Tesis sobre el tema "Composite materials C"

AN ABSTRACT OF THE THESIS OFChristoph Michael Goettler, for the Master of Science degree in Mechanical Engineering, presented on Nov 6, 2020, at Southern Illinois University Carbondale. TITLE: EFFECT OF DENSITY ON FRICTION AND WEAR PERFORMANCE OF CARBON-CARBON COMPOSITE MATERIALSMAJOR PROFESSOR: Dr. Peter FilipCarbon-carbon (C/C) composite materials exhibit high thermal conductivity, high thermal stability, low density, and high mechanical strength. Due to these properties, C/C composites are ideal for use in high performance braking systems. However, C/C composites are incredibly expensive to manufacture, and thus improving the longevity of these materials is vital. C/C composite materials inherently have a density gradient due to manufacturing limitations. By determining the effect of density on friction and wear performance of C/C composite materials, manufacturers could use that data to alter manufacturing methods to improve the lifespan of C/C composites. In this study, the effect of density on friction and wear performance of C/C composite materials was studied. Friction tests were conducted through use of a universal mechanical tester (UMT) manufactured by Bruker and subsequent analysis was done through use of scanning electron microscopy, energy dispersive x-ray spectroscopy, and polarized light microscopy. Numerous samples from depths of 0 mm and 5 mm were taken from two C/C composite materials with varying matrices and friction tested at varying conditions to determine friction properties, friction surface characteristics, microstructure just below the friction surface characteristics, friction layer characteristics, and wear characteristics. Density, apparent density, and apparent porosity gradients were also measured to be able to correlate observations to density differences. It was observed that while density does not seem to be the main cause in differences in friction and wear performance of C/C materials at depths of 0 mm and 5 mm, there still existed significant differences in friction performance, wear performance, and post friction test material characteristics when comparing 0 mm samples to 5 mm samples. In conclusion, density was not found to be a significant cause in variations in friction performance. However, friction surface depth was found to have a significant effect on friction performance, wear performance, and the friction surface. Further research is needed to be able to determine the exact cause of the variations in performance at depths of 0 mm and 5 mm. Keywords: carbon-carbon, composite, C/C, density, friction, wear, brake

Thesis (Ph. D.)--Southern Illinois University Carbondale, 2008.
"Department of Engineering Science." Keywords: Carbon composite, Friction materials, Carbon-fiber reinforcement Includes bibliographical references (p. 106-115). Also available online.

This research project aimed at the development of a PECVD process for the deposition of C60-PPPE (plasma polymerized polyethylene) NC thin films. A continuous throughput PECVD system was designed for the co-deposition of a polymer matrix and C60 particles, in effect, yielding composite thin films on 1" quartz and silicon substrates. In this process, the C 60 molecules are sublimated from their solid powder form, transported to the plasma chamber, pre-coated in-flight before being dispersed and co-deposited in the polymeric matrix. The plasma polymerization of ethane in the low pressure, radio frequency (RF) plasma was studied with a mapping of the polymer thin film growth at various deposition times. Percentage coverage of C60 films was studied at several sublimation temperatures ranging from 500-750 °C. Compositional studies of PPPE and C60 films obtained were carried out using FPA-FTIR. The surface morphology and topography of composite films was analyzed using OM and FESEM. Furthermore, samples of C60 deposited in the reactor were analyzed via TEM for possible deagglomeration and nanocoatings.

Thesis (DTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2008
In recent years, due to rapid advances in technology there has been an increasingly high demand for large displacement and large force, precise positioning, fast response, low power consuming miniature piezoelectric actuators. In certain smart structure applications, the use of curved piezoelectric actuators is necessary. The present work extends the earlier investigations on the C- shape actuator by providing a detailed investigation on the influence of geometric and material properties of the individual layers of the C-shape piezocomposite for its optimal performance as an actuator. Analytical models have. been used to optimize the geometry of the actuator. Experimental and finite element analyses (using general purpose finite element software i.e. CoventerWare and MSC. Marc) have been used for validation. The present work has established that, by maintaining the thickness of the substrate and piezoceramic layers constant; changing the external radius, for example increasing it, the stiffness of the structure decreases and thus yielding large displacement This has a negative effect on the force produced by the actuator. With fixed thickness of the substrate and varying the thickness of the piezoceramic (for fixed external radius) the result is as follows: Increasing the thickness of the piezoceramic layer has the effect of decreasing the displacement while the force increases. With fixed PZT thickness as well as the external radius, varying the substrate thickness has the following effect: As the thickness of the substrate increases the displacement increases reaching a maximum. Subsequent increase in the thickness of the substrate the displacement is reduced. The force continues increasing at least for the ratios up to 1.0, further increase of the substrate, subsequent decrease of force is also noted. In addition to changing the thickness of the substrate, the choice of different material for the substrate has the following effect: For substrate/PZT ratios of up to 0.6. an actuator with substrate material having higher elastic modulus will produce larger displacement while for ratios beyond this ratio the situation is reversed. The causes for this kind of behaviour have been addressed. In all cases both force and displacement are found to be directly proportional to applied voltage.

La réduction du poids des avions est l'un des grands défis de l'industrie aérospatiale. Afin d'atteindre les objectifs ambitieux en matière de consommation de carburant et de réduction des émissions, des composites renforcés de fibres de carbone, ont été introduits sur le marché. Ces matériaux suscitent un intérêt croissant, néanmoins, ils possèdent une faible conductivité électrique, ne permettant pas de garantir une protection contre la foudre. Pour cette raison, les composites chargés de particules conductrices font l'objet d'activités de recherche en cours. L'objectif est le développement de composites multifonctionnels avec des propriétés électriques accrues. Pour l'heure, la matrice thermoplastique de référence est le PEEK mais ce polymère reste toutefois cher, et sa température d'élaboration élevée. Dans ce but, des matrices thermoplastiques, telles que le PEKK, sont à nouveau étudiées. Entre la matière première et la pièce finale, la matrice thermoplastique subit plusieurs cycles de traitement à haute température (imprégnation, consolidation, procédés d'assemblage) au cours desquelles sa capacité à cristalliser évolue sans cesse. Afin d'évaluer l'impact du procédé et des constituants du composite sur les propriétés du composite, la cristallisation a fait l'objet d'une attention particulière. Deux dispositifs expérimentaux complémentaires ont été utilisés afin de caractériser la cristallisation : une platine chauffante, permettant d'appliquer un cycle thermique et d'observer la cristallisation en microscopie optique ainsi que la calorimétrie différentielle à balayage. L'influence des fibres de carbone et des particules conductrices sur la cinétique de cristallisation a été évaluée. Une diminution des temps de cristallisation a été observée à travers l'augmentation du taux de germination. Les données recueillies ont servi à développer un modèle de cinétique de cristallisation identifié à travers une approche originale en se basant sur des données microscopiques et enthalpiques. Ce modèle permet de prédire les cinétiques de cristallisation des composites à matrice PEKK mais il ne permet pas de rendre compte de la microstructure finale engendrée. Or, cette dernière a un impact non négligeable sur les propriétés mécaniques comme cela a été prouvé à travers des essais de nano-indentation. Pour prévoir la microstructure finale, un modèle basé sur l'approche pixel coloring a été développé. L'influence des fibres de carbone a été introduite à travers la formation d'une phase transcristalline. Une bonne corrélation est constatée entre l'approche analytique, la simulation et les données expérimentales en termes de cinétique de cristallisation. Des caractérisations mécaniques et électriques ont été effectuées afin d'évaluer les performances de ces nouveaux matériaux. Sur les matériaux étudiés, la réponse mécanique n'est pas homogène comme observé sur des essais de traction suivis en stéréo-corrélation. L'étude de la santé matière montre l'existence de défauts, en particulier, à l'échelle de la microstructure. Afin de prendre en compte ces particularités, il est ainsi nécessaire de décrire plus finement la microstructure. Pour cela, la tomographie à rayons X a été utilisée afin de caractériser le composite. Les récents développements de cette technique permettent, en combinaison avec des outils de segmentation, de reconstruire une géométrie représentative du matériau. Cette géométrie est utilisée pour simuler le comportement mécanique ainsi que la cristallisation. Les simulations numériques d'un VER sont capables de prédire les propriétés d'un pli, puis celles du stratifié. Cette modélisation multi-échelle pourrait réduire le nombre et le coût des campagnes expérimentales. Ainsi, déterminer les propriétés de la structure finale en se basant sur des caractérisations et simulations à l'échelle de la microstructure est un enjeu scientifique et industriel stratégique. Ce travail constitue une contribution vers cette approche
Reducing aircraft weight is one of the major challenges facing the aerospace industry. In order to achieve the ambitious goals of fuel consumption and emission reduction, carbon-fiber reinforced composites have been introduced to the market. These materials are attracting increasing interest, however, they have low electrical conductivity to ensure protection against lightning strike. For this reason, composites filled with conductive particles are the subject of ongoing research activities. The objective is the development of multifunctional composites with enhanced electrical properties. Actually, the most used thermoplastic matrix is PEEK, but this polymer remains expensive, and its processing temperature is high. For this purpose, thermoplastic matrices, such as PEKK, are again studied. Between the raw material and the final part, the thermoplastic matrix undergoes several thermal steps with high temperature exposure (impregnation, consolidation, forming and assembly processes) during which its ability to crystallize evolves continuously. In order to evaluate the impact of the process and the composite constituents on its properties, crystallization has been the subject of particular attention. Two complementary experimental devices were used to characterize the crystallization. The heating stage, allows to apply a thermal cycle and observe the crystallization in optical microscopy and differential scanning calorimetry. The influence of carbon fibers and conductive fillers on the crystallization kinetics was evaluated. A decrease in crystallization times was observed through the increase of the nucleation rate. The collected data were used to develop a kinetic model identified through an original approach based on microscopic data. This model makes it possible to predict the crystallization kinetics of PEKK composites. Nevertheless, it does not make it possible to predict the final microstructure. However, the microstructure has a significant impact on mechanical properties as it has been proven through nano-indentation tests. To predict the final microstructure, a model based on the pixel coloring approach has been developed. The influence of carbon fibers has been introduced through the formation of a transcrystalline phase. A good correlation is found between the analytical approach, the simulation and the experimental data in terms of crystallization kinetics. Mechanical and electrical characterizations were performed to evaluate the performance of these new materials. On the studied materials, the mechanical response is not homogeneous as observed on tensile tests followed in stereo-correlation. The study of matter health shows the existence of defects, in particular, at the microstructure level. In order to take this particularity into account, it is thus necessary to describe the microstructure more finely. For this, X-ray tomography was used to characterize the composite. Recent developments in this technique allow, in combination with segmentation tools, to reconstruct a representative geometry of the material. This geometry is used to simulate the mechanical behaviour as well as the crystallization. The numerical simulations of an RVE are able to calculate the properties of a ply, then those of a laminate. This multi-scale modelling could reduce the number and cost of experimental campaigns. Thus, determining the properties of the final structure based on characterizations and simulation at the microstructure scale is a strategic scientific and industrial issue. This work is a contribution towards this approach

L’évaluation non destructive (NDT) des matériaux composites est compliquée en raison de la vaste gamme de défauts rencontrés (y compris délaminage, microfissuration, fracture de la fibre, retrait des fibres, fissuration matricielle, inclusions, vides et dommages aux chocs). La capacité de caractériser quantitativement le type, la géométrie et l’orientation des défauts est essentielle. La thermographie infrarouge (IRT), en tant que technique de diagnostic d’image, peut satisfaire le besoin industriel croissant de NDT&E. Dans la thèse, la thermographie par excitation optique et mécanique a été utilisée pour étudier différents matériaux composites, dont 1) des préformes sèches en fibres de carbone, 2) des composites de fibres naturelles, 3) des composites hybrides de basalte-fibres de carbone soumis à une charge d’impact (séquence de type sandwich et séquence d’empilement intercalé), 4) des défauts micro-dimensionnés dans un composite polymère renforcé de fibre de carbone (CFRP) en 3D avec une couture de type « joint en T », et 5) des peintures sur toile qui peuvent être considérées comme des matériaux composites. Une nouvelle technique IRT de thermographie de ligne par micro-laser (micro-LLT) a été proposée pour l’évaluation des porosités submillimétriques dans le CFRP. La microscopie de points par micro-laser (micro-LST) et la micro-vibrothermographie (micro-VT) ont également été présentées avec l’utilisation de microlentilles. La thermographie pulsée (PT) et la thermographie modulée « à verrouillage » (LT) ont été comparées à la tomographie par rayons X (TC) pour validation. Le C-scan ultrasonore (UT) et l’imagerie par ondes tera-hertziennes en onde continue (CW THz) ont également été réalisés à des fins comparatives. L’inspection par techniques thermographiques est une question ouverte à discuter pour le public scientifique. En fait, la thermographie par impulsions (PPT) basée sur la transformation de phase a été utilisée pour estimer la profondeur des dommages. Pour traiter les données thermographiques, on a également utilisé la reconstruction de signal thermographique de base (B-TSR), la thermographie des composants principaux (PCT) et la thermographie des moindres carrés partiels (PLST). Enfin, une analyse complète et comparative basée sur le diagnostic d’images thermographiques a été menée en vue d’applications industrielles potentielles.
Non-destructive testing (NDT) of composite materials is complicated due to the wide range off laws encountered (including delamination, micro-cracking, fiber fracture, fiber pullout, matrix cracking, inclusions, voids, and impact damage). The ability to quantitatively characterize the type, geometry, and orientation of flaws is essential. Infrared thermography (IRT), as an image diagnostic technique, can satisfy the increasing industrial need for NDT&E. In the thesis, optical and mechanical excitation thermography were used to investigate different composite materials, including 1) carbon fiber dry preforms, 2) natural fiber composites, 3) basalt-carbon fiber hybrid composites subjected to impact loading (sandwich-like and intercalated stacking sequence), 4) micro-sized flaws in a stitched T-joint 3D carbon fiber reinforced polymer composite (CFRP), and 5) paintings on canvas which can be considered as composite materials. Of particular interest, a new IRT technique micro-laser line thermography (micro-LLT) was proposed for the evaluation of submillimeter porosities in CFRP. Micro-laser spot thermography (micro-LST) and micro-vibrothermography (micro-VT) were also presented with the usage of a micro-lens. Pulsed thermography (PT) and lock-in thermography (LT) were compared with x-ray computed tomography (CT) for validation. Ultrasonic C-scan (UT) and continuous wave terahertz imaging (CW THz) were also conducted for the comparative purpose. The inspection by thermographic techniques is an open matter to be discussed for the scientific audience. In fact, pulse phase thermography (PPT) based on phase transform was used to estimate the damage depth. Basic thermographic signal reconstruction (B-TSR), principal component thermography (PCT) and partial least squares thermography (PLST) (another more recent advanced image processing technique) were also used to pro-cess the thermographic data. Finally, a comprehensive and comparative analysis based on thermographic image diagnostics was conducted in view of potential industrial applications.

