Orientador: Edison Zacarias da Silva / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-23T16:18:47Z (GMT). No. of bitstreams: 1 Pereira_ZennerSilva_D.pdf: 11614247 bytes, checksum: d882692dfdab010e889cb1717d250a1f (MD5) Previous issue date: 2013 / Resumo: Nas últimas décadas uma geração de nanodispositivos foi desenvolvida. Estes dispositivos nanoeletrônicos são fabricados por novas técnicas fundamentadas em física, química e engenharia. Muitos desses nanomateriais têm suas propriedades físicas alteradas pelo efeito de tamanho, por causa desses novos efeitos é importante entender como estes dispositivos trabalham propriamente a fim de encontrarmos formas de obter novas aplicações baseadas nestes novos efeitos. Nanofios metálicos estão sendo largamente estudados tanto teoricamente como experimentalmente. Recentemente uma nova possibilidade de soldagem foi mostrada experimentalmente entre nanofios de ouro em temperatura ambiente, sem necessidade de aplicação de calor adicional e com baixa pressão, chamada de solda fria (cold welding). Usando Dinâmica Molecular (MD) com potenciais efetivos, nós simulamos o processo de soldagem fria em nanofios de ouro, prata e ouro-prata com diâmetros de 4.3nm em 300 K. Nós mostramos que a soldagem fria é um processo possível até mesmo quando os nanofios sofrem fortes deformações e defeitos antes do processo de soldagem. Durante o processo de soldagem os nanofios resultaram com poucos defeitos. Pequenas pressões foram necessárias para que a soldagem fosse atingida. Nós também realizamos cálculos de Dinâmica Molecular com embedded-atom-method para modelar o crescimento de filmes-finos de paládio depositados em um substrato de ouro para um sistema de aproximadamente 100 mil átomos. Nós mostramos que o filmes-finos de paládio cresceu sob stress sobre o substrato de ouro. Após a deposição de 9 monocamadas o stress armazenado no filmes de paládio relaxou formando defeitos na estrutura do cristal. Defeitos do tipo falhas de empilhamento surgiram nos filmes de paládio formando um padrão de deformação no mesmo. Para quantificar o stress nós também calculamos a evolução do tensor de stress durante o crescimento. Existem fenômenos físicos como fraturas em materiais que são caracterizados pela quebra das ligações atômicas que levam a efeitos macroscópicos. Para estudarmos este tipo de problema, nós desenvolvemos um código inicial que acopla Dinâmica Molecular com Peridyvii namics (PD) (uma recente teoria de contínuo). A ideia básica para acoplar Dinâmica Molecular e Peridynamics está baseada no teorema de Schwarz. Este teorema fornece uma maneira de resolver equações diferenciais em diferentes subdomínios conectados por uma interface. O acoplamento é feito trocando condições de contorno entre subdomínios conectados por esta interface. A parte mais difícil deste acoplamento encontra-se em tratar os dados com ruídos oriundos da Dinâmica Molecular e passá-los para a Peridynamics. Para isto nós usamos uma interpolação estatística chamada interpolação de Kriging. Desta forma nós pudemos alcançar um acoplamento entre MD e PD / Abstract: Over the last decades a new generation of nanoeletronic devices have been developed. These nanoeletronic devices have been made by new techniques based on physics, chemistry and engineering. Many of these nanomaterials have shown changes in their physical properties and therefore, it is very important to understand how they work properly in order to find ways to obtain new applications supported by these new effects. Metallic nanowires have been largely studied theoretical and experimentally. Recently a new possibility of welding was experimentally shown in the case of gold and silver nanowires (NWs) at ambient temperatures, without need of additional heat and with low pressures, called cold welding. Using molecular dynamics with effective potentials, we simulated cold welding of gold, silver, and silver-gold NWs with diameters of 4.3 nm at 300 K. We show the cold welding is a possible process in metal NWs and that these welded NWs, even after losing their crystalline structure after breaking, can reconstruct their face-centered-cubic structure during the welding process with the result of very few defects in the final cold welded NWs. The stress tensor shows a low average value during welding with oscillations indicating tension and relaxation stages. Small pressures are required for the process to occur, resulting in a fairly perfect crystal structure for the final NW after being broken and welded. We