L’ingénierie tissulaire vise à l’élaboration de prothèses biologiques par la régénération ou la culture, in vitro ou in vivo, de tissus ou d’organes. Dans la stratégie de culture in vitro, le développement de nouveaux outils, tels que des bioréacteurs, permettant la culture de cellules ou de tissus sous sollicitations mécaniques spécifiques au tissu est primordial. De plus, l’avancée de cette discipline dans la régénération des tissus nécessite de développer, dès à présent, des méthodes d’évaluation mécanique satisfaisantes permettant de comparer ces néo-tissus aux tissus sains selon des critères de sollicitations physiologiques. En effet, pour parvenir à une bonne évaluation de ces matériaux, il est nécessaire de pouvoir les tester sur des chargements représentatifs des sollicitations physiologiques auxquelles ils sont soumis. Nous avons ainsi, dans un premier temps, conçu et développé un bioréacteur de ligaments permettant la culture de cellules stimulées mécaniquement par des sollicitations cycliques de traction-torsion. Ce bioréacteur a été dimensionné afin de pouvoir obtenir des bio-prothèses de taille comparable aux ligaments et tendons à remplacer (4 à 5 cm de long). Nous avons, dans un deuxième temps, développé un modèle du comportement mécanique global de ces tissus à partir du formalisme thermodynamique développé au sein de notre laboratoire et des observations faites sur des tendons d’Achille de lapin. Ce modèle a pour but d’approfondir la compréhension des structures intervenant de façon prépondérante dans la qualité mécanique de ces tissus ainsi que l’évaluation et l’optimisation des matrices de support et des néo-tissus devant s’y substituer / Tissue Engineering aims to fabricate bio-prostheses by regenerating or culture, in vivo or in vitro, tissues or organs. In the in vitro strategy, developing new tools such as bioréactors which allow the culture of cells or tissues under their specific mechanical solicitations is a huge point. Moreover, the last advances of this discipline in regeneration of tissues require new mechanical model allowing their evaluation and comparison to native tissue under physiological loading. Indeed, in order to obtain a good evaluation of their mechanical quality, it is important to be able to applied mechanical solicitations linked to physiological ones. As a first step, a bioreactor of ligament allowing the culture of cells under mechanical solicitations of cyclic traction-torsion was designed and developed. This bioreactor was sized to potentially obtain a bio-prosthesis comparable to native tissue in term of size (4 to 5 cm long). In a second time, a mechanical model was elaborated based on a thermodynamic formalism developed in our laboratory and the observation made on rabbit Achilles tendons. The goals of this model are to improve our knowledge on the mayor structures involved into the mechanical quality of theses tissues and to evaluate and optimise the scaffolds and neo-tissues of substitution

En raison de sa stabilité microstructurale l'acier martensitique 'X10CrMoVNb9-1' est considéré comme un des candidats pour plusieurs futurs composants des réacteurs à hautes températures 'Very High Temperature Reactor' (VHTR). Ces épais composants (200 mm) sont assemblés par soudage TIG multi-passe. Ce procédé de soudage génère des cycles thermiques et thermomécaniques complexes au niveau de la Zone Affectée Thermiquement (ZAT). Cette thèse est la suite de celle de G.-M. Roux. Ce travail de six ans a pour but de prédire l'état microstructural après soudage dans la ZAT. G.-M. Roux a déjà développé une première version d'un modèle Thermo-Métallurgico-Mécanique (TMM) et a été validée en termes de contraintes résiduelles sur des essais de soudage simples mono-passe. Dans cette thèse une nouvelle version du modèle TMM est proposée, permettant d'améliorer les prévisions en termes de l'état microstructural post soudage dans la ZAT, et les contraintes résiduelles engendrées par l'opération de soudage.Cette thèse s¿appuie sur une approche de modélisation fine des transformations de phases, à savoir la modélisation de la transformation matériau de base - austénite lors d'un chargement anisotherme complexe, la modélisation de la transformation austénite - martensite et finalement la modélisation du revenu de la martensite. Sans oublier la caractérisation du comportement mécanique de chaque phase et l'étude du comportement multi-phasique. La simulation numérique avec le code éléments finis Cast3M de plusieurs procédés de soudage permet de comparer les modèles aux résultats expérimentaux. / Due to its microstructural stability, the martensitic steel 'X10CrMoVNb9-1 is considered a candidate for several future high temperatures reactor components. These thick components (200 mm) are assembled by GTA multi-pass welding. This welding process generates complex thermal and thermomechanical cycles in the Heat Affected Zone (HAZ). This thesis is following that of G.-M. Roux. This work of 6 years aims to predict the microstructural state after welding in the HAZ. A first version of a Thermo-Metallurgical-Mechanical model (TMM) has been developed and validated in terms of residual stresses on single-pass welding simple tests. In this thesis a new version of the TMM model is proposed to improve the forecasts in terms of the microstructural state and residual stresses post welding in the HAZ. The main improvements of this model TMM its capabilities to take into account the successive heating and cooling cycles, characterizing the multi-pass welding process. This thesis is based on a detailed modeling approach for phase transformations, namely modeling the transformation base material - austenite during anisothermal complex loadings, modeling transformation austenite - martensite and finally the martensite tempering modeling. Not to mention the characterization of the mechanical behavior of each phase and the study of multiphase behavior. Numerical simulation with the finite element code Cast3M of several welding processes was used to compare models with experimental results.