Les matériaux composites Carbone/Carbone sont utilisés dans l’industrie aéronautique ainsi que dans l’aérospatial du fait de leurs excellentes propriétés thermomécaniques, de la température ambiante jusqu’à de très hautes températures (< 3000°C). Cependant l’évolution de ces propriétés à hautes températures est peu connue, notamment sous des sollicitations de type freinage auxquelles ces composites peuvent être soumis pour des applications aéronautiques ou dans les sports mécaniques.L’objectif de ce travail était donc d’étudier le comportement mécanique d’un composite C/C stratifié sous des sollicitations mécaniques pouvant intervenir dans une situation de freinage. Ainsi, la compression et le cisaillement ont été particulièrement étudiés, afin de déterminer l’évolution des mécanismes d’endommagement en fonction de la température sous ces modes de chargement. Afin de mener à bien cette étude, plusieurs aspects expérimentaux ont été abordés, tels que la géométrie et la taille des éprouvettes, de même que les difficultés de mesures liées à la réalisation des essais mécaniques à hautes températures. C’est ainsi que des essais originaux de cisaillement interlaminaire à chaud ont pu être réalisés. Parallèlement à ces essais, la microstructure du matériau a été étudiée in-situ et post-mortem par une analyse multi-échelle (à l’échelle des strates, des torons et au niveau des fibres à l’intérieur des torons). L’évolution des propriétés mécaniques a été mise en relation avec les observations microstructurales pour les différents modes de chargement étudiés (compression « Z », compression « XY » et cisaillement interlaminaire), afin de proposer des scenarii d’endommagement du matériau en fonction de la température. Grâce à cette approche, le rôle majeur des dilatations thermiques différentielles des torons sur le frettage des aiguilletages a pu être mis en évidence pour des températures allant jusqu’à 1500°C. Pour des températures supérieures, des effets de plasticité ont été identifiés
Carbon/Carbon composites are used in aeronautics and space industries for their excellent thermomechanical properties, from room temperature to very high temperatures (up to 3000°C). Nevertheless, these properties and their evolution at elevated temperatures are not known well enough, specifically for braking-like solicitations such as plane braking or motorsport braking.The main objectives of this work was to study the mechanical behavior of this composite under mechanical solicitations that may occur during a braking situation. Thereby, compressive and shear behavior were studied in particular, in order to determine the evolution of the damage mechanisms depending on the temperature for these loading modes. In order to lead this study successfully, various experimental aspects have been approached, such as sample geometry, as well as measurements issues due to the mechanical testing at high temperatures. This is how original mechanical testing of the interlaminar shear behavior have been performed. Concurrently with these tests, the material microstructure has been studied in-situ and post-mortem with a multi-scale approach (at ply level, at yarn level and at fiber level inside the strands). The evolution of the mechanical properties has been linked to the microstructure evolution for the different loading modes (Z-compression, XY-compression and interlaminar shear) in order to propose damage scenario of the material as a function of the temperature. This approach allowed us to understand the major role of the thermal differential dilatations of the yarn on the shrinking of the needles for temperatures up to 1500°C. For temperatures higher than 1500°C, plasticity effects have been identified

L'objectif de cette thèse est de développer un procédé peu coûteux d'élaboration en continu, sous air et à pression atmosphérique, de fils composites à fibres longues de carbone (50% en volume) incorporées dans une matrice daluminium. Cela passe nécessairement par la maîtrise de deux problèmes inhérents au couple C/Al : le non mouillage des fibres par laluminium liquide en dessous de 900°C et la formation de carbures fragiles à l'interface carbone/aluminium liquide. L'activation chimique du mouillage est assurée par un sel fluoré à base de potassium et de zirconium. Il s'agit de dissoudre la couche d'alumine et d'engendrer localement une réaction exothermique suffisante à l'interface C/Al pour promouvoir le mouillage.
La mèche de fibre (Torayca T700S-12K) étant commercialisée avec 1% en masse densimage, une première étape a consisté en l'élimination de cette couche d'époxy par dégradation thermique sous air. D'une part, il a été construit un diagramme pour le choix des paramètres de désensimage (température du four, vitesse de défilement) minimisant la perte des propriétés mécaniques des fibres. D'autre part, la cinétique du phénomène de désensimage a été établie afin de prévoir le désensimage " dynamique " sur le pilote en connaissant le profil thermique de la mèche pour les conditions opératoires données.
La mèche est ensuite trempée dans une solution aqueuse saturée d'un sel fluoré à 95°C puis séchée sous air, dans la seconde étape, dite de traitement au flux pour laquelle les paramètres opératoires sont la vitesse de défilement et la composition du flux. Il s'est agi ici d'étudier, plus particulièrement, le vieillissement de la solution aqueuse et la qualité du dépôt de cristaux sur la mèche (morphologie, répartition et quantité). D'une manière générale, le coeur de la mèche est beaucoup moins bien traité que sa surface. Laction de plusieurs composés fluorés sur le mouillage des fibres par l'aluminium a été regardé. Un schéma réactionnel s'appuyant essentiellement sur une étude ATD a mis en évidence le rôle favorable de l'oxydation par l'air de l'aluminium natif pour l'imprégnation du coeur du composite. Comparée à la toute première réaction flux/alumine, cest principalement la réaction flux/aluminium liquide qui engendre lélévation suffisante de température permettant dinitier l'infiltration.
Enfin, la mèche passe par un bain d'aluminium liquide (99,7% en masse) à 710°C sous air : c'est l'étape d'infiltration dont les paramètres sont la température du bain et la vitesse de défilement. Dans cette dernière étape, le but était de définir la microstructure et les propriétés du fil composite élaboré selon les conditions optimales. Des observations fines au MET indiquent la présence de précipités Al3Zr et Al4C3 à linterface fibre/matrice. Cette adhésion chimique contribue à limiter la tenue mécanique du fil tout comme la distribution inhomogène des fibres, la présence de porosités naturelles et de cryolithe solidifiée. Le meilleur fil composite a été obtenu pour une vitesse lente (1m/min) et une température moyenne du bain (710°C)°. Sa résistance à la traction ne dépasse pas 520Mpa pour une fraction volumique de fibres de 40%, ce qui suggère de minimiser les dégradations diverses subies par le renfort dans les trois étapes et les défauts liés à l'infiltration réactive.

Ce mémoire est consacré à l'étude de matériaux composites innovants du type Si/Intermétallique/Al/C utilisés comme matériaux d'électrodes négatives pour les batteries lithium ion. L'objectif de ces travaux est d'optimiser un matériau de composition 20Ni-48Sn-20Si-3Al-9C ayant été développé auparavant pour obtenir les meilleures performances électrochimiques. Ce matériau se présente sous la forme de nanoparticules de silicium enrobées par une matrice submicrométrique. Plusieurs stratégies ont été mises en œuvre : optimisation des teneurs en carbone et en silicium, influence de l'état de surface du silicium sur les propriétés électrochimiques et remplacement de l'intermétallique Ni3+xSn4 par d'autres alliages : un composé zinc-aluminium Al0, 23Zn0,77 et deux intermétalliques Cu6Sn5 et CoSn. Les composés intermétalliques ont été synthétisés par métallurgie des poudres et les matériaux composites par mécanosynthèse. Les propriétés chimiques et structurales de ces matériaux ont été déterminées par microsonde de Castaing, diffraction des rayons X et microscopies électroniques. Les caractérisations électrochimiques ont été réalisées en demi-cellules (Swagelok et bouton) par cyclage galvanostatique et par voltamétrie cyclique. Ce mémoire détaille l'influence des paramètres étudiés sur les propriétés structurales. Une large étude a notamment été menée sur l'influence des teneurs en carbone et en silicium sur l'obtention d'une matrice homogène, une condition nécessaire pour atteindre de bonnes performances électrochimiques. Le même type d'étude a été mené sur l'influence de l'effet de surface du Si et la nature de l'alliage utilisé. Il a par exemple été montré de meilleurs résultats électrochimiques pour les intermétalliques présentant une réactivité modérée avec le silicium lors du broyage mécanique. Les meilleures performances ont été obtenues pour la composition Ni0.13Sn0.15Si0.26Al0.04C0.42. Ce composite présente une capacité de 650 mAh.g-1 pendant 1000 cycles. L'utilisation d'un silicium carboné en surface améliore la stabilité en cyclage de la SEI même si son utilisation reste à optimiser
This study focuses on the optimization of innovative composite materials Si/Intermetallic/Al/C used as negative electrode in lithium-ion batteries. The aim of this work is optimization of the composition for the material (20Ni-48Sn-20Si-3Al-9C) to improve its electrochemical performances. All materials are made up of silicon nanoparticles embedded in a sub micrometrical matrix. Several issues have been studied in this essay: optimization of the silicon and carbon contents, influence of the silicon surface composition, and substitution of the former intermetallic Ni3+xSn4 by other ones: zinc aluminium compound Al0,23Zn0,77 and two intermetallics Cu6Sn5 et CoSn. Metallic compounds and composites have been synthesised by powder metallurgy and mechanical alloying, respectively. Their chemical and structural properties have been determined by electron probe microanalysis, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Electrochemical characterisations have been carried out by galvanostatic cycling and cyclic voltammetry in coin and Swagelok half cells. This report details the influence of the studied parameters on the structural properties of the composite materials. A large study was devoted to the influence of carbon and silicon contents on the achievement of a homogeneous matrix, which is mandatory to get good electrochemical performances. Influence of the composition of silicon surface and intermetallic on the microstructure and electrochemical properties of the composites was also studied. Thus, we have shown that intermetallics reacting moderately with Si during mechanical alloying have better electrochemical properties. The best electrochemical properties have been obtained for the nominal composition Ni0.13Sn0.15Si0.26Al0.04C0.42. This material provides a reversible capacity of 650 mAh.g-1 during 1000 cycles. The use of carbon coated silicon improves the stability of the SEI during cycling even if this composite still has to be optimized

Le travail est réalisé en collaboration avec le centre d'études de Gramat. Le but est de fournir des outils numériques fiables de prévision de la tenue aux chocs de structures en composites 3D C/C. Pour des sollicitations de quelques microsecondes, une modélisation méso rend bien compte des observations expérimentales. Le traitement numérique d'un tel modèle conduit à des problèmes de taille importante. Nous développons une méthode de sous structuration mixte par interface, itérative, globale en temps et en espace, paramétrée par des directions de recherche qu'il faut optimiser. Les directions de recherche constantes sont peu efficaces. Pour des directions de recherche variables, un algorithme de gradient conjugué est utilisé et optimisé pour réduire le nombre d'itérations. La méthode est validée sur un exemple 1D 1/2. Le cas d'un calcul 3D d'impact plaque/plaque est également traité grâce à l'utilisation du calcul parallèle.

L’utilisation d’un composite Carbone/Carbone 2D est envisagée pour des pièces de structure, travaillant entre 150 et 400°C, dans l’aéronautique civile. Dans ce domaine de température, la durabilité de ces matériaux n’est pas connue car ils n’ont jamais été développés pour de telles applications. Une première approche a permis de corréler la réactivité chimique des constituants élémentaires (fibres et matrices) à leur état d’organisation structurale. Les vieillissements réalisés sur matériau composite ont ensuite mis en évidence qu’un faible taux d’oxydation pouvait conduire à un abaissement significatif des propriétés mécaniques résiduelles. Les fissures et les décohésions consécutives au procédé d’élaboration conduisent à une oxydation préférentielle du composé le plus réactif et à la ruine prématurée du composite par délaminage. L'évolution des propriétés de ce matériau sur de longues durées est finalement discutée afin d’évaluer sa capacité à remplacer les matériaux métalliques dans des pièces aéronautiques
A 2D Carbon/Carbon composite is envisaged for structural parts, operating between 150 and 400°C, in civil aircraft. In this temperature range, the durability of these materials remains unknown because they have never been developed for this kind of applications. A first approach allowed us to correlate the chemical reactivity of the elemental constituents (fiber and matrix) to their structural organization. Then, thermal ageing tests performed on the composite material have demonstrated that a low rate of oxidation could be responsible to a significant reduction of residual mechanical properties. Cracks and fiber/matrix debonding resulting to the elaboration process create an extended pathway to a preferential oxidation of the most reactive compound. This latter is followed by a premature failure by delamination. The reduction of the material properties over long periods is finally discussed in order to evaluate its ability to replace metallic materials in aircraft structural parts

