Le silicium est connu pour être un poison sévère des catalyseurs d'hydrotraitement (HDT). L’objectif de la thèse a donc été de mettre en place des outils analytiques pour la spéciation du silicium afin d'identifier toutes les molécules silicées réellement formées dans les charges d'HDT. Différents outils analytiques de pointe basés sur des couplages entre la chromatographie en phase gazeuse et la spectrométrie de masse (MS et ICP/MS) ont été développés. Étant donnée la réactivité de certaines espèces silicées, des échantillons représentatifs de la dégradation du PDMS ont été produits dans des conditions de craquage thermique d'un mélange heptane/xylène. L'application à ces échantillons de la stratégie analytique, développée initialement, a démontré la présence du silicium sous différentes formes chimiques. Plus d’une centaine de molécules réparties en 10 familles comprenant un nombre d’atomes de silicium entre 1 et 1500 a été caractérisée. Ces composés silicés vont donc pouvoir être présents dans toutes les coupes pétrolières, des fractions gaz aux fractions les plus lourdes, couvrant ainsi un domaine de coupes pétrolières beaucoup plus vaste que celui des essences. Les siloxanes cycliques (Dn) ont été confirmés comme produits majoritaires de dégradation du PDMS. Les autres composés silicés, jamais caractérisés pour la plupart, sont présents à l’état de traces mais possèdent des groupements réactifs de type hydroxy, métoxy, hydropéroxy susceptibles d’interagir fortement avec le support du catalyseur (Al2O3) et donc de conduire à sa désactivation. / Silicon is known to be a severe poison for hydrotreatment (HDT) catalysts especially in naphtha and gasoline samples. The objective of the PhD was to develop analytical methods for silicon speciation in order to characterize silicon molecules formed during refining steps which potentially affects HDT catalysts. For the analytical strategy, different high-technology analytical tools based on gas chromatography coupled to mass spectrometry (MS and ICP/MS) were developed. Due to the high reactivities of several silicon species, representative samples of PDMS degradation were produced under thermal cracking of a mixture of heptane/xylene (500°C) using a pilot plant. The previously developed analytical strategy was applied to these samples and demonstrated the occurrence of silicon under a wide array of chemical forms. More than a hundred of silicon species belonging to 10 chemical families with a number of silicon atoms ranging from 1 to 1,500 were characterized. These silicon compounds could be present in all petroleum cuts, from the gas fractions to the heavier fractions. Therefore, the investigated range of boiling points was inevitably more important than for naptha and gasoline cuts. Cyclic siloxanes (Dn) were confirmed as the major PDMS degradation products. The other silicon compounds, almost never characterized before, were recovered at trace levels but consisted of reactive groups such as hydroxy, methoxy and hydroperoxy. These silicon species were able to strongly react with the catalytic support (Al2O3) and led to its deactivation

Made available in DSpace on 2014-12-17T15:41:47Z (GMT). No. of bitstreams: 1 KesiaKV.pdf: 2272602 bytes, checksum: 46f23a52fbc9d4e74dfd9f25d2f58e11 (MD5) Previous issue date: 2009-02-19 / In present work, mesoporous materials of the M41S family were synthesized, which were discovered in the early 90s by researchers from Mobil Oil Corporation, thus allowing new perspectives in the field of catalysis. One of the most important members of this family is the MCM-41, which has a hexagonal array of mesopores with pore diameters ranging from 2 to 10 nm and a high surface area, enabling it to become very promising for the use as a catalyst in the refining of oil in the catalytic cracking process, since the mesopores facilitate the access of large hydrocarbon molecules, thereby increasing the production of light products, that are in high demand in the market. The addition of aluminum in the structure of MCM-41 increases the acidity of the material, making it more beneficial for application in the petrochemical industry. The mesoporous materials MCM-41 and Al-MCM-41 (ratio Si / Al = 50) were synthesized through the hydrothermal method, starting with silica gel, NaOH and distilled water. CTMABr was used as template, for structural guiding. In Al-MCM-41 the same reactants were used, with the adding of pseudoboehmite (as a source of aluminum) in the synthesis gel. The syntheses were carried out over a period of four