L'objet de ces travaux est de se doter d'outils de modélisation qui constituent aujourd'hui un passage incontournable pour maîtriser le procédé R.T.M. Ces outils reposent sur la prédiction de grandeurs macroscopiques caractérisant les renforts. La représentation fidèle du renfort à l'échelle microscopique dans une cellule élémentaire est la clé de voûte de notre travail. Une méthode d'initialisation de fonction caractéristique a ainsi été mise au point permettant de déterminer fidèlement les interfaces entre la résine et les renforts. Cette méthode possède la particularité d'être applicable à des renforts à structure périodique mais aussi aléatoire. La simulation de l'écoulement 3D de la résine dans les pores entre les fibres permet de déterminer la perméabilité de la structure représentée. Le passage de l'échelle microscopique à l'échelle macroscopique est réalisé en homogénéisant les champs de vitesse et de pression obtenus numériquement dans la cellule élémentaire.Une démarche similaire a été développée pour étudier les phénomènes thermiques dans les milieux poreux. Cette approche permet de déterminer des valeurs de conductivité thermique équivalente en considérant dans un premier temps, le fluide au repos et ensuite en couplant les phénomènes thermiques à l'écoulement engendrant des fluctuations thermiques à l'échelle microscopique. Ce phénomène est important et modifie grandement les résultats. Sa prise en compte introduit des termes non linéaires couplant la conductivité thermique équivalente à la vitesse d'écoulement du fluide au travers du renfort.La connaissance précise de ces paramètres permet la réalisation de simulations 3D réalistes du procédé R.T.M.

The increasing demand for polymer matrix composites (PMCs) from the airframe industry raises the issues of productivity, cost and reproducibility of manufactured PMC components. Performance reproducibility is closely related to the manufacturing technique. Resin transfer moulding (RTM) offers the advantage of flexible manufacturing of net-shape PMC components with superior repeatability starting from ready-to-impregnate dry reinforcements. An RTM apparatus was developed for manufacturing PMC plates and demonstrator components representative of actual, PMC components and PMC moulds made and used in the airframe industry. The RTM process developed in this work involved making net-shape dry carbon fibre preforms and impregnating them an epoxy resin, targeting mould applications. Thermal repeatability of different net-shape PMC components manufactured using the RTM apparatus developed in-house was investigated. Effects of bonding an outer copper plate onto the PMC material, targeting mould applications known as integrally heated copper tooling (IHCT), were explored. Heat conduction through the PMC components was studied using simulation models validated by experimental data obtained primarily by thermography. Manufactured PMC components showed good repeatability, particularly in terms of thermal behaviour. The IHCT technique was found to be well suited for mould applications. Expected advantages of thermography were materialised. Finally, the simulation models developed were in good agreement with experimental data.

This thesis focuses on the incorporation of carbon nanoparticles within continuous fibre reinforcements by liquid composite moulding processes, in order to provide enhanced electrical and delamination properties to the multiscale composites. The mechanisms controlling the flow and filtration of these nanoparticles during liquid composite moulding are studied, in order to develop a predictive 1-D model which allows design of the processing of these composite materials. Five different carbon nanoparticles at 0.25 wt% loading, three unmodified and one surface modified carbon nanotube systems and one carbon nanofibre system, were utilised to modify a commercial two-component epoxy resin utilised to impregnate carbon and glass reinforcements at high fibre volume fraction by resin transfer moulding. The dispersion of the nanofillers in the prepolymer was carried out by ultrasonication, high shear mixing or triple roll milling or a combination of the three. Electrical conductivity measurements of the carbon nanoparticle liquid suspensions during dispersion, alongside optical microscopy imaging and rheological analysis of these allowed the selection of the concentration of nanofiller and the appropriate dispersion technique for each nanoparticle system. The resin transfer moulding process required adaptation to incorporate the dispersion and modify degassing steps, especially when utilising unmodified carbon nanoparticles suspensions, due to their higher viscosity and tendency to be filtered. Nanoparticle filtration was identified by electrical conductivity measurements and microscopy of specimens cut at increasing distances from the inlet. Cake filtration was observed for some of the unmodified systems, whereas deep bed filtration occurred for the surface modified CNT material. Property graded composites were obtained due to filtration, where the average electrical conductivity of the carbon and glass composites produced increased by a factor of two or one order of magnitude respectively. The effect of filler on the delamination properties of the carbon fibre composites was tested under mode I. The results do not show a statistically significant improvement of delamination resistance with the presence of nanoparticles, although localised toughening mechanisms such as nanoparticle pull-out and crack bridging as well as inelastic deformation have been observed on fracture surfaces. Particle filtration and gradients in concentration resulted in non-linear flow behaviour. An 1-D analytical and a finite difference model, based on Darcy’s law accompanied by particle mass conservation and filtration kinetics were developed to describe the flow and filtration of carbon nanoparticle filled thermosets. The numerical model describes the non-linear problem by incorporating material property update laws, i.e. permeability, porosity and viscosity variations on concentration of retained and suspended particles with location and time. The finite difference model is consistent and converges to the analytical solution. The range of applicability of the analytical model is limited to lower filtration coefficients and shorter filling lengths, providing an approximate solution for through thickness infusion; whereas the numerical model presents a solution outside this range, i.e. in-plane filling processes. These models allow process design, with specified carbon nanoparticle concentration distributions achieved via modifying the nanofiller loading at the inlet as a function of time.

