Spark plasma sintering (SPS) is a powder consolidation technique used to rapidly densify a variety of material systems. SPS is capable of precisely controlling material microstructures and achieving non-equilibrium phases due to rapid heating and cooling rates through the simultaneous application of pressure and direct current. Due to these characteristics, SPS is an ideal processing technique for high temperature ceramics which require processing at temperatures greater than 1500°C. Due to the desirable properties obtained on small diameter materials processed by SPS, larger and more complex geometries are desired while maintaining sample microstructures. In order to accurately scale ceramics produced by SPS, a finite element model must be developed that can be used as a predictive tool. My research focuses on developing a finite element model for the spark plasma sintering furnace at the University of Arizona and validating modeled results using experimentally obtained data. Electrical and thermal conductivity as functions of temperature vary widely among different grades of commercially available electrode grade graphite at constant density. Modeled material properties are optimized in order to calibrate modeled results to experimentally obtained data (i.e. measured current, voltage, and temperature distributions). Sensitivity analysis is performed on the model to better understand model physics and predictions. A calibrated model is presented for 20mm ZrB2 and Si3N4 discs. Sample temperature gradients are experimentally confirmed using grain size and β-Si3N4 phase composition. The model is used to investigate scale up from 20mm to 30mm discs and 30mm rings as well as effects of processing conditions on β-Si3N4 content.

Dans ce travail de thèse, une méthode d’identification inverse des propriétés mécaniques du matériau viscoélastique (module de cisaillement et facteur de perte) fonctionnalisé dans une structure sandwich à trois couches symétriques est proposée. L’objectif de ce travail est de pouvoir identifier les propriétés mécaniques in situ. A travers un modèle éléments finis basé sur le modèle Zig-Zag de Rao, notre modèle assure la détermination des paramètres modaux de la poutre sandwich. L'approche inverse consiste en une procédure itérative qui détermine les formes de mode étant donné les paramètres matériaux puis calcule les propriétés viscoélastiques à partir des modes en utilisant un quotient de Rayleigh jusqu'à ce que la convergence sur les propriétés du matériau soit satisfaite. Les paramètres d’entrée du modèle inverse sont les fréquences de résonance et facteurs de perte de la poutre sandwich obtenues expérimentalement. En conséquence, la dépendance en fréquence des propriétés du matériau viscoélastique de la poutre sandwich est déterminée par une démarche automatisée. La méthode a été comparée avec succès aux formules de Ross-Kerwin-Ungar ; à une approche d'optimisation standard et à la littérature. A partir des résultats, nous avons pu déduire les lois de comportement du cœur viscoélastique suivant des modèles rhéologique tels que le modèle de Maxwell généralisé, d’ADF, de GHM et du Zéner fractionnaire. Ce dispositif expérimental couplé à la méthode d’indentification a permis l’investigation des paramètres modaux de la poutre à différentes températures pour étudier l’effet de la température sur les lois rhéologiques. Pour étudier la robustesse de notre méthode, nous avons procédé des essais de reproductibilité, de reproductibilité sur une population d’échantillon. L’efficacité de notre méthode étant été prouvée, une étude de sensibilité a été menée sur les caractéristiques géométriques de notre structure et les paramètres d’entrée. Les résultats obtenus montrent le fort impact de certains paramètres sur l’identification / In this work, a inverse identification method of the mechanical properties of the viscoelastic material (shear modulus and loss factor) functionalized in a sandwich structure with three symmetrical layers is proposed. The objective of this work is to be able to identify the mechanical properties in situ. Through a finite element model based on Rao's Zig-Zag model, our model ensures the modal parameter determination of the sandwich beam. The inverse approach consists of an iterative procedure that determines the mode shapes given the material parameters and then calculates the viscoelastic properties from the modes using a Rayleigh quotient until convergence on the properties of the material is satisfied. The input parameters of the inverse model are the resonance frequencies and loss factors of the sandwich beam obtained experimentally. As a result, the frequency dependence of the viscoelastic properties of the sandwich beam is determined by an automated way. The method has been successfully compared to Ross-Kerwin-Ungar formulas; a standard optimization approach and the literature. From the results, we have been able to deduce the constitutive laws of the viscoelastic heart according to rheological models such as the generalized Maxwell model, ADF, GHM and fractional Zener. This experimental device coupled to the method of identification allowed the investigation of modal parameters of the beam at different temperatures to study the effect of the temperature on the rheological laws. To study the robustness of our method, we carried out tests repeatability, reproducibility on a sample population. Since the effectiveness of our method has been proven, a sensitivity study has been carried out on the geometrical characteristics of our structure and the input parameters. The results obtained show the strong impact of certain parameters on identification