days with a daily adjustment of pH. The optimum conditions of calcination for the removal of the organic template (CTMABr) were discovered through TG / DTG and also through analysis by XRD, FTIR and Nitrogen Adsorption. It was found that both the method of hydrothermal synthesis and calcination conditions of the studies based on TG were promising for the production of mesoporous materials with a high degree of hexagonal array. The acidic properties of the materials were determined by desorption of n-butylamine via thermogravimetry. One proved that the addition of aluminum in the structure of MCM-41 promoted an increase in the acidity of the catalyst. To check the catalytic activity of these materials, a sample of Atmospheric Residue (RAT) that is derived from atmospheric distillation of oil from the Pole of Guamar?- RN was used. This sample was previously characterized by various techniques such as Thermogravimetry, FTIR and XRF, where through thermal analysis of a comparative study between the thermal degradation of the RAT, the RAT pyrolysis + MCM-41 and RAT + Al- MCM-41. It was found that the Al-MCM-41 was most satisfactory in the promotion of a catalytic effect on the pyrolysis of the RAT, as the cracking of heavy products in the waste occurred at temperatures lower than those observed for the pyrolysis with MCM-41, and thereby also decreasing the energy of activation for the process and increasing the rates of conversion of residue into lighter products / No presente trabalho, foram sintetizados materiais mesoporos da fam?lia M41S que foram descobertos no in?cio dos anos 90 por pesquisadores da Mobil Oil Corporation, possibilitando assim novas perspectivas no ramo da cat?lise. Um dos mais importantes membros desta fam?lia ? o MCM-41, que possui um arranjo hexagonal de mesoporos com di?metros de poros entre 2 a 10 nm e uma alta ?rea superficial, tornando-o bastante promissor para ser utilizado como catalisador no refino do petr?leo para o craqueamento catal?tico, j? que seus mesoporos facilitam o acesso de mol?culas grandes de hidrocarbonetos, aumentando assim a produ??o de produtos leves com uma alta demanda no mercado. A adi??o de alum?nio na estrutura do MCM-41 aumenta a acidez do material, tornando-o mais positivo para aplica??o na ind?stria petroqu?mica. Os materiais mesoporosos do tipo MCM-41 e Al-MCM- 41 (raz?o Si/Al=50) foram sintetizados atrav?s do m?todo hidrot?rmico partindo da S?lica gel, NaOH e ?gua destilada. Como direcionador estrutural foi utilizado CTMABr. Para o Al- MCM-41 utilizaram-se os mesmos reagentes acrescentando a pseudobohemita (fonte de alum?nio) no gel de s?ntese. As s?nteses foram realizadas durante um per?odo de quatro dias com corre??o di?ria de pH. As melhores condi??es de calcina??o para remo??o do direcionador org?nico (CTMABr) foram otimizadas por TG/DTG e atrav?s de an?lises por DRX, FTIR e adsor??o de nitrog?nio verificou-se que tanto o m?todo de s?ntese hidrot?rmica como as condi??es de calcina??o baseado nos estudos por TG foram promissores para produ??o de materiais mesoporosos com alto grau de ordena??o hexagonal. As propriedades ?cidas dos materiais foram determinadas pela dessor??o de n- butilamina via termogravimetria. Comprovou-se que a adi??o de alum?nio na estrutura do MCM-41 promoveu um aumento na acidez deste catalisador. Para verificar a atividade catal?tica desses materiais utilizou-se uma amostra do Res?duo Atmosf?rico (RAT) que ? proveniente da destila??o atmosf?rica do petr?leo proveniente do P?lo de Guamar?- RN previamente caracterizado por v?rias t?cnicas como: Termogravimetria, FTIR e FRX, realizando-se atrav?s da an?lise t?rmica um estudo comparativo entre a degrada??o t?rmica do RAT, pir?lise do RAT+MCM-41 e RAT+Al-MCM-41. Verificou-se que o Al-MCM-41 promoveu um efeito catal?tico mais satisfat?rio na pir?lise do RAT, j? que o craqueamento dos produtos pesados presentes no res?duo ocorreu em temperaturas inferiores ?s observadas para a pir?lise com MCM-41 e com isso diminuindo tamb?m a energia de ativa??o para o processo, bem como aumentando os valores de convers?o do res?duo em produtos leves