Submitted by Mery Piedad Zamudio Igami (mery@ipen.br) on 2017-03-10T14:01:35Z No. of bitstreams: 1 22055.pdf: 3779679 bytes, checksum: 1767805f3b1e9fdf7bf631de29d2a79c (MD5)
Made available in DSpace on 2017-03-10T14:01:35Z (GMT). No. of bitstreams: 1 22055.pdf: 3779679 bytes, checksum: 1767805f3b1e9fdf7bf631de29d2a79c (MD5)
Os eletrocatalisadores quartenários PtSnAuRh/C e PtRuAuRh/C foram preparados nas proporções 50:40:5:5, 60:30:5:5, 70:20:5:5, 80:10:5:5, 90:4:3:3 e para as composições terciárias PtSnAu/C, PtSnRh/C, PtRuAu/C, PtRuRh/C preparados na proporção atômica 50:45:5 com (20% em massa) pelo método da redução por álcool utilizando H2PtCl6.6H2O, RuCl3·xH2O, SnCl2.2H2O, HAuCl4.3H2O e RhCl3.xH2O, como fonte de metais e carbono Vulcan XC72 como suporte e, por último, etileno glicol como agente redutor. Os eletrocatalisadores obtidos foram caracterizados fisicamente por difração de raios-X (DRX), energia dispersiva de raios X (EDX) e microscopia eletrônica de transmissão (MET). As análises por EDX mostraram que as razões atômicas dos diferentes eletrocatalisadores, preparados pelo método da redução por álcool, foram similares às composições nominais de partida indicando que esta metodologia é eficiente para a preparação destes eletrocatalisadores. Em todos os difratogramas para os eletrocatalisadores preparados observa-se um pico largo em aproximadamente 2θ = 25°, o qual é associado ao suporte de carbono e quatro outros picos de difração em aproximadamente 2θ = 40°, 47°, 67° e 82°, que por sua vez são associados aos planos (111), (200), (220) e (311), respectivamente, da estrutura cúbica de face centrada (CFC) de platina. Os resultados de difração de raios X apresentaram tamanhos médios de cristalitos entre 2,0 e 5,2 nm para PtSnAuRh/C, PtSnAu/C, PtSnRh/C e 2,0 a 2,6 nm para PtRuAuRh/C, PtRuAu/C, PtRuRh/C. Os estudos para a oxidação eletroquímica do etanol em meio ácido foram realizados utilizando as técnicas de voltametria cíclica e de cronoamperometria em uma solução 0,5 mol.L-1 H2SO4, + 1,0 mol.L-1 de C2H5OH. As curvas de polarização obtidas na célula a combustível unitária, alimentada diretamente por etanol, estão de acordo com os resultados de voltametria e cronoamperometria constatando o efeito benéfico da adição do ouro e ródio na composição dos eletrocatalisadores.
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Ce travail s'inscrit dans le cadre du développement des piles à combustible à céramique conductrice protonique (PCFC) opérant dans le domaine de température 400 – 600 °C et concerne l'optimisation des composants de la cellule élémentaire. L'optimisation du matériau électrolytique consiste à rechercher le meilleur compromis entre stabilité chimique et conductivité élevée. Le matériau BaCe0.9Y0.1O2.95, synthétisé par la voie flash combustion, présente la conductivité protonique la plus élevée (10-2 S.cm-1 à 600 °C) mais réagit fortement avec le CO2. La substitution partielle du cérium par le zirconium (BCZY) et le niobium (BCYN30) a conduit à une amélioration significative de la stabilité chimique tout en conservant une conductivité de l'ordre de 5 × 10-3 S.cm-1 à 600 °C. En ce qui concerne les électrodes, l'enjeu est de développer des matériaux présentant une conductivité électronique élevée, une porosité suffisamment importante et une bonne tenue mécanique. L'approche a consisté en la mise au point de stratégies d'élaboration (synthèse en une étape, utilisation de porogène) permettant le contrôle de la microstructure des matériaux anodiques afin de minimiser les résistances spécifiques surfaciques (ASR). Comme dans le cas des SOFC, les matériaux cathodiques sont conducteurs mixtes ionique-électronique (MIEC). Le développement de cathodes composites MIEC-électrolyte a permis de réduire significativement les ASR. Les tests en pile de cellules élémentaires PCFC ont révélé que les performances dépendaient essentiellement de la nature et de l'épaisseur du matériau électrolytique et de la mise en œuvre de matériaux d'électrode de morphologie contrôlée et architecturée. L'optimisation des assemblages a permis d'accroître sensiblement les performances (156 mW.cm-2 à 600 °C)
Materials components for a Proton Conducting Fuel Cell (PCFC) operating in the 400 – 600 °C temperature range have been optimised. Electrolyte material optimisation involved finding the best compromise between chemical stability and conductivity. BaCe0.9Y0.1O2.95, synthesised by flash combustion, exhibits the highest protonic conductivity (10-2 S.cm-1 at 600 °C) but reacts strongly with CO2. Partial substitution of cerium by zirconium (BCZY) and niobium (BCYN30) led to a significant improvement of the chemical stability without drastic effect on the conductivity (5 × 10-3 S.cm-1 at 600 °C). The aim for the electrodes is to develop materials which exhibit high electronic conductivity, sufficient degree of porosity and good mechanical properties. The approach comprised the development of elaboration strategies (one-step synthesis, use of porogen) that allow the control of microstructure in order to minimize area specific resistances (ASR) at the anode. As in the case of SOFCs, cathodic materials are mixed ionic-electronic conductors (MIEC). Development of composite cathodes MIEC-electrolyte led to a significant reduction of ASR. PCFC single cell tests showed that performance was mostly dependent on electrolyte thickness and composition, and on the characteristics of nanostructured electrodes with controlled architecture and porosity. Optimisation of assemblies led to fuel cells performances of 156 mW.cm-2 at 600 °C

Ni/TiC metal matrix composites have been processed using the laser engineered net shaping (LENS) process. As nickel does not form an equilibrium carbide phase, addition of a strong carbide former in the form of titanium reinforces the nickel matrix resulting in a promising hybrid material for both surface engineering as well as high temperature structural applications. Changing the relative amounts of titanium and carbon in the nickel matrix, relatively low volume fraction of refined homogeneously distributed carbide precipitates, formation of in-situ carbide precipitates and the microstructural changes are investigated. The composites have been characterized in detail using x-ray diffraction, scanning electron microscopy (including energy dispersive spectroscopy (XEDS) mapping and electron backscatter diffraction (EBSD)), Auger electron spectroscopy, and transmission (including high resolution) electron microscopy. Both primary and eutectic titanium carbides, observed in this composite, exhibited the fcc-TiC structure (NaCl-type). Details of the orientation relationship between Ni and TiC have been studied using SEM-EBSD and high resolution TEM. The results of micro-hardness and tribology tests indicate that these composites have a relatively high hardness and a steady-state friction coefficient of ~0.5, both of which are improvements in comparison to LENS deposited pure Ni.

Non-destructive testing (NDT) of glass-fibre reinforced polyester (GRP) composite materials has been becoming increasingly important due to their wide applications in engineering components and structures. Electronic Speckle Pattern Interferometry (ESPI) has promising potential in this context because it is a non-contact, whole-field and real-time measurement system. This potential has never been fully exploited and there is only limited knowledge and understanding available in this area. This reality constrains the wide popularity and acceptance of ESPI as a novel NDT technique. Therefore it is of considerable importance to develop an understanding of the capability of ESPI with respect to damage evaluation in GRP composite materials. The research described in this thesis is concerned with an investigation into the applicability of ESPI in the NDT of GRP composite materials. Firstly, a study was carried out to determine excitation techniques in terms of practicality and effectiveness in the ESPI system. Three categories of defects were artificially introduced in GRP composite materials, namely holes, cracks and delaminations each with different geometrical features. ESPI was then employed to evaluate the three kinds of defects individually. It has been found that cracks and holes on back surfaces can be defined when the technique is used in conjunction with thermal excitation. Internal Temperature Differential (ITD) induced fringe patterns were more efficient than External Thermal Source (ETS) induced fringe patterns with regard to detecting the presence of holes and cracks. In the case of delamination, ESPI was found to be capable of detecting the damage when used in combination with mechanical excitation originating from a force transducer hammer. The geometrical features and magnitudes of delaminations were also established as being quantifiable. The validation of ESPI as an NDT technique was carried out in an attempt to establish a better understanding of its suitability and have more confidence in its applications. Four damaged specimens were Subjected to ESPI examination in conjunction with visual inspection, ultrasonic C-scan and sectioning techniques. The geometrical features and magnitudes of damage evaluated using ESPI showed a good correlation with those evaluated by conventional techniques. Poor visibility and readability is an inherent problem associated with ESP! due to an overlapping between the noise and signal frequencies. An improvement of image quality is expected in an attempt to achieve a wide acceptance of ESPI as a novel NDT technique. It has also been demonstrated that this problem can be tackled using optical phase stepping techniques in which optical phase data can be extracted from the intensity fringes. A three-frame optical phase stepping technique was employed to produce the "wrapped" and "unwrapped" phase maps which are capable of indicating internal damage with high visibility and clarity. Finally ESPI was practically employed to evaluate damage in GRP composites introduced by quasi-static and dynamic mechanical loading. It was found that ESP! was capable of monitoring the progressive damage development of specimens subjected to incremental flexural loading. The initial elastic response, damage initiation, propagation and ultimate failure of specimens were clearly characterised by the abnormal fringe pattern variations. In a similar manner, ESPI was employed to evaluate the low velocity falling weight impact induced damage. A correlation was established between the magnitude of damage and the impact event parameters as well as the residual flexural properties.

Les travaux de cette thèse ont été menés en collaboration entre l’UCCS et l’entreprise Safran Landing Systems (Safran LS) et ont porté sur l’élaboration d’une nouvelle voie de protection anti-oxydation (PAO) pour des matériaux composites carbone/carbone (C/C) commercialisés comme composants de freins d’avion. Le principe de cette PAO innovante est basé sur une barrière de diffusion amorphe silicatée dite interne car appliquée sous la surface du composite C/C, combinée à une phase aluminophosphate qui joue un rôle piège pour les catalyseurs d’oxydation. Cette PAO est formée par l’imprégnation des porosités du composite C/C par un mélange de précurseurs liquide, suivi d’un traitement thermique. Plusieurs voies d’imprégnation du composite C/C ont été explorées : (i) une imprégnation séquentielle du composite C/C avec une première couche d’aluminophosphate et une deuxième couche de phase vitreuse (ou inversement) ou (ii) une imprégnation simultanée du matériau avec un mélange combinant les précurseurs des deux phases. Dans un premier temps, une étude des évolutions chimiques (par RMN, micro-tomographie X synchrotron et DRX) et morphologiques (par MEBE-HT) à haute température de l’aluminophosphate a été effectuée. Cette étude a permis de comprendre l’origine de la perte d’efficacité de l’aluminophosphate après un flash thermique à 1200 °C. Puis, pour les deux voies d’imprégnation que nous avons développées, des tests de performance des PAO ont été menées en condition industrielle et des caractérisations (par RMN, MEBE-HT, analyses thermiques ATD, ATG, HSM) ont permis de relier ces performances à la structure chimique des PAO. Nous avons montré que certaines formulations de PAO séquentielles permettent d’améliorer les performances anti-oxydation en comparaison aux performances d’une PAO industrielle basée seulement sur de l’aluminophosphate
This work has been developed as part of a collaboration between the UCCS laboratory and the Safran Landing Systems (Safran LS) company. The aim of this work was to elaborate a new anti-oxidation protection (AOP) for carbon/carbon (C/C) composites marketed as airplane brakes components. The principle of this innovative AOP is based on a so-called internal silicate vitreous diffusion barrier because it is applied under the surface of the C/C composite, combined with an aluminophosphate phase which has a trapping role for the oxidation catalysts. This PAO is formed by impregnating the porosities of the C/C composite with a liquid mixture of precursors, followed by a heat treatment. Several ways of impregnating the C/C composite have been explored: (i) a sequential impregnation of the C/C composite with a first layer of aluminophosphate and a second layer of vitreous phase (or vice versa) or (ii) a simultaneous impregnation of the material with a mixture combining the precursors of the two phases. First, a study of the chemical (by NMR, X-ray micro-tomography synchrotron and XRD) and morphological (by MEBE-HT) evolutions at high temperature of the aluminophosphate was carried out. This study allowed to understand the origin of the loss of efficiency of the aluminophosphate based AOP after a thermal flash at 1200 °C. Then, for the two impregnation routes that we have developed, AOP performance tests were carried out in industrial conditions and characterizations (by NMR, MEBE-HT, thermal analyzes ATD, ATG, HSM) made it possible to link these performances to the chemical structure of the AOP. We have shown that some sequential AOP formulations improve anti-oxidation performance compared to the performance of an industrial AOP based only on aluminophosphate

La sensibilisation accrue aux questions environnementales concerne aujourd'hui les structures aéronautiques en termes d'impact environnemental et traitements de fin de vie. Dans cette optique,la possibilité de remplacer, dans les composites à matrice organique (CMO) utilisés pour des applications aéronautiques, leur matrice thermodurcissable non recyclable par une matrice thermoplastique recyclable est étudiée. En outre, les polymères thermoplastiques, tels que le PEKK, ont la possibilité d'être utilisés dans des structures plus chaudes (par exemple le pylône d'un avion), faisant l'objet de sollicitations de longue durée (fluage). Les températures de service de ces structures plus élevées que celles de la température de transition vitreuse du PEKK : il en découle, dans le matériau, une perte de propriétés due au changement d'état de solide à caoutchoutique, et éventuellement l'activation de phénomènes de cristallisation etde dégradation, qui pourraient également interagir. Ce travail vise à identifier et à modéliser ces mécanismes caractérisant le comportement du PEKK, dans ces conditions extrêmes particulières.Ceci est réalisé à partir de l'analyse des résultats des essais thermomécaniques, physico-chimiques et thermomécaniques couplés avec l’oxydation. Le modèle analytique 1-D du comportement duPEKK qui résulte de l’analyse des essais est étendu en 3-D et implémenté dans une méthode d'homogénéisation/localisation semi-analytique multi-échelle pour simuler le comportement dans mêmes conditions de composites stratifiés à matrice PEKK, en faisant varier l'orientation des plis et la séquence d'empilement
The nowadays increased awareness towards environmental issues concerns aircraft structures in terms of environmental impact and end-of-life disposal. In this optics, the possibility of replacing in the organic matrix composites (CMO) employed for aircraft applications the non-recyclable thermosetting matrix with a recyclable thermoplastic one is investigated. Moreover, thermoplastic polymers, such PEKK, have the possibility of being employed in warmer structures (e.g. the aircraft pylon), undergoing long duration solicitations (creep).The service temperatures for those structures are higher than the PEKK glass transition temperature, provoking, in the material, a loss of properties deriving from a change of state from solid to rubber, and possibly the activation of crystallization and degradation phenomena, which could also interact. This work aims to identify and model the mechanisms characterizing PEKK behavior, under the structure operative service conditions. This is achieved from the analysis of the results of thermomechanical, physical-chemical and coupled thermomechanical/oxidation tests. The resulting 1-D analytical model of the PEKK behavior, is extended in 3-D and implemented in a multi-scale semi-analytical homogenization / localization method to simulate PEKK based composites under the same conditions, varying the plies orientation and stacking sequence

Dans ce travail, nous décrivons les différentes formes, la structure, les propriétés et la croissance catalytique de nanotubes et nanofibres de carbone (Chapitre I). L'hydroxyapatite a été utilisée comme support de la phase active pour la synthèse de nanotubes de carbone multi-feuillet (MWCNTs) et de nanofibres de carbone (CNFs-H) par la technique de dépôt chimique en phase de vapeur catalytique (C-CVD) en lit fluidisé (Chapitre II). Après l'élimination du support par un simple lavage à l'acide chloridrique dilué, une étude théorique et expérimentale de l'oxydation de la surface de nanotubes de carbone par un traitement à l'acide nitrique a permis d'une part d'identifier et de quantifier les groupes formés à la surface de nanostructures carbonées et d'autre part de proposer un mécanisme pour la formation de ces groupes (Chapitre III). Les matériaux résultants après génération des fonctions carboxyliques de surface ont été utilisés comme support de catalyseur. L'hydrogénation du p-halogénonitrobenzène a été choisit comme réaction modèle pour comparer les performances catalytiques de catalyseurs à base de ruthénium en fonction de la nature du support utilisé, MWCNTs ou CNFs-H. L'influence de certains paramètres tels que la température, la nature du substrat et un traitement thermique du catalyseur (activation) est présentée. Une explication des performances catalytiques est proposée après caractérisation du catalyseur par MET, TPD, TPR et PZC (Chapitre IV). Les nanostructures carbonnées produites et caractérisées ont été utilisées comme charge de renforcement d'hydroxyapatites connue comme biomatériaux. Nous avons étudié en particulier la capacité de germination du phosphate octocalcique par la méthode de croissance cristalline à composition constante (C4) (Chapitre V)
In this work, we describe the different forms, the catalytic growth, the structure and properties of carbon nanotubes and nanofibres (Chapter I). Hydroxyapatite was used as catalyst support for the synthesis of multi-walled carbon nanotubes (MWCNTs) and nanofibres (CNFs) by catalytic chemical vapour deposition (C-CVD) in a fluidized bed reactor (Chapter II). After support removal by washing with diluted hydrochloric acid, a theoretical and experimental study of surface oxidation of carbon nanotubes by nitric acid treatment has been performed. It allows to identify and quantify the groups formed on the surface of carbon nanostructures and also to propose a mechanism for the formation of these groups (Chapter III). The functionalized nanotubes and nanofibers have been used as supports for heterogeneous catalysis. The hydrogenation of p-halonitrobenzene was used as model reaction to compare the catalytic performances of ruthenium supported on MWCNTs or CNFs-H catalysts. The influence of experimental parameters such as temperature, nature of the substrate and prior heat treatment (activation) of the catalyst on the catalytic activity and selectivity is presented. The catalytic performances have been correlated to the structure of the catalyst as determined from TEM, TPD, TPR and PZC analysis (Chapter IV). The carbon nanostructures produced have also been used as reinforcement fillers for hydroxyapatite-nanotube composites. We have studied in particular, the germination of octacalcium phosphate crystals under conditions of constant solution composition on the surface of the composite (Chapter V)

