23 research outputs found
Développement d'expérimentations pour la caractérisation des milieux fibreux : Des matériaux manufacturés aux tissus biologiques
QualifieÌs sous le terme geÌneÌrique de « milieux fibreux anisotropes », les mateÌriaux auxquels je me suis interessĂ©s au cours de mes recherches sont soit d'origine syntheÌtique noyeÌs dans une matrice (composite) ou non (fibres et fils de nylon, carbone, verre, composites ...), soit d'origine biologique (veines, arteÌres et aneÌvrismes, os, diaphragme ...). L'essentiel de mon travail s'est concentreÌ sur la compreÌhension aux Ă©chelles meso et microscopiques des deÌformations de mateÌriaux et structure sous charges, ainsi que la caracteÌrisation du comportement meÌcanique macroscopique par le deÌveloppement dispositifs expeÌrimentaux originaux. Le fil conducteur de mon manuscrit de HDR est la "Mise au point dâexpeÌrimentations pour milieux fibreux : des mateÌriaux manufactureÌs aux milieux biologiques". L'objectif de mon projet de recherche est de comprendre les meÌcanismes de deÌformation et de fonctionnement des tissus biologiques fibreux (au cours de la croissance ou lors de perçage par exemple) dans le but de les reÌparer notamment en deÌveloppant des substituts de remplacement aÌ base de fibres
Anisotropic Mechanical Behavior of Nonwoven Geotextiles Stressed by Uniaxial Tension
The complex behavior of nonwoven structures can be studied by tensile tests. To understand the influence of mesoscopic phenomena on macroscopic behavior, the whole thermomechanical behavior was considered. During uniaxial tensile tests three parameters were measured: the load, the strain, and the temperature on the surface of the specimen. Mesoscopic phenomena corresponding to a rise of temperature are said to be dissipative. Two nonwoven structures were considered: a needlepunched and a thermo-bonded fabric. The needlepunched structure was quite anisotropic in terms of the strain field as well as the temperature. The dissipative phenomena involved were the anelastic extension of filaments and their failure. The thermo-bonded structure was more isotropic but was also a locked structure. The mechanical behavior was similar in the two directions and a rise of temperature was noticed during the whole test as a consequence of the failure of the bonded points, the anelastic extension, and the failure of filaments
Comportement dynamique sous différentes températures des polypropylÚnes recyclés
National audienceIn order to satisfy the different customer requirements such as use temperature and speed, recyclers introduce additives and/or fillers to the regenerated polypropylene. However, this addition can change significantly the mechanical properties as well as the deformation mechanisms. Moreover, the properties of the regenerated material depend necessarily on the waste deposit origins and on the chemical constituents. The objective of this paper is to understand the influence of adjuvants, fillers and/or contaminants on the dynamic behavior of the regenerated polypropylene under different temperatures. We considered a first sample of regenerated PP which contains three references with three different fluidity indices (grades). To determine the variability of the mechanical properties over a one-year period, different samples of regenerated PP grade 10 from the same recycling process were collected every three months and studied. The chemical constituents of the recycled polypropylene were determined by physico-chemical analysis in a previous study [1]. Dynamic compression tests on Hopkinson bars are then performed at different temperatures, below and above the glass transition temperature. This experimentation allows Comptes Rendus des JNC 21-Bordeaux INP-1-3 juillet 2019 2 identifying the sensitivity of the dynamic behavior to the temperature. The results obtained are finally compared with those of a non-regenerated (Virgin) PP in order to explain the combined effect of additives and recycling.Pour rĂ©pondre Ă des cahiers des charges trĂšs variables en termes de conditions d'usage telles que la tempĂ©rature et la vitesse, les recycleurs de polypropylĂšne PP sont amenĂ©s Ă ajouter des adjuvants et/ou des charges. Toutefois, l'ajout de certains Ă©lĂ©ments peut modifier considĂ©rablement les propriĂ©tĂ©s mĂ©caniques ainsi que les mĂ©canismes de dĂ©formation. De plus, les propriĂ©tĂ©s du matĂ©riau recyclĂ© dĂ©pendent forcĂ©ment de l'origine des dĂ©pĂŽts des dĂ©chets. L'objectif de cette Ă©tude est de comprendre l'influence des adjuvants et des charges et/ou contaminants sur le comportement dynamique sous diffĂ©rentes tempĂ©ratures des polypropylĂšnes recyclĂ©s. Nous avons considĂ©rĂ© un premier