Este trabalho apresenta um estudo sobre o comportamento de sistemas de pesagem em movimento baseados em plataformas comumente utilizadas no Brasil. Parâmetros relevantes nesse comportamento são modelados: rugosidade aleatória da pista, dinâmica vertical do veículo e sua velocidade, desnível entre a pista e plataforma e dinâmica da plataforma. Duas classes de veículos são simuladas trafegando a diferentes velocidades e sendo pesados utilizando uma proposta de modelo de plataforma rígida e uma proposta de plataforma flexível. As forças de reação do solo e históricos de aceleração em vários GDL são registrados a fim de obter a carga estática por eixo e os erros nas estimativas do peso para o modelo de plataforma rígida. Já para o modelo de plataforma flexível, as forças de reação servem de entrada no modelo de elemento finitos de viga Euler-Bernoulli com consideração da área de contato do pneu através de um trem de cargas. Conclusões relacionadas à redução da precisão do sistema com o aumento da velocidade do veículo são confirmadas, embora importantes conclusões não tão óbvias sobre a importância da dinâmica do veículo, do nível de rugosidade da pista, da altura do degrau pista-plataforma e da dinâmica da plataforma de pesagem são ressaltadas. / This work proposes a numerical study on the behavior of weigh-in-motion systems based on load platforms useful in Brazil. Some important parameters that may control this behavior that are modeled are random road roughness, vehicle vertical dynamics, vehicle speed, load platform step’s height to the road and platform dynamics. Two vehicles types are modelled travelling at different speeds and being weighted using a rigid platform proposal and another proposal with a flexible platform. Ground reaction force and acceleration time history on several degree-of-freedom are recorded in order to obtain the static load per axis and the corresponding estimated errors for the rigid platform model. For the flexible platform model, the reaction forces serve as inputs into the Euler-Bernoulli finite element model with consideration of the contact area of the tire by train of loads. Some usual conclusions related to the reduction in the accuracy of the measuring system with increased vehicle speed are confirmed in the numerical study, although important conclusions not so obvious concerning the importance of road roughness, vehicle vertical dynamics, and vehicle speed, load platform step’s height to the road and platform dynamics are highlighted.

Cette thèse porte sur la simulation et la réduction du bruit acoustique d’origine magnétique des alternateurs à griffes ainsi que sur la compréhension des phénomènes mis en jeu dans la génération du bruit. La structure, les différents composants et les particularités du bruit acoustique de l’alternateur à griffes sont détaillés dans la première partie. La problématique ainsi que l’approche générale de cette thèse sont ensuite exposées. Cette approche se base sur la simulation du bruit acoustique d’origine magnétique. Un état de l’art des études sur le bruit acoustique d’origine magnétique des machines électriques est présenté dans la seconde partie. Les modèles électromagnétiques, mécaniques et acoustiques utilisés pour l’étude de ces machines ainsi que les principales solutions de réduction du bruit sont exposés. Les nouvelles approches de modélisation électromagnétique et vibro-acoustique de la machine à griffes sont développées dans la troisième partie. Deux modèles électromagnétiques sont étudiés : un modèle numérique qui repose sur l’utilisation de la méthode des éléments finis et un modèle hybride qui allie le modèle numérique à un modèle analytique. Ce dernier s’appuie sur la décomposition de l’induction magnétique dans l’entrefer en un produit d’une fonction de perméance avec une fonction de force magnétomotrice. Chaque fonction prend en compte les variations axiales dues à la géométrie des griffes. Ce modèle nécessite toutefois l’utilisation d’un modèle numérique afin de prendre en compte la saturation et les forces tangentielles. Un modèle mécanique purement numérique est ensuