Comparative studies were carried out on the curing kinetics, physical and mechanical properties of conventionally and microwave cured epoxy resins. Epoxy resins Araldite LY 5052 and DLS 772 were used for this study. 4 4' Diaminodiphenyl sulfone was used as a hardener in the preparation of both systems. Nuclear magnetic resonance and gel permeation chromatography were used to identify the chemical structure of the resins. Differential scanning calorimetry was used to monitor the curing kinetics of conventionally cured epoxy samples while a microwave heating calorimeter was used to monitor the curing kinetics of microwave cured epoxy samples 'in situ'. These studies were carried out under non-isothermal and isothermal conditions. For both conditions, there was a significant increase in the fractional conversion of the microwave cured samples compared to the conventionally cured samples. The curing reactions for samples cured using microwave heating took place over a smaller temperature range. Higher reaction rates were observed in the samples cured using microwave heating.There were some differences in the kinetic parameters of the non-isothermal curing reactions of samples cured using microwave and conventional heating. For the Araldite LY 5052 / 4 4' DDS epoxy system, the microwave cured samples had higher activation energy than conventionally cured samples, while for the Araldite DLS 772 / 4 4' DDS epoxy system, the microwave cured samples had lower activation energy. The activation energies of the microwave isothermal curing of both Araldite LY 5052 / 4 4' DDS and Araldite DLS 772 / 4 4'DDS epoxy systems were lower than the activation energies of the conventionally cured samples.Infrared spectroscopy showed that the curing reaction followed the same path during conventional and microwave heating. It also revealed that the reaction rate of the microwave cured samples was higher than the conventionally cured samples.For both epoxy systems, the microwave cured samples had a higher glass transition temperature (Tg) , higher cross-link density (v) and lower molecular weight between cross-links. These showed that the microwave cured samples had a more compact network structure than the conventionally cured samples, which is an indication of better mechanical properties.A microwave reaction system was used to successfully dissolve conventional and microwave cured samples of Araldite DLS 772 / 4 4' DDS epoxy system. The chemical structure of the decomposed product was determined.

Applications of rapid prototyping are expanding to new domains. This is particularly true of the selective laser sintering (SLS) process. In order for that process to be competitive and become a strong candidate for new applications, such as rapid manufacturing, the material used needs to be improved. The aim of the work presented in this thesis was to develop a new composite material made up of Polyamide 12 (a common SLS material) and cement, an inexpensive additive, for the purpose of improving the mechanical properties, as well as reducing the cost of the sintered components. An experimental study was conducted of the thermal properties of the cement-Polyamide 12 composite material with different proportions of cement and Polyamide 12. The purpose of the study was to determine optimal SLS parameters to produce good quality fabricated SLS specimens. The research also involved an experimental investigation of the mechanical properties (Young‟s modulus, tensile, flexural, compression and impact strengths, and density) as a function of the proportion of cement additive to Polyamide 12. Finally, a method of quickly and inexpensively producing test specimens by casting instead of using SLS was developed and experiments conducted to demonstrate the similarity in properties between cast and SLS specimens. II This research has shown that adding cement to Polyamide 12 yields a composite material that enables the production of sintered specimens with mechanical properties that are superior to those of pure Polyamide 12 specimens. As cement is much cheaper than Polyamide 12, the composite material is also obviously less expensive than pure Polyamide 12.