Shape memory alloys (SMAs) provide exciting opportunities for miniature actuation systems. As SMA actuators are scaled down in size, cooling increases and bandwidth, improves. However, the inclusion of a bias element with which to cycle the SMA actuator becomes difficult at very small scales. One technique used to avoid the necessity of having to include a separate bias element is the use of local annealing to fabricate a monolithic device out of nickel titanium (NiTi). The actuator geometry is machined out of a single piece of non-annealed NiTi. After locally annealing a portion of the complete device, that section exhibits the shape memory effect while the remainder acts as structural support and provides the bias force required for cycling. This work proposes one such locally-annealed monolithic SMA actuator for future incorporation in a device that navigates the digestive tract. After detailing the derivation of lumped electro-mechanical models for the actuator, a description of the prototyping procedure, including fabrication and local annealing of the actuator, is provided. This thesis presents the experimental prototype actuator behaviour and compares it with simulations generated using the developed models.

Shape memory alloys (SMAs) provide exciting opportunities for miniature actuation systems. As SMA actuators are scaled down in size, cooling increases and bandwidth, improves. However, the inclusion of a bias element with which to cycle the SMA actuator becomes difficult at very small scales. One technique used to avoid the necessity of having to include a separate bias element is the use of local annealing to fabricate a monolithic device out of nickel titanium (NiTi). The actuator geometry is machined out of a single piece of non-annealed NiTi. After locally annealing a portion of the complete device, that section exhibits the shape memory effect while the remainder acts as structural support and provides the bias force required for cycling. This work proposes one such locally-annealed monolithic SMA actuator for future incorporation in a device that navigates the digestive tract. After detailing the derivation of lumped electro-mechanical models for the actuator, a description of the prototyping procedure, including fabrication and local annealing of the actuator, is provided. This thesis presents the experimental prototype actuator behaviour and compares it with simulations generated using the developed models.

