Les matériaux cellulaires sont des échantillons à très forte porosité qui peuvent être décrits à deux échelles : la mésostructure et la microstructure. Le lien entre l'architecture des matériaux et les propriétés mécaniques a été largement étudié dans la littérature. Les caractéristiques microstructurales peuvent avoir une influence importante sur les propriétés macroscopiques. Le but de ce travail est de relier les caractéristiques architecturales et microstructurales des matériaux cellulaires à leurs propriétés mécaniques grâce notamment à la tomographie aux rayons X. Une nouvelle approche combinant l'imagerie 3D à plusieurs résolutions, le traitement d'images et la modélisation éléments finis a permis de prendre en compte la microstructure de la phase solide. Quatre matériaux cellulaires modèles ont ainsi été étudiés : des mousses d'aluminium, des structures cellulaires périodiques en alliage de cobalt-chrome, des échantillons de β-TCP et des composites hydroxyapatite/β-TCP. Les matériaux métalliques ont été fournis par des collègues d'autres laboratoires, tandis que les matériaux céramiques ont été fabriqués dans le cadre de cette étude. Pour chaque type de matériaux (métaux et céramiques), une structure régulière et une stochastique ont été comparées. Pour utiliser la méthode multi-échelle développée dans ce travail, les échantillons ont d'abord été scannés grâce à la tomographie locale dans laquelle l'échantillon est placé près de la source de rayons X. La tomographie locale permet de scanner la petite partie irradiée de l'échantillon et d'obtenir une image agrandie par rapport aux images à plus basse résolution. Ces images permettent d'observer certains détails de la phase solide non visibles à plus basse résolution. Différentes étapes de traitement d'images ont ensuite été mises en œuvre pour obtenir une image à basse résolution incluant les informations provenant des images à haute résolution. Ceci a été réalisé grâce à une série d'opération de seuillage et sous-résolution des images à haute résolution. Le résultat de ces différentes étapes de traitement d'images donne une image de l'échantillon initial à basse résolution mais qui inclut l'information supplémentaire décelée à haute résolution. Ensuite, des essais mécaniques in situ ont été réalisés dans le tomographe pour suivre à basse résolution l'évolution des échantillons pendant la déformation. Les images initiales citées plus haut ont été utilisées pour produire des maillages éléments finis. Des programmes Java ont été adaptés pour créer des fichiers d'entrée pour les modèles éléments finis à partir des images initiales et des maillages. Les images initiales contenant les informations à propos de la phase solide, les images des essais mécaniques et les modèles éléments finis ont permis d'expliquer le comportement mécanique des échantillons en reliant les sites d'endommagement expérimentaux et les lieux de concentrations de contraintes calculés. / Cellular materials are highly porous systems for which two scales are mainly important: the mesostructure and the microstructure. The mesostructure corresponds to the architecture of the materials: distribution of solid phase “walls” and macroporosity and can be characterized by X-ray tomographic low resolution images. The link between the architecture of the materials and the mechanical properties has been frequently studied. The microstructure refers to the characteristics of the solid phase. Its microstructural features (presence of a secondary phase or of defects due to the sintering) can have a strong influence on the macroscopic properties. The aim of this work is to link the morphological and microstructural features of metallic and ceramic based cellular materials and their mechanical properties thanks to X-ray tomography and finite element modelling. A new method combining X-ray tomography at different resolutions, image processing and creation of finite element modelling enabled to take into account some microstuctural features of the cellular samples. Four different cellular materials were studied as model materials: aluminium foam fabricated by a liquid state process, cobalt periodic structures made by additive manufacturing, β-TCP porous samples fabricated by conventional sacrificial template processing route and hydroxyapatite/β-TCP composites made by additive manufacturing (robocasting). The metal based materials were provided by colleagues while the ceramic based porous materials were fabricated in the frame of the current study. For each type (metals or ceramics), a stochastic and a regular structure have been compared. For implementing the multiscale method developed in this work, the samples were firstly scanned in a so called “local” tomography mode, in which the specimen is placed close to the X-ray source. This allowed to reconstruct only the small irradiated part of the sample and to obtain a magnified image of a subregion. These images enable to observe some details which are not visible in lower resolution. Different image processing steps were performed to generate low resolution images including microstructural features imaged at high resolution. This was done by a series of thresholding and scaling of the high resolution images. The result of these processing steps was an image of the initial sample. Then, in situ mechanical tests were performed in the tomograph to follow the deformation of the sample at low resolution. The above mentioned initial images were used to produce finite element meshes. Special Java programs were adapted to create finite element input files from initial images and meshes. The initial images containing information about the solid phase, the images from the mechanical tests and the finite element models were combined to explain the mechanical behaviour of the sample by linking the experimental damage locations in the sample and the simulated stress concentration sites.

The development of micro-mesoporous hybrid aims to obtain materials with improved characteristics, since it tries to bring together to high acidity and thermal and hydrothermal stability of zeolites, with larger pore system and consequently better chance of diffusion of molecules within the mesoporous materials. Micro-mesoporous hybrid materials of ZSM-12/MCM-41 type with different micro and mesoporosity contributions were prepared by a procedure that uses the desilicalization of the zeolite in an alkaline medium, followed by recrystallization on the mesostructure, where the zeolite is used as the silica source in the formation of mesoporous phase. The ZSM-12 pure zeolite and MCM-41 pure were also prepared. The materials were characterized by X-ray diffraction, nitrogen adsorption-desorption at 77 K, scanning electron microscopy, infrared absorption spectroscopy and thermal analysis. The catalytic activity of these was analyzed in the catalytic cracking of cumene. The results shown that the methodology utilized is efficient to obtain hybrid materials of ZSM-12/MCM-41 type with micro-and mesoporosity optimized, and catalytic tests showed that the hybrid have the potential for cracking reactions, showing better results than the pure materials, pointing to it, the existing synergistic effect in these. / O desenvolvimento de híbridos micro-mesoporosos visa a obtenção de materiais com características melhoradas, uma vez que busca unir a elevada acidez e estabilidade térmica e hidrotérmica das zeólitas, com o maior sistema de poros e consequentemente melhor possibilidade de difusão de moléculas dos materiais mesoporosos. Materiais híbridos micro-mesoporosos do tipo ZSM-12/MCM-41 com diferentes contribuições de micro e mesoporosidade foram preparados por meio de um procedimento que se utiliza da dessilicalização de zeólitas em meio alcalino, seguida de recristalização em mesoestrutura, onde a zeólita é utilizada como fonte de sílica na formação da fase mesoporosa. A zeólita ZSM-12 pura e o MCM-41 puro também foram preparados. Os materiais foram caracterizados por difratometria de raios-X, adsorção-desorção de nitrogênio a 77 K, microscopia eletrônica de varredura, espectroscopia de absorção na região do infravermelho e análise termogravimétrica. A atividade catalítica destes foi analisada no craqueamento catalítico do cumeno. Os resultados obtidos através das técnicas de caracterização mostraram que a metodologia utilizada é eficiente para a obtenção de materiais híbridos do tipo ZSM-12/MCM-41 com contribuição de micro e mesoporosidade otimizadas, e os testes catalíticos mostraram que os híbridos têm potencial em reações de craqueamento, apresentando melhores resultados que os materiais puros, evidenciando com isso, o efeito sinérgico existente nestes.