Aviation and aerospace structural components made of composite laminates due to their internal structure and manufacturing methods contain a number of inter- and intracomponent defects, which size, dispersion and interaction alter significantly the critical compression strain level. While there are a plethora of theoretical and experimental work on the problems stability loss and fracture of composites with internal defects in the scope of classic problems of fracture mechanics, there are few theoretical and numerical analyses available for the nonclassical problems of fracture mechanics of composites compressed along layers with interface cracks. These analyses usually have been considered the simplest problems, where the composite material with pronounced microstructure and interface defects (cracks, delaminations) have been analysed as two-dimensional (2-D) continuum in the condition of plane strain state. In the scope of these analyses only parallel defects have been considered, allowing for the interpenetration of the stress-free crack faces, or assuming so-called interfacial cracks with connected edges. This thesis broadens knowledge in the area of non-classical problems of fracture mechanics. It investigates the effect of interfacial cracks interaction on the critical buckling strain in layered and fibrous composite materials under compressive static loading. The behaviour of composite is analysed on several length-scales, starting from a ply and laminate levels (in 2-D approximation), down to a single-fibre level (a full 3-D model). The statements of the problems are based on the model of piecewise-homogeneous medium model, the most accurate within the framework of the mechanics of deformable bodies as applied to composite materials with pronounced microstructure. All composite constituents are modelled as linear-elastic material, where both isotropic and anisotropic materials are considered depending on the length-scale. It is assumed that the moment of stability loss in the microstructure of materials is treated as the onset of the fracture process. Besides that, the critical strain that corresponds to loss of stability in the microstructure of the composite, either surface or internal instability, must be smaller than the critical strain that corresponds to loss of stability of the entire composite. This project involves parameterised variables, such as the crack size, the crack spacing, the layer volume fraction and the fibre volume fraction. At each length-scale two types of cracks are analysed, namely, cracks with stress-free crack faces and cracks with frictionless Hertzian contact of the crack faces. A number of finite-element models for each length-scale are developed, and are validated analytically and numerically. The models' ability to simulate practical composite structures to a useful degree of accuracy with suitable material properties is discussed. A number of parameters, which quantifies the interfacial crack interaction and crack faces contact interaction phenomena, are introduced and discussed. Qualitative discussion on the crack faces contact zones, post-critical behaviour of composites and crack propagation are presented and discussed. Finally, the subject areas for the future work are outlined.

Le travail de thèse porte sur l’étude du phénomène d’impact balistique dans le cas d’un tissu 2D et 3D avec 3 approches : numérique, expérimentale et analytique. Un protocole expérimental spécifique a été développé pour réaliser des essais dynamiques sur un fil en utilisant des moyens de suivi avec des systèmes d’acquisition rapide. Les essais balistiques ont été effectués à l’aide d’une instrumentation permettant le suivi de la vitesse du projectile et la déformation du tissu. 2 modèles numériques ont été utilisés : macroscopique et mésoscopique. Le modèle macroscopique du tissu 2D permet une prédiction sommaire des paramètres d’impact. Pour mieux mettre en évidence les interactions entre les fils d’un tissu 2D, un modèle mésoscopique, utilisant des éléments coques, a été développé. La confrontation des résultats numériques obtenus avec les données expérimentales démontre la robustesse du modèle mésoscopique puisque le phénomène des contacts fil/fil et projectiles/fils peut être analysé. Par ailleurs, dans un souci d’optimisation de temps de calcul, une combinaison entre les modèles mésoscopique et macroscopique a permis le développement d’un modèle multi échelle méso-macro. Un outil numérique est développé afin de modéliser géométriquement un tissu 3D. Ce modèle permet d’étudier les effets des frottements et des bords sur un tissu 3D soumis à un impact balistique. Un modèle analytique a été élaboré en prenant en compte les réflexions des ondes de déformation sur les fils pendant l’impact d’un tissu multi-couches. Ce modèle permet de prédire d’une façon continue l’évolution de plusieurs paramètres décrivant l’impact. / This thesis deals with the study of ballistic impact in the case of 2D and 3D fabrics using 3 approaches: numerical, experimental and analytical to improve the body armour protection. A totally new specific experimental protocol was developed for dynamic testing on yarn by using monitoring systems with fast acquisition. Ballistic tests were performed using a gas gun with instrumentation for monitoring projectile velocity and deformation of fabric. Two numerical models were used: macroscopic and mesoscopic models. Indeed, the macroscopic model, which considers 2D fabric as a homogeneous plate, allows a summary prediction of various impact parameters as: residual velocity, impact energies, deformation pyramid. To describe better interactions between yarns in a 2D fabric, a mesoscopic model was developed using shell elements. Comparisons between results obtained by both models and experimental data have demonstrated the modelling robustness at the mesoscopic scale since yarn/yarn and projectile/yarn contacts can be analyzed. Furthermore, in order to optimize computation time, a combination of mesoscopic and macroscopic models has allowed creating a multi-scale model distinguishing between different working areas of fabric during impact. A new numerical tool has been developed to model geometrically 3D fabrics taking into account yarns cross section. This model allows studying the effects of frictions and boundary conditions of a 3D fabric subjected to ballistic impact.In addition, an analytical model was carried out taking into account reflections of strain waves on yarns in the case of impact of a multi-layer fabric. This model predicts continuous evolutions of several parameters describing the impact.