Le béton est un matériau très utilisé dans l'industrie de construction. Une limite essentielle à un usage de ce matériau est sa dégradation par écaillage lorsqu’il est exposé au feu. Le phénomène d'écaillage consiste en une éjection du béton sous forme d'écailles à la surface du béton exposée à l'incendie. La section de béton s'en trouve progressivement réduite. De plus, ce phénomène expose les armatures et peut conduire à une rupture prématurée de structures telles que les tunnels, les gratte-ciels, les centrales nucléaires etc. De nombreuses recherches ont été consacrées à la mise au point de méthodes de prévention de l'écaillage et à la détermination des paramètres qui ont une influence sur ce phénomène. Cependant, la physique qui contrôle l'écaillage n'est pas encore entièrement comprise. L'objectif principal de la thèse est de fournir une meilleure compréhension des mécanismes impliqués dans l’écaillage du béton en utilisant une approche numérique-expérimentale, i.e., la tomographie neutronique couplée à la modélisation numérique avancée à une échelle adéquate.Dans ce travail, les premières mesures 3D de la teneur en eau du béton (grandeur locale indispensable au suivi du processus de déshydratation potentiellement responsable de l’écaillage) soumis à un chargement thermique sévère ont été réalisées à l'aide de tomographies neutroniques rapides. Le suivi de la déshydratation rapide du béton a été possible en réalisant un scan 3D toutes les minutes grâce à la source neutrons de l'Institut Laue Langevin (leader mondial), à Grenoble, France. Cette vitesse d'acquisition est dix fois plus rapide que toute autre étude tomographique rapportée dans la littérature. Un dispositif, adapté à l'imagerie neutronique et aux essais à haute température, a été développé pour réaliser de telles expériences. L'influence de la taille des agrégats sur la distribution de l'humidité au sein de l'échantillon est présentée. Les résultats quantitatifs sur l'accumulation d'humidité derrière le front de déshydratation, connue sous le nom de 'moisture-clog" et considérée comme un des facteurs principaux engendrant un excès de pression, sont également présentés et discutésEn parallèle, un modèle thermo-hydro-mécanique (THM) entièrement couplé a été mis en œuvre sur le logiciel élément fini Cast3M afin d'étudier et prédire le comportement du béton à haute température. Le code nouvellement implémenté est remarquablement plus rapide (20-30 fois) que le code existant sur lequel il est basé. Une approche mésoscopique a été adaptée au modèle pour prendre en compte l'hétérogénéité du béton. D'abord, le modèle est appliqué à des expériences de la littérature, qui étu-dient les paramètres standards tels que la température, la pression du gaz et la perte de masse. En-suite, des profils d'humidité 1D obtenus à partir d'expériences de radiographie neutronique sont utili-sés pour vérifier et améliorer le modèle en termes de lois de comportement critiques telles que les courbes de déshydratation et de rétention d'eau. Enfin, le modèle est utilisé pour prédire la distribution d'humidité 3D mesurée dans ce travail de doctorat par tomographie neutronique. Entre autres, des simulations THM mésoscopiques sont effectuées pour étudier l'influence d'un agrégat sur le front de séchage. / Concrete has been extensively used in the construction industry as a building material. A major drawback of this material is its instability at high temperature, expressed in the form of violent or non-violent detachment of layers or pieces of concrete from the surface of a structural element. This phenomenon, known as fire spalling, can lead to the failure of concrete structures such as tunnels, high rise buildings, nuclear power-plants, underground parkings etc. because the reinforcement steel is directly exposed to high temperature and the designed cross section of the concrete elements (e.g., columns, beams, slabs) is reduced. A lot of research has been dedicated on developing preventing methods for spalling and also on determining the parameters that have an influence on it. However, the physics behind this phenomenon is not yet fully understood.In this doctoral, the first 3D measurements of moisture content in heated concrete, which is believed to be one of the processes directly related to spalling, have been performed using in-situ neutron tomography. In order to follow the fast dehydration process of concrete, one 3D scan (containing 500 radiographs) per minute was captured thanks to the world leading flux at the Institute Laue Langevin (ILL) in Grenoble France. This acquisition speed, which is ten times faster than any other experiment reported in the literature, was sufficient to follow the dehydration process. A dedicated setup, adapted to neutron imaging and high temperature, has been developed for performing such kind of experiments. Concrete samples with different aggregate size have been tested. Quantitative analysis showing the effect of the aggregate size on the moisture distribution is presented. Results on the moisture accumulation behind the drying front, known as the moisture-clog, are also presented and discussed.In parallel, a numerically-efficient coupled thermo-hydro-mechanical (THM) model has been implemented in the finite element software Cast3M for understanding and predicting the complex behavior of concrete at high temperature in the context of spalling. The newly implemented code is remarkably faster (20-30 times) than an existing one, on which it is based. A mesoscopic approach has been adapted to the model for taking into account the heterogeneity of concrete. First the model is applied to experiments from literature monitoring standard parameters such as temperature, gas pressure and mass loss. Then, 1D moisture profiles obtained from neutron radiography experiments are used for verifying and improving the model in terms of some critical constitutive laws such as dehydration and water retention curves. Finally, the model is employed for predicting the 3D moisture distribution measured in this doctoral work via neutron tomography. Among others, mesoscopic THM simulations are performed for investigating the influence of an aggregate on the drying front.