lot de PP rĂ©gĂ©nĂ©rĂ©s comportant trois rĂ©fĂ©rences qui correspondent Ă trois indices de fluiditĂ© (grades) diffĂ©rents. Afin de dĂ©terminer la variabilitĂ© des propriĂ©tĂ©s mĂ©caniques sur une durĂ©e d'une annĂ©e, diffĂ©rents lots de PP rĂ©gĂ©nĂ©rĂ©s de grade 10 issus du mĂȘme procĂ©dĂ© de recyclage ont Ă©tĂ© prĂ©levĂ©s tous les trois mois et Ă©tudiĂ©s. Les constituants chimiques des polypropylĂšnes recyclĂ©s ont Ă©tĂ© dĂ©terminĂ©s par analyses physico-chimiques lors d'une prĂ©cĂ©dente Ă©tude [1]. Des essais de compression dynamique sur des barres d'Hopkinson sont ensuite rĂ©alisĂ©s Ă diffĂ©rentes tempĂ©ratures, en dessous et au-dessus de la tempĂ©rature de transition vitreuse, permettant ainsi d'identifier la sensibilitĂ© du comportement Ă la tempĂ©rature lors de sollicitations sĂ©vĂšres de type choc. Les rĂ©sultats obtenus sont finalement comparĂ©s Ă ceux d'un PP non rĂ©gĂ©nĂ©rĂ© pour expliquer l'effet combinĂ© des additifs et du recyclage
Transverse compression behavior of textile rovings: finite element simulation and experimental study
International audienceResults from finite element simulation of the transverse compression of Polyamide 6.6 rovings made of 40 filaments are compared in this paper against experimental data. The finite element simulation, using a finite strain beam model to represent each filament of the roving, focuses on the modeling of contact-friction interactions between filaments. Experimental tests, consisting in crushing rovings between two rigid planes, varying the twist and the tensile force, are reproduced by simulation. Experimental and simulation results are compared with a good agreement. The simulation studies the influence of the roving twist, the applied tensile force, and the friction coefficient on the transverse compression behavior. The occurrence of plateaus in the transverse compression curve is highlighted and discussed
Experimental evaluation of transverse friction between fibers
International audienceThe mechanical behavior of fibrous assemblies, particularly the transverse behavior of fiber yarns and multifilament strands depends, inter alia, on the fiber-to-fiber contact and sliding. All studies on inter fiber friction presented in the literature focus on cases where the relative inter fiber motion occurs either in longitudinal-to-longitudinal or longitudinal-to-transverse direction. The transverse-to-transverse inter fiber friction plays an important role as far as the mechanical transverse behavior of fiber yarns and multifilament strands are concerned. In order to evaluate the case named here âtransverse friction, the present study proposes an original method and an associated model analyzing the transversal component of friction between two oblique crossing fibers. A relatively simple and original statistical approach has also been developed to evaluate the confidence interval of friction coefficient. The first results show a relative stability of the transverse friction. This coefficient is also significantly inferior to the longitudinal one
Multiscale description and prediction of the thermomechanical behavior of multilayered plasticized PVC under a wide range of strain rate
International audiencePlasticization of polymers largely contributed to their worldwide utilization, especially for automotive crashworthiness, by making them a more ductile material. For such applications, a clear understanding of the mechanical properties evolution over a large range of strain rate and temperature is needed. In this study, we investigate a plasticized poly(vinyl chloride) manufactured through a multilayered process for the automotive industry. Analysis of the microstructure before and after mechanical testing, at different temperature and strain rate, highlighted the presence of sodium aluminosilicate within material microstructure. After thermal degradation analysis, these particles seem to be the only one to remain at high temperature. Moreover, it is important to mention that for the possible applications of this material, the temperature range is around the glass transition region leading. Thus, careful attention should be focused on the evolution of the material properties and on the way to model them. Numerical prediction of the storage modulus and yield stress using homemade models show a good agreement with the experimental data. More, these models will make reliable the use of these materials over a wide range of temperatures and strain rates that are difficult to obtain by experience, such as intermediate strain rates between quasi-static and dynamic loading
Finite element study of Poisson's ratio for soft tissues with helical fibre structure
International audienc