Made available in DSpace on 2014-12-17T15:42:08Z (GMT). No. of bitstreams: 1 Geraldo Eduardo da Luz Junior_TESE.pdf: 1318067 bytes, checksum: bc521809cc7c08b9ef99f31a1034f3a2 (MD5) Previous issue date: 2010-04-26 / In order to obtain a biofuel similar to mineral diesel, lanthanum-incorporated SBA- 15 nanostructured materials, LaSBA-15(pH), with different Si/La molar ratios (75, 50, 25), were synthesized in a two-steps hydrothermal procedure, with pH-adjusting of the synthesis gel at 6, and were used like catalytic solids in the buriti oil thermal catalytic cracking. These solids were characterized by X-ray fluorescence (XRF), powder X-ray diffraction (XRD), thermogravimetric analysis (TG/DTG), infrared spectroscopy (FTIR), nitrogen porosimetry and ethanol dehydration, aiming to active sites identify. Taken together, the analyses indicated that the synthesis method has employed to obtain materials highly ordered mesostructures with large average pore sizes and high surface area, besides suggested that the lanthanum was incorporated in the SBA-15 both into the framework as well as within the mesopores. Catalytic dehydration of ethanol over the LaSBA-15(pH) products has shown that they have weak Lewis acid and basic functionalities, indicative of the presence of lanthanum oxide in these samples, especially on the La75SBA-15(pH) sample, which has presented the highest selectivity to ethylene. The buriti oil thermal and thermal catalytic cracking, realized from the room temperature to 450 ?C in a simple distillation system, has allowed obtaining two liquid fractions, each consisting of two phases, one aqueous and another organic, organic liquid (OL). The OL obtained from first fractions has shown high acid index, even in the thermal catalytic process. One the other hand, OL coming from second ones, called green diesel (GD), have presented low acid index, particularly that one obtained from the thermal catalytic process realized over LaSBA-15(pH) samples. The acid sites presence in these samples, associated to their large average pore sizes and high surface areas, have allowed them, especially the La75SBA-15(pH), to present deoxygenating activity in the buriti oil thermal catalytic cracking, providing an oxygenates content reduction, particularly carboxylic acids, in the GD. Furthermore, the GD comes from the second liquid fraction obtained in the buriti oil thermal catalytic cracking over this latest solid sample has shown hydrocarbons composition and physic-chemical properties similar to that mineral diesel, beyond sulfur content low / Com o objetivo de obter um biocombust?vel semelhante ao diesel mineral, materiais nano-estruturados do tipo SBA-15 com lant?nio incorporado, LaSBA-15(pH), com raz?es molares Si/La = 75, 50 e 25, foram sintetizados em dois est?gios, com ajuste do pH do gel de s?ntese a 6, e utilizados como s?lidos catal?ticos no craqueamento termocatal?tico de ?leo de buriti. As amostras s?lidas foram caracterizadas por fluoresc?ncia de raios-X (FRX), difra??o de raios-X (DRX), an?lise termogravim?trica (TG/DTG), espectroscopia na regi?o do infravermelho (FTIR), adsor??o-dessor??o de nitrog?nio e desidrata??o de etanol, para identifica??o dos s?tios ativos. Os resultados destas caracteriza??es indicaram que o m?todo de s?ntese empregado proporcionou a obten??o de materiais mesoestruturados altamente ordenados com grande di?metro m?dio de poros e elevada ?rea superficial, al?m de sugerir que o lant?nio foi incorporado na SBA-15 tanto no interior das paredes, quanto dentro dos mesoporos. A desidrata??o catal?tica de etanol sobre os s?lidos LaSBA-15(pH) mostrou que eles apresentam s?tios ?cidos e b?sicos de Lewis, indicativo da presen?a de ?xido de lant?nio nestes, especialmente na amostra La75SBA-15(pH), que apresentou a maior seletividade para etileno. Os craqueamentos t?rmico e termocatal?ticos do ?leo de buriti, realizados da temperatura ambiente a 450 ?C em um sistema de destila??o simples, possibilitaram a obten??o de duas fra??es l?quidas, compostas por duas fases, uma aquosa e outra org?nica, l?quido org?nico (LO). O LO obtido a partir das primeiras fra??es apresentou ?ndice de acidez muito elevado, at? mesmo nos processos termocatal?ticos. Por outro lado, o LO oriundo das segundas fra??es, denominado de diesel verde (DV), apresentou baixo ?ndice de acidez, particularmente aquele obtido nos processos realizados sobre as amostras LaSBA-15(pH). Os s?tios ?cidos presentes nestas amostras, associados aos seus grandes di?metros m?dios de poros e ?s elevadas ?reas superficiais, permitiram que elas, especialmente a La75SBA-15(pH), apresentassem atividade desoxigenante no craqueamento temocatal?tico do ?leo de buriti, ocasionando uma diminui??o da concentra??o de oxigenados no DV, particularmente ?cidos carbox?licos. Al?m disso, o DV obtido sobre esta ?ltima amostra s?lida apresentou composi??o de hidrocarbonetos e propriedades f?sico-qu?micas semelhantes ?s do diesel mineral, al?m de um baixo teor de enxofre