Carbon-fiber/SiC-matrix composites are under development for applications in hypersonic vehicles due to their exceptional capabilities at high temperatures. As a subset of these materials, textile-based composites are of particular interest because they offer the possibility of accommodating complex geometries and features in engineering components. Among the numerous obstacles hindering the widespread adoption of these composites, two are addressed in the present work: (i) the incomplete understanding of the influence of textile architecture on thermoelastic properties, damage initiation and failure, and (ii) the lack of robust computational tools for predicting their thermomechanical performance at the appropriate length scales. Accordingly, an experimental study is performed of the thermal and mechanical properties of several prototypical textile C/SiC composites with various fiber architectures. In turn, the experimental results are used to guide the development of computational tools for predicting composite response that explicitly account for fiber architecture.

Textile architecture is found to influence composite response at four length-scales: the panel, the coupon, the tow, and the sub-tow. At the panel scale, distortions to the architecture introduced during weaving or handling of the fabric influence the packing density and the relative rotation of tows. Even when large distortions are intentionally introduced their influence on mechanical response is minimal. At the coupon scale the tow architecture has the largest effects on composite mechanical response. Young's modulus, ultimate tensile strength, and strain to failure are all influenced. Changes in each of these are a function of tow shape, tow anisotropy, and the degree of constraint provided by the matrix. At the tow scale, architecture effects give rise to heterogeneity in measured surface strains under both tensile and thermal loading. Methods for the calibration of tow-scale elastic and thermoelastic properties were developed to enable simulation of these effects with a geometrically-accurate virtual model. Virtual tensile and thermal tests using this model have indicated that interaction between tows has an important influence on local strains. At the sub-tow scale, architecture effects influence the location of matrix cracking. Simulations of the cooling cycle following matrix processing predict that matrix cracks should develop in the matrix above underlying tows due to thermal expansion mismatch between the tows and the matrix. This is consistent with experimental observations. Two methods are presented to extend the virtual tests to explicitly simulate the onset and evolution of these cracks.

Carbon-carbon (C/C) composites are notable among engineering materials in aerospace and defense industries possessing excellent specific mechanical, thermal, frictional and wear properties. C/C maintain their properties at temperatures where most of the high end alloys give in, and maintain their dimensional stability at temperatures above 2000 oC. C/C is frequently used in aircraft and automotive industries as brake materials. However, frictional performance is dependent on various parameters: microstructure, fiber type, fiber orientation distribution, fiber/matrix interfacial bond, heat treatment, and oxidation. The present study in dissertation provides an insight into the impact of heat treatment, and oxidation on microstructure, mechanical and thermal properties. The heat treatment (performed at 1800, 2100, 2400 oC in argon) of two-directional (2-D) pitch-fiber with charred resin carbon matrix, and three-directional (3-D) PAN-fiber with CVI carbon matrix influenced microstructure, mechanical and thermal properties. Microstructure characterized by polarized light microscopy (PLM), XRD, and Raman spectroscopy changed with increasing heat treatment temperature. The RL microstructure of 3-D C/C progressively highly organized, whereas ISO microstructure of 2-D C/C's charred resin hardly organized into an ordered structure as evident from Raman spectroscopy and Raman profiling of polished samples. Pitch-fiber organized more than the ISO microstructure of charred resin matrix. On the other, PAN-fiber became more ordered, but was organization was lower than pitch-fiber. Thermal conductivity increased for both (2-D, 3-D C/C) materials in comparison to non-heat treated (NHT) C/Cs. Thermal conductivity of oxidized samples decreased significantly than non-oxidized samples. In-plane thermal conductivity of 3-D C/C was much higher than that of 2-D C/C, and was attributed to the rough laminar (RL) microstructure of carbon matrix and continuous PAN-fiber when compared to the short pitch-fiber in isotropic (ISO) carbon matrix. Mechanical properties (tensile, compressive, shear) deteriorated with increasing heat treatment. However, statistical analysis using ANOVA showed that there was not any significant difference between the NHT and heat treated C/C materials in terms of mechanical strength, modulus, failure strain and fracture energy. The oxidized samples of heat treated (1800/2100/2400 oC) C/C materials (2-D, 3-D) showed an appreciable decrease in mechanical strength and modulus than non-oxidized samples, with progressively heat treated C/C becoming more oxidation resistant than NHT C/C. The study demonstrated a highly inhomogeneous nature of C/C, and sample size is a very important parameter in governing mechanical properties. Since, the slightest change in the dimension of samples could bring about a radically different outcome in terms of mechanical properties, and can hardly be representative of the bulk properties. Therefore, in order to obtain a good estimate of the bulk properties, the sample size must be comparable to the bulk material. The research nonetheless showed the impact of sample size in estimating the mechanical properties of bulk properties, which are highly significant after statistical analysis, and, therefore, it must be taken into account to understand the processing-structure-property-analysis relationships.

We have studied the process of interaction between the components in the system «β-SiO2–Fe3O4–Na2O» in the temperature range from 20 to 1100 °C. Nano-reinforced composite building materials were developed on the base of quartz raw material. Developed materials are produced by low-temperature cal-cining technology. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35246

MAX phase ceramics are ternary ceramics with both metallic and ceramic properties. The existing backing materials in grinding wheels can be made of ceramics or metals. In these applications, ceramics have the disadvantage of low toughness, and most metals have the disadvantages of relatively high density and intolerance to some very high temperatures. The MAX phases have a combination of the main advantages of both metals and ceramics: they are soft and machinable yet also heat-tolerant, strong and lightweight. Cubic boron nitride (c-BN) is a widely used abrasive in grinding wheels, which is exceeded in hardness only by diamond. Composites of c-BN and selected MAX phases may result in materials of some interesting and useful properties for application in industry. Firstly MAX phases, Ti₃SiC₂; Ti₃AlC₂ and Ti₂AlC were synthesised, then reaction couples of MAX-cBN are made in order to investigate the best conditions for composite synthesis, and to analyse the interfacial phases which occur. Finally, the MAX-cBN composites were synthesised from the reaction couple studies. The following results were obtained: 1. Samples synthesised to obtain Ti₃AlC₂ were largely composed of the Ti₂AlC, and thus synthesis of the Ti₃AlC₂ MAX phase was deemed unsuccessful. 2. Nearly pure samples of Ti₂AlC and Ti₃SiC₂ were successfully synthesised with high densities, 99.16% and 98.21%, respectively, of the theoretical density. 3. Reaction couple studies revealed that the Ti₃SiC₂ /c-BN couple was successfully made at 1400°C, 10MPa pressure for 30 minutes, and Ti₂AlC/c-BN couple was successfully made at 1500°C, 10MPa pressure for 30 minutes. The interfacial phases characterised by XRD and SEM found here were TiN, TiC, TiB₂ and AlN for the latter and TiN, TiS₂ and TiB₂ for the former. 4. These conditions were used to successfully synthesise MAX/c-BN composites where both could react and still remain intact. The interfacial phases characterised by XRD and SEM found here were TiAl, TiC, TiB₂ and AlN for Ti₂AlC/c-BN and TiN, TiC, TiS₂ and TiB₂ for Ti₃SiC₂ /c-BN. From these results the following conclusion was drawn: Ti₂AlC and Ti₃SiC₂ are fully compatible with c-BN in order to synthesise a composite with notable properties such as the fracture toughness, suggested by the observed fracture mechanism seen from the fracture surface of these composites.