Composite materials show heterogeneity at different length scales. hence concurrent multiscale analysis is the only reliable method to analyze them. But unfortunately there is no concurrent multi-scale strategy that is efficient, and accurate while addressing all kinds of problems. This lack of reliability is partly because there is no micro-mechanical model which inherently keeps all relevent global information with it. This thesis tries to fill this gap. The presented micro-mechanical model not only homogenizes the micro-structure but also keeps the global information with it. Most of the micro-mechanical models in the literature extract the Representative Volume Element (RVE) from the continuum for analysis which results in loss of information and accuracy. In the present approach also, the RVE has been extracted from the continuum but with the major difference that all the macro/meso-scopic parameters are accounted for. Five macro/meso-scopic one dimensional parameters have been defined which completely define the effect of continuum. 11 for one dimensional stretch, _1 for torsion, __ (_ = 2, 3) for bending and _33 for uniform pressurization due to the presence of the continuum. Further, the above macro/meso-scopic parameters are proven, by the asymptotic, theory to be constant at a cross section but vary, in general, over the length of the fiber. Hence, the analysis is valid for any location and is not restricted to any local domain. Three major problems have been addressed: • Homogenization and analysis of RVE without any defects • Homogenization and analysis of RVE with fiber-matrix de-bonding • Homogenization and analysis of RVE with radial matrix cracking. Variational Asymptotic Method (VAM) has been used to solve the above mentioned problems analytically. The results have been compared against standard results in the literature and against 3D FEA. At the end, results for “Radial deformation due to torsion” problem will be presented which was solved “accidentally.”

Prestressed concrete is a popular construction material for highway bridges. A variety of girder span values, cross-sectional shapes, and prestressing strand layouts has been used in bridges across the United States. A major concern for such bridges is the possibility of corrosion damage in the prestressing strands or reinforcing bars, which is commonly caused by the use of deicing salts on the deck or saltwater spray in coastal regions. The present study aims at establishing analytical tools for the accurate simulation of chloride ingress, corrosion and mechanical damage (cracking) in the concrete, and for the evaluation of the impact of corrosion on the flexural and shear strength of bridge girders. First, an efficient and accurate analytical scheme is formulated to enable the calculation of the load-carrying capacity of corrosion-damaged girders. The analyses rely on two types of models, namely, beam models and nonlinear truss models. The latter are deemed necessary to obtain reliable estimates of the shear capacity, as beam models are not well-tailored for capturing shear failures. A procedure to account for the reduction in area and deformability of corroded strands, based on visually observed corrosion damage, is proposed and implemented. The models are calibrated and validated with the results of experimental tests on prestressed girders which exhibited varying levels of corrosion damage. Further analyses allow the comparison of the capacity of corrosion-damaged girders to that of their undamaged counterparts. The accuracy of a simplified procedure, using equations in the AASHTO code to determine the flexural and shear capacity of the damaged girders, is also determined. Subsequently, a computation scheme was proposed to describe the intrusion of chloride ions in prestressed bridge girder sections. The approach accounts for multiple, coupled processes, i.e., heat transfer, moisture transport, and chloride advective and diffusive transport. The constitutive models for moisture and chloride transport rely on previous pertinent work, with several necessary enhancements. The modeling scheme is calibrated with data from previous experimental tests on concrete cylindrical and prismatic specimens. The calibrated models are then validated using data from chloride titration tests conducted on girders removed from two bridges in Virginia after 34 and 49 years of service. The results indicate that the proposed framework can accurately reproduce the experimentally measured chloride content. The modeling approach also allows the evaluation of the accuracy of simplified, design-oriented tools for estimating the evolution of chloride content with time. The multi-physics simulation scheme is further refined to account for the corrosion-induced mechanical damage (cracking), by incorporating a phenomenological description of the electrochemical reaction kinetics, generation of expansive corrosion products, and subsequent development of tensile stresses and cracking in the surrounding concrete. The impact of cracking on the chloride and moisture