Ce travail de thèse présente le développement de modèles numériques pour la modélisation de l’endommagement des matériaux composites à fibres continues et matrice polymère. L’objectif est de fournir des outils numériques efficaces pour prédire l’endommagement sous chargement monotone et cyclique. Deux modèles ont été développés, un basé sur une approche multi-échelle d’homogénéisation et l’autre défini dans le cadre de la mécanique de l’endommagement. Ce dernier est utilisé dans une nouvelle approche pour prédire la durée de vie des matériaux composites. La première approche est une méthode multi-échelle afin d’étudier l’influence de l’endommagement à l’échelle microscopique sur le comportement macroscopique du composite. Le comportement macroscopique est déterminé par homogénéisation d’une cellule unitaire. L’approche est appliquée au cas d’un composite unidirectionnel afin d’étudier l’influence de l’endommagement de la matrice. Pour contourner les difficultés d’une approche multi-échelle, un modèle mésoscopique basé sur le couplage entre la plasticité et l’endommagement est proposé. Le modèle est validé et confronté à d’autres modèles ainsi qu’à des résultats expérimentaux. La dernière contribution est le développement d’une nouvelle approche pour la prédiction de la durée de vie des matériaux composites s’appuyant sur l’hypothèse que le matériau atteint un état stabilisé d’endommagement. Cette hypothèse permet d’utiliser l’analyse simplifiée pour prédire les états stabilisés. Le modèle de fatigue proposé est une loi puissance entre le nombre de cycles et les forces thermodynamiques associées à l’endommagement. L’approche est validée à partir de résultats expérimentaux. / A numerical framework for the modeling of the damage in fibre reinforced polymer composite materials has been developped. The objectives were to provide efficient numerical tools to predict the damage under static and cyclic loading. Two different models were proposed, one based on a fully computational multi-scale homogenization technique and a second one under the hypothesis of the meso-mechanics associated with a coupled damage-plastic constitutive model. The latter has been used in a new approach developped to predict the life of composite structures. As a first approach, a multi-scale application has been developed to better understand the influence of the damages occuring at lower scales on the macroscopic response. The macroscopic is defined by homogenization of a unit cell. The scheme is used to analyze the effect of the matrix damage on the material response in the case of unidirectional composites. To overcome the difficulties of the multi-scale approach, a meso-scale phenomenological model based on the coupled plasticity with continuous damage mechanics is proposed. All comparisons of the simulation with experiments and other models have shown good agreements. The third contribution is the development of a new approach to predict the life of composite materials based on the assumption that the material reaches a damage stabilized state during his life. This assumption makes it possible to use the simplified analysis. The life of the material is considered depending on the level of the thermodynamical forces associated with damage at the stabilized state by the use of a power law. Good agreements are obtained with experimental results.

GaN et ses alliages ternaires et quaternaires du système Ga(B,In,Al) sont devenus au cours des dernières années des semiconducteurs phare de l'optoélectronique. Plus spécifiquement l'alliage InGaN qui présente une énergie de bande interdite (0, 77eV, pour l'InN à 3, 4eV, pour le GaN) permettant l'absorption quasi totale du spectre visible se positionne comme un excellent candidat pour la réalisation de cellules solaire multi-jonctions à très haut rendement. La croissance de couches épitaxiales d'InGaN avec une forte teneur en indium et une bonne qualité structurale et morphologique reste néanmoins un challenge. Notre groupe a été parmi les premiers à relever ce challenge en proposant une technique de croissance originale consistant à insérer périodiquement de fines couches de GaN dans la couche épaisse d'InGaN. Ce travail s'inscrit dans ce contexte et porte sur les caractérisations morphologiques, structurales et optiques des différentes structures élaborées et qui ont permit l'optimisation du procédé de croissance et l'obtention de couches d'InGaN avec une teneur en indium de 15%, une épaisseur de 120nm et des qualités structurales et optiques de premier ordre. La partie centrale du travail a consisté en la mise en oeuvre et l'utilisation de la technique de cathodoluminescence pour l'étude des matériaux InGaN élaborés au laboratoire par MOVPE. Les principales avancées de ce travail, outre la contribution au succès de l'obtention de couches d'InGaN de grande qualité, concernent la confirmation du mode de croissance des couches d'InGaN (transition 2D-3D, type et rôle des inclusions de surface), la détermination de l'épaisseur critique des couches en fonction du taux d'indium, et la modélisation du phénomène de cathodoluminescence par méthode Monte-Carlo / GaN and its ternary and quaternary alloys Ga(B, In, Al)N have become in recent years one of the most important semiconductor materials for applications in optoelectronics. More specifically, the InGaN alloy, that has a band gap energy (0.77eV for InN, 3.4eV for GaN) allowing almost full absorption of the visible spectrum can be an excellent candidate for the realization of highly efficient multi-junctions solar cells. However, the growth of InGaN epitaxial layers with high indium content and good structural and morphological quality remains a challenge. Our group was among the first to meet this challenge by proposing an original growth technique consisting in the periodical insertion of thin GaN layers in the thick InGaN layer. The present work falls in this context and focuses on the morphological, structural and optical characterization of different InGaN structures that have been developed, allowing the optimization of the growth process and the obtention of InGaN layers with an indium content of 15%, a thickness of 120nm and a high structural and optical quality. The main aspect of the present work consist in the implementation and use of the cathodoluminescence technique to study the InGaN materials grown by our group using MOVPE. The main achievements of this work, in addition to the contribution to the success of getting high quality InGaN layers, relate to the confirmation of the growth mode of InGaN layers (2D - 3D transition, type and role of surface inclusions), the determination of the critical layer thickness according to the indium content, and the modeling of the cathodoluminescence phenomenon using Monte Carlo method