Titanium oxide has been widely studied for its potential application in many scientific and technological fields. In particular, its photoelectrochemical properties are of great interest for possible applications in the conversion of solar energy into electricity, hydrogen production by water photosplitting and photocatalytic degradation of recalcitrant organic and inorganic pollutants (O'Regan and Grätzel 1991; Linsebigler, Lu et al. 1995; Mills and Le Hunte 1997; Grätzel 2001; Carp, Huisman et al. 2004; Mor, Varghese et al. 2006; Aprile, Corma et al. 2008; Varghese, Paulose et al. 2009). During the three years of the Ph.D. School in Molecular Sciences, the experimental work, performed at the Institute for Energetics and Interphases (IENI) of the Italian National Research Council (CNR) of Padua (Italy) (under supervision of Dr Monica Fabrizio), was focused on the study and optimization of vapor deposition techniques, physical vapor deposition (PVD) e chemical vapor deposition (CVD), of titanium oxide-based nanostructured materials for photocatalytic applications and their chemical-physical, morphological and functional characterizations. The PVD magnetron sputtering instrumentation (located at IENI-CNR laboratories) was adapted for ceramic thin film deposition, varying the geometrical and mechanical configuration. Therefore, the optimal synthesis conditions of photocatalytic titanium oxide thin films were identified by tuning the main process parameters: power supply (DC or RF), deposition time, substrate heating and motion, target-substrate distance, total pressure, inlet gas partial pressure. In order to improve the photocatalytic efficiency of titanium oxide thin films, several nitrogen doping attempts were carried out. Such kind of doping, indeed, was reported in literature as the most efficient way to reduce the titanium oxide band gap thus permitting the absorption of a larger solar spectrum fraction maintaining its photochemical stability (Asahi, Morikawa et al. 2001; Kitano, Funatsu et al. 2006; Asahi and Morikawa 2007). A large part of the experimental work was addressed towards the development and setting up of an apparatus for the photoinduced current measurement in titanium oxide electrodes under UV irradiation. The thin film deposition process studies performed on several planar substrates, such as soda-lime glass, ITO or fused quartz, the optimization of the process parameters and the knowledge of the titanium oxide-based system behavior permitted to figure out and develop new materials with improved photocatalytic efficiency. In particular, hybrid nanocomposites employing single wall carbon nanohorns (SWCNHs) as substrate for titanium oxide deposition were developed. In recent years, many published papers aimed to improve the titanium oxide photocatalytic behavior with mesoporous carbon-based hybrid nanocomposites (Orlanducci, Sessa et al. 2006; Liu and Zeng 2008; Wang, Ji et al. 2008; Yu, Quan et al. 2008). As a potential titanium oxide support, SWCNHs are very interesting nanostructures in virtue of their electronic properties, morphological features and high production yield (Kasuya, Yudasaka et al. 2002; Gattia, Vittori Antisari et al. 2007). Part of the great family of carbon nanotubes, they consist of a single layer of a graphene sheet wrapped into an irregular cone-shaped tubule with a variable diameter of generally few nanometers and a length of about ten nanometers (Iijima, Yudasaka et al. 1999; Murata, Kaneko et al. 2000). Depending on synthesis parameters, the SWCNHs assemble together in three types of spherical aggregates with diameters in the order of hundred nanometers (Yudasaka, Iijima et al. 2008). The photocatalytic efficiency improvement of titanium oxide in the hybrid material SWCNHs/TiO2 is due to the mesoporous morphology with high surface area (over than 300 m2g-1) of such carbon nanostructure aggregates and to the formation of the heterojunction with the oxide, which can reduce the electron-hole recombination process and therefore the overall efficiency of photocatalytic process (Cioffi, Campidelli et al. 2007; Petsalakis, Pagona et al. 2007). An important result obtained during the Ph.D. activity was the synthesis, through magnetron sputtering, of a novel nanostructured morphology of titanium oxide named “strelitzia-like titanium oxide” induced by the SWCNHs employed as substrates (Battiston, Bolzan et al. 2009). Therefore, the experimental activity was focused on the comprehension and optimization of nucleation and growth of this novel titanium oxide architecture. Moreover, in collaboration with the Institute of Inorganic Chemistry and Surfaces (ICIS) of the Italian National Research Council (CNR) of Padua (Italy), the TiO2 metal-organic chemical vapor deposition (MOCVD) was performed (Battiston, Bolzan et al. 2009) obtaining the SWCNH coating with different morphologic features with respect to the PVD synthesized morphologies. The characterization the hybrid nanocomposite obtained via MOCVD, that showed a homogeneous covering of SWCNH grains, suggested its employment as substrate for the magnetron sputtering deposition thus maximizing the strelitzia-like titanium oxide structure nucleation on all SWCNH aggregates. The broad nucleation of such novel nanostructures permitted to perform a deeper structural and functional characterization which finally showed that strelitzia-like nanocomposites have higher photocatalytic performances compared to the other kinds of titanium oxide samples investigated. The characterizations of thin films and hybrid nanocomposites were carried out in close cooperation with Padua University (Italy), IENI-CNR, ICIS-CNR, ITC-CNR (Construction Technologies Institute in Milan, Italy), Turin University (Italy) and Piezotech Japan Ltd (spin off of Research Institute for Nanoscience Kyoto, Japan), where a three month stage was performed with a fellowship of Italian Interuniversity Consortium on Materials Science and Technology. The structural, compositional, morphological and functional analyses were performed respectively by XRD, Raman spectroscopy, ICP-MS, SIMS, XPS, Cathodoluminescence, SEM, TEM, AFM, mechanical profiler, photocurrent measurements and photocatalytic degradation of phenol under UV irradiation.
L'ossido di titanio è considerato un eccellente materiale fotocatalizzatore grazie alla sua elevata efficienza, alla stabilità fotochimica, all’atossicità e al basso costo. Grazie a queste proprietà, i materiali nanostrutturati di ossido di titanio sono largamente studiati e impiegati in diversi settori tecnologici quali quelli della fotocatalisi, della degradazione fotocalitica di composti organici ed inorganici, della sensoristica e della conversione dell’energia solare in elettricità (O'Regan and Grätzel 1991; Linsebigler, Lu et al. 1995; Mills and Le Hunte 1997; Grätzel 2001; Carp, Huisman et al. 2004; Mor, Varghese et al. 2006; Aprile, Corma et al. 2008; Varghese, Paulose et al. 2009). Il lavoro svolto nell’arco dei tre anni di attività di ricerca effettuata, nell’ambito della Scuola di Dottorato in Scienze Molecolari, presso i laboratori dell’Istituto per l’Energetica e le Interfasi (IENI) del CNR di Padova (sotto supervisione della Dott.ssa Monica Fabrizio), è stato focalizzato sullo studio e ottimizzazione di tecniche di deposizione da fase vapore, physical vapor deposition (PVD) e chemical vapor deposition (CVD), e caratterizzazione chimico-fisica, morfologica e funzionale di materiali nanostrutturati a base di ossido di titanio per applicazioni fotocatalitiche. La strumentazione PVD magnetron sputtering, presente presso i laboratori IENI, è stata adattata per la deposizione di film di natura ceramica, intervenendo sulla configurazione geometrica e meccanica dell’apparato. In seguito, è stato possibile individuare le condizioni ottimali di sintesi per la deposizione di film sottili di ossido di titanio efficienti dal punto di vista fotocatalitico, studiando ed agendo sui principali parametri di processo: modalità DC o RF, tempo di deposizione, movimentazione e riscaldamento del substrato, distanza target-substrato, pressione totale, pressioni parziali dei gas introdotti in camera e potenza trasferita al plasma. Al fine di incrementare l’efficienza fotocatalitica dei film sottili, sono stati condotti diversi tentativi di sintesi introducendo azoto come drogante dell’ossido di titanio. Tale drogaggio è riportato in letteratura (Asahi, Morikawa et al. 2001; Kitano, Funatsu et al. 2006; Asahi and Morikawa 2007) come il metodo più idoneo per ridurre l’energy gap efficace del materiale, permettendo contemporaneamente l’assorbimento di una frazione più ampia dello spettro solare ed il mantenimento della stabilità fotochimica. Parte consistente del lavoro sperimentale è stata impiegata, inoltre, per intraprendere lo sviluppo e l’allestimento di un sistema per la misura della corrente fotoindotta, in seguito ad irraggiamento di luce UV-VIS, dell’ossido di titanio. Lo studio del processo di deposizione su vari tipi di substrati piani (vetro, ITO, silice pura), l’identificazione dei parametri di processo ottimali e la conoscenza acquisita del comportamento di tali sistemi ha permesso, infine, lo sviluppo e la progettazione di nuovi materiali più efficienti dal punto di vista fotocatalitico. In particolare, sono stati progettati e realizzati nanocompositi ibridi, impiegando Single Wall Carbon Nanohorn (SWCNH) come substrati per le deposizioni di ossido di titanio. Negli ultimi anni, infatti, sono stati pubblicati numerosi articoli sulla sintesi di materiali nanocompositi ibridi che impiegano materiali mesoporosi a base di carbonio, con lo scopo di incrementare le proprietà fotocatalitiche dell’ossido di titanio (Orlanducci, Sessa et al. 2006; Liu and Zeng 2008; Wang, Ji et al. 2008; Yu, Quan et al. 2008). Con questo scopo, i SWCNH rappresentano un buon candidato grazie alle loro proprietà elettroniche, caratteristiche morfologiche e all’alta resa di produzione (Kasuya, Yudasaka et al. 2002; Gattia, Vittori Antisari et al. 2007). Essi sono costituiti da aggregati, a simmetria sferica e delle dimensioni dell’ordine del centinaio di nanometri, di coni irregolari di grafene a parete singola di qualche nanometro di diametro e qualche decina di nanometri di lunghezza (Iijima, Yudasaka et al. 1999; Murata, Kaneko et al. 2000; Yudasaka, Iijima et al. 2008). L’incremento dell’efficienza fotocatalitica dell’ossido di titanio nel materiale ibrido SWCNH/TiO2 è giustificato dalla morfologia mesoporosa ad elevata area superficiale di questi aggregati (superiore a 300 m2 g-1) e dalla formazione dell’eterogiunzione con l’ossido, che può ridurre sensibilmente la ricombinazione elettrone-lacuna e incrementare, perciò, l’efficienza globale del processo fotocatalitico (Cioffi, Campidelli et al. 2007; Petsalakis, Pagona et al. 2007). Un importante risultato conseguito nello svolgimento dell’attività di dottorato riguarda l’ottenimento, grazie all’impiego del magnetron sputtering, di una nuova singolare morfologia nanostrutturata dell’ossido di titanio, chiamata “strelitzia-like titanium oxide”, indotta proprio dalla particolare morfologia dei SWCNH impiegati come substrati (Battiston, Bolzan et al. 2009). La successiva attività sperimentale è stata, quindi, indirizzata alla comprensione e all’ottimizzazione dei meccanismi di nucleazione e crescita di queste innovative strutture nanocomposite ibride SWCNH/TiO2. A questo proposito, in collaborazione con l’Istituto di Chimica Inorganica e delle Superfici (ICIS) del CNR di Padova, è stato eseguito un approfondito studio sull’influenza del metodo di deposizione utilizzato su nucleazione e crescita dell’ossido di titanio sui SWCNH, impiegando anche la tecnica metal-organic chemical vapor deposition (MOCVD) (Battiston, Bolzan et al. 2009), che ha permesso di ottenere morfologie del rivestimento molto differenti da quelle ottenute tramite magnetron sputtering. Lo studio e la caratterizzazione del nuovo materiale nanocomposito, ottenuto via MOCVD, ne ha suggerito l’impiego come substrato per la deposizione via magnetron sputtering permettendo, infine, di giungere all’ottimizzazione della nucleazione delle strelitzie di ossido di titanio, sfruttando ogni singolo aggregato di SWCNH. Tale risultato ha permesso, inoltre, di eseguire una approfondita caratterizzazione di tipo strutturale e funzionale della nuova morfologia dell’ossido di titanio che, infine, ha dimostrato possedere proprietà fotocatalitiche superiori rispetto a tutti i materiali a base di ossido di titanio con cui è stata comparata. Le caratterizzazioni dei film sottili e dei nanocompositi ibridi sono state eseguite in stretta collaborazione con diversi gruppi di ricerca appartenenti, oltre che all’Università di Padova e al CNR IENI, anche al CNR-ICIS, al CNR-ITC (Istituto per le Tecnologie delle Costruzioni), l’Università di Torino e Piezotech Japan Ltd, spinoff del Research Institute for Nanoscience con sede a Kyoto (Giappone), presso cui è stato svolto uno stage della durata di tre mesi nell’ambito della convenzione Italia-Giappone a cui prende parte il Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM). Le analisi effettuate sono state di tipo strutturale (XRD e Spettroscopia Raman), composizionale (ICP-MS, SIMS, XPS, Catodoluminescenza), morfologico (SEM, TEM, AFM e profilometro meccanico) e funzionale (misure di fotocorrente e degradazione fotocatalitica di composti organici).

Na busca de novos materiais que possuam boa resistência mecânica, baixo peso e de fácil manufatura, surgem os compósitos e os compósitos reforçados direcionando a uma ampla área de aplicações e estudos em desenvolvimento. Os materiais compósitos têm um vasto campo de aplicação, porém quando sujeitos a maiores esforços, não apresentam grande resistência e bom desempenho frente aos materiais metálicos. Os materiais compósitos quando reforçados com fibras multiplicam sua resistência consideravelmente, tornando-se um excelente substituto de materiais que possuem boa resistência mecânica como os metais, sendo um material resistente à oxidação. Em muitos casos os compósitos reforçados substituem os metais com um desempenho superior, como exemplo a aplicação de materiais reforçados com fibra de carbono. Este trabalho tem como objetivo criar uma plataforma para o desenvolvimento de um software para o cálculo otimizado das trajetórias das fibras em materiais compósitos, com fibras que venham a reforçar o mesmo e que venham a ser utilizados pela comunidade em diversas áreas como mecânica, medicina, elétrica, entre várias outras.
In the search of new materials, which have good mechanic strength, low weight and easy manufacturing, appear the composites and reinforced composites leading to an ample area of applications and studies in development. The composites materials have a vast field of application, however when subjected to a bigger effort, they do not show a great strength and a good development when compared to metallic materials. The composites materials when reinforced with fibers multiply their strength considerably, becoming an excellent substitute of materials, which have mechanic strength like metals, which in a strong material to corrosion. In many cases, the reinforced composites substitute the metals with a higher development, for example, like applications of reinforced materials with carbon fiber. This production has to objective, to create a platform to development of a software to a calculation optimization of course the fibers in a composite material, using fibers that come to reinforce it and are able to used by the community in many areas like mechanic, medicine, electric and among others.

Le matériau composite carbone/carbone ou C/C est utilisé en temps que matériau de friction en freinage aéronautique. Matériau complexe tant du point de vue de sa description microstructurale que de son comportement sous sollicitations tribologiques, il a été l’objet de nombreuses études visant à mieux comprendre les mécanismes régissant sa réponse (frottement, endommagement, usure) à ces sollicitations. Dans cette étude nous nous focalisons sur l’aspect mécanique de cette réponse. En particulier, nous nous intéressons aux endommagements présents dans le matériau : nous souhaitons étudier tant leurs origines que leur influence sur le comportement du matériau. Pour cela, nous choisissons une approche combinée numérique et expérimentale, nous permettant d’identifier de façon exhaustive ces endommagements puis de construire un modèle numérique tribologique permettant d’étudier les mécanismes d’usure du matériau. Nous montrons comment les mécanismes d’accommodation en volume du 1er corps influent sur les détachements de particules en surface, nous conduisant à parler de dialogue tribologique surface/volume. Le modèle numérique utilise la méthode des éléments discrets pour représenter 1er et 3ième corps simultanément. Un travail est réalisé autour de la représentativité du modèle vis-à-vis des caractéristiques mécaniques du composite C/C. Nous proposons également une démarche de recherche d’un Volume Elémentaire Représentatif sous condition de contact. Ce modèle ainsi que les observations du matériau nous permettent de proposer un scenario de comportement tribologique du composite C/C, en fonction des sollicitations thermomécaniques qui lui sont appliquées et correspondant aux différents types de freinages aéronautiques. Les endommagements identifiés dans le volume du matériau se révèlent être bénéfiques dans certains cas de figure au travers d’un mécanisme de rigidification du matériau intervenant à haute température, ce qui nous conduit à parler d’ « endommagement utile ». Le scenario intègre donc ce phénomène, ainsi que d’autres tant mécaniques que physicochimiques et identifiés par cette étude ou dans la littérature, et montre comment leur équilibre « dynamique » produit le comportement tribologique identifié du matériau pour les différentes gammes de sollicitations qui lui sont appliquées
Carbon/Carbon (or C/C) composite is used as a friction material in aeronautical braking applications. This is a complex material from both microstructural and tribological behavior points of view. Thus, it has been studied through various works for several years, aiming at understanding what mechanisms guide this material response (friction, damage, wear) under tribological conditions. In this study, a focus is performed on mechanical aspects such as damages that occur in the numerical and experimental approach, in view to identify and classify the damages as well as to build a numerical model used to investigate wear mechanisms. It is underlined how first-body accommodation mechanisms have a great influence on particles detachment at the interface, as a surface/volume tribological dialogue take place. This model is based on the Discrete Elements method and represents simultaneously first- and third-body; such model is able to represent fist-body degradation as well as creation and flow of third-body particles. Its representativeness is ensured through experimental comparisons, particularly on mechanical aspects. A procedure is proposed for the research of a Representative Elementary Volume under contact conditions. Model results and material observations allow proposing a global scenario explaining C/C composite behavior under tribological conditions, which are representative of different aeronautical braking cases. Damages, identified in the volume of the first-body, reveal themselves to be sometimes beneficial, and could be characterized as “useful damages”. The scenario takes into account this phenomenon, as well as thermal, mechanical and physicochemical ones, identified from this work or literature. It explains the influences of these parameters on C/C tribology and show how the dynamic equilibrium between them results on the C/C response, particularly its wear mechanism

Ce mémoire est consacré à l'étude de nouveaux matériaux composites de type Si/Sn-Ni/Al/C pour former des électrodes négatives de batteries lithium ion. La microstructure de ces matériaux se présente sous la forme de nanoparticules de Si enrobées dans une matrice conductrice constituée de carbone et d'un composé intermétallique Ni3,4Sn4. La nanostructure et la composition du matériau composite lui confèrent de très bonnes performances en termes de capacité réversible, de stabilité électrochimique, et de cinétique de réaction. La mécanosynthèse a été choisie comme méthode d'élaboration. Les propriétés structurales et chimiques du composite ont été déterminées par analyses DRX, par microscopies électroniques MET et MEB, par analyses EDX et EFTEM et par spectroscopie Mössbauer de 119Sn. La caractérisation électrochimique a été réalisée par cyclage galvanostatique et par voltamétrie cyclique. La réactivité de ces matériaux envers le lithium a été étudiée par analyses DRX et spectroscopie Mössbauer de 119Sn in-situ. Ce mémoire détaille les résultats structuraux et électrochimiques obtenus pour différents matériaux composites basés sur Ni3,4Sn4 en ajoutant les éléments C, Al et Si. Une étude des mécanismes réactionnels lors du broyage mécanique ainsi que pendant le cyclage électrochimique a été effectuée et le rôle des différents éléments a été mis en évidence. Enfin, une discussion sur l'influence de la microstructure sur les performances électrochimiques des matériaux composites est donnée. Les meilleures performances électrochimiques sont obtenues pour le composite de composition nominale Ni0,14Sn0,17Si0,32Al0,04C0,35. Il présente une capacité réversible de 920 mAh/g avec une très bonne stabilité sur 280 cycles. Le matériau possède une excellente cinétique de délithiation : 90% de la capacité peut être délivrée en moins de 5 minutes. La capacité irréversible (20%) reste toutefois élevée et doit être encore améliorée en stabilisant l'interface solide/électrolyte (SEI)

