Si, pour les matériaux composites élaborés, de nombreuses études expérimentales ainsi que des modèles locaux de comportement ont été développés, la maîtrise du comportement des interfaces entre couches de surface ou d’assise de chaussées est actuellement un réel verrou scientifique. La méthode de dimensionnement française actuelle ne prend en compte, aux interfaces, que des conditions conventionnelles de collage ou de glissement parfait. Afin d’appréhender le comportement local de l’interphase\interface, les outils de la photomécanique apparaissent incontournables. La présente thèse propose une modélisation de l’interface rugueuse et endommageable par un modèle de zone cohésive en mode mixte. Ce manuscrit de thèse comporte trois chapitres. D’abord, le chapitre I présente un état de l’art sur les interfaces dans les matériaux et les structures et en particulier dans les couches de chaussées. Ensuite dans le chapitre II, une identification expérimentale des paramètres mécaniques et géométriques du modèle d’interface est proposée à travers des essais de traction et de cisaillement et des mesures de la texture (PMT et projections de franges). Les résultats obtenus (adhésion, rugosité,…) seront les paramètres d’entrée d’un modèle d’endommagement d’interface. Enfin, le chapitre III aborde la modélisation des interfaces entre couches de chaussées sous l’angle des modèles de zones cohésives avec la prise en compte de la rugosité géométrique. A l’issu de cette étude, une loi est proposée permettant de prendre en compte l’effet de la rugosité à une échelle locale dans une interface lisse équivalente à l’échelle globale. / Interface between bituminous layers is an important parameter for the pavement computational design.New pathologies in pavement structure require today rational methods taking into account theinterfaces behavior. Due to these concerns, the current study is based on a damage cohesive zonemodel (CZM) in mixed mode of the rough interfaces. The model was initially proposed by Allix-Ladevèze. This thesis presents a comprehensive interface modeling including delay effect, based ondamage energy release rate. The process of the present study is presented in three chapters. The firstchapter present the stat of art of interfaces. The second devoted to identify the parameters of theinterface model and material properties through advanced optical method as Digital Image Correlation(DIC) and (H-DIC). In the third chapter, a study of the influence of the elastic normal and tangentialstiffness and coupling parameters in the mixed mode on the debonding interfacial energy is presented.An analytical model provides relations between the interfaces stiffness, the coupling parameter of theCZM and the interfacial roughness. Then, a parametric numerical analysis is conducted to study theroughness effect on the interface constitutive law. Results show clearly the roughness influence in thiskind of structures. The damage behaviours predicted by the proposed model for pure mode I, puremode II and for mixed mode with taking into account of roughness are found in good agreement withexperimental results.

Microfibrillated cellulose (MFC) is an alternative material that has been widely studied to enhance the mechanical properties of a polymer matrix due to a number of perceived advantages over traditional plant fibre forms. Mechanical properties of MFC networks were found to depend on parameters such as the modulus of fibrils, bonding strength, porosity, degree of crystallinity, contact area of fibrils and possibly the modulus of the cellulose crystals of the raw materials (cellulose I or II). Even though the longer processing time used to produce MFC was found to yield networks with fewer fibre aggregates, finer fibrils and higher density, some properties, for instance thermal stability and degree of crystallinity, decreased due to the degradation of fibrils caused by the harsh treatment. The aims of this thesis were to assess the mechanical properties and interfaces of composites produced using of a range of MFC materials, prepared using different treatments and from different sources. Raman spectroscopy has been used to detect the molecular orientation of cellulose chains within an MFC network, and to monitor the deformation micromechanics of MFC networks. The Raman band initially located at ~1095 cm-1 obtained from MFC networks was observed to shift towards a lower wavenumber position upon the application of tensile deformation. The intensity of this band as a function of rotation angle of MFC networks was similar, indicating randomly oriented networks of fibrils. From the Raman band shift rate data, the effective moduli of MFC single fibrils produced from pulp were estimated to be in the range of 29-41 GPa. Poly(lactic acid) (PLA) composites reinforced with MFC networks were prepared using compression moulding. Enhanced mechanical properties of MFC reinforced composites were reported, compared to neat PLA films. The mechanical properties of these composites were found to mainly depend on the interaction of the PLA matrix and the reinforcement phase. The mechanical properties of the composites reinforced with dense networks were shown to be dominated by the network properties (fibril-fibril interactions), while matrix-fibril interactions played a major role where more opened networks were used to reinforce a polymer matrix. The penetration of the matrix into the network was found to depend on the pore sizes, fibre width and porosity within the network. It was found that the matrix easily penetrates into the network with a range of mean fibril dimensions, rather than for networks with only fine fibrils present. The stress-transfer process in MFC reinforced PLA composites was monitored using Raman spectroscopy. Greater Raman band shift rates with respect to tensile deformation for the composites were observed compared to pure MFC networks. This indicates that stress is transferred from the PLA matrix to MFC fibrils, supporting the enhancement of the mechanical properties of the composites.

High performance polymer composites are materials with emphasis on specific chemical and mechanical properties due to their broad scope of applications. The main advantages are high strenght and toughness in comparison with their low weight and density. An increased adhesion at composite interfaces is important to ensure excellent composite properties. Bundles of glass fibers were coated by plasma-polymerised interlayers of tetravinylsilane (pp-TVS) of different thicknesses and at different effective powers. The prepared interlayers of pp-TVS were analyzed to evaluate chemical composition (RBS, FTIR, XPS) and mechanical properties (NI-AFM). Microindentation test and fiber-bundle pull-out test were used to determine the interfacial shear strenght.

La mise ne oeuvre par voie liquide de matériaux composites à matrice d'alliage de titane renforcés par des filaments de carbure de silicium conduit, malgré la rapidité du procédé utilisé pour enduire les filaments par l'alliage liquide, à d'importantes interactions physico-chimiques au niveau des interfaces formées.<br />Ces interactions entre le revêtement de carbone des filaments et le titane liquide contrôlent en particulier la cinétique de mouillage du filament et les transferts de carbone du filament vers la matrice.<br />Des modèles, confirmés par des observations et analyses microscopiques, ont permis de comprendre les mécanismes mis en jeu au cours du procédé d'élaboration et en particulier de la solidifications. <br />Il est apparu que le dépôt par voie chimique réactive de carbure de titane sur le revêtement de carbone du filament de carbure de silicium était un moyen efficace pour favoriser le mouillage du filament par l'alliage de titane liquide et pour contrôler non seulement les transferts de carbone mais aussi les conditions d'obtention de composites filamentaires correspondant aux spécifications attendues.