Die vorliegende Dissertation berichtet über die Untersuchung von selbst-aggregierten Einfach- und Mehrfachschichten aus Nanographenen-Derivate mit Hilfe der Rastertunnelmikroskopie (RTM) an Fest-Flüssig-Grenzflächen. Die -Konjugation bringt einzigartige elektronische Eigenschaften mit sich, so dass die Nanographen-Derivate viel versprechende Bausteine für eine molekulare und organische Elektronik sind, da sie maßgeschneidert und kostengünstig prozessiert werden können, und leicht und flexibel sind. Für elektronische Anwendungen ist es notwendig, die Nanographene in ultradünnen Filmen mit geordneten supramolekularen Strukturen zu organisieren. Nanostrukturen werden für Nanographene-Derivate auf hoch orientiertem pyrolytischem Graphit (HOPG) untersucht, wie zum Beispiel alkylierte Hexi-peri-hexabenzocoronene (HBCs) unterschiedlicher Symmetrie und dreiecksförmige polyzyklische aromatische Kohlenwasserstoffe (PAK). Es zeigt eine erstaunliche Vielfalt von supramolekularen Strukturen, z.B. Zick-Zack-, Blumen- oder Honigwaben-Muster. Eine faszinierende Besonderheit besteht in den Honigwaben Strukturen, die sich durch Selbstaggregation dreieckiger alkylierter Phenyl-PAKs bilden, und die damit Nanotemplate für Gastmoleküle darstellen. In vielen Fällen bilden Nanographene-Derivate nicht nur Monoschichte sondern auch Multischichten auf Graphit. Die Selbstorganisation von Doppelschichten aus einer HBC-Stern-Verbindung bietet das Potenzial für Baustelemente in der organischen Elektronik, zum Beispiel für Nanodrähte. Die alkylierten Phenyl-HBCs bilden polykristalline Strukturen sowohl in der "face-on"-Anordnung in Monoschichten auf Graphit wie in der "edge-on"-Anordnung in Multischichten, die sich in einem äußeren elektrischen Feld bilden. Beides kann nützlich sein, da für die mögliche Anwendung in einer Photovoltaik-Zelle die "face-on"-Orientierung auf Oberflächen erforderlich ist, während für organische Feldeffekt-Transistoreneine "edge-on" Nanostruktur benötigt wird. / This thesis reports on the investigation of self-assembled mono- and multilayers from nanographene derivatives via scanning tunneling microscopy (STM) at solid-liquid interfaces. Because of the unique electronic properties associated with their -bonded topology, nanographenes are promising building blocks for molecular and organic electronics, which provide the possibility of tunability together with low-cost processing, light weight, and flexibility. For the application in electronics it is necessary to organize nanographenes in ultrathin films with well-ordered supramolecular structures. Nanostructures of monolayers on Highly Oriented Pyrolytic Graphite (HOPG) are studied for different nanographene derivatives, such as alkylated hexa-peri-hexabenzocoronenes (HBCs) with different symmetries, and triangle-shaped polycyclic aromatic hydrocarbons (PAHs). They exhibit a surprising diversity of supramolecular structures, for example zigzag, flower-like or honeycomb shapes. A fascinating peculiarity provides the honeycomb structures which are self-assembled from triangle-shaped alkylated phenyl PAHs, which provide nanotemplates to accommodate guest molecules. In many cases, nanographene derivatives not only form monolayers but also multilayers on HOPG. Star-shaped HBC molecules self organize into bilayers in polar solvents, which exhibit the potential for the formation of building blocks of organic electronics, for instance nanowires. The alkylated phenyl HBCs form polycrystalline structures both in the “face-on” arrangement in a monolayer on HOPG, and “edge-on” in multilayers within an external electric field. Both may be useful for potential applications, since in a photovoltaic cell, the “face-on” orientation on surfaces is required, while for the purpose to be applied in organic field-effect transistors, the “edge-on” nanostructure on the electrodes is necessary.

