Student Number: 0008522F Master of Science Faculty of Engineering & The Built Environment School of Mechanical, Industrial & Aeronautical Engineering / An aircraft travelling at supersonic speeds close to the ground generates a bow wave, which is reflected off the ground surface. When the aircraft enters a valley, the three-dimensional bow wave is reflected off the valley walls, such that it could focus behind the aircraft. Complex threedimensional wave surfaces will result. The real situation of an aircraft entering a valley can be modelled and tested experimentally in a shock tube. To simulate the process a planar shock wave, generated in a shock tube, is moved over several notched wedge configurations. Schlieren photographs were produced to identify the resulting complex three-dimensional wave structures and then verified by three-dimensional CFD. The valley geometries investigated are rectangular, triangular, parabolic and conical. Three hill geometries were also investigated. The three-dimensional reflected surfaces from the rectangular valleys were found to vary only slightly as the valley floor inclination is increased. As the incident wave interacts with both the wedge and valley floor surfaces two prominent reflections occur. A primary reflected wave surface is generated from regular reflection off the wedge. This surface flows over into the valley contacting the incident wave at a second contact point. A secondary reflected wave is found underneath the primary reflected wave, generated due to Mach reflection occurring over the full width off the valley floor. The area of the incident wave between the second contact point and the triple point is seen to bow out into the downstream flow. The Mach stem of the reflection off the valley floor tends to become less pronounced for the larger valley floor inclination angles. In all the rectangular valleys, a shear layer is present, cascading down the valley wall and then along the valley entrance. The shear layer tends to decrease in size as the valley floor inclination increases. Both prominent reflected shock surfaces are almost conical in nature at close proximity to the valley wall. The triangular valleys show similar reflection patterns as the rectangular valleys. As the incident shock wave initially interacts with the wedge surface only regular reflection occurs. The resulting reflected wave forms the primary reflected surface which flows over into the valley. The reflection changes to Mach reflection as the incident wave interacts with the valley floor. The Mach stem of the reflection off the valley floor increases in characteristic height as one moves from the valley entrance wall to the plane of symmetry. The Mach stem is much smaller for the higher valley floor inclinations. A secondary reflected wave is found underneath the primary reflected surface. The secondary wave is Mach reflection near the plane of symmetry which turns iii to regular reflection closer to the valley wall. The primary and secondary reflected surfaces merge near the plane of symmetry and again along the wedge surface. A shear layer is found to cascade down the valley entrance wall for all geometries, decreasing in strength as the valley inclination angle increases. The parabolic valleys show similar reflection patterns as the triangular valleys. As the incident wave interacts with both the wedge and valley surfaces two reflections occur. The reflection off the wedge surface is regular. As the incident wave flows over into the valley the initial reflection off the valley floor is regular. This regular reflection then turns into Mach reflection the closer one moves to the symmetry plane. The Mach reflection off the valley floor forms a secondary reflected wave underneath the primary reflected wave that is found to flow over into the valley. The primary reflected wave contacts the incident wave at a second contract point found above the triple point. This contact point moves closer to the triple point and eventually along the secondary reflected wave as the incident wave advances downstream. The second contact point at a single time instant is also seen to move closer to the triple point as one moves closer to the plane of symmetry. A shear layer is found cascading down the valley entrance wall. The secondary reflected wave of the Mach reflection off valley floor forms a semi-circular surface which contacts the floor just after the shear layer. The Mach reflection off the valley floor changes to regular reflection as the surface begins to climb up along the valley entrance wall. The conical valleys once again show similar reflection patterns as those found in the other valley geometries. As the incident wave interacts with both the wedge and valley surfaces two reflections occur. Regular reflection occurs off the wedge surface with the resulting primary reflected wave flowing over into the valley. This primary reflected wave contacts the incident shock at a second contact point in the valley. The reflection off the valley floor is regular close to the valley entrance wall changing to Mach reflection nearer the symmetry plane. The reflected wave from the Mach reflection forms the secondary reflected surface found beneath the primary reflected wave. The secondary reflected Mach wave changes to regular reflection as the surface nears the valley wall, with the reflection point travelling along the valley floor until coincident with the valley entrance wall, where it then travels along the entrance wall. The second contact point found on the incident wave is found above the triple point and moves down the incident shock to eventually coincide with the triple point. A weak shear layer is found to cascade down the valley entrance wall. A weak separation also occurs at the entry point of the valley. iv The three hill geometries, triangular, parabolic and conical, all display similar reflection patterns. As the incident wave advances downstream regular reflection occurs off both the wedge and hill surfaces. The reflected waves come together at a point off the surface. At this point a double triple point occurs with two resulting Mach stems. One Mach stem contacts the wedge surface while the other contacts the hill surface. The resulting double Mach stem surface wraps around the base of the hill getting progressively tighter the closer it gets to the incident wave. The only major differences between all three geometries is the shape of the resulting reflected wave off the hill surface (which tends to follow the same geometric shape as the hill) and the distance between the two triple points for the conical and parabolic hills tends to be larger than that found for the triangular hill.