Les comportements experimentaux des materiaux de synthese contenant silicium, carbone et oxygene ou azote, a haute temperature, et leurs simulations thermodynamiques, presentent des desaccords quantitatifs importants qui peuvent etre expliques par des donnees thermodynamiques peu precises ou incompletes, ou par des cinetiques de reactions particulierement lentes. Pour lever toute ambiguite sur les donnees des composes cristallins, amorphes et gazeux du systeme si-c-n-o de nouvelles mesures d'enthalpie de formation ont ete effectuees par la technique des cellules d'effusion multiples couplee a la spectrometrie de masse. Il a ete mis en evidence que le sio(s) ne constitue pas une phase stable. La temperature de l'eutectique si+sic et les activites du silicium dans le liquide en equilibre avec sic ont ete mesurees. L'etude du ternaire si-n-o a permis de proposer une nouvelle valeur de l'enthalpie de formation de si#2n#2o. En plus des mesures de grandeurs thermodynamiques, l'etude de ces systemes a mis en evidence l'importance des cinetiques de reaction de decomposition (par exemple le faible coefficient d'evaporation de si#3n#4), ou entre phases solides (par exemple si+sio#2 ou sio#2+c). La prise en compte de la reduction des incertitudes sur les donnees thermodynamiques s'est revelee grandement insuffisante pour expliquer les desaccords entre le comportement des fibres et sa simulation. Le comportement de materiaux de synthese a base de sic et le comportement de melanges de phases connues ont ete etudies. Les resultats de ces experiences ont montre que les pressions mesurees de sio(g) et co(g) sont bien plus faibles que les pressions d'equilibre pour les materiaux dont la composition globale est dans le ternaire sic+sio#2+c. Les fibres sicn(o) (ex-pcsz) apparaissent plus stables que les fibres sico (ex-pcs). L'ensemble des resultats exposes peut etre exploite pour aider a expliquer et prevoir les traitements des fibres ceramiques en milieu industriel

Da oltre 20 anni vengono utilizzati i materiali compositi per il rinforzo e/o adeguamento strutturale di singoli elementi o interi fabbricati in c.a.. I materiali compositi maggiormente diffusi in edilizia sono a base di fibre di carbonio e/o fibre aramidiche e/o fibre di vetro e matrice epossidica. Come noto, la scarsa resistenza al fuoco delle resine epossidiche limita l’utilizzo dei materiali compositi. Infatti, per temperature superiori alla Tg della matrice si verifica un rapido calo del modulo elastico del composito. Solitamente per le resine epossidiche laminate in situ, il valore di Tg è inferiore a 100°C. Nel presente articolo vengono presentati i risultati di una sperimentazione condotta su travi in c.a. rinforzate con resine a base acqua del tipo IPN e nastri unidirezionali in carbonio. Queste resine IPN presentano una struttura microcristallina costituita da una fase polimerica ed una cristallina interpenetrata, tale da essere classificate come reazione al fuoco di classe 1 ai sensi dell’UNI 9177. In particolare, le travi sono state rafforzate con diverse configurazioni di rinforzo a taglio e flessione. Sono stati confrontati i risultati delle prove di carico dei rinforzi applicati con le resine IPN con quelli applicati con le resine epossidiche. Al vantaggio della resistenza al fuoco delle resine IPN, la sperimentazione condotta ha evidenziato l’eccellenti proprietà meccaniche dei rinforzi applicati con la matrice IPN con valori analoghi a quelli dei rinforzi applicati con l’epossidica
ABSTRACT For over 20 years composite materials have been used for the reinforcement and / or structural adjustment of individual elements or complete reinforced concrete buildings. The composite materials most widely used in construction are based on carbon fibers and / or aramid fibers and /or glass fibers and epoxy matrix. As known, the poor fire resistance of epoxy resins restricts the use of composite materials in building construction. Indeed, for temperatures above the Tg of the matrix occurs a rapid decrease of the composite elastic modulus. Usually for the epoxy resins laminated on site, the Tg value is less than 100 ° C. The article presents the results of an experiment conducted on RC beams reinforced with water-based IPN resins and unidirectional tapes carbon. As these IPN resins have a microcrystalline structure consisting of a polymer phase and a crystalline interpenetrated, they are material with class1 reaction to fire (according to UNI 9177). Particularly, the beams have been reinforced with different configurations of strengthening to shear stress and bending. By comparing the results of load tests applied on IPN resins and on epoxy resins, it has been proved that not only IPN resins have a better fire resistance, but also excellent mechanical properties of the reinforcements applied with the IPN matrix, showing similar values to the one obtainable with epoxy reinforcements.

Da oltre 20 anni vengono utilizzati i materiali compositi per il rinforzo e/o adeguamento strutturale di singoli elementi o interi fabbricati in c.a.. I materiali compositi maggiormente diffusi in edilizia sono a base di fibre di carbonio e/o fibre aramidiche e/o fibre di vetro e matrice epossidica. Come noto, la scarsa resistenza al fuoco delle resine epossidiche limita l’utilizzo dei materiali compositi. Infatti, per temperature superiori alla Tg della matrice si verifica un rapido calo del modulo elastico del composito. Solitamente per le resine epossidiche laminate in situ, il valore di Tg è inferiore a 100°C. Nel presente articolo vengono presentati i risultati di una sperimentazione condotta su travi in c.a. rinforzate con resine a base acqua del tipo IPN e nastri unidirezionali in carbonio. Queste resine IPN presentano una struttura microcristallina costituita da una fase polimerica ed una cristallina interpenetrata, tale da essere classificate come reazione al fuoco di classe 1 ai sensi dell’UNI 9177. In particolare, le travi sono state rafforzate con diverse configurazioni di rinforzo a taglio e flessione. Sono stati confrontati i risultati delle prove di carico dei rinforzi applicati con le resine IPN con quelli applicati con le resine epossidiche. Al vantaggio della resistenza al fuoco delle resine IPN, la sperimentazione condotta ha evidenziato l’eccellenti proprietà meccaniche dei rinforzi applicati con la matrice IPN con valori analoghi a quelli dei rinforzi applicati con l’epossidica
ABSTRACT For over 20 years composite materials have been used for the reinforcement and / or structural adjustment of individual elements or complete reinforced concrete buildings. The composite materials most widely used in construction are based on carbon fibers and / or aramid fibers and /or glass fibers and epoxy matrix. As known, the poor fire resistance of epoxy resins restricts the use of composite materials in building construction. Indeed, for temperatures above the Tg of the matrix occurs a rapid decrease of the composite elastic modulus. Usually for the epoxy resins laminated on site, the Tg value is less than 100 ° C. The article presents the results of an experiment conducted on RC beams reinforced with water-based IPN resins and unidirectional tapes carbon. As these IPN resins have a microcrystalline structure consisting of a polymer phase and a crystalline interpenetrated, they are material with class1 reaction to fire (according to UNI 9177). Particularly, the beams have been reinforced with different configurations of strengthening to shear stress and bending. By comparing the results of load tests applied on IPN resins and on epoxy resins, it has been proved that not only IPN resins have a better fire resistance, but also excellent mechanical properties of the reinforcements applied with the IPN matrix, showing similar values to the one obtainable with epoxy reinforcements.

On a etudie le comportement a la rupture de composites ceramiques a fibres c-sic et sic-sic pour les trois orientations principales, et on a utilise les modeles proposes dans la litterature pour tenir compte des perturbations induites par les deformations non-elastiques de ces materiaux. Les resultats obtenus indiquent que ces modeles sont effectivement valides lorsque la propagation de fissure dans le materiau se fait sans pontage de la fissure principale par les fibres (cas de c-sic). Ce travail met en avant l'importance des mecanismes de rupture non-lineaire (microfissurations, deviations de fissure, dechaussement de fibres, rupture et sortie de fibres de la matrice) dans l'energie totale consommee, ainsi que l'orientation de la fissure initiale par rapport a la geometrie du renfort fibreux

Ce travail a pour but d'étudier la tolérance à l'impact de 3 stratifiés carbone/époxy soumis simultanément à différents types de chargements hygrothermiques et mécaniques. Ces stratifications présentant des caractéristiques mécaniques globales particulières d'isotropie, il s'agit ici de déterminer l'influence de la séquence d'empilement sur le développement de l'endommagement lors d'un impact. Dans un premier temps, la cinétique de vieillissement hygrothermique des trois stratifications est étudiée et analysée. Ensuite, leur tolérance à un unique impact ainsi qu'à des impacts répétés est évaluée. L'endommagement résultant de ces impacts est analysé par contrôle ultrasonore. La morphologie générale et l'amplitude de l'endommagement dans la profondeur des matériaux sont mises en relation avec les propriétés mécaniques et la séquence d'empilement spécifique à chaque stratifié. Dans un deuxième temps, l'influence combinée de plusieurs sollicitations est étudiée. Différents scénarii associant un vieillissement hygrothermique ainsi qu'un ou deux impacts sont mis en oeuvre. L'endommagement résultant est mis en rapport avec les temps relatifs de vieillissement et la position des impact durant le cycle de vieillissement. Ensuite, l'influence d'une précharge de traction sur la tolérance à l'impact est mise en évidence. Un montage spécifique a été conçu et fabriqué pour réaliser ces tests. Enfin, l'association d'un vieilllissement hygrothermique et d'une précharge de traction est abordée afin d'identifier la sollicitation la plus pénalisant en terme de tolérance et d'impact
This study examines impact damage processes in three types of CFRP composite materials simultaneously subjected to different hygrothermal and mechanical loading conditions. The composite structures tested are chosen for having particular global isotropic responses when loaded, the aim being to ascertain the exact influence of lay-up sequence on impact damage propagation. The work is presented in four main sections. Firstly by establishing hygrothermal ageing dynamics for the three composite structure types and their behaviour when impacted once or several times ; impact damage is measured and analysed using ultrasonic method. The extent and general morphology of the damage through the material thickness is correlated with mechanical properties and lay-up sequence specific to each material. Secondly the influence of simultaneous load combinations is examined. These include different durations of hygrothermal ageing associated with single or double impacts.The resulting damage incurred is analysed with respect to overall ageing time and time during the ageing cycle when the impact was applied. Thirdly the effect of tensile loading during impact on damage within the material was studied. This was achieved using a specially designed test apparatus that allows loading and impacting conditions to be independently modified. By associating a high-speed digital camera to film specimen impacts it is possible to evaluate a relationship between overall composite specimen stiffness and the impact damage. Finally, in order to identify the most unfavourable situation with regard to impact damage resistance an association between hygrothermal ageing and an applied tensile load is examined

Made available in DSpace on 2015-04-14T13:29:54Z (GMT). No. of bitstreams: 1 431091.pdf: 6484611 bytes, checksum: ee0b40e71498d6a5f8496211522ca10f (MD5) Previous issue date: 2011-03-18
O objetivo desse estudo foi avaliar a influ?ncia de quatro cimentos resinosos (um convencional e tr?s autoadesivos) na deflex?o de c?spides, carga de fratura e tipos de fratura de pr?-molares com acesso endod?ntico e restaurados com inlays em resina composta. Setenta e dois primeiros pr?-molares foram divididos aleatoriamente em seis grupos (n=12): G1 (controle) - h?gidos; G2 cavidades sem restaura??o; G3 RelyX ARC; G4 RelyX U100; G5- Maxcem Elite; G6 SeT. Os Grupos 2-6 receberam preparos cavit?rios MOD e acesso endod?ntico. Os grupos 3-6 foram moldados com silicona por adi??o e vazados com gesso especial para confec??o de inlays em resina composta Z350 XT. As restaura??es indiretas foram cimentadas nas respectivas cavidades com carga de 1 Kg e fotoativadas. Ap?s armazenagem em ?gua destilada a 37? C por 72 horas, carga de 200 N foi aplicada na regi?o oclusal com uma esfera de 8 mm de di?metro acoplada na m?quina de ensaio universal EMIC DL 2000, sendo medida a deflex?o de c?spides com um micr?metro digital. Os corpos de prova foram ent?o submetidos a 500.000 ciclos de fadiga mec?nica, e novo teste de deflex?o de c?spides foi realizado. Em seguida, os corpos de prova foram submetidos ao ensaio de compress?o at? a fratura na m?quina de ensaio universal. De acordo com o teste de Kruskal-Wallis, a maior deflex?o de c?spides pr?-fadiga foi obtida para o grupo 2 (69 μm), n?o diferindo estatisticamente do grupo 6 (51 μm). As menores deflex?es de c?spides foram obtidas para o grupo 1 (4 μm), o grupo 3 (4 μm) e o grupo 4 (5 μm), os quais n?o diferiram estatisticamente entre si. Valor intermedi?rio foi obtido para o grupo 5 (21 μm), n?o diferindo estatisticamente dos grupos 3, 4 e 6. De acordo com o teste de Wilcoxon, n?o houve diferen?a estat?stica entre a deflex?o de c?spides pr? e p?s-fadiga apenas para o grupo 3 (p=0,015). De acordo com Kruskal-Wallis, a maior carga de fratura foi obtida para o grupo 1 (1902 N), diferindo estatisticamente dos outros grupos. Segundo maior valor foi obtido para o grupo 3 (980,8 N), diferindo estatisticamente dos outros grupos. Grupo 4 (670,6 N), grupo 5 (533,5 N), grupo 6 (601,3 N) e grupo 2 (526,6 N) n?o diferiram estatisticamente entre si. Para os grupos restaurados, houve predomin?ncia de fraturas recuper?veis. Inlays em resina composta cimentadas com RelyX ARC mantiveram a estabilidade da deflex?o de c?spides, proporcionaram maior recupera??o da resist?ncia da estrutura dent?ria, assim como fraturas mais favor?veis para a reabilita??o.