L'apparition récente de nouveaux matériaux dans les structures de chaussée associée à une diminution de l'épaisseur des couches de surface et une augmentation du chargement des poids lourds et de leur fréquence de passage a entrainé de nouvelles pathologies de dégradation. Outre les problèmes d'orniérage bien connus, apparaissent désormais des fissures descendantes (top down cracking) ainsi que des problèmes de décohésion aux interfaces. Ces nouvelles pathologies entrainent des dépenses considérables sur l'ensemble du réseau (environ 15 milliards d'euros par an), particulièrement en zones urbanisées plus sujettes aux dégradations de surface et ne permettent pas d'estimer convenablement les durées de vie de la chaussée, le plus souvent surestimée dans les méthodes de dimensionnement actuelles. Ce travail de doctorat propose une nouvelle approche du contact pneu-chaussée permettant de mieux appréhender les contraintes principales et résiduelles dans une structure de chaussée bitumineuse. A l'aide d'un outil numérique rapide de calcul basé sur une approche semi-analytique (« Semi-Analytical Methods » (SAM)), la géométrie précise du pneumatique est intégrée afin d'obtenir une répartition de pression de contact ainsi qu'un cisaillement surfacique réelle sur la chaussée. Dans un premier temps, un modèle de contact roulant tractif élastique est implémenté pour des cas théoriques simples et validé par des résultats analytiques et numériques de la littérature. Ensuite, ce modèle est étendu pour prendre en compte le comportement élasto-plastique des corps en contact. Ce dernier est comparé à un résultat numérique basé sur la méthode des éléments finis issu de la littérature. Les résultats, pour une application contact pneu-chaussée, montrent une répartition non homogène des contraintes dans la structure et principalement dans les premiers centimètres sous la surface avec des niveaux beaucoup plus importants que peuvent le prédire les modèles actuels qui utilisent une charge uniformément répartie. La pression de contact est comparée aux mesures effectuées par un système nommé TekScan et les champs mécaniques en sous couches sont comparés à ceux d'Alizé-LCPC dans le cas d'une structure simple. Les cisaillements surfaciques sont déterminés dans le cas du roulement tractif. Une application est effectuée sur la modélisation des dégradations des chaussées en surface. Dans un premier temps, des analyses sur le comportement de la chaussée en surface sont effectuées pour une couche de béton bitumineux semi grenu (BBSG) semi-infinie supposée élastique, homogène sous conditions d'accélération, de freinage et de virage. Pour des études sur le top down cracking, des déformations et directions principales sont déterminées et analysées. Ensuite, le modèle de contact élasto-plastique est appliqué sur une couche semi-infinie de grave bitume GB3. Des déformations et contraintes résiduelles générées dans la structure sont déterminées en vue d'une analyse sur les ornières d'instabilité. Une fois validés, ces résultats permettront d'estimer plus fidèlement la durée de vie résiduelle des chaussées mais également de comprendre et d'éviter les mécanismes de dégradation en surface ou proche de la surface. / The recent appearance of new materials in road structures associated with surface layers thickness decreasing and the increasing of trucks loading and their passage frequency has led to new pathologies of degradation. In addition to the well-known rutting problems, top down cracking is now appearing as well as problems of decohesion at the interfaces. These new pathologies led to considerable expenditure on the entire network (around 15 billion euros per year), particularly in urbanized areas that are more prone to surface damage and do not make it possible to adequately estimate the lifetimes of the roadway, most often overestimated in current design methods. This doctoral work proposes a new approach of the tire-road contact allowing for better apprehend of the main and residual stresses in a bituminous pavement structure. Using a fast numerical tool based on a semi-analytical approach ("Semi-Analytical Methods" (SAM)), the precise geometry of the tire is integrated in order to obtain a real contact pressure distribution as well as surface shear on the pavement surface. Initially, an elastic tractive rolling contact model is implemented for simple theoretical cases and validated by analytical and numerical results from the literature.Then, this model is extended to take into account the elastoplastic behavior