Animating by hand can be a long and challenging process in part because of the necessity of drawing every frame by hand. 3D animation media minimize this problem with the use of automatically interpolated frames, but despite significant research no universally acceptable techniques have been demonstrated for 2 dimensional interpolation. In this paper we explore computer-assisted optimizations to the animation pipeline. Specifically, we utilize 3D motion fields to create more realistic in-between frames for sets of 2D ``key frames.'' We demonstrate our method by using it to create 2D special effects for a 30-second clip of an animated short film.

In dieser Arbeit werden die dynamischen Strukturen und Mannigfaltigkeiten in geschlossenen chaotischen Systemen untersucht. Das Wissen um diese dynamischen Strukturen (und Mannigfaltigkeiten) ist von Bedeutung, da sie uns einen ersten Überblick über die Dynamik des Systems geben, dass heisst, mit ihrer Hilfe sind wir in der Lage, das System zu charakterisieren und eventuell sogar seine Dynamik vorherzusagen. Die Visualisierung der dynamischen Strukturen, speziell in geschlossenen chaotischen Systemen, ist ein schwieriger und oft langer Prozess. Hier werden wir die sogenannte 'Leaking-Methode' (an Beispielen einfacher mathematischer Modelle wie der Bäcker- oder der Sinus Abbildung) vorstellen, mit deren Hilfe wir die Möglichkeit haben, Teile der Mannigfaltigkeiten des chaotischen Sattels des Systems zu visualisieren. Vergleiche zwischen den gewonnenen Strukturen und Strukturen die durch chemische oder biologische Reaktionen hervorgerufen werden, werden anhand eines kinematischen Modells des Golfstroms durchgeführt. Es wird gezeigt, dass mittels der Leaking-Methode dynamische Strukturen auch in Umweltsystemen sichtbar gemacht werden können. Am Beispiel eines realistischen Modells des Mittelmeeres erweitern wir die Leaking-Methode zur sogenannten 'Exchange-Methode'. Diese erlaubt es den Transport zwischen zwei Regionen zu charakterisieren, die Transport-Routen und Austausch-Bassins sichtbar zu machen und die Austausch-Zeiten zu berechnen. Austausch-Bassins und Zeiten werden für die nördliche und südliche Region des westlichen Mittelmeeres präsentiert. Weiterhin werden Mischungseigenschaften im Erdmantel charakterisiert und die geometrischen Eigenschaften von Mannigfaltigkeiten in einem 3dimensionalen mathematischen Modell (ABC-Abbildung) untersucht. / In this thesis, dynamical structures and manifolds in closed chaotic flows will be investigated. The knowledge about the dynamical structures (and manifolds) of a system is of importance, since they provide us first information about the dynamics of the system - means, with their help we are able to characterize the flow and maybe even to forecast it`s dynamics. The visualization of such structures in closed chaotic flows is a difficult and often long-lasting process. Here, the so-called 'Leaking-method' will be introduced, in examples of simple mathematical maps as the baker- or sine-map, with which we are able to visualize subsets of the manifolds of the system`s chaotic saddle. Comparisons between the visualized manifolds and structures traced out by chemical or biological reactions superimposed on the same flow will be done in the example of a kinematic model of the Gulf Stream. It will be shown that with the help of the leaking method dynamical structures can be also visualized in environmental systems. In the example of a realistic model of the Mediterranean Sea, the leaking method will be extended to the 'exchange-method'. The exchange method allows us to characterize transport between two regions, to visualize transport routes and their exchange sets and to calculate the exchange times. Exchange times and sets will be shown and calculated for a northern and southern region in the western basin of the Mediterranean Sea. Furthermore, mixing properties in the Earth mantle will be characterized and geometrical properties of manifolds in a 3dimensional mathematical model (ABC map) will be investigated.