L'etude porte sur des materiaux susceptibles d'etre utilises comme contact electrique, constitues de particules de graphite dans une solution solide cu, ni. Ces materiaux anisotropes contiennent 3 a 20 vol % de graphite, un peu de porosite residuelle et presentent trois types de microstructures caracterisees par analyse d'images. La conductivite electrique est mesuree sur des materiaux de texture soit parallele soit perpendiculaire a la direction du courant. Les resultats experimentaux font ressortir le role isolant du graphite, et une decroissance de la conductivite produite par l'augmentation de fraction de phase isolante, beaucoup plus rapide pour les textures perpendiculaires que paralleles. Le modele d'ondracek conduit a evaluer trois effets principaux dus a la fraction volumique, a l'anisotropie de forme de phase isolante et a l'anisotropie de texture. Est ensuite etudiee la resistance de contact, somme de la resistance de constriction specifique au materiau, et d'un terme pelliculaire fonction de la conductivite electrique et de la morphologie de la couche de surface. Les valeurs experimentales approchees de resistance de constriction sont confrontees au modele de holm: les fortes variations de conductivite electrique produisent sur la resistance de constriction des variations significatives mais faibles devant l'effet pelliculaire minimal. L'effet pelliculaire des materiaux soumis a l'arc electrique est analyse a partir de donnees experimentales d'erosion, de resistance de contact et de caracterisation des couches de surface. Ces resultats mettent en evidence le role important de la teneur en graphite des materiaux; on propose deux mecanismes prrincipaux pour l'interpreter

Made available in DSpace on 2015-04-14T13:30:19Z (GMT). No. of bitstreams: 1 Helen Cristina Vieira da Rosa.pdf: 575465 bytes, checksum: 907bc1dd4c8788ff1bcb0479b1249fc5 (MD5) Previous issue date: 2013-03-01
The aim of this study was to evaluate the influence of different resin cements in the cuspal deflection of teeth with endodontic treatment. Sixty superior premolars were randomly divided into five (n=12) groups: 1 sound teeth; 2 cavity; 3 - Rely X ARC; 4 RelyX U100; 5 SeT. The teeth from groups 2, 3, 4 and 5 received a MOD preparation and endodontic treatment. Impressions were made with vinyl polysiloxane and poured using type IV die stone in groups 3, 4 and 5. Inlays with Z250 composite resin were built over each cast and luted with the resin cements according manufacturer s instructions. The specimens were stored in distilled water at 37o C for 72 hours. The specimens were positioned in a universal testing machine and a load of 200 N was applied in the oclusal region with a steel rod with 8 mm in diameter. The cusp deflection was measured after and before the load by means a micrometer that contacted the buccal and palatine faces. After 24 h, the cuspal deflection was measured again using a load of 300 N. According to ANOVA and Tukey s test ( α= 0.05), for both occlusal loads, the sound teeth presented the lowest mean cuspal deflection, differing statistically from the other groups. Intermediate values were obtained in RelyX ARC group and RelyX U100 group, differing statistically between them. The highest cuspal deflections were obtained in SeT group and cavity group, not differing statistically between them. According to the Student t-test, there was a statistically significant difference among the 200 N and 300 N occlusal loads for the cavity group (p = 0.002), RelyX U100 group (p = 0.000), and SeT group (p = 0.004). There was no statistical difference for the sound teeth group (p = 0.389), and RelyX ARC group (p = 0.188). The inlays luted with RelyX ARC obtained lower cuspal deflection in comparison with the self-adhesive resin cements; RelyX U100 showed lower cuspal deflection than SeT.
O objetivo desse trabalho foi avaliar a influ?ncia de diferentes cimentos resinosos na deflex?o de c?spides de dentes com tratamento endod?ntico. Sessenta pr?-molares superiores foram divididos aleatoriamente em cinco grupos (n=12): 1 - h?gidos; 2 - cavidades; 3 - RelyX ARC; 4 - RelyX U100; 5 - SeT. Os dentes dos grupos 2, 3, 4 e 5 receberam preparos MOD e tratamento endod?ntico. Os dentes dos grupos 3, 4 e 5 foram moldados com silicone por adi??o, seguido de vazamento de gesso tipo IV. Sobre cada modelo foi confeccionada uma restaura??o inlay em resina composta Z250. As restaura??es foram cimentadas com os cimentos resinosos, de acordo com cada grupo experimental, seguindo as instru??es dos fabricantes. Os corpos de prova foram armazenados em ?gua destilada a 37? C por 72 horas. Em m?quina de ensaio universal, uma carga de 200 N foi aplicada na regi?o oclusal com esfera de a?o de 8 mm de di?metro e, com o aux?lio de um micr?metro posicionado nas faces vestibular e palatina, a deflex?o das c?spides foi medida antes e ap?s a carga. Ap?s 24 horas, foi realizado o mesmo procedimento aplicando uma carga de 300 N na regi?o oclusal. De acordo com ANOVA e teste de Tukey (α=0,05), para ambas as cargas, o menor valor m?dio de deflex?o de c?spides ocorreu no grupo dente h?gido, diferindo estatisticamente dos demais grupos. O segundo menor valor foi obtido para o grupo RelyX ARC, seguido do grupo RelyX U100, os quais diferiram estatisticamente entre si. As maiores m?dias de deflex?o de c?spides foram obtidas com o grupo SeT e o grupo dente com cavidade, n?o diferindo estatisticamente entre si. De acordo com o teste t-student para amostras pareadas (α=0,05), houve diferen?a estat?stica para a m?dia de deflex?o de c?spides entre as cargas de 200 N e 300 N para o grupo cavidade (p = 0,002), o grupo RelyX U100 (p = 0,000), e o grupo SeT (p = 0,004). N?o houve diferen?a estat?stica para o grupo dente h?gido (p = 0,389) e para o grupo RelyX ARC (p = 0,188). As inlays fixadas com RelyX ARC tiveram deflex?o de c?spides inferior ? obtida com os cimentos resinosos autoadesivos, sendo que o RelyX U100 proporcionou menor deflex?o de c?spides em rela??o ao SeT.

Silicon carbide multilayer composites containing short carbon fibres (Csf/SiC) were prepared by tape casting and pressureless sintering. The short C fibres were firstly dispersed in solvents with the aid of dispersant and then mixed with SiC slurry to limit fibre breakage. The relative densities, mechanical properties, oxidation behavior of Csf/SiC multilayer composites were evaluated. Thermal expansion, diffusivity and conductivity behavior in three directions were tested. The effect of addition of short C fibres on shrinkage, mechanical and thermophysical behavior was discussed. Triton X100 was found to be the best one for Toho Tenax HTC124 (with water soluble coating) among BYK-163, BYK-410, BYK-2150, BYK-9076, BYK-9077 and Triton X100 dispersants. Although the average fibre length (0.5 to 0.6 mm) after mixing was only one-sixth or -fifth of original length (3 mm), it is still much longer than in other Csf/SiC composites using ball-milling, indicating that mixing the SiC slurry with the fibre-predispersed solution is an effective method for adding fibres with limited breakage. Fibres were homogeneously distributed in the tapes and tended to align fairly well along the tape casting direction. The relative density of the composite containing short C fibres decreased with the fibre amount. The Csf/SiC multilayer composites demonstrated significant anisotropic shrinkage behavior in different directions, while the addition of short C fibres hindered the shrinkage in the plane containing the fibres (X and Y directions) during sintering. Elastic modulus, bending strength and fracture toughness decreased with increased porosity, which implies that bending properties are affected significantly by residual porosity. However, due to residual thermal stress, the fracture toughness of SiC/(Csf/SiC) multilayer composites was higher than that of SiC multilayer, which indicates that the fracture toughness of SiC-based thermal protection system could be improved through designing its architecture. The weight loss during oxidation tests was larger for Csf/SiC multilayer composites than for SiC multilayer and increased with the porosity and the fibre amount. Passive oxidation of SiC was still occurred after addition of short fibres. Specific heat of Csf/SiC multilayer composites slightly increased with fibre amount. No significant different in thermal expansion behavior of SiC, 5 and 10 vol.% Csf/SiC multilayer composites in different directions was found. In X direction before oxidation treatment, the thermal conductivity firstly slightly increased after addition of 5 vol.% short C fibre, and then decreased with further fibre addition. However, in Y and Z directions, the thermal conductivities decreased with the increase of fibre amount before oxidation treatment. After oxidation treatment, the thermal conductivities decreased with the increase of fibre amount regardless of test directions. Since fibre aligned along tape casting direction, Csf/SiC multilayer composites demonstrated highest thermal conductivity in X direction regardless of fibre amount. Moreover, due to the presence of the interface between adjacent layers, Z direction showed lowest thermal conductivity. Because of the oxidation of C fibre (in Csf/SiC multilayer composites) and formation of silica (both in SiC multilayer and Csf/SiC multilayer composites), thermal conductivities of SiC multilayer and Csf/SiC multilayer composites decreased after oxidation treatment.

Cette étude s'intéresse aux performances des matériaux composites Carbone/Carbone 2,5D lors d'un freinage aéronautique de basse énergie. Durant la vie avion, l'état de surface des disques de frein évolue et les performances de freinage s'en trouvent modifiées. Les études expérimentales et les modélisations réalisées ont pour buts la maîtrise et la prédiction de l'évolution des propriétés de la surface, cela en fonction à la fois des conditions tribologiques mais également de la distance dans deux environnements d'étude: à sec et lubrifié. Un premier volet de ce travail consiste à caractériser finement le comportement mécanique en compression du composite Carbone/Carbone 2,5D, afin de comprendre les répercussions du frottement en sous-couche. Après la détermination des caractéristiques élastiques du matériau, le comportement élasto-endommageable en compression est relevé. Ces caractéristiques sont implémentées dans une simulation 1D et permettent de reproduire les courbes d'essais de compression cyclique à contrainte croissante. Parallèlement, une étude du comportement tribologique du C/C 2,5D à sec via des essais courts a permis de connaître les caractéristiques des coefficients de frottement de différents états de surface. Les coefficients de frottement moyens sont mis en relation avec le paramètre de rugosité Sk. Les essais tribologiques longue distance mis en oeuvre ont modifié l'état de surface des échantillons tant sur le plan topographique que sur le plan morphologique. Des fissures en sous-couche apparaissent, conséquence des efforts tribologiques subis. Ces observations ont menés à la détermination d'un mécanisme d'évolution d'état de surface des disques en environnement sec. Enfin, deux types d'essais en environnement lubrifié ont été proposés, afin de séparer le comportement ponctuel d'un état de surface du comportement tribologique avec la distance. Premièrement, une procédure d'essais tribologiques courts a été mise en place et s'affiche comme un moyen de caractérisation d'état de surface in-situ à part entière, avec des caractéristiques des courbes de Stribeck directement liées aux états morphologiques et topographiques. Ensuite, un plan d'expérience réunit les essais longs destinés à modifier l'état de surface d'éprouvettes pour plusieurs jeux de paramètres tribologiques. Les courbes de Stribeck de ces nouveaux états de surface sont analysées. Ainsi, les états de surface expérimentaux sont comparés à ceux des disques de frein industriels
This study focuses on the performance of 2.5D Carbon/Carbon composite materials for low energy aeronautical braking. During aircraft life, the surface condition of the brake discs evolves and the braking performances change. The experimental studies and the modelizations carried out aim in controlling and predicting the evolution of surface properties, both in terms of the tribological conditions but also of the distance in two study environments: dry and lubricated. For this purpose, a characterization of the mechanical behavior in compression of the 2.5D Carbon/Carbon composite is performed in order to understand the repercussions of friction underlayer. The elastic characteristics of the material and the elasto-damaging behavior in compression are identified. These characteristics are used in a 1D simulation, that allows reproducing the cyclic compression test curves with increasing stress. At the same time, a study of the tribological behavior of the dry 2.5D C/C composite via short tests made it possible to know the friction coefficient of different surface conditions. The average friction coefficients are related to the roughness. The long-range tribological tests used have modified the topographic and morphological surface conditions of the samples. Cracks appear at the underlayer, as a result of the tribological efforts. These observations led to the determination of a mechanism for the evolution of surface condition of discs in a dry environment. Finally, two types of lubricated environment tests have been proposed in order to separate the instantaneous behavior of a surface state from the tribological behavior with the distance. First, a short tribological test procedure is set up and is displayed as a means of in-situ surface condition characterization in its own right, with characteristics of the Stribeck curves directly related to the morphological and topographical states. Next, an experimental plan combines long tests to modify the surface condition of test pieces for several sets of tribological parameters. The Stribeck curves of these new surface states are analyzed. Experimental surface conditions are compared with those of industrial brake disks

Kohlenstofffaserverstärkter Kohlenstoff weist ausgezeichnete thermische, mechanische und chemische Eigenschaften auf. Aufgrund seiner Faserarchitektur und Porosität zeigt dieser eine mit metallischen und polymeren Werkstoffen vergleichbar hohe Schadenstoleranz. Die Herstellung komplexer Leichtbaustrukturen aus C/C-Verbunden ist jedoch zeit- und kostenintensiv. Ein neuer Ansatz stellt die Integration geometrisch simpler C/C-Verbunde in komplexe, problemlos zu realisierende polymere Strukturen dar. Ein derartiges Werkstoffkonzept vereint die Vorteile seiner Komponenten in einem ganzheitlichen Werkstoffsystem. Einen Nachteil stellt jedoch die geringe wechselseitige Adhäsion seiner Komponenten dar. Die Innovation dieses Beitrags stellt sich einerseits der Herausforderung die mechanischen Eigenschaften der C/C-Verbunde in Abhängigkeit der intrinsischen Porosität zu beeinflussen. Dies geschieht durch Veränderung der chemischen und physikalischen Vernetzungsbedingungen des Matrixprecursors. Andererseits soll die dadurch herrührende inhärente Porosität zur Vergrößerung der wirksamen äußeren Oberfläche und zur gezielten Verbesserung der Adhäsion zum Polymer führen. Es wird ein Kohlenstoffprecursor mit variabler offener Porosität entwickelt und daraus neuartige verschiedenporöse C/C-Verbunde hergestellt und untersucht. Im Anschluss werden die verschiedenporösen C/C-Verbunde mit ausgewählten Polymeren unter definierten Konsolidierungsparametern thermisch gefügt und deren wechselseitiges Adhäsionsverhalten bewertet
Fibre-reinforced ceramic matrix composite materials are characterized by excellent thermal, mechanical and chemical properties. Their high tolerance regarding damaging is a result of the intrinsic fibre structure and porosity. Due to this fact, they offer outstanding dampening characteristics, as is the case for polymeric materials. The production of complex structures is very time consuming and expensive. The integration of simple geometric ceramic composite materials in complex polymeric structures is regarded as a new approach for the production of these materials. These easy-to-produce hybrid ceramic/polymer compound materials combine the advantages of ceramics and polymers in one material system. However, one main disadvantage of these materials is the mutual adhesion of the two components. This article deals with the challenge of the manipulation of the mechanical properties of the C/C composites depending on the intrinsic porosity. This is realized by altering the physical and chemical wetting/coating conditions of the matrix precursor. In addition, the inherent porosity is supposed to increase the effective outer surface and specifically improve the adhesion. For this purpose, a novel carbon precursor with an adjustable open porosity is developed and investigated further. During this different versions of the CFRP and various C/C materials of different production steps are produced and examined. The variation of the precursors is supposed to take place in the polymeric state. The different C/C composites are subsequently thermally bonded with selected polymers and defined consolidation parameters. The mutual joining and connection behaviour is investigated further

La matrice des composites thermostructuraux est obtenue par infiltration chimique en phase vapeur : une préforme placée dans un four est pénétrée par des gaz précurseur qui vont déclencher la formation matricielle par réaction hétérogène. Une modélisation numérique de ce procédé est proposée. Deux programmes furent développés puis validés. Le premier est dédié au calcul des propriétés effectives de la préforme à l'échelle de la fibre tandis que second les exploite propriétés pour accomplir une infiltration macroscopique. Ils s'appuient sur des algorithmes de marche aléatoire et requièrent des images 3D de la préforme. Dans cette optique, plusieurs tomographies de préformes ont été acquises aux deux échelles d'intérêt. Par cette méthode, l'étude des prévisions de densification de composites SiC/SiC a permis de comparer leur infiltrabilité. De plus, l'outil développé, combiné à un modèle chimique, simule l'infiltration de composites C/C et anticipe la microtexture de la matrice déposée.