have also performed Molecular Dynamics calculations with embedded-atom-method to model the growth of a Pd thin film deposited on Au(100) for a system with approximately 100,000 atoms. We showed that the Pd film grew under stress on the Au substrate. After the deposition of 9 monolayers, the stress stored in the Pd film relaxed with the formation of defects, stacking faults in the structure of Pd forming a pattern of deformation in the film. To quantitatively access the defect formation we also measured the stress tensor evolution during growth. There are physical phenomena like brittle fracture that is characterized by breaking of atomic bonds leading to macroscopic effects. In order to study this kind of problems, we developed the initial programming code that couples molecular dynamics (MD) and Peridyix namics (PD) (a new model to continuum). The basic idea to coupling Molecular Dynamics and Peridynamics is based on a mathematical theorem that is known as Schwarz theorem. It gives a way to solve differential equations in different subdomains that are connected by an interface (overlap). The coupling is made by exchanging boundary conditions through of the interface between subdomains. The hardest part is to treat noise molecular dynamics data and after that to pass those data to continuum theories. In order to pass data from MD to Peridynamics we have used a statistical interpolation called Kriging interpolation. This way we can achieve an algorithm to coupling DM with PD / Doutorado / Física / Doutor em Ciências

The continuing trends of miniaturisation, mass customisation, globalisation and wide use of the Internet have great impacts upon manufacturing in the 21st century. Micro manufacturing will play an increasingly important role in bridging the gap between the traditional precision manufacturing and the emerging technologies like MEMS/NEMS. The key requirements for micro manufacturing in this context are hybrid manufacturing capability, modularity, reconfigurability, adaptability and energy/resource efficiency. The existing design approaches tend to have narrow scope and are largely limited to individual manufacturing processes and applications. The above requirements demand a fundamentally new approach to the future applications of micro manufacturing so as to obtain producibility, predictability and productivity covering the full process chains and value chains. A novel generic modular reconfigurable platform (GMRP) is proposed in such a context. The proposed GMRP is able to offer hybrid manufacturing capabilities, modularity, reconfigurablity and adaptivity as both an individual machine tool and a micro manufacturing system, and provides a cost effective solution to high value micro manufacturing in an agile, responsive and mass customisation manner. An integrated framework has been developed to assist the design of GMRPs due to their complexity. The framework incorporates theoretical GMRP model, design support system and extension interfaces. The GMRP model covers various relevant micro manufacturing processes and machine tool elements. The design support system includes a user-friendly interface, a design engine for design process and design evaluation, together with scalable design knowledge base and database. The functionalities of the framework can also be extended through the design support system interface, the GMRP interface and the application interface, i.e. linking to external hardware and/or software modules. The design support system provides a number of tools for the analysis and evaluation of the design solutions. The kinematic simulation of machine tools can be performed using the Virtual Reality toolbox in Matlab. A module has also been developed for the multiscale modelling, simulation and results analysis in Matlab. A number of different cutting parameters can be studied and the machining performance can be subsequently evaluated using this module. The mathematical models for a non-traditional micro manufacturing process, micro EDM, have been developed with the simulation performed using FEA. Various design theories and methodologies have been studied, and the axiomatic design theory has been selected because of its great power and simplicity. It has been applied in the conceptual design of GMRP and its design support system. The implementation of the design support system is carried out using Matlab, Java and XML technologies. The proposed GMRP and framework have been evaluated through case studies and experimental results.