A microtomografia computadorizada (uCT) é uma técnica de ensaio não destrutivo, frequentemente utilizada no estudo da estrutura interna de ossos, com uma resolução espacial da ordem de mícrons. Neste trabalho, seis pares de amostras ósseas (fêmur de rato) foram estudados através da uCT. Os ensaios foram conduzidos na presença ou não de filtros de alumínio (espessura de 0,25; 0,50 e 0,75 mm), utilizando-se três níveis de resolução (33,3; 15,0 e 9,5 um). Os parâmetros de arquitetura óssea BS (área óssea da amostra), BV (volume ósseo da amostra), TS (área superficial da amostra), TV (volume da amostra), BV/TV (razão entre o volume ósseo e o volume da amostra), BS/BV (razão entre a área óssea da amostra e o volume ósseo da amostra), Tb.N (densidade trabecular), Tb.Th (espaçamento entre as trabéculas), Tb.Sp (separação trabecular), conectividade e anisotropia foram determinados através das análises em duas (2D) e/ou três (3D) dimensões. A comparação entre os valores dos parâmetros obtidos através dessas análises foi realizada através do teste t pareado e da correlação de Pearson. Com base nos resultados, foi possível determinar a influência da resolução da imagem na qualidade dos parâmetros da arquitetura óssea obtidos através das análises 2D e/ou 3D. Os dados mostram que a presença de filtro de alumínio também afeta a qualidade desses parâmetros. Assim, os melhores resultados são obtidos com resolução máxima e filtro de alumínio com espessura de 0,25 ou 0,50 mm. / X-Ray Computed Microtomography (uCT) is a nondestructive technique used to study the internal structure of bones with a spatial resolution of the order of microns. In this study, six pairs of bone samples (femur mouse) were studied by uCT. The tests were conducted in the absence or presence of aluminum filters (thickness of 0.25, 0.50 and 0.75 mm), using three different resolution levels: 33.3, 15.0 and 9.5 um. The bone architecture parameters BS (surface area of the trabecular bone), BV (bone volume of the sample), TS (surface area of the sample), TV (sample volume), BV/TV (bone volume fraction), BS/BV (ratio bone surface and volume), Tb.N (trabecular density), Tb.Th (trabecular spacing), Tb.Sp (trabecular separation), connectivity and anisotropy were determined by 2D and/or 3D analysis. The comparison between the values of the parameters obtained in these analysis was performed using the t test and Pearson correlation. Based on the results it was possible to determine the influence of image resolution on the quality of the bone architecture parameters obtained in the 2D and/or 3D analysis. The data also show that the presence of aluminum filter affects the quality of these parameters. Thus, the best results are obtained with maximum resolution and aluminum filter with a thickness of 0.25 or 0.50 mm.

