Experimental analysis of the contact between layers of dry fabrics

International audienceA better apprehension of the behaviour of the interface between sheets of woven reinforcement during the forming of dry fabrics is necessary for a better optimization of the LCM processes. Even if numerical studies are carried out to simulate multi-layer forming, the contact between the layers is very roughly modelled using an approximate friction coefficient. To knowledge, only few preliminary results can be found concerning the contact fabric/fabric. In order to understand and characterize the contact between layers of different fabrics, a specific friction device has been designed in our lab. This machine was designed with the aim of carrying out tests as well on fabric/ fabric, fabric/metal but also fibre/fibre friction. After a short presentation of the device, results concerning steel/steel friction will be presented in order to validate the device. Then first results obtained about fabric/fabric contact will be given, in order to point out the contacts mechanism involved

The bias-extension test for the analysis of in-plane shear properties of textile composite reinforcements and prepregs: a review

The bias-extension test is a rather simple experiment aiming to determine in-plane shear properties of textile composite reinforcements. However the mechanics during the test involves fibrous material at large shear strains and large rotations of the fibres. Several aspects are still being studied and are not yet modeled in a consensual manner. The standard analysis of the test is based on two assumptions: inextensibility of the fibers and rotations at the yarn crossovers without slippage. They lead to the development of zones with constant fibre orientations proper to the bias-extension test. Beyond the analysis of the test within these basic assumptions, the paper presents studies that have been carried out on the lack of verification of these hypothesis (slippage, tension in the yarns, effects of fibre bending). The effects of temperature, mesoscopic modeling and tension locking are also considered in the case of the bias-extension test

La mesure des déformations pour l'étude du comportement et la mise en forme des renforts de composites

Nous faisons ici le bilan de campagnes d'essais mécaniques sur des renforts secs de composites réalisées au LMSP, au cours desquelles les déformations ont été mesurées par des méthodes optiques. La nature des renforts conduit dans certains cas à utiliser la corrélation d'images et dans d'autres le suivi de marqueurs. Dans tous les cas il est nécessaire d'avoir un marquage adapté des renforts pour faire ces mesures. Il faut éviter le fractionnement des marqueurs à deux échelles : celle des fibres puis celle des mèches. La brillance des fibres gêne souvent les mesures. Ces problèmes techniques résolus, ces méthodes permettent d'obtenir des résultats très intéressants pour l'étude de ces matériaux

All -optical control of the quantum flow of a polariton condensate

Although photons in vacuum are massless particles that do not appreciably interact with each other, significant interactions appear in suitable nonlinear media, leading to hydrodynamic behaviours typical of quantum fluids(1-6). Here, we show the generation and manipulation of vortex-antivortex pairs in a coherent gas of strongly dressed photons (polaritons) flowing against an artificial potential barrier created and controlled by a light beam in a semiconductor microcavity. The optical control of the polariton flow allows us to reveal new quantum hydrodynamical phenomenologies such as the formation of vortex pairs upstream from the optical barrier, a case of ultra-short time excitation of the quantum flow, and the generation of vortices with counterflow trajectories. Additionally, we demonstrate how to permanently trap and store quantum vortices hydrodynamically generated in the wake of a defect. These observations are supported by time-dependent simulations based on the non-equilibrium Gross-Pitaevskii equation(7)

Polariton superfluids reveal quantum hydrodynamic solitons

A quantum fluid passing an obstacle behaves differently from a classical one. When the flow is slow enough, the quantum gas enters a superfluid regime and neither whirlpools nor waves form around the obstacle. For higher flow velocities, it has been predicted that the perturbation induced by the defect gives rise to the turbulent emission of quantised vortices and to the nucleation of solitons. Using an interacting Bose gas of exciton-polaritons in a semiconductor microcavity, we report the transition from superfluidity to the hydrodynamic formation of oblique dark solitons and vortex streets in the wake of a potential barrier. The direct observation of these topological excitations provides key information on the mechanisms of superflow and shows the potential of polariton condensates for quantum turbulence studies.Comment: Published version with corrected colorbar scale for Fig. 3. Raw data available as ancillary file