Le procédé " Resin Transfer Molding " consiste à injecter un polymère thermodurcissable à travers des fibres de renfort, qui polymérise ensuite pour former une pièce composite. L'objectif est de modéliser numériquement l'écoulement à différentes échelles, celle des mèches composants le tissu (mésoscopique) et celle des fibres composants les mèches (microscopique). Cette thèse se décompose en deux parties. La première concerne le calcul de perméabilité d'un volume élémentaire représentatif par prise de moyenne des champs de vitesse et de pression, dans le cadre de la méthode d'immersion de domaines. A l'échelle microscopique, le calcul de perméabilité a été validé en utilisant des lois analytiques. A l'échelle mésoscopique, un couplage entre les équations de Stokes et de Darcy, pour les écoulements entre les mèches et à l'intérieur des mèches a été effectué. La seconde partie aborde l'étape d'imprégnation du renfort à l'échelle microscopique, ce qui inclut la modélisation de l'avancée du front de matière entre les fibres avec prise en compte de la tension de surface. Nous avons implémenté des méthodes pour prendre en compte les phénomènes capillaires. Une méthode d'imposition de l'angle de contact statique de l'interface avec une surface solide, et la condition aux limites de Navier permettant d'imposer un glissement à la ligne triple, ont été implémentées et validées. Tous les développements ont été effectués dans une méthode éléments finis mixtes linéaires en vitesse pression, stabilisée par une fonction bulle (MINI-élément), et en utilisant la méthode d'immersion de domaines.

The increasing demand for polymer matrix composites (PMCs) from the airframe industry raises the issues of productivity, cost and reproducibility of manufactured PMC components. Performance reproducibility is closely related to the manufacturing technique. Resin transfer moulding (RTM) offers the advantage of flexible manufacturing of net-shape PMC components with superior repeatability starting from ready-to-impregnate dry reinforcements. An RTM apparatus was developed for manufacturing PMC plates and demonstrator components representative of actual, PMC components and PMC moulds made and used in the airframe industry. The RTM process developed in this work involved making net-shape dry carbon fibre preforms and impregnating them an epoxy resin, targeting mould applications. Thermal repeatability of different net-shape PMC components manufactured using the RTM apparatus developed in-house was investigated. Effects of bonding an outer copper plate onto the PMC material, targeting mould applications known as integrally heated copper tooling (IHCT), were explored. Heat conduction through the PMC components was studied using simulation models validated by experimental data obtained primarily by thermography. Manufactured PMC components showed good repeatability, particularly in terms of thermal behaviour. The IHCT technique was found to be well suited for mould applications. Expected advantages of thermography were materialised. Finally, the simulation models developed were in good agreement with experimental data.