A microtomografia computadorizada (uCT) é uma técnica de ensaio não destrutivo, frequentemente utilizada no estudo da estrutura interna de ossos, com uma resolução espacial da ordem de mícrons. Neste trabalho, seis pares de amostras ósseas (fêmur de rato) foram estudados através da uCT. Os ensaios foram conduzidos na presença ou não de filtros de alumínio (espessura de 0,25; 0,50 e 0,75 mm), utilizando-se três níveis de resolução (33,3; 15,0 e 9,5 um). Os parâmetros de arquitetura óssea BS (área óssea da amostra), BV (volume ósseo da amostra), TS (área superficial da amostra), TV (volume da amostra), BV/TV (razão entre o volume ósseo e o volume da amostra), BS/BV (razão entre a área óssea da amostra e o volume ósseo da amostra), Tb.N (densidade trabecular), Tb.Th (espaçamento entre as trabéculas), Tb.Sp (separação trabecular), conectividade e anisotropia foram determinados através das análises em duas (2D) e/ou três (3D) dimensões. A comparação entre os valores dos parâmetros obtidos através dessas análises foi realizada através do teste t pareado e da correlação de Pearson. Com base nos resultados, foi possível determinar a influência da resolução da imagem na qualidade dos parâmetros da arquitetura óssea obtidos através das análises 2D e/ou 3D. Os dados mostram que a presença de filtro de alumínio também afeta a qualidade desses parâmetros. Assim, os melhores resultados são obtidos com resolução máxima e filtro de alumínio com espessura de 0,25 ou 0,50 mm. / X-Ray Computed Microtomography (uCT) is a nondestructive technique used to study the internal structure of bones with a spatial resolution of the order of microns. In this study, six pairs of bone samples (femur mouse) were studied by uCT. The tests were conducted in the absence or presence of aluminum filters (thickness of 0.25, 0.50 and 0.75 mm), using three different resolution levels: 33.3, 15.0 and 9.5 um. The bone architecture parameters BS (surface area of the trabecular bone), BV (bone volume of the sample), TS (surface area of the sample), TV (sample volume), BV/TV (bone volume fraction), BS/BV (ratio bone surface and volume), Tb.N (trabecular density), Tb.Th (trabecular spacing), Tb.Sp (trabecular separation), connectivity and anisotropy were determined by 2D and/or 3D analysis. The comparison between the values of the parameters obtained in these analysis was performed using the t test and Pearson correlation. Based on the results it was possible to determine the influence of image resolution on the quality of the bone architecture parameters obtained in the 2D and/or 3D analysis. The data also show that the presence of aluminum filter affects the quality of these parameters. Thus, the best results are obtained with maximum resolution and aluminum filter with a thickness of 0.25 or 0.50 mm.

L’objectif de cette thèse était de développer de nouveaux biomatériaux nanofibreux architecturés (2D ou 3D) grâce à la méthode d’électrospinning puis d’étudier l’influence de ces structures nanofibreuses sur le comportement des cellules osseuses. L’électrospinning est une technique qui permet d’obtenir des nanofibres en projetant sous l’action d’un champ électrique intense une solution de polymère sur un collecteur. Les nanofibres sont alors généralement disposées aléatoirement sous forme de mats (ou scaffolds). Ces scaffolds trouvent des applications en ingénierie tissulaire grâce à leur structure mimant la matrice extracellulaire des tissus vivants. Toutefois, il a été montré que lorsque le collecteur est micro-structuré, il est alors possible de contrôler l’organisation des fibres lors de leur dépôt grâce à la perturbation locale du champ électrique au voisinage de la surface du collecteur. Ces collecteurs architecturés jouent ainsi le rôle de « templates » électrostatiques. Dans un premier temps, nous avons développé des scaffolds 2D nanofibreux monocomposants en forme de nids d’abeilles grâce à l’utilisation d’un collecteur micro-structuré en nids d’abeilles lors du procédé d’électrospinning. Ces scaffolds ont été développés à partir de deux biopolyesters le poly(ε-caprolactone) (PCL) ou le poly(lactic acid) (PLA). Nous avons prouvé que la morphologie des nanofibres de PCL (distribution bimodale du diamètre des fibres) conduisait à un scaffold présentant un relief beaucoup plus marqué alors qu’avec les fibres de PLA, qui présentent une distribution monomodale du diamètre des fibres, les scaffolds obtenus sont beaucoup plus plats. Nous avons montré qu’il est possible de contrôler l’organisation spatiale de cellules osseuses de type MG-63, des ostéoblastes, en jouant sur le relief et l’architecture du scaffold. Puis, nous avons démontré qu’en couplant la micro-structuration des nanofibres de PCL (par l’utilisation d’un collecteur en nid d’abeilles lors du procédé d’électrospinning) avec les propriétés d’auto-assemblage du PCL, nous pouvions élaborer de nouveaux scaffolds nanofibreux 3D ayant la particularité de présenter des pores de tailles contrôlées