The present paper is devoted to the fast solution of boundary integral equations on unstructured meshes by the Galerkin scheme. On the given mesh we construct a wavelet basis providing vanishing moments with respect to the traces of polynomials in the space. With this basis at hand, the system matrix in wavelet coordinates can be compressed to $\mathcal{O}(N\log N)$ relevant matrix coefficients, where $N$ denotes the number of unknowns. The compressed system matrix can be computed within suboptimal complexity by using techniques from the fast multipole method or panel clustering. Numerical results prove that we succeeded in developing a fast wavelet Galerkin scheme for solving the considered class of problems.

Cette thèse porte sur l'étude du comportement mécanique et l'endommagement d'un composite tressé 3D, utilisé pour fabriquer des réservoirs multiformes destinés à l'industrie automobile. L'analyse du matériau se base sur une approche expérimentale et une approche numérique. Sur le plan expérimental, des essais de caractérisation ont permis d'identifier l'ensemble des modules d'élasticité nécessaires pour établir la matrice de rigidité du matériau. De même, des essais expérimentaux ont permis d'étudier le processus d'endommagement du matériau en utilisant deux méthodes de suivie. La première consiste à utiliser une caméra munie d'un zoom pour observer les mécanismes d'endommagement qui se créent au cours du chargement. La deuxième méthode, quant à elle, utilise la technique de l'émission acoustique pour détecter en temps réel les mêmes phénomènes. Le couplage des deux méthodes a permis de dresser la chronologie de l'apparition de ces mécanismes d'endommagement. Sur le plan numérique, une analyse multiéchelle a permis d'évaluer l'influence des fissurations transversales et des décohésions d'interface sur les propriétés mécaniques du matériau. Pour cela, une cellule de base caractéristique de la microstructure a été modélisée. Par une technique d'homogénéisation appliquée à différentes échelles du matériau, les propriétés macroscopiques du composite ont été déterminées à partir de celles de ses constituants de base. Par la suite, des défauts sont introduits de manière discrète sur la même cellule de base. Par le même processus d'homogénéisation à l'échelle mésoscopique, les propriétés du matériau endommagé sont déterminées et comparées à celles du matériau non endommagé. Enfin, un pré-dimensionnement des réservoirs a été effectué en utilisant des critères de rupture classiques pour validation. / This thesis focuses of the mechanical behavior and damage of a 3D braided composite. The material analysis is based on experimental and numerical approaches. First, mechanical tests have identified all the necessary elastic moduli to determine the stiffness matrix of the material. Similarly, experimental tests were performed to study the material damage process using two investigation methods. The first consists on using a camera with a large magnifier in order to observe damage mechanisms created during loading. The second uses the acoustic emission technique to detect in real time the same phenomena. The coupling of the two methods allowed to establish the chronology of the development of these damage mechanisms. In numerical terms, a multiscale analysis approach enables to evaluate the impact of transverse cracks and debonding on the mechanical properties. Thus, a representative cell of the material microstructure is built to predict the macroscopic properties of the material from the properties of its constituents. Defects are introduced during the meshing using a program that allows duplication of nodes at the interfaceto create debonding or to create transverse cracks inside yarns. Through the same homogenization process, the damaged material properties are determined and compared to that of the undamaged material. Finally, a design of tanks are proposed by using strength criteria for their validation.

Cette étude porte sur la modélisation de la durée de vie à l'écaillage des barrières thermiques pour aubes de turbines aéronautiques. La caractérisation expérimentale de l'adhérence du revêtement combine l'identification de la durée de vie - qualifiée par l'écaillage macroscopique de la céramique - à une caractérisation de l'endommagement à l'échelle de la microstructure du revêtement et en particulier à la dégradation des interfaces céramique / oxyde / métal. Des essais de compression uniaxiale sur des éprouvettes en AM1 revêtues NiAlPt et YSZ par EB-PVD, vieillies en fatigue thermique et mécano-thermique permettent d'estimer l'adhérence du revêtement. Ces essais sont complétés par des essais de propagation du délaminage interfacial par compression. Un essai original de compression in situ en laminographie aux rayons X a également permis d'analyser l'écaillage et la propagation du front de délaminage. Tous ces essais sont instrumentés et équipés de moyens d'observation permettant de réaliser des mesures de surfaces délaminées ou écaillées et de déterminer leur évolution en fonction des déformations locales mesurées.Une analyse microstructurale complète l'étude afin de comprendre l'influence du vieillissement thermique ou mécano-thermique sur l'évolution de l'endommagement du système. Cette analyse porte sur les mécanismes d'oxydation, de diffusion, de changement de phase principalement dans l'oxyde et la sous-couche. Elle est complétée par l'étude de l'ondulation de surface au cours du cyclage thermique, phénomène de « rumpling », et de ses conséquences, notamment au niveau de l'endommagement global de l'interface et de son adhérence. Le lien entre endommagement de l'interface à l'échelle d'imperfections de rugosité (quelques microns) et de la propagation d'une fissure d'interface (quelques dizaines à quelques centaines de microns) est analysé numériquement par la méthode des zones cohésives.Ces deux études complémentaires ont permis d'établir un modèle phénoménologique de durée de vie à l'écaillage. Celui-ci se base sur une estimation de l'énergie contenue dans la couche de céramique comparée à la valeur théorique d'énergie critique à rupture obtenue par un modèle d'endommagement, fonction de l'oxydation et des paramètres de chargement mécano-thermique. Ce modèle est implémenté en post-processeur d'un calcul par éléments finis facilitant son utilisation industrielle. / This study aims to model lifetime of thermal barrier coating (TBC) used on aircraft turbine blades. Experimental characterization of the coating adherence combines the lifetime identification – described by macroscopic spallation of the ceramic – with damage estimation trough the analysis of the influence of the microstructure of the coating and evolutions of interfaces ceramic / oxide / metal.Adherence of the ceramic is assessed using uniaxial mechanical compressive tests on AM1 specimen coated with NiAlPt bond coat and EB-PVD yttria stabilized zirconia varying the thermal and thermo-mechanical fatigue ageing conditions. Those tests are completed with analysis of interfacial crack propagation. A pioneering in situ compressive test using X-ray laminography has also been developed to analyze spallation and further delamination. The use of in-situ surface imaging by CCD cameras has enabled measurement of delaminated or spalled areas as function of measured local strain.The influence of thermal or thermo mechanical ageing on damage evolution of TBCs is studied through a microstructural analysis. Oxidation, diffusion and phase transformation mechanisms in the alumina and the bond coat are main parts of this analysis. Moreover the oxide rumpling and its consequences have been detailed, particularly through the measurement of global interfacial damage and adherence evolution. The link between interfacial damage at the scale of local defects (few microns) and the propagation of an interfacial crack (from tens to hundreds of microns) is numerically analyzed with a cohesive zone model.Those two spatial length of analysis were used to build a phenomenological lifetime model to spallation. This model was based on the assessment of the elastic strain energy stored in the ceramic layer and it comparison to fracture energy. A damage model is used to model the fracture strain energy evolution as a function of oxidation and thermo mechanical loading. This model is implemented in post processor of a FEM analysis, making its industrial use easier.

Les fibres naturelles telles que le lin, le chanvre, le bambou ou la miscanthus sont de plus en plus utilisées pour renforcer les composites industriels afin de réduire le poids, le coût et l’impact environnemental des produits. Elles remplacent les composites conventionnels tels que les composites à base de résine polymère et fibres synthétiques. Les méthodes de parachèvement par usinage de ces produits agrocomposites demeurent un verrou technologique et un défi scientifique. Ceci est dû principalement à la structure complexe des fibres végétales constituée de cellulose et issue des feuilles ou des tiges de plantes cultivées. Ce travail de thèse propose une analyse multiéchelle du comportement à la coupe de ces matériaux renouvelables qui exploite un procédé 2D de coupe orthogonale et un procédé 3D de coupe par fraisage. L’objectif étant de mieux appréhender les mécanismes physiques majeurs activés par le processus d’enlèvement de matière des agrocomposites. Aussi, pour identifier les effets d’échelle observés en usinage, une caractérisation tribo-mécanique des agrocomposites stratifiés par nanoindentation et rayage ainsi que des essais mécaniques spécifiques ont été réalisés. Les fibres végétales se différencient des fibres synthétiques par une flexibilité transversale qui leur confère une grande capacité à se déformer lors du contact avec l’outil de coupe. Ainsi, la rigidité mécanique du contact outil/matière contrôle ici la coupe par cisaillement plastique des fibres végétales et, par conséquence, la qualité de la surface usinée des agrocomposites. Les fibres végétales, associées à une matrice polymère thermoplastique, présentent par ailleurs un comportement mécanique élastoplastique avec un endommagement ductile lorsqu’elles sont sollicitées suivant leur direction transversale. Ceci explique la production de copeaux continus en usinage par opposition aux composites synthétiques conventionnels. Les comportements mécanique et tribologique des fibres végétales en usinage sont fonction de l’échelle de contact. Ceci explique le caractère multiéchelle de la coupe des agrocomposites dont l’usinabilité est intiment liée à la taille du renfort fibreux. / Natural fibers such as flax, hemp, bamboo or miscanthus are increasingly used as fibrous reinforcement in order to reduce the weight, the cost and the environmental impact of products. They replace the conventional composites based on polymer resin and synthetic fibers. The finishing operations by machining of these biocomposite products remain a technological issue and a scientific challenge. This is mainly due to the complex structure of natural fibers composed of cellulose and extracted from plant leaf or plant stem. This research work provides a multiscale analysis of cutting behavior of these renewable materials in 2D orthogonal cutting and 3D milling processes. The primary objective is to better understand the major physical mechanisms activated by the material removal process of biocomposites. Furthermore, to identify the scale effects observed in machining, a tribo-mechanical characterization of stratified biocomposites by nanoindentation and scratch as well as specific mechanical tests were carried out. Natural fibers are distinguished from synthetic fibers by a transverse flexibility, which enable them good ability to deform upon contact with the cutting tool. Thus, the mechanical tool/material contact stiffness controls the cutting by plastic shearing of plant fibers and, consequently, it controls the quality of the biocomposite-machined surfaces. Otherwise, natural fibers, associated with a thermoplastic polymer matrix, have an elastoplastic behavior with a ductile damage when they are stressed in their transverse direction. This explains the production of continuous chips when machining biocomposites, unlike conventional synthetic composites. The mechanical and tribological behaviors of plant fibers in machining are dependent on the contact scale. This explains the multiscale cutting character of biocomposites where the machinability is intimately related to the size of the fibrous reinforcement.

Des nouvelles méthodes de gélification avec association de différents composés permettent l’élaboration d’hydrogels sous forme de matrices 3D présentant des propriétés optimales et des fonctions intéressantes. Cette technique d’assemblage peut être effectuée par mélange de plusieurs polymères ou/et par incorporation de nanoparticules dans la matrice polymérique. Ce travail de thèse a montré l’intérêt de mettre en œuvre des réseaux interpénétrés de polymères à base d’alginate et de GelMA, et a mis en évidence l’effet de l’incorporation de nanoliposomes sur les propriétés physico-chimiques des hydrogels. Une caractérisation multi-échelle des hydrogels, a été complétée par une étude des interactions possibles au sein de la matrice 3D. Dans une première partie du travail, une analyse des propriétés de surface des matrices composites à différentes concentrations d’alginate, avant et après fonctionnalisation par des nanoparticules molles, a montré une amélioration de la mouillabilité et de l’énergie de surface des hydrogels. Les propriétés mécaniques des hydrogels ont été déterminées par une caractérisation multi-échelle incluant la microscopie à force atomique (nanoscopique) et le rhéomètre (mésoscopique). Ces analyses ont pris en compte les différentes concentrations d’alginate ainsi que les deux concentrations différentes de liposomes incorporés dans la matrice 3D. Les résultats obtenus ont montré l’intérêt de l’assemblage des deux polymères et l’effet des nanoliposomes sur le processus de gélification de l’alginate dû à une interaction entre les nanoparticules molles et l’agent réticulant (CaCl2). Une étude morphologique des hydrogels a montré la possibilité de contrôler la taille des pores en modifiant la concentration des différents composants des hydrogels ou en fonctionnalisant les matrices 3D par des nanoparticules molles. Les interactions physico-chimiques ont ensuite été étudiées par Spectroscopie de Photoélectrons X, spectroscopie de Résonance Magnétique Nucléaire et Spectroscopie Infrarouge à Transformée de Fourier / Novel crosslinking methods to design 3D hydrogels consist on an innovative combination of various components in order to create 3D structure with optimal properties and functionalities. This blending technic can be carried out by mixing several polymers or/and incorporation of nanoparticles into the polymer network. The present work showed the advantages of interpenetrating polymer networks forms composed of alginate and GelMA and highlighted the effect of the incorporation of nanoliposomes on the physico-chemical properties of the hydrogels. It consisted primarily on a multiscale characterization of the hydrogels and then on the study of the possible interactions in the 3D structure. At first, the surface characterization of the composite hydrogels at different alginate concentrations, before and after the functionalization with soft nanoparticles, showed an improvement of the wetting properties and the surface energy. The mechanical properties of the hydrogels were determined by multiscale analysis using the atomic force microscopy (nanoscopic) and the rheometer (mesoscopic). These analysis took into account the various concentrations of alginateas well as the two different concentrations of the liposomes added in the 3D structure. The results showed the effectiveness of mixing the polymers and the influence of the nanoliposomes on the alginate coagulation due to an interaction between the soft nanoparticules and the coagulation agent (CaCl2). A morphological study of the hydrogels showed the possibility to control the size of the pores by the modification of concentration for each component of hydrogel or by functionalization the 3D structure. The physicochemical interactions were then studied thanks to the X-ray Photoelectron Spectroscopy, the Nuclear Magnetic Resonance Spectroscopy and the Fourier Transform Infrared spectroscopy

Shape memory alloys (SMAs) are materials that show reversible, thermo-elastic, diffusionless, displacive (solid to solid) phase transformation, due to the application of temperature and/ or stress (/strain). Among different SMAs, NiTi is a popular one. NiTi shows reversible phase transformation, the shape memory effect (SME), where irreversible deformations are recovered upon heating, and superelasticity (SE), where large strains imposed at high enough temperatures are fully recovered. Phase transformation process in NiTi SMA is a very complex process that involves the competition between developed internal strain and phonon dispersion instability. In NiTi SMA, phase transformation occurs over a wide range of temperature and/ or stress (strain) which involves, evolution of different crystalline phases (cubic austenite i.e. B2, different monoclinic variant of martensite i.e. B19', and orthorhombic B19 or BCO structures). Further, it is observed from experimental and computational studies that the evolution kinetics and growth rate of different phases in NiTi SMA vary significantly over a wide spectrum of spatio-temporal scales, especially with length scales. At nano-meter length scale, phase transformation temperatures, critical transformation stress (or strain) and phase fraction evolution change significantly with sample or simulation cell size and grain size. Even, below a critical length scale, the phase transformation process stops. All these aspects make NiTi SMA very interesting to the science and engineering research community and in this context, the present focuses on the following aspects. At first this study address the stability, evolution and growth kinetics of different phases (B2 and variants of B19'), at different length scales, starting from the atomic level and ending at the continuum macroscopic level. The effects of simulation cell size, grain size, and presence of free surface and grain boundary on the phase transformation process (transformation temperature, phase fraction evolution kinetics due to temperature) are also demonstrated herein. Next, to couple and transfer the statistical information of length scale dependent phase transformation process, multiscale/ multiphysics methods are used. Here, the computational difficulty from the fact that the representative governing equations (i.e. different sub-methods such as molecular dynamics simulations, phase field simulations and continuum level constitutive/ material models) are only valid or can be implemented over a range of spatiotemporal scales. Therefore, in the present study, a wavelet based multiscale coupling method is used, where simulation results (phase fraction evolution kinetics) from different sub-methods are linked via concurrent multiscale coupling fashion. Finally, these multiscale/ multiphysics simulation results are used to develop/ modify the macro/ continuum scale thermo-mechanical constitutive relations for NiTi SMA. Finally, the improved material model is used to model new devices, such as thermal diodes and smart dampers.