of the bodies in contact. This is compared to a numerical result based on the nite element method from the literature. The application for tire-pavement contact results, show a non-uniform distribution of stresses in the structure and mainly in the rst centimeters below the surface with much higher levels than can be predicted by current models that use a uniformly distributed load. The contact pressure is compared to the measurements made by a system called TekScan and the mechanical elds in sublayers are compared to those of Alizé-LCPC in the case of a simple structure. The surface shears are determined in the case of tractive rolling. An application is carried out on the modeling of surface pavement damage. Firstly, analyzes of the behavior of the surface pavement are carried out for a semi-innite semi-grit asphalt concrete layer supposed to be elastic, homogeneous under conditions of acceleration, braking and turning. For studies on top down cracking, principals deformations and directions are determined and analyzed. Then, the elastoplastic contact model is applied on a semi-innite asphalt agragate layer. Deformations and residuals stresses generated in the structure are determined for an analysis on the instability ruts. Once validated, these results will make it possible to more accurately estimate the residual life of pavements but also to understand and avoid surface or near surfacedegradation mechanisms.

Les aciers TWIP (TWinning Induced Plasticity) à haute teneur en manganèse sont particulièrement prometteurs pour les applications automobiles de par leur excellent compromis entre résistance mécanique et ductilité. Cependant, la microstructure austénitique leur confère une sensibilité à la fragilisation par le zinc liquide durant les procédés de soudage ; le zinc liquide provenant de la fusion du revêtement résultant de l’élévation de température à la surface de l’acier. Dans cette étude, la fissuration d’un acier austénitique à haute teneur en manganèse a été étudiée en rapport avec le phénomène de fragilisation par les métaux liquides par des essais de traction à chaud réalisés sur des éprouvettes électrozinguées au moyen d’un simulateur thermomécanique Gleeble 3500. L’influence de nombreux paramètres tels que la température et la vitesse de déformation sur la fissuration a été étudiée. La fragilisation apparaît dans un domaine de température limité qui dépend des conditions expérimentales. Les conditions pour lesquelles la fissuration apparaît peuvent être rencontrées durant les procédés de soudage. L’existence d’une contrainte critique pour laquelle la fissuration apparait a été mise en évidence et celle-ci peut être utilisée comme critère de fissuration. Enfin, l’étude de l’influence de différents paramètres tels que le temps de contact entre l’acier et le zinc liquide avant l’application des contraintes, le revêtement et l’acier sur l’apparition de la fragilisation apporte des éléments de compréhension du mécanisme de fissuration et permet de proposer des solutions pour éviter la fissuration durant le soudage par point de l’acier étudié. / High manganese TWIP (TWinning Induced Plasticity) steels are particularly attractive for automotive applications because of their exceptional properties of strength combined with an excellent ductility. However, as austenitic steels, they appear to be sensitive to liquid zinc embrittlement during welding, the liquid zinc arising from the melted coating due to the high temperatures reached during the welding process. In this framework, the cracking behaviour of a high manganese austenitic steel has been investigated in relation to the liquid metal embrittlement (LME) phenomenon by hot tensile tests carried out on electro-galvanized specimens using a Gleeble 3500 thermomechanical simulator. The influence of different parameters such as temperature and strain rate on cracking behaviour has been studied. Embrittlement appears within a limited range of temperature depending on experimental conditions. Conditions for which cracking occurs could be experienced during welding processes. The existence of a critical stress above which cracking appears has been evidenced and this critical stress can be used as a cracking criterion. Finally, the study of the influence of different parameters such as time of contact between steel and liquid zinc before stress application, coating and steel on LME occurrence provides understanding elements of LME mechanism and permits to suggest solutions for preventing cracking during spot welding of such steels.