ainsi qu’un gradient de porosité dans l’épaisseur du scaffold. Puis nous nous sommes intéressés à l’élaboration de membranes composites micro-structurées 2D et 3D. En couplant le procédé d’électrospinning avec le procédé d’électrospraying sur des collecteur micro-structurés, nous avons démontré que nous pouvions déposer de manière contrôlée les particules spécialement sur les murs des nids d’abeilles grâce notamment à la présence d’une très fine couche de fibres électrospinnées au préalable sur le collecteur. Cette fine couche de nanofibres joue le rôle de « template électrostatique » pour le dépôt des particules. Nous avons ensuite appliqué cette technique pour développer des membranes composites nanofibreuses bicouches à base de nanofibres de PCL et de microparticules d’hydroxyapatite (HA). Ces membranes composées de 21 microarchitectures différentes (barres, plots, hexagones, labyrinthe) ont ensuite été intégrées dans des mini plaques de culture cellulaire, formant ainsi un nouveau type de biopuce, appelés biochips, qui permettent pour le screening des microarchitectures nanofibreuses. Enfin, en combinant simultanément l’électrospinning de nanofibres et l’électrospraying de particules sur des collecteur micro-structurés en nid d’abeilles, des scaffolds composites 3D présentant des pores cylindriques de tailles contrôlées ont été élaborés. / The aim of this thesis was to develop new architectured nanofibrous biomaterials (2D or 3D) using the electrospinning method and to study the influence of these nanofibrous structures on bone cells behaviors. Electrospinning is a technique allowing the production of nanofibers by projecting, under the action of a strong electric field, a polymer solution on a collector. The nanofibers are generally randomly deposited and form mats or scaffolds. These scaffolds are interesting for tissue engineering applications because of their structure mimicking the extracellular matrix of living tissues. However, it has been shown that when the collector is microstructured, it is possible to control the organization of the fibers during their deposition through the local perturbation of the electric field at the vicinity of the surface of the collector. These micropatterned collectors act as "electrostatic templates". First, 2D honeycomb nanofibrous scaffolds were elaborated using micropatterned honeycomb collectors during the electrospinning process. These scaffolds were made either with poly(ε-caprolactone) (PCL) or poly(lactic acid) (PLA). We showed that the morphology of the PCL nanofibers (bimodal distribution of the fiber diameter) led to a scaffold with a strong relief. Despite, with PLA fibers which presented a monomodal distribution of the fiber diameter, the obtained scaffolds were much flatter. It was possible to control the spatial organization of bone-like cells MG-63 (osteoblasts), playing on the relief and the architecture of the scaffold. Subsequently, 3D materials were elaborated using micropatterned collectors in order to open new paths for the development of filling materials for bone regeneration. Microstructuration of PCL nanofibers (by the use of micropatterned honeycomb collector during the electrospinning process) coupled with the self-assembling properties of the PCL lead to the development of new 3D nanofibrous scaffolds, with controlled pore size and porosity gradient in the thickness of the scaffold. Afterwards, micropatterned composite 2D and 3D membranes were elaborated. By coupling the process of electrospinning with the process of electrospraying on micropatterned collector, we demonstrated that we can deposit the particles in a controlled way, especially on the walls of honeycomb patterns thanks to the presence of a thin fiber layer first deposited on the collector. This thin nanofiber layer plays the role of an "electrostatic template" for the particles deposition. Thereafter, this technique was applied to develop bilayers composite nanofibrous membranes containing PCL nanofibers and hydroxyapatite (HA) microparticles. These membranes consisted of 21 different microarchitectures (bars, blocks, hexagons, maze) were then incorporated into a small cell culture plate, thereby forming a new type of biochip for the screening of nanofibrous architectures. Indeed, these biochips allowed the screening of nanofibrous microarchitectures to identify the most relevant for bone regeneration. It turned out that the HA hexagonal structures (with an average diameter of 300 microns) and circular HA structures (with an average diameter of 150 microns) are the structures that enhance the most the mineralization process of bone cells. Finally, by combining simultaneously electrospinning nanofibers and electrospraying particles on micropatterned honeycomb collector, 3D composite scaffolds were elaborated. It was possible to control the size of cylindrical pores of these 3D composite from tens to hundreds of microns by changing the size of the honeycomb patterns of the collector.