Half-solitons in a polariton quantum fluid behave like magnetic monopoles

Monopoles are magnetic charges, point-like sources of magnetic field. Contrary to electric charges they are absent in Maxwell's equations and have never been observed as fundamental particles. Quantum fluids such as spinor Bose-Einstein condensates have been predicted to show monopoles in the form of excitations combining phase and spin topologies. Thanks to its unique spin structure and the direct optical control of the fluid wavefunction, an ideal system to experimentally explore this phenomenon is a condensate of exciton-polaritons in a semiconductor microcavity. We use this system to create half-solitons, non-linear excitations with mixed spin-phase geometry. By tracking their trajectory, we demonstrate that half-solitons behave as monopoles, magnetic charges accelerated along an effective magnetic field present in the microcavity. The field-induced spatial separation of half-solitons of opposite charges opens the way to the generation of magnetic currents in a quantum fluid.Comment: 19 pages, includes Supplmentary Informatio

EFFECT OF INTER-PLY SLIDING ON THE APPEARANCE OF DEFECTS FOR MULTILAYERED COMPOSITE SHAPING

International audienceThe transport sector is one of the fastest growing consumer of energy and producer of greenhouse gases in the world. Consequently, transportation means with a low energy consumption, and thus global warming, are more and more demanding as being a major concern again the protection of the environment and hence respect a durable development. This aim can be achieved by reducing the mass of the transportation means and this by replacing metallic materials by composites ones on structural parts subjected to severe mechanical solicitations and this with equal mechanical performances. Indeed, composite materials are able to propose credible answers to the optimization of the thick structural parts with significant size through their good ratio strength/weight and especially their anisotropy which can be adapted to the mechanical solicitation of the structure. To manufacture the composites pieces, the RTM is the more interesting process because it offers the best compromise in terms of repeatability, production rates and low final cost [ une référence]. The first step of the process consists in draping a dry preform before injection of the liquid resin. This stage is a delicate phase and the mechanisms taking place are complex and different than the ones occurring during the stamping of metallic sheets. These mechanisms are far from being fully understood [1] which hampers the mastery of the manufacturing process and development of composite materials. In addition, the increasing use of materials with low environmental effect (biomaterials ...) and complex weaving architectures (interlock, 3D fabrics), makes it more difficult. Many methods have been proposed recently to achieve representative sheet forming simulations of dry fabric, with different approaches [2-4]. These studies need several key entries such as the dry fabric mechanical properties and the fabric/tool friction coefficient, which have been widely studied [5-8]. When dealing with the multiply forming of composite thick parts, a significant relative sliding of the layers occurs [9]. This sliding generates fabric/fabric friction that has been recently studied [10, 11] and where the effect of woven meso-structure on the behavior has been highlighted. However, this relative sliding coupled with the phenomena that occur during the friction [11] can leads to the defects apparition or their amplification. The aim of this study is then to investigate experimentally the effect of fabric/fabric friction behavior on defects apparition when dealing with multilayered shaping of composite dry fabric. For this purpose, forming tests of interlock fabric (G1151) with prismatic punch were carried out on a specific device [12]. Tests conditions allowing defects apparition, such as wrinkles, in the useful areas of the shapes are used. Tests were realized with one layer and several layers of dry fabric with the same test conditions. Defects and shear angles were quantified in the useful shape areas (fig. 1) for each test then quantitative and qualitative comparisons were made between the different configurations. These comparisons showed that the shear angles on different areas of interest are almost identical between the multilayered shapes and single-ply ones. For defects, the locations of areas on which they appear are the same (fig. 1). However, the importance of each defect and the extent of the affected areas are more significant in the case of multilayered shapes. Additional defects, such as fiber breakage, were also observed in the same areas for this configuration. These measures and observations carried out in this study highlight the effect of the fabric/fabric friction behavior and relative sliding between layers on the defects and their appearance