transport mechanisms is also taken into account. The last part of this dissertation pursues the quantification of the uncertainty governing the chloride ingress in bridge girders, through the use of a stochastic collocation approach. The focus is on understanding how the inherent uncertainty in the value of input parameters (e.g., material transport parameters, ambient conditions etc.) is propagated, leading to uncertainty in the evolution of chloride content and the expected corrosion initiation time for a given bridge. / Doctor of Philosophy / Prestressed concrete is widely utilized in the construction of highway bridges in the United States. A significant concern arises regarding potential corrosion damage in the prestressing strands or reinforcing bars, which is commonly attributed to the application of deicing salts on the deck or exposure to saltwater spray in coastal regions. This study aims to develop analytical tools that can accurately simulate the intrusion of corrosive agents (namely chloride ions), and subsequent damage (cracking) in concrete. Furthermore, the research seeks to assess the impact of corrosion on the bearing capacity of bridge girders. Two different classes of analytical approaches are pursued. The first class employs purely mechanical (stress/deformation) models for capturing the strength, deformability and failure modes of girders with visual corrosion damage. These models rely on two approaches to capture the flexural and shear capacity of specimens, namely, beam-based models and truss-based models. The impact of corrosion is established through appropriate modification of the model parameters, based on the extent of visually observed corrosion damage. The analytical approaches are validated through a series of experimental tests previously conducted on corrosion-damaged girders. The second class of analytical approaches employs multi-physics models, to describe the mechanisms leading to corrosion-induced damage. The models account for heat transfer, moisture transport, and chloride transport in prestressed beam sections. Model parameters are calibrated with experimental tests in literature. The computational scheme is used to quantitatively describe the chloride ingress on bridge girders decommissioned from two different bridges in Virginia, after 34 and 49 years of service. The analysis results are found capable of capturing the actual chloride content at various depths from the exposure surface, as determined by chloride titration tests. The temporal evolution of chloride on the surface of prestressing strands indicates that corrosion has been taking place over a period of time for the two bridges. The multi-physics simulation approach is further enhanced to account for the corrosion-induced mechanical damage (cracking), by explicitly incorporating a description of the reaction kinetics, generation of expansive corrosion products and subsequent development of cracking in the surrounding concrete. The last part of this dissertation pursues the quantification of the uncertainty in the expected service life of prestressed concrete bridge structures. Given the inherent uncertainty to key values of model parameters, a parametric study is employed to investigate the propagation of uncertainty to the time history of chloride content at particular locations of the section and the probability of corrosion initiation at specific age values.

<p> Tuned Liquid Dampers (TLDs) are increasingly being used to suppress the dynamic vibration of tall buildings. An equivalent mechanical model is essential for rapid analysis and design of a TLD. The most common TLD tank geometries are circular, annular and rectangular. Rectangular tanks are utilized for 1-D and 2-D TLDs, whereas circular and annular are usually applied to axisymmetric structures. The amount of fluid that participates in the sloshing motion is directly influenced by the tank geometry. Although not commonly used, a TLD having a curved-bottom tank is expected to perform more effectively due to its relatively large value of effective mass. The main objective of this study is to develop mechanical models for seven TLDs with different tank geometries including the curved-bottom case, and to theoretically investigate the performance of rectangular, vertical-cylindrical and horizontal-cylindrical TLDs.</p> <p> Potential flow theory, linear long wave theory, Lagrange's equations and virtual work method are employed to develop the equivalent mechanical model parameters of TLDs with rectangular, vertical-cylindrical, horizontal-cylindrical, hyperboloid, triangular, sloped-bottom, and parabolic tank geometries. A rectangular, vertical-cylindrical and horizontal-cylindrical TLD are selected for further study using a single-degree-of-freedom (SDOF) model and a two degree of freedom structure-TLD system model applying the derived equivalent mechanical parameters.