[pt] Em uma barragem de terra homogênea responsável pelo abastecimento de água de um empreendimento privado, observou-se um processo inicial de carreamento de partículas finas próximo ao pé do talude de jusante, situação tida como um dos principais modos de falha de barragens. Embora esta anomalia tenha sido devidamente controlada na estrutura em estudo, este trabalho buscou encontrar as causas para a ocorrência detectada, visando aprofundar o conhecimento sobre o assunto. Para isso, investigou-se o histórico da estrutura, coletou-se amostras indeformadas próximo a região de interesse com a função de realizar ensaios de laboratório para caracterizar o solo no local, determinar os parâmetros físicos, aferir coeficientes de permeabilidade sob diferentes tensões efetivas e encontrar a sua curva característica (SWCC) através de ensaios de papelfiltro. Com os resultados dos ensaios, foram elaborados modelos computacionais sob diferentes cenários para investigar o comportamento dos gradientes hidráulicos. Foi empregado o software Plaxis LE para esta função. Avaliou-se se a adoção de parâmetros não saturados ou a consideração de análises tridimensionais promoveria alguma alteração no padrão de fluxo na estrutura em estudo, o que não ocorreu. Também foi considerado se a interação solo-atmosfera poderia gerar gradientes hidráulicos críticos através de ciclos de chuva e evaporação, mas também não houve resultados críticos. Ao variar o coeficiente de permeabilidade no corpo da barragem, observou-se que existe uma relação inversamente proporcional com o gradiente hidráulico. Desta forma, entende-se que a presença de solos orgânicos no pé do talude de jusante pode ter acarretado o processo de carreamento observado. / [en] In a homogeneous earthfill dam responsible for the water supply of a private company, an initial process of internal erosion was observed near the base of the downstream slope, which is listed as one of the main dam failures causes in the world. Although this problem has been correctly solved at the studied structure, this thesis aimed to find the causes for the detected anomaly in order to increase knowledge about this subject. To do so, the history of the structure was investigated, undisturbed samples were collected near the region of interest to carry out laboratory tests to characterize the soil, determine the physical parameters, measure permeability coefficients under different effective stresses and find its characteristic curve (SWCC) through filter paper tests. With the results of the tests, computational models were elaborated under different scenarios to investigate the behavior of hydraulic gradients. The software Plaxis LE was used in this work. It was evaluated whether the adoption of unsaturated parameters or 3D analysis would promote any change in the flow pattern in the studied structure, which did not occur. It was also considered whether the soil-atmosphere interaction could generate critical hydraulic gradients through rainfall and evaporation cycles, but there were no critical results either. Although, permeability seems to have a an inversely proportional relationship with hydraulic gradient. Thus, it is understood that the formation of organic soils at the toe of the downstream slope may have led to the observed internal erosion process.

Ossos trabeculares possuem uma microestrutura porosa e podem ser modelados como um sólido elástico linear, heterogêneo e anisotrópico. A microtomografia tridimensional por raios-x (uCT) tem sido mundialmente utilizada para a caracterização de osso trabecular em pesquisas relacionadas à qualidade óssea e à doenças do metabolismo ósseo como a osteoporose. Na literatura há poucas investigações comparando as análises morfométricas 2D e 3D de osso trabecular. Nesta investigação amostras de osso trabeculares cilíndricas extraídas da cabeça femoral bovina foram utilizadas para a comparação dessas análises por \'mü\'CT. O software CT-Analyser foi utilizado para medidas em três direções (crânio-caudal, lateral-medial e anterior-posterior) de diversos parâmetros da microestrutura trabecular tais como espessura trabecular, separação trabecular, número trabecular e os autovalores do tensor de anisotropia (M). A comparação entre os valores dos parâmetros medidos por análises morfométricas 2D e 3D foi realizada pelo teste-t pareado com nível de significância p < 0,05 e por correlação linear de Pearson. Os autovalores da matriz M mostram que a microestrutura trabecular bovina tem uma tendência para a simetria transversalmente isotrópica. Os resultados obtidos mostram que a microtomografia tridimensional por raios-X é uma técnica de grande potencial para caracterização da qualidade óssea gerando bons parâmetros para o diagnóstico de doenças do metabolismo ósseo. / Trebecular bones have a porous microstructure and can be modeled as a linear elastic solid, heterogenous and anisotropic. The x-ray tridimensional microtomography (\'mü\'CT) has been worldwide used for the assessment of trabecular bone in investigations related to bone quality and aimed to the diagnostic of bone metabolic diseases such as osteoporosis. In the literature few investigations have compared the 2D and 3D morphometric analysis of trabecular bone. In this investigation cylindrical trabecular bone samples were harvested from bovine head femur to carry out that comparison by \'mü\'CT. The CT-Analyser software was used to measure in three directions (superior-inferior, lateral-medial and anterior-posterior) several microstructural trabecular parameters such as trabecular thickness, trabecular separation, trabecular number and the eigenvalues of the fabric tensor (M). The comparison between the parameters values measured by 2D and 3D morphometric analysis was performed by the paired-sample t test with a level of significance p < 0,05 and the Pearson\'s linear correlation. The eigenvalues show that the bovine trabecular microstructure has a tendence to transverse isotropy symmetry. The results show that x-ray tridimensional microtomography (\'mü\'CT) is a technique of great potential for characterization of generating good bone quality parameters for the diagnosis of diseases of bone metabolism.