Le dimensionnement par analyse des équipements sous pression est encadré par des règles normalisées. Deux méthodologies s’opposent : une méthode de classification des contraintes élastiques, et une méthode élastoplastique basée sur les théorèmes d’analyse limite et d’analyse d’adaptation. La première a été mise au point dans les années 1960 et devient obsolète par rapport aux besoins technologiques et aux capacités de calcul actuelles, tandis que la seconde souffre de problèmes d’applicabilité.Le travail de thèse effectué a consisté dans un premier temps en une étude bibliographique, qui s’est penchée sur les aspects législatifs de ce secteur et sur les règles et critères de dimensionnement communément appliqués. Parmi les modes de ruine identifiés, deux d’entre eux – déformation excessive et déformation progressive – se sont détachés par leur importance. Ainsi, des méthodes directes prémunissant contre ces derniers, actuellement développées en laboratoires de recherches, ont été étudiées, implémentées, mises au point, et les critères de dimensionnement ont été ajustés afin de tenir compte des marges réglementaires. Différentes voies ont été explorées : l’analyse cyclique directe, l’ajustement de limite d’élasticité, ainsi que la compensation élastique.Par suite, les différentes méthodes ont fait l’objet d’études comparatives, portant sur leur précision, le temps de calcul qu’elles requièrent, ainsi que la relation entre ces deux grandeurs. Les modèles utilisés ont été variés, de cas académiques simples à une structure réelle, et ont permis de dégager des tendances, reliant l’intérêt de l’emploi d’une procédure à la complexité d’un problème à traiter. / Design by analysis of pressure vessels is placed within guidelines. Two methodologies are currently considered in international standards. The first one was proposed in the 60’ : it considers an elastic stress classification, depending on the nature of loads. It nowadays suffers from obsolescence, as technological demand and computational facilities increased considerably. The – much more recent – second one deals with elastoplastic calculations : it is based on limit and shakedown analysis theory, but causes applicative difficulties. The work achieved in this thesis begins with a state of the art, dealing with legal aspects of this industry, and detailing commonly-applied design rules and criteria. Several failure modes were identified, and the study focuses on two of them : gross plastic deformation and ratchet. Direct methods were selected for their relevance toward design considerations. Currently developed in research labs, they were studied, implemented, tested, and criteria were modified so as to take into account safety margins. Three solutions were explored : direct cyclic analysis, yield modification, and elastic compensation. For comparison purposes, methodologies were evaluated on academic and realistic cases. Accuracy and computational time were measured, along with the relation between these datas. Trends could be established, relating the pertinent use of a methodology to a problem complexity.

