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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Influence du vieillissement hydrique suer le comportement mécanique de l'interface fil/matrice dans les composites chanvre/époxy / Influence of Water Ageing on the Mechanical Behaviour of the Yarn/Matrix Interface in Hemp/Epoxy Composites

Perrier, Amélie 06 December 2016 (has links)
Cette étude porte sur l’analyse de l’influence de l’eau sur des composites chanvre/époxy. Deux résines ont été utilisées, l’une 100 % pétrochimique (Epolam) et l’autre partiellement bio-sourcée (Greenpoxy). L’absorption d’eau d’éprouvettes de composites tissés a d’abord été suivie par des mesures gravimétriques. Les résultats ont mis en évidence une cinétique d’absorption de type Langmuir dépendant de plusieurs paramètres (types de résine, de fibres et de tissu, fraction volumique de fibres et épaisseur). Des essais de DMA et DSC sur les résines ont montré un effet plastifiant de l’eau ainsi qu’une modification irréversible de leurs propriétés après le vieillissement hydrique. Des observations microscopiques réalisées sur le composite et à l’échelle du fil ont permis de détecter que des fissures entre les fibres de chanvre et la matrice époxy apparaissent et se développent dès le début de la désorption. De surcroît, des observations en photoélasticimétrie ont montré une réorganisation des contraintes internes irréversible due à ces endommagements. Des essais de traction quasi-statiques ont ensuite été réalisés sur des composites tissés et sur les résines seules. Le vieillissement hydrique modifie les grandeurs mécaniques ainsi que l’évolution des endommagements, suivie par émission acoustique et tomographie X.Pour mieux appréhender le comportement de l’interface fil/matrice, différents tests ont été développés sur des éprouvettes monofilamentaires spécifiques dans lesquelles le fil est orienté à 45° ou 90° par rapport à l’axe de sollicitation. Tout d’abord, des tests de nanoindentation ont été effectués de manière à mesurer in situ les propriétés de chaque constituant des composites avant et après vieillissement hydrique. Un second type de test basé sur le principe du choc laser a été utilisé pour déterminer la qualité de l’adhérence entre le fil et la résine. Enfin, des essais de traction sur micromachine sous microscope optique ont été mis au point dans le but de mesurer les champs de déformations par corrélation d’images. Les résultats ont démontré que les déformations locales sont plus importantes après un vieillissement hydrique et que ce phénomène est plus accentué dans le chanvre/Greenpoxy que dans le chanvre/Epolam. Le développement d’un modèle numérique simplifié a permis d’approcher la loi de comportement locale des différents constituants du composite et d’étudier l’évolution des modules après vieillissement. / This study deals with the analysis of the influence of water on hemp/epoxy composites. Two resins have been used, one being 100 % petrochemical (Epolam) and the other one partially bio-based (Greenpoxy). The water absorption of the woven composites have been measured with gravimetric analyses. The results showed a Langmuir-type absorption, and depends on several parameters (type of resin, fibres and fabric, fibre ratio and thickness). DMA and DSC tests realised on resins showed the plasticizing effect of water and an irreversible modification of their properties after the water ageing. Microscopic observations of the composite at the yarn scale helped to detect that cracks between hemp fibres and epoxy matrix appear and develop right from the start of the desorption. Moreover, observations by photoelasticimetry showed an irreversible reorganisation of internal stresses due to this damage. Next, quasi-static tensile tests have been performed on woven composites and resins. The water ageing has modified the mechanical properties of the materials as well as the evolution of damage, which has been studied by acoustic emission and X-ray tomography.For a better understanding of the yarn/matrix interface behaviour, different tests have been developed with specific single yarn composites, in which the yarn is oriented at 45° or 90° in regard to the main axis of the specimen. First, nanoindentation tests have been performed, to measure the properties in situ of each component of the composites before and after water ageing. A second type of tests, based on the laser shock wave method, has been used to determine the quality of adhesion between the yarn and the resin. Finally, tensile tests on a micromachine under an optical microscope have been developed with the aim of measuring strain fields by digital image correlation. The results demonstrated that local strains are higher after a water ageing and that this phenomenon is more pronounced in the hemp/Greenpoxy than in the hemp/Epolam. The development of a finite element model led to estimate the local constitutive law of the different components of the composites and to study the evolution of the modulus after the ageing.
2

Quantitative methods to characterize the impregnation of a glass multifilament yarn by a cementitious matrix

Aljewifi, Hana, Fiorio, Bruno, Gallias, Jean-Louis 03 June 2009 (has links) (PDF)
This paper focuses on two experimental methods that give indicators linked to the impregnation level of the yarn / matrix interface, in the case of Textile Reinforced Concrete (TRC). These methods have been tested on three different glass yarns laid in a cementitious matrix, with three different impregnation levels resulting from the manufacturing process. The first method (comparative mercury intrusion porosity test) is based on the evaluation by mercury intrusion porosity of the pores volume associated to the porosity inside and near the yarn. The second method (flow test) consists in measuring the flow rate of water along the yarn, with imposed flow conditions. The physical parameters measured by these two methods are both related to the pore size and to the porosity of the yarn / matrix interface. The results of the two methods are discussed and drawn in parallel to a qualitative characterization of the yarn matrix interface made by scanning electron microscopy. As a result, the connection between the results of the two methods and the SEM characterization is studied. It is shown how these methods can participate to characterize the yarn impregnation. Limitations of the methods are also discussed.
3

Quantitative methods to characterize the impregnation of a glass multifilament yarn by a cementitious matrix

Aljewifi, Hana, Fiorio, Bruno, Gallias, Jean-Louis 03 June 2009 (has links)
This paper focuses on two experimental methods that give indicators linked to the impregnation level of the yarn / matrix interface, in the case of Textile Reinforced Concrete (TRC). These methods have been tested on three different glass yarns laid in a cementitious matrix, with three different impregnation levels resulting from the manufacturing process. The first method (comparative mercury intrusion porosity test) is based on the evaluation by mercury intrusion porosity of the pores volume associated to the porosity inside and near the yarn. The second method (flow test) consists in measuring the flow rate of water along the yarn, with imposed flow conditions. The physical parameters measured by these two methods are both related to the pore size and to the porosity of the yarn / matrix interface. The results of the two methods are discussed and drawn in parallel to a qualitative characterization of the yarn matrix interface made by scanning electron microscopy. As a result, the connection between the results of the two methods and the SEM characterization is studied. It is shown how these methods can participate to characterize the yarn impregnation. Limitations of the methods are also discussed.

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