La tomographie en contraste de diffraction est une nouvelle technique non destructive d'imagerie synchrotron qui caractérise la microstructure et l'orientation des grains dans les matériaux polycristallins en trois dimensions (3D). En la combinant avec la tomographe par contraste de phase. Il est pour la première fois possible d'observer in situ la propagation 3D des fissures de fatigue courtes au sein d'un ensemble de grains entièrement caractérisé (orientation et forme). L'approche combinée, appelée « tomographie tri-dimensionnelle par rayons X des fissures courtes et de la microstructure »(T3DXFM), a été développée sur l’alliage de titane métastable "Beta21S". Une grande partie de ce travail porte sur le développement de la méthodologie T3DXFM. Dans le jeu de données combinées, chaque point de la surface de rupture 3D peut être associé à une structure de données multidimensionnelle contenant des variables décrivant l'orientation des grains, l'orientation locale de la surface de rupture ainsi que l'histoire de la propagation. La méthode utilise un maillage de surface composé de triangles qui décrit la fissure (en d'autres termes: la surface de rupture) dans l'état de propagation mesuré au dernier cycle de fatigue réalisé. Les orientations des grains, les différents fronts de la fissure, les vitesses de croissance locales ainsi que les joints de grains peuvent être visualisés en attribuant des couleurs à ce maillage. Des outils d'extraction des figures de pôle ont été créés et mis en œuvre. Un algorithme a été développé qui est capable de mesurer la vitesse de propagation locale 30 d'une fissure contenant des branchements. / X-Ray Diffraction Contrast Tomography (DCT) is a recently developed, non-destructive synchrotron imaging technique which characterizes microstructure and grain orientation in polycrystalline materials in three dimensions (3D). By combining it with propagation based phase contrast tomography (PCT) it is for the first lime possible to observe in situ the 3D propagation behavior of short fatigue cracks (SFCs) within a set of fully characterized grains (orientation and shape). The combined approach, termed 3D X-ray Tomography of short cracks and Microstructure (3DXTSM), has been developed on the metastable beta titanium alloy "Beta21S". A large part of this work deals with the development of the 3DXTSM methodology. In the combined dataset, each point on the 3D fracture surface can be associated with a multidimensional data structure containing variables describing the grain orientation, the local fracture surface normal and the propagation history. The method uses a surface mesh composed of triangles that describes the crack (in other words: the fracture surface) in the last propagation state measured. Grain orientations, crack fronts, local growth rates and grain boundaries can be visualized by assigning colors to this mesh. The data structure can be interrogated in a number of different ways. Tools for extracting pole figures and pole density distribution functions have been implemented. An algorithm was developed that is capable of measuring the 3D local growth rate of a crack containing branches. The accuracy of the grain boundaries as reconstructed with OCT was evaluated and the elastic constants of Beta21S were determined.

Cette thèse s’inscrit dans une démarche d’investigation des mécanismes d’endommagement de réfractaires électrofondus à très haute teneur en zircone. L’accent est en particulier mis sur la compréhension du phénomène de microfissuration, mécanisme de dégradation le plus dommageable pour ces matériaux. S’opérant au refroidissement, il conduit à la fracture des blocs électrofondus. Réalisés dans le cadre du programme NOREV (NOouveau REfractaires Verriers) soutenu par l’ANR, les travaux présentés sont le fruit d’une collaboration avec Saint Gobain CREE, le Centre des Matériaux P.M. FOURT de l’Ecole des Mines de Paris, le laboratoire GEMH de l’ENSCI de Limoges, ICAR et Euro Physical Acoustics. Ils font suite aux travaux réalisés lors du programme PROMETHEREF (2002-2005). Des expériences préliminaires ont permis de définir et d’affiner les orientations de l’étude. Prenant en considération l’anisotropie de dilatation de la zircone monoclinique et quadratique décrite dans la littérature, l’imagerie des électrons rétrodiffusés a notamment permis de révéler un lien entre l’arrangement de domaines cristallographiques et la fissuration observée. D’autres expérimentations conduites dans le domaine de l’émission acoustique ont mis en lumière son applicabilité et ses apports pour notre problématique ainsi que la nécessité de développer un algorithme de traitement adapté. Ainsi, trois axes de recherche ont été développés. Ils visent, par leur complémentarité, à permettre une analyse à plusieurs échelles de l’endommagement des matériaux de l’étude tout en s’appuyant sur leur comparaison. Ils permettent respectivement d’évaluer l’endommagement de manière indirecte, d’en examiner les origines à l’échelle microscopique et d’en déterminer l’occurrence en température à l’échelle globale de l’échantillon. Le premier volet consiste en une évaluation des propriétés mécaniques en températures soulignant les incidences de la fissuration. La mise en évidence de la fissuration sous-critique, l’évolution des propriétés élastiques ainsi que la détermination des propriétés à la rupture apportent autant d’éléments qui permettent ensuite d’enrichir l’étude fractographique. Le deuxième volet s’attache, après une interrogation quant à la présence simultanée de zircone monoclinique et quadratique, à déterminer les paramètres de maille et les coefficients de dilatation de ces