Ce travail porte sur l'incorporation de nanorenforts biosourcés, c'est-à-dire des nanofibrilles de cellulose (NFC), dans les matériaux composites à matrice polymère et les mousses. Ces nouveaux matériaux biosourcés peuvent par exemple être utilisés pour la conception de structures sandwich. L'étude à caractère expérimental, théorique et numérique s'articule autour de trois axes visant à optimiser tant les procédés d'élaboration que les propriétés en service de ces matériaux.Dans un premier temps, la rhéologie des suspensions concentrées de NFC, fluides à seuil thixotropes, a été étudiée aux échelles macro- et mésoscopiques en utilisant un dispositif original de rhéométrie couplé à des mesures de champs cinématiques par vélocimétrie ultra-sonore. Nous montrons ainsi que l'écoulement des suspensions de NFC est fortement hétéro-gène et présente des glissements aux parois, de multiples bandes de cisaillement couplés avec des écoulements de type « bouchon ». Sur la base de cette étude, un modèle rhéolo-gique multi-échelles est proposé. Ce modèle tient compte d'une part de l'architecture aniso-trope des réseaux connectés de NFC dans ces suspensions, et d'autre part des interactions mécaniques et physico-chimiques aux échelles nanométriques. Il permet de montrer que les interactions colloïdales et hydrodynamiques, ainsi que la tortuosité et l'orientation des NFC jouent un rôle majeur sur la contrainte seuil et sur le comportement rhéofluidifiant de ces suspensions.Dans un deuxième temps, des nanocomposites à matrice polymère ont été élaborés sous forme de films en faisant varier sur une très grande plage la fraction volumique de NFC. En utilisant d'une part des techniques de microscopie (AFM, MEB) et de diffraction aux rayons X, et d'autre part des essais mécaniques (traction, DMA) nous montrons (i) que les NFC ont une orientation plane et s'organisent en réseaux connectés par des liaisons hydro-gènes, (ii) que ces réseaux jouent un rôle majeur sur le comportement mécanique des nano-composites et (iii) que le comportement élastique des nanocomposites est bien en deçà des prévisions données par les modèles micromécaniques de la littérature. De là, nous proposons un modèle multi-échelles alternatif où les principaux nano-mécanismes de déformation sont ceux se produisant dans les parties amorphes des NFC et au niveau des très nombreuses interfaces entre NFC.Enfin, nous avons étudié l'influence des conditions d'élaboration, de la nature et de la con-centration des NFC sur les microstructures (microtomographie synchrotron à rayons X), les propriétés mécaniques (essais de compression) et les micro-mécanismes de déformation (essai in situ en microtomographie) de mousses préparées par cryodessiccation de suspensions aqueuses de NFC. / This study focuses on the use of cellulose nanofibrils (NFCs) as bio-based nano-reinforcement in polymer composites and foams. These renewable materials can be used in place of traditional materials such as for instance to produce sandwich panels. This experi-mental, theoretical and numerical work aims at optimizing the processing of these NFC-based materials as well as their use properties.In the first part of this work, the rheology of concentrated NFC suspensions, that behave as thixotropic yield stress fluids, is investigated at macro- and mesoscales using an original rheo-ultrasonic velocimetry (rheo-USV) setup allowing the local flow kinematic to be obtai-ned. We show that the flow of NFC suspensions is highly heterogeneous and exhibits com-plex situations with the coexistence of wall slippage, multiple shear bands and plug-like flow bands. Using this experimental database, we develop an original multiscale rheological model for the prediction of the rheology of NFC suspensions. The model takes into account the anisotropic fibrous nature of NFC networks as well as colloidal and mechanical interaction forces occurring at the nanoscale. The model predictions prove that colloidal and hydrody-namic interaction forces together with the orientation and the wavy nature of NFCs play a major role on the yield stress and shear thinning behaviour of the suspensions.In the second part of this work, NFC-reinforced polymer nanocomposite films are processed for a wide range of NFC contents. Using advanced microscopy techniques (AFM, SEM), X-ray diffraction and mechanical tests (tensile and DMA tests), we show (i) that NFCs form highly connected nanofibrous structures with in-plane random orientation, (ii) that these connected NFC networks play a leading role on the mechanical behaviour of the nanocompo-sites and (iii) that the elastic properties of nanocomposite films are much lower than those predicted from the micromechanical models of the literature. In light of these observations, we propose an alternative multiscale model in which the main involved deformation nano-mechanisms are those occurring both in the amorphous segments of the nanofibers and in the numerous nanofiber-nanofiber contact zones.Finally, in a third part we focus on the influence of the processing conditions, the suspension type and the NFC concentration on the microstructure (using X-ray synchrotron microto-mography), the mechanical properties (using compression tests) and the deformation micro-mechanisms (using in situ compression test with X-ray microtomography) of various foams prepared from NFC suspensions by freeze-drying.

Ossos trabeculares possuem uma microestrutura porosa e podem ser modelados como um sólido elástico linear, heterogêneo e anisotrópico. A microtomografia tridimensional por raios-x (uCT) tem sido mundialmente utilizada para a caracterização de osso trabecular em pesquisas relacionadas à qualidade óssea e à doenças do metabolismo ósseo como a osteoporose. Na literatura há poucas investigações comparando as análises morfométricas 2D e 3D de osso trabecular. Nesta investigação amostras de osso trabeculares cilíndricas extraídas da cabeça femoral bovina foram utilizadas para a comparação dessas análises por \'mü\'CT. O software CT-Analyser foi utilizado para medidas em três direções (crânio-caudal, lateral-medial e anterior-posterior) de diversos parâmetros da microestrutura trabecular tais como espessura trabecular, separação trabecular, número trabecular e os autovalores do tensor de anisotropia (M). A comparação entre os valores dos parâmetros medidos por análises morfométricas 2D e 3D foi realizada pelo teste-t pareado com nível de significância p < 0,05 e por correlação linear de Pearson. Os autovalores da matriz M mostram que a microestrutura trabecular bovina tem uma tendência para a simetria transversalmente isotrópica. Os resultados obtidos mostram que a microtomografia tridimensional por raios-X é uma técnica de grande potencial para caracterização da qualidade óssea gerando bons parâmetros para o diagnóstico de doenças do metabolismo ósseo. / Trebecular bones have a porous microstructure and can be modeled as a linear elastic solid, heterogenous and anisotropic. The x-ray tridimensional microtomography (\'mü\'CT) has been worldwide used for the assessment of trabecular bone in investigations related to bone quality and aimed to the diagnostic of bone metabolic diseases such as osteoporosis. In the literature few investigations have compared the 2D and 3D morphometric analysis of trabecular bone. In this investigation cylindrical trabecular bone samples were harvested from bovine head femur to carry out that comparison by \'mü\'CT. The CT-Analyser software was used to measure in three directions (superior-inferior, lateral-medial and anterior-posterior) several microstructural trabecular parameters such as trabecular thickness, trabecular separation, trabecular number and the eigenvalues of the fabric tensor (M). The comparison between the parameters values measured by 2D and 3D morphometric analysis was performed by the paired-sample t test with a level of significance p < 0,05 and the Pearson\'s linear correlation. The eigenvalues show that the bovine trabecular microstructure has a tendence to transverse isotropy symmetry. The results show that x-ray tridimensional microtomography (\'mü\'CT) is a technique of great potential for characterization of generating good bone quality parameters for the diagnosis of diseases of bone metabolism.