Made available in DSpace on 2015-04-14T13:29:57Z (GMT). No. of bitstreams: 1 432037.pdf: 401361 bytes, checksum: f080ce3dd2c0d49690aab2a7f9731a56 (MD5) Previous issue date: 2011-03-30
O objetivo do estudo foi avaliar, in vitro, a influ?ncia de duas t?cnicas de selamento dentin?rio imediato (SDI) na deflex?o de c?spides, carga de fratura e tipos de fratura de pr?-molares restaurados com inlays em resina composta. Quarenta e oito primeiros pr?-molares foram divididos aleatoriamente em quatro grupos (n=12): G1 (controle) - h?gidos; G2 sem SDI; G3 t?cnica do SDI com Clearfil SE Bond; G4 - t?cnica do SDI com Clearfil SE Bond e resina de baixa viscosidade Protect Liner F. Os dentes dos grupos 2, 3 e 4 receberam preparos m?sio-ocluso-distal. Os preparos foram moldados com silicone por adi??o, seguido de provis?rio e armazenamento em ?gua a 37? C por 7 dias. Os moldes foram vazados com gesso tipo IV e confeccionados inlays em resina composta Filtek Z250. As restaura??es foram cimentadas nos preparos com ED Primer A e B e cimento resinoso Panavia F. Ap?s armazenagem em ?gua destilada a 37? C por 24 horas, carga de 200 N foi aplicada na regi?o oclusal com uma esfera de 8 mm de di?metro acoplada na m?quina de ensaio universal EMIC DL 2000, sendo medida a deflex?o de c?spides com um micr?metro digital. Em seguida, os corpos de prova foram submetidos ao ensaio de compress?o at? a fratura na m?quina de ensaio universal. As m?dias de deflex?o de c?spides (μm) e carga de fratura (N) seguida de mesma letra n?o t?m diferen?a estat?stica de acordo com ANOVA e teste de Tukey (p<0.05). Deflex?o de c?spide: G1=3,1 (?1.5)a, G2=10,3 (?4.6)b, G3=5,5 (?1.80)ac, G4=7,7 (?5.1)bc. Carga de fratura: G1=1974 (?708)a, G2=1162 (?474)b, G3=700 (?280)b, G4=810 (?343)b. A maioria das fraturas ocorridas nos grupos experimentais permite a recupera??o da estrutura dental. A t?cnica do SDI com Clearfil SE Bond proporcionou deflex?o de c?spides compar?vel ao dente h?gido. A aplica??o da resina de baixa viscosidade Protect Liner F sobre o Clearfil SE Bond n?o contribuiu para a redu??o da deflex?o de c?spides. As t?cnicas de SDI n?o foram capazes de restituir a resist?ncia do dente h?gido.

Possibilities of modeling non-linear behavior of concrete within standard room temperatures and increased fire-load values using FEM software ANSYS are studied. Temperature dependences of material models are considered. Fire resistance of reinforced concrete and concrete-steel composite construction is analyzed. Fire loads are defined in accordance with relevant standards. Non-linear structural transient analyses are calculated after temperatures were determined by transient thermal analyses. Results obtained from analyses of simple reinforced concrete structure are compared with approach of isotherm 500 °C method.

Le carbure de silicium (sic) presente des caracteristiques physiques interessantes pour la realisation de dispositifs electroniques fonctionnant dans des conditions extremes de puissance, de temperature et de frequence. L'etude de la cristallogenese par sublimation du carbure de silicium de structure cristallographie hexagonale fait donc l'objet de ce memoire. Dans un premier chapitre, les principales caracteristiques du sic sont presentees. Une description des techniques d'elaboration du sic et un etat de l'art des substrats obtenus precise les objectifs de ce travail. Le dispositif experimental ainsi que les parametres critiques de la sequence de croissance sont exposes dans un deuxieme chapitre. La croissance sur le germe est realisee par une methode originale basee sur le controle du gradient de temperature entre la source et le depot. Cette methode de germination remplace avantageusement celle de tairov basee sur la maitrise de la pression d'argon. Le troisieme chapitre de ce memoire est dedie a la modelisation magneto-thermique du creuset d'elaboration de sic. La validite du modele employe a ete etudiee en comparant simulation et resultats experimentaux. Cet outil a permis d'optimiser la geometrie du creuset et de maitriser le frittage et la carbonisation de la poudre source. Les principaux resultats obtenus sur la cristallogenese du sic sont reportes au cours du quatrieme chapitre. L'influence des differents parametres experimentaux sur les caracteristiques des monocristaux de sic est exposee. Une attention particuliere a porte sur la cristallogenese du 4h-sic, ce qui nous a permis de determiner le role preponderant du germe sur le polytype du lingot obtenu. Dans le dernier chapitre, sont presentes les principaux defauts rencontres dans le sic ainsi que leur mecanisme de creation. Une etude approfondie des macrodefauts a ete menee, ce qui a permis leur elimination.

L'etude de la croissance de monocristaux de carbure de silicium de structure cristallographique hexagonale 6h par la methode de lely modifiee fait l'objet de ce memoire. L'obtention de monocristaux de carbure de silicium de bonne qualite est un facteur limitant pour le developpement de ce materiau ainsi que des materiaux tels que gan ou aln, dans le secteur de la microelectronique. Apres une description des varietes cristallines du sic, le reacteur experimental mis en place est presente. Les etapes d'elaboration des monocristaux ainsi que les sequences de croissance developpees sont detaillees. Les cristaux obtenus sont etudies en fonction de leurs conditions de croissance afin de degager les parametres importants du systeme. Une fois ces parametres identifies, leurs influences sur la qualite du cristal, sa nature et sur la vitesse de depot sont analysees. Les techniques mises en uvre pour caracteriser les echantillons obtenus sont par ailleurs decrites. Outre ce travail experimental, nous avons tente de simuler les differents phenomenes physiques intervenant lors de la croissance de monocristaux de carbure de silicium dans notre reacteur afin d'ameliorer la comprehension du systeme. Pour cela, nous avons d'une part calcule les equilibres thermodynamiques, d'autre part etudie les transferts thermiques et le transport de masse dans le creuset. Ce travail de simulation, deja utilise dans les procedes de depot chimique en phase gazeuse, est applique pour la premiere fois au transport physique en phase gazeuse

La m. O. C. V. D. D'yba#2cu#3o#7#-#x necessite la synthese de precurseurs volatils et stables thermiquement, probleme crucial dans le cas du baryum, le tetramethylheptanedionate de baruym actuellement utilise presente une instabilite thermique entrainant des problemes de reproductibilite des depots. Afin d'ameliorer la volatilite des precurseurs du baryum, plusieurs voies ont ete explorees. La saturation de la sphere de coordination du ba(thd)#2 par l'action de bases de lewis bidentes a conduit a des adduits ba(thd)#2l#x#y, dont ba(thd)#2(hochmech#2nme#2)#2 et ba(thd)#2(tmeda)#2, caracterises par diffraction des rx sur monocristaux. Ils ont permis d'augmenter la stabilite thermique du ba(thd)#2 mais se dissocient en phase vapeur. La reactivite du thdh sur un aminoalcoxyde a egalement conduit a ba#5(oh)(ochmech#2nme#2)#4(thd)#5, premier beta-dicetonatoalcoxyde de baryum structuralement caracterise. La construction d'edifices heterometalliques y-ba et ba-cu volatifs a ensuite ete etudiee a partir de ligands or assembleurs entre les metaux et de ligands thd chelatants pour reduire la nuclearite et augmenter la volatilite. Plusieurs beta-dicetonatoalcoxydes heterometalliques ont ete isoles par reactions acide-base de lewis entre les alcoxydes de baryum et les tetramethylheptanedionates d'yttrium et de cuivre, notamment yba#3(o#tbu)#6(thd)#3(thf), volatil et ba#2cu(ochmech#2nme#2)#2(thd)#4(#iproh)#2, qui montre a l'etat solide la presence d'interactions metal-heteroatome. L'acces a des composes heterometalliques volatils a enfin ete realise grace a l'emploi de ligands fluoroalcoxydes susceptibles de reduire les forces de van der waals des complexes. Ba#5(oh)(hfip)#9(thf)#4(thf)#4(h#2o), (hfip=och(cf#3)#2) premier fluoroalcoxyde de baryum structuralement caracterise a ete obtenu. La reactivite de ce dernier a conduit a bacu#2(hfip)#4(thd)#2 et y#2ba(hfip)#4(thd)#4, volatils et stables thermiquement. Les particularites structurales de ba#5(oh)(hfip)#9(thf)#4(h#2o) et y#2ba(hfip)#4(thd)#4 sont la presence d'interactions ba-f. Ycu(hfip)#2(thd)#3 a egalement ete isole a partir de y(hfip)#3(thf)#3. Y#2ba(hfip)#4(thd)#4 bacu#2(hfip)#4(thd)#2 et ycu(hfip)#2(thd)#3 ont montre de meilleures proprietes de transport que ba(thd)#2

Le travail presente dans cette these porte sur une etude par imagerie au rayonnement synchrotron de deux materiaux semi-conducteurs, le silicium poreux (sip) et le carbure de silicium (sic), dont l'interet technologique s'est considerabilment accru ces dernieres annees, notamment pour la fabrication de capteurs de gaz (sip) et de circuits electroniques de puissance (sic). Les deformations et les defauts engendres dans ces deux materiaux lors de leur croissance (sic) ou de la production de composants (sip et sic) ont ete etudies non seulement pour comprendre leur origine, mais aussi pour diminuer leur importance en modifiant le procedes. Pour atteindre ces objectifs l'imagerie aux rayons x a ete choisie comme technique d'investigation, en exploitant les caracteristiques uniques du rayonnement x disponible sur la ligne de lumiere id19 de l'esrf (grenoble), telles que la grande taille du faisceau, sa coherence transversale, le large spectre et le flux important de photons. Le manuscrit comporte deux aspects complementaires : - un developpement instrumental concernant la realisation d'un diffractometre haute resolution apte a l'utilisation conjointe de la topographie et de la diffraction, ainsi qu'un developpement methodologique dedie a l'analyse de la forme et de la taille des images obtenues par topographie en rayonnement monochromatique dans le cas de deux geometries de montage du cristal. Cette derniere analyse a ete demontree de grande utilite afin de determiner des importants parametres tels que la courbure des echantillons et le desaccord parametrique entre une couche mince epitaxiee sur un substrat et le substrat meme. - l'application de l'imagerie aux rayons x aux deux materiaux etudies. Dans le cas du sip il s'agit de comparer deux procedes technologiques de realisation de fenetres : masques de nitrure de silicium ou bien implantation de phosphore. Les differentes configurations de topographies aux rayons x sont utilisees et permettent de suivre les defauts au cours de differentes etapes du procede. On peut noter, en particulier, la presence d'une distribution de desaccord parametrique dans le sip et l'existence de gradients de contrainte en bord de motif. Dans le cas du sic la croissance de lingots, par la methode de lely modifiee, a ete etudiee par topographie en exploitant les proprietes de haute energie des photons et de flux important qui ont permis de les analyser sans les decouper. De plus, grace aux proprietes de choerence du faisceau x nous avons visualise la presence dans le volume des cristaux de macro et micro-defauts par contraste de phase. Un recent procede technologique, la fabrication de couches minces de carbure de silicium sur isolant (sicoi) a ete etudie dans la derniere partie de ce travail de these.

Du fait de sa large bande interdite, d'un fort champ de claquage, d'une tres bonne conductivite thermique et de nombreuses autres proprietes specifiques, le carbure de silicium (sic) est un excellent candidat pour des applications haute temperature, haute puissance et haute frequence. Ce memoire est consacre a l'analyse de dispositifs mos sic par la caracterisation electrique. Le premier chapitre donne une description detaillee de la structure cristallographique et des proprietes physiques et electriques du materiau sic. Les principales etapes technologiques sont egalement presentees. Dans le second chapitre, nous developpons une analyse des proprietes des etats electroniques de l'interface sic/sio#2. Cette etude a permis d'une part, de degager les caracteristiques des etats d'interface et d'autre part, d'evaluer et de localiser la charge fixe dans l'oxyde. Le troisieme chapitre est dedie a l'aspect fiabilite des structures mos sic, de la temperature ambiante jusqu'a 350c. Dans une premiere partie, la hauteur de barriere entre la bande de conduction du sic et celle du sio#2 est estimee. Dans la seconde, les proprietes de piegeage des oxydes thermiques realises sur sic sont degagees a partir d'injections fowler-nordheim, realisees en fonction de la temperature et du champ electrique. Le dernier chapitre traite des phenomenes de transport electronique dans les transistors mos sic. Le desordre dont souffrent les couches d'inversion sic limite les performances des transistors mos sic actuels, surtout autour de la temperature ambiante. Le transport electronique particulier qui en resulte est mis en evidence par des mesures de conductivite et l'etude du bruit electrique basse frequence. L'effet du desordre sur les porteurs chauds est egalement traite par l'etude du courant substrat.

Le carbure de silicium est un materiau semiconducteur qui presente des proprietes interessantes pour des applications microelectroniques a haute temperature, haute puissance et haute frequence. L'apparition recente sur le marche de materiau massif en sic-6h permet la fabrication de dispositifs electroniques integres. La metallisation constitue une etape importante dans l'assemblage de ces dispositifs electroniques en carbure de silicium. Le projet a concerne la metallisation du sic et plus precisement, cette etude a porte sur le choix d'un metal permettant de former de bons contacts ohmiques sur sic dope de type n. Ce travail a comporte deux aspects: l'etude sur le plan physique de la caracterisation electrique du contact ohmique et d'un point de vue metallurgique, la caracterisation physico-chimique de l'interface metal/sic. La correlation entre ces deux aspects a constitue l'originalite de ce travail. Nous nous sommes interesses a plusieurs metaux et compose metallique: le tungstene, le titane, le disiliciure de titane et le nickel. Nous avons montre que le tungstene forme un contact ohmique a l'etat non recuit sur sic-6h de type n pour des dopages superieurs a 10#1#8 cm#-#3. De plus, nous avons demontre que le traitement thermique permet d'ameliorer ce contact ohmique. La resistance de contact specifique a ete mesuree en utilisant plusieurs methodes de mesures. Une valeur a ete mesuree a 2,6x10#-#6. Cm#2 pour un dopage de type n a 6x10#1#9 cm#-#3. La reactivite interfaciale des differents metaux: w, ti, tisi#2 et ni sur le sic a ete etudiee par rutherford backscattering spectrometry, secondary ion mass spectrometry, diffraction rx, microscopie electronique a transmission. L'etude thermodynamique du systeme ternaire nous a permis de determiner si les phases formees lors du recuit etaient stables sur sic