</p> <p> The dynamic characteristics of the TLDs as a SDOF system are investigated. The mechanical model is verified by comparing calculated values with experimental results for a rectangular TLD. The free surface motion, sloshing force and energy dissipation are found to be dependent upon the excitation amplitude. Analytical results also indicate that the horizontal-cylindrical TLD possesses the greatest normalized sloshing force and energy dissipation among the TLDs considered.</p> <p> The performances of various TLDs installed in a structure are studied in terms of effective damping, efficiency and robustness. Tuning ratio, structural response amplitude, mass ratio and liquid depth are adjusted to investigate their affect on the performance of the studied TLDs. Performance charts are developed and subsequently used to present the results. It is found that small liquid depth ratio and large mass ratio can lead to a robust structure-TLD system with small relative motion ratio between the structure and the vibration absorber. Comparisons of performance between the three TLDs are made and it can be concluded that the horizontal-cylindrical TLD is the most robust and effective device with the smallest relative motion ratio.</p> / Thesis / Master of Applied Science (MASc)

Die verformungsinduzierten Phasenumwandlungen und die Zwillingsbildung wurden in drei metastabilen austenitischen Cr-Mn-Ni-Stählen mit unterschiedlichem Nickelgehalt im breiten Temperaturbereich untersucht. Die entwickelten STU- und DTU-Diagramme fassen die gewonnenen Erkenntnisse zusammen und charakterisieren die verformungsinduzierten Gefügeänderungsprozesse in Abhängigkeit von der Spannung und der Temperatur. Die thermodynamischen Berechnungen bestätigen die Unterschiede in der chemischen Triebkraft für die Martensitumwandlung zwischen den Stählen und erklären unterschiedliches Werkstoffverhalten. Ein thermodynamisch-mechanisches Modell der verformungsinduzierten α‘-Martensitbildung wurde entwickelt. Der maximale α‘-Martensitanteil wird als Funktion der Gesamttriebkraft und der Temperatur mit einer guten Genauigkeit beschrieben. Des Weiteren wurde ein Modell der Umwandlungsplastizität mit Berücksichtigung der Plastizitätsverringerung infolge der isothermen oder spannungsinduzierten Martensitbildung entwickelt. Außerdem wurde der Einfluss von Mikroseigerungen auf die verformungsinduzierte Martensitbildung anhand drei Modellstähle untersucht und bestätigt.

Ce travail porte sur la simulation numérique et la modélisation du comportement thermo-mécanique des matériaux composites renforcés par des fibres. Spécifiquement les matériaux SMC (Sheet Moulding Compound) sont utilisés dans le processus de moulage par compression pour construire des pièces automobiles de haute performance. Ce travail est divisé en quatre chapitres, décrivant tout d’abord un modèle thermo-mécanique entièrement couplé pour les matériaux SMC standards et innovants à haute concentration en fibres (> 25% en volume). Le SMC est traité comme un mélange incompressible de fibre et de résine complété éventuellement par une phase de porosité compressible. Son anisotropie est modélisée au moyen de tenseurs structurels. La cinétique de réaction et de consolidation de la pièce est également modélisée et étudiée. Les données expérimentales mécaniques et thermiques enregistrées sur des échantillons de matériaux SMC sont comparées au modèle et à la solution numérique fournie par ce travail. D’un point de vue numérique, nous utilisons la méthode des domaines immergées o`u chaque phase est distinguée par une fonction distance signée. Nous décrivons le procédé de moulage par compression en proposant une résolution compressible anisotrope unifiée capable de décrire la transition compressible / incompressible du matériau SMC sous déformation. Cela permet de décrire la réponse mécanique du SMC et de prédire localement la consolidation (durcissement) de la pièce le long du cycle thermique. / This work deals with the numerical simulation and modeling of thermomechanical analysis of fiber reinforcedcomposites materials. Specifically for SMC (Sheet Molding Compound) materials that are used in compression molding processes to build automotive high performance parts. The work is divided into fourchapters, firstly describing a fully coupled thermo-mechanical model for standard SMC materials and for innovative SMC with high fiber concentration (> 25% in volume). The SMC is treated as an incompressible mixtureof fibers and paste complemented by a compressible porosity phase. Its anisotropy is modeled by means of structural tensors. Kinetic of reaction and consolidation of the part is also modeled and studied. Mechanicaland thermal experimental data recorded on samples of SMC materials are compared to the model and numerical solution provided in this work. A numerical framework, we use the immersed boundary method and the level set method. We describe the compression molding process by proposing an unified anisotropic compressible resolution able to describe the transition between compressible/ incompressible of SMC materials under deformation. We are able to describe the mechanical response of the SMC and to predict locally the consolidation (curing) of thepart throughout the thermal cycle.