This thesis aims to improve sales forecasting in the context of passenger airlines. We study two important issues that could potentially improve forecasting accuracy: day-to-day price change rather than price itself, and linking flights that are likely to be considered as pairs for a round trip by passengers; we refer to the latter as the Round-Trip Model (RTM). We find that price change is a significant variable regardless of days remaining to flight in the last three weeks to flight departure, which opens the possibility of planning for revenue maximizing price change patterns. We also find that the RTM can improve the precision of the forecasting models, and provide an improved pricing strategy for planners. In the study of the effect of price change on sales, analysis of variance is applied; finite regression mixture models were tested to identify linked traffic in the two directions and the linked flights on a route in reverse directions; adaptive neuro-fuzzy inference system (ANFIS) is applied to develop comparative models for studying sales effect between price and price change, and one-way versus round-trip models. The price change model demonstrated more robust results with comparable estimation errors, and the concept model for the round-trip with only one linked flight reduced estimation error by 5%. This empirical study is performed on a database with 22,900 flights which was obtained from a major North American passenger airline.

The purpose of this study was to investigate the effects of mold temperature, initial resin temperature, and the vacuum, applied at resin exit ports, on the mechanical properties of epoxy matrix woven glasss fiber reinforced composite specimens produced by Resin Transfer Molding (RTM). For this purpose, six different mold temperatures (25&ordm / , 40&ordm / , 60&ordm / , 80&ordm / , 100&ordm / , and 120&ordm / C), two initial resin temperatures (15&ordm / and 28&ordm / C), and vacuum (0.03 bar) and without vacuum (~1 bar) conditions were used. Specimens were characterized by using ultrasonic (C-Scan) inspection, mechanical tests (Tensile, Flexural, Impact), thermal analyses (Ignition Loss, TGA) and scanning electron microscopy (SEM). It was generally observed that mechanical properties of the specimens produced with a mold temperature of 60&ordm / C were the best (e.g. 16%, 43%, and 26% higher tensile strength, Charpy impact toughness and flexural strength values, respectively). When vacuum was not applied, the percentage of &ldquo / voids&rdquo / increased leading to a decrease in mechanical properties such as 26% in Charpy impact toughness and 5% in tensile and flexural strength. Lower initial resin temperature also decreased mechanical properties (e.g. 14% in tensile strenght and 18% in Charpy impact toughness).

Composite materials have the potential to revolutionize life in the 21st century. They are contributing significantly to developments in aerospace, hydrogen fuel cells, electronics and space exploration today. While a number of composite material processing methods exist, resin transfer molding (RTM) has the potential of becoming the dominant low-cost process for the fabrication of large, high-performance products. RTM has many advantages over alternative processes, including the capability of producing complex 3D shapes with a good surface finish, the incorporation of cores and inserts, a tight control over fiber placement and resin volume fraction and the possibility of embedding sensors into manufactured components for structural health monitoring. Part of the reason RTM has not received widespread use is due to its drawbacks such as its relatively trial and error nature, race tracking, washout, high cycle time and void formation. The basic operation of the process involves loading a fiber reinforcement preform into a mold cavity, closing the mold, injecting resin into the mold and allowing the resin to cure. To study the resin transfer molding process and issues affecting it, a laboratory containing an experimental RTM apparatus has been established. The apparatus has a glass window to observe the mold filling process and can incorporate various mold shapes such as a quasi-2D panel, a 3-D rectangular section and a 3-D semicircular section. To characterize the flow through the molds a commercial CFD software has been used. This thesis describes the establishment of this laboratory and preliminary studies that have been conducted.

This thesis aims to improve sales forecasting in the context of passenger airlines. We study two important issues that could potentially improve forecasting accuracy: day-to-day price change rather than price itself, and linking flights that are likely to be considered as pairs for a round trip by passengers; we refer to the latter as the Round-Trip Model (RTM). We find that price change is a significant variable regardless of days remaining to flight in the last three weeks to flight departure, which opens the possibility of planning for revenue maximizing price change patterns. We also find that the RTM can improve the precision of the forecasting models, and provide an improved pricing strategy for planners. In the study of the effect of price change on sales, analysis of variance is applied; finite regression mixture models were tested to identify linked traffic in the two directions and the linked flights on a route in reverse directions; adaptive neuro-fuzzy inference system (ANFIS) is applied to develop comparative models for studying sales effect between price and price change, and one-way versus round-trip models. The price change model demonstrated more robust results with comparable estimation errors, and the concept model for the round-trip with only one linked flight reduced estimation error by 5%. This empirical study is performed on a database with 22,900 flights which was obtained from a major North American passenger airline.