L’homogénéisation est une technique de passage Micro-Macro en tenant compte de l’influence des paramètres morphologiques, mécaniques et statistiques de la microstructure représentative d’un matériau hétérogène. La modélisation numérique a contribué fortement au développement de cette technique en vue de déterminer les propriétés physico-mécaniques des matériaux hétérogènes bi et multiphasiques. L’objectif principal de ce travail est la prédiction du comportement macroscopique élastique et thermique de matériaux hétérogènes. Les comportements mécaniques et thermiques ont été déterminés numériquement puis comparés aux résultats expérimentaux et analytiques. La variation du volume élémentaire représentatif (VER) en fonction de la fraction volumique et du contraste a été analysée. Cette étude a mis en évidence l’intérêt d’une détermination rigoureuse de la taille optimale du VER. En effet, celle-ci doit prendre en compte plusieurs paramètres tels que la fraction volumique, le contraste, le type de la propriété et la morphologie de l’hétérogénéité. Un nouveau concept de morphologie équivalente a été proposé. Ce concept introduit le principe d’équivalence des caractéristiques élastiques et thermiques des matériaux hétérogènes d’une microstructure de morphologie complexe avec celles d’une microstructure contenant des particules sphériques. Ce travail a conduit à l’élaboration d’une démarche globale de design microstructural en intégrant la morphologie réelle des phases des microstructures hétérogènes intégrant à la fois la visualisation des images, l’étude morphologique et la modélisation géométrique et numérique. / The homogenization is a technique of Micro-Macro passage taking into account the influence of morphological, mechanical and statistical parameters of the representative microstructure of an heterogeneous material. Numerical modeling has contributed significantly to the development of this technique to determine the physical and mechanical properties of bi-and multi-phase heterogenous materials. The main objective of this work is the prediction of the macroscopic elastic and thermal behaviors of heterogeneous materials. The mechanical and thermal behaviors was determined numerically and compared with experimental and analytical results. The variation of the representative volume element (RVE) versus volume fraction and the contrast was analyzed. This study showed the importance of a rigorous determination of the optimal RVE size. Indeed, it must take into account several parameters such as : volume fraction, contrast, type of property and the morphology of the heterogeneity. A new concept of the equivalent morphology was proposed. This concept introduces the equivalence of the elastic and thermal characteristics of a microstructure of heterogeneous materials with complex morphology and those of a microstructure containing spherical particles. This work led us to developement of a comprehensive approach to microstructural design by integrating the real morphology of heterogeneous microstructure phases incorporating at the same time the image visualization, the morphological study and the geometric and numerical modeling.

This thesis addresses the behaviour of glass in fire condition. The behaviour of glazing could influence the growth of fires. Radiation is often the most significant heat transfer mechanism and its modelling is critical to an accurate prediction of temperature distribution in the glass and the time to breakage. A literature review on the theoretical modelling and experimental aspects of glazing systems exposed to fire are presented. Theoretical issues of glazing modelling in fire conditions were identified. To address the limitations of existing approaches, a more robust computer tool, referred to as Fire Dynamics Simulator - One Dimensional & Three Dimensional Spectral Discrete Ordinate Method (FDS-1D & 3D-SDOM) was developed in this thesis. The new computer tool is comprised of (i) a CFD part for the fire dynamics and fluid flow simulation, (ii) a spectral Discrete Ordinates radiation model for radiative source term calculations in the glass, and (iii) a FEA part for the 3D thermal conduction thermal stress, thermal strain and the probability of failure in glass material. For verification purposes, the model is applied to some typical fires/glazing scenarios from the literature. Good agreements are found between predictions and experimental data. The study also investigates the effects of the glass thickness, thermal conductivity and emissivity on the glass temperature.

This thesis describes investigations performed into the ion exchange and intercalation properties of aluminium triphosphate, AlH\(_2\)P\(_3\)O\(_{10}\)•2H\(_2\)O (AlTP). Materials synthesised were characterised using a variety of techniques, including powder neutron and X-ray diffraction, Rietveld analysis, thermogravimetic analysis and environmental scanning microscopy. Monovalent ion exchange (with Na, K, Rb, Cs and Ag) gave complete and facile exchange of the host’s hydrogen ions and gave crystalline products. A thermodynamically favoured phase with two waters of crystallisation was observed for all monovalent cation exchanges. The alkali metals also showed metastable phases with differing numbers of waters of crystallisation, four for Na and one for K, Rb and Cs. Unit cells have been assigned to the exchanged phases, with all showing a more than doubling of the \(a\) parameter. Structural characterisation of the rubidium and caesium phases show this to be a result of a change of symmetry to C2/c causing adjacent layers to shift half a unit cell along [010] with respect to one another. Ion exchange with divalent cations (Cu, Mn, Zn, Ca and Sr) has also been shown to be possible, with phases showing altered XRD patterns and decomposition products. Intercalation with a range of increasingly complex amines was found to be possible in AlTP. Multifunctional molecules, including amino acids, were also found to intercalate into AlTP, with evidence in the intercalation of 6-aminohexanoic acid that interactions between intercalated molecules within the inter-lamellar region are possible. Trends were found to be similar to other layered phosphates with respect to the amounts and angles of intercalation of simple monoamines and the effects of pK\(_b\) and sterics upon an amines ability to intercalate into AlTP. In addition, intercalation with silver exchanged AlTP was also found to be possible. This was able to intercalate several similar amines to AlTP, but showed its own unique intercalation properties including the ability to intercalate thiols.