplastic materials (concerning prepreg fabrics). 7-9The draping operation consists of setting, mainly by hand, pieces of fabric on tools. This method is used particularly to manufacture nondevelopable shapes and involves fabrics impregnated with nonpolymerized resin (called prepreg). Several layers are set on the shape, each of which is subjected to successive deformation and stretching. This technique, being only partially automated, is long and, therefore, costly. The RTM process to manufacture thin composites uses initially dry fabrics (without resin) and includes several stages, with two essential ones. In one, the fabric is deeply drawn by a punch on a die; in another, a liquid resin is injected into the fabric to give the part its final rigidity. Until the 1980s, the use of this method, essentially to make relatively simple parts of intermediate volume, was relatively infrequent. Because of new market demands, the use of this process is greatly increasing. Nevertheless, the RTM process is not yet totally controlled; many studies were and are carded out on resin injection. These studies allow one to understand better the phenomena involved and to eliminate some problems. Studies relative to the fabric-shaping operation are less frequent; however, problems resulting from this step can be multiple and strongly prejudicial with regard to the use of the composite part:9 The emergence of folds when the angular variations between yams (the main deformation mode) are more than what the fabric can bear, after which the yams overla...

The COVID-19 pandemic has highlighted environmental and supply issues related to single-use protective masks for both the general public and some healthcare workers. Reusable fabrics are an interesting alternative to disposable nonwovens and offer a prospect of protection in other fields such as against fine particles in urban areas. In this paper, the behavior of 22 woven fabrics regarding air permeability, simulating breathability through the material, and filtration against 3 µm diameter particles is investigated. First, basic laws are verified between the performance of a single layer of fabrics and that of a stack. A relationship is established between air permeability and filtration efficiency, allowing one to be calculated when the other is known. Second, the influence of parameters defined at various scales of the structure (fibers, yarns and fabrics) is analyzed. The most sensitive structural parameters that can be considered as predictors are then identified and used in a model allowing the calculation of air permeability. In this model two levels of porosity are taken into account: a macroscopic porosity at the scale of the woven structure and a microscopic porosity at the scale of the thread. The model proposed in this study offers a convenient method to design an effective filter from data easily measurable during manufacturing.

For shape morphing application, thermal activation coupling to a bimetallic strip effect can be a substitute for classical actuators, piezoelectrical or shape memory alloys. The controlled behaviour of composite material (CBCM) is a thermaly activated composite material. The thermal activation is made thanks to carbon yarns which are connected to a power supply. If the anisotropy of the structure is well organized, the desired deformation is reached when the temperature within the composite is rising. To obtain a CBCM morphing composite structure, it is necessary to design a specific structure. The aim of this work is to show that it is possible to adapt the CBCM principle in order to transform any kind of classical composite structure to an active structure. The first part of this work consists in presenting the experimental results for two examples of composite beams. The second part is about the active structure FEM modeling and the development of adapted tools for this particular design.