deux structures pour les différents matériaux. La modélisation des mailles correspondantes se révèle alors d’un grand intérêt pour l’analyse de cartographies EBSD. Enfin, la validation et l’application d’un process de traitement novateur des données d’émission acoustique, intégrant un algorithme génétique, permet de quantifier l’endommagement et d’apporter des précisions quant à son action en température. Ces constatations sont confortées par des suivis par acousto-ultrasons. / This thesis falls under an approach of investigation on the damage mechanisms of high zirconia fused-cast refractories. The focus is particularly set on the comprehension of the phenomenon of microcracking responsible for the degradation of these materials. Taking place at cooling time, it leads to the fracture of the fused-cast blocks. Realized within the framework of the French research programme NOREV (NOouveau REfractaires Verriers) supported by the ANR, the work presented in this manuscript is the fruit of a collaboration with Saint Gobain CREE, the Centre des Materiaux P.M. FOURT of the Ecole des Mines de Paris, the laboratory GEMH of the ENSCI of Limoges, ICAR and Euro Physical Acoustics. It follows the works completed at the time of the previous programme (PROMETHEREF, 2002-2005). Preliminary experiments have enabled to define and specify the directions of this study. Taking into account the thermal expansion anisotropy of both monoclinic and tetragonal zirconia as described in the literature, the imagery of the backscatter electrons has in particular revealed a link between the presence of crystallographic domains and the observed cracking. Other experiments conducted in the field of acoustic emission have clarified its applicability and its contributions to our problems as well as the need for developing an adapted algorithm to process data. Thus, three research orientations have been developed. They aim, by their complementarity, to allow an analysis of the different scales of the damage on the study materials and is based on their comparison. They respectively allow to assess the damage in an indirect way, to examine its origins at a microscopic level and to determine its occurrence in temperature at the global scale of the sample. The first axis consists in the evaluation of the mechanical properties in temperatures emphasizing the incidences of cracking. The description of subcritical cracking, the evolution of the elastic properties as well as the determination of the fracture properties bring elements which enable to enrich the fractographic study. The second axis aims, after an interrogation as for the simultaneous presence of monoclinic and tetragonal zirconia, to determine the cell parameters and the thermal expansion coefficients of both structures for the different materials. The modeling of the corresponding cells then appears of great interest for the analysis of EBSD maps. Lastly, the validation and the application of an innovative process for the treatment of the acoustic emission data integrating a genetic algorithm enable to quantify the damage and to bring precise details as for its action in temperature. These observations are consolidated by acousto-ultrasounds follow-ups.

Le sujet concerne l’influence des effets tridimensionnelles sur les champs de déformation et de contrainte au voisinage d’une éprouvette chargée en mode I. La loi de comportement caractéristique des polymères amorphes avec un seuil d’écoulement viscoplastique suivi d’un adoucissement et d’un durcissement à mesure que la déformation augmente est prise en compte. La loi est implantée dans une UMAT abaqus. Les champs au voisinage de l’entaille sont analysés et les résultats 3D comparés à ceux correspondant à un calcul 2D sous l’hypothèse de déformation plane. L’influence de l’épaisseur de l’échantillon est étudiée et nous montrons qu’au-delà d’un rapport épaisseur t sur rayon d’entaille rt, t/rt>20, les champs de déformation plastique sont qualitativement similaires entre les calculs 3D et 2D. En revanche, nous montrons que la répartition des contraintes et notamment celle de la contrainte moyenne est sur-estimée avec un calcul 2D en comparaison à une simulation 3D. Nous prenons en compte par la suite la rupture par craquelage, modélisée avec un modèle cohésif. Une étude paramétrique est menée afin de définir une procédure d’identification des paramètres caractéristiques du modèle cohésif. Par ailleurs les simulations montrent qu’au-delà d’un rapport t/rt supérieur à 20, une ténacité minimum peut être estimée : ceci constitue un résultat important pour la détermination expérimentale de la ténacité des polymères ductiles. / We investigate 3D effect of crack tip palsticity and the influence of the thickness on 3D glassy polymer fracture. The characteristuc constitutive law with a viscoplastic yield stress followed by softening and progressive hardening is accoutne for and implemented in a UMAt routine, in abaqus. The crack tip fields are investigated and 2D plasne strain versus 3D calculations compared. Qualitatively, the palstic distribution are comparableas soon as the ratio thickness over crack tip radius is larger than 20. However, the 2D calculations over estimate the stress distribution compared to the 3D cases. We have accounted for failure by crazing that is described with a cohesive models. A parametric study sheds light on the methodology to use for the calibration of the cohesive parameters. The simulations show that for a ratio thickness over craci tip radius larger than 20, a minimum tuoghness can be observed. This results has implication on the definition of a thickness larger enough experimentally.

Les dépôts de YSZ, élaborés par projection plasma, sont des céramiques réfractaires généralement utilisées pour les applications de barrières thermiques (TBC). Sa faible conductivité thermique associée à sa bonne résistance mécanique assure aux TBC de hautes performances et de bons rendements. La structure et la microstructure complexe sont à l'origine de ces propriétés mécaniques, et celles doivent être contrôlées. Tout comme les céramiques denses la YSZ se dégrade en température et sous vapeur d'eau.La dégradation des propriétés mécaniques dans le temps (module d'élasticité et contrainte à rupture)est accélérée par la température. Pour cette étude les propriétés ont été évaluées en flexion 3 points à température ambiante. Les observations structurales et microstructurales ont été réalisées respectivement par DRX et microscopie électronique à balayage au cours du vieillissement. Un model analytique a pu être proposé pour prédire le comportement du matériau dans le temps sous humidité. / Yttria Stabilized Zirconia (YSZ) coatings, deposited by plasma sprayed process, are refractory ceramics mostly used as the Thermal Barrier Coating (TBC) applications. The low YSZ thermal conductivity associated to the good mechanical resistance ensures a high performances and efficiencies of these TBC. The structure and the complex microstructure are responsible for the mechanical properties and must be controlled. Like brittle ceramic materials, the YSZ is affected by degradation at low temperature due to water vapor. Material ageing results from the progressive degradation of the mechanical properties (such as fracture strength and Young’s modulus), which seem to decrease in time and accelerate depending on temperature. In this study, the mechanical properties have been evaluated by means of three-point bending tests at room temperature. The observations of the structure and the microstructure are respectively investigated by X-ray diffraction and SEM-technique with material ageing. An analytical model is suggested in order to predict the evolution of the properties under humidity atmosphere.

Two failure mechanisms in a double lap joint are investigated. Analytical models of net-section and gross-section failure modes are proposed to describe these mechanisms. The effects of lamping force, interference fit, maximum axial load and WDCP on fatigue performance of the joint are included in the models. The effect of WDCP is assumed to give a reduction in friction coefficient. Three types of stress reduction factors are proposed in the net-section failure model to account for these parameters. The stress reduction factors modify stress range that is used in crack growth calculation. If there are no effects of these parameters, the stress reduction factors are equal to one. Two types of fretting stress are introduced in gross-section failure model to describe either sliding contact or incipient sliding contact on faying surface. The fretting stress is combined with body stress to modify stress range. The net-section failure model predicts that fatigue life is increasing as interference fit, clamping force and friction coefficient increase. The gross-section failure model predicts that fatigue life is decreasing as clamping force and friction coefficient increase. Both models predict that fatigue life is decreasing as maximum axial load increases. Transition of the failure mode occurs earlier as friction coefficient and interference fit increase, while it is delayed as maximum axial load increases. A transition parameter is proposed to establish a relationship between the four main parameters. The transition parameter is expressed in a polynomial equation. It gives an optimum combination of the four main parameters in order to achieve relatively higher fatigue life by having gross-section failure mode. Finite element analysis and fatigue testing are performed to validate the models. The finite element and the analytical models show that stress concentration factor at the edge of the hole is decreasing as clamping force increases. The rate of decrease of stress concentration factor is increasing as friction coefficient increases. While stress concentration factor on the faying surface is increasing as clamping force and friction coefficient increase. Fatigue testing reveals that the fatigue life of the joint is in good agreement with the predicted fatigue life of the proposed models.