Les composites C/C sont principalement utilisés dans les applications à très haute température et notamment dans le domaine du spatial. Savoir concevoir ces matériaux est essentiel pour améliorer leurs performances et diminuer les coûts de production. Ce mémoire présente le développement d’un modèle multiéchelle basé images du comportement thermomécanique d’un composite C/C à renfort 3Daiguilleté. L’utilisation de méthodes classiques ne permet pas de décrire correctement cette architecture très complexe. La méthode CEPI (Computing Effective Properties using Images) présentée s’appuie d’une part sur les propriétés des constituants, dont certaines ont été caractérisées au laboratoire, etd’autre part sur l’architecture de ces matériaux, qui a été obtenue à partir d’une image tomographique.Les propriétés mesurées des constituants ont été directement utilisées dans un modèle microscopique de fil idéal, le modèle macroscopique étant lui directement basé sur l’image de tomographie. Les paramètres des calculs aux différentes échelles ont ensuite été étudiés et discutés pour en déterminer l’influence et permettre de valider certaines hypothèses. La comparaison des résultats numériques et expérimentaux a enfin permis de valider la méthode CEPI sur le comportement mécanique linéaire et de mettre en avant les principaux axes d’améliorations pour le comportement en dilatation des ces composites. / C/C composites are used in very high temperature applications, especially in space activities. The ability to design these materials is essential in order to enhance their performances and lower their production costs. This work introduces an images-based multiscale modeling of the thermomechanical behavior of a C/C needled composites. Standard methods cannot describe this very complex architecture.The CEPI model (Computing Effective Properties using Images) is based on one hand on the components properties, some of them having been characterized in the laboratory, and on the other hand on the architecture of the material which is directly obtained using tomography images. The components properties were used on a microscopic model of an idealistic yarn, while the macroscopic model was based on the CT scan data itself. The influence of the internal parameters of the method was studied and discussed, and allowed validating some hypotheses. Finally, the comparison between the numerical and experimental results validates the CEPI model on the linear mechanical behavior and stressed the key axes of improvement for the thermal expansion behavior of these composites.

Computational models of complex biological systems can provide a better understanding of how living systems function but need to be validated before they are employed for real-life (e.g. clinical) applications. One of the most frequently employed in silico approaches for validating such models is model checking. Traditional model checking approaches are limited to uniscale non-spatial computational models because they do not explicitly distinguish between different scales, and do not take properties of (emergent) spatial structures (e.g. density of multicellular population) into account. This thesis defines a novel multiscale multidimensional spatio-temporal meta model checking methodology which enables validating multiscale (spatial) computational models of biological systems relative to how both numeric (e.g. concentrations) and spatial system properties are expected to change over time and across multiple scales. The methodology has two important advantages. First it supports computational models encoded using various high-level modelling formalisms because it is defined relative to time series data and not the models used to produce them. Secondly the methodology is generic because it can be automatically reconfigured according to case study specific types of spatial structures and properties using the meta model checking approach. In addition the methodology could be employed for multiple domains of science, but we illustrate its applicability here only against biological case studies. To automate the computational model validation process, the approach was implemented in software tools, which are made freely available online. Their efficacy is illustrated against two uniscale and four multiscale quantitative computational models encoding phase variation in bacterial colonies and the chemotactic aggregation of cells, respectively the rat cardiovascular system dynamics, the uterine contractions of labour, the Xenopus laevis cell cycle and the acute inflammation of the gut and lung. This novel model checking approach will enable the efficient construction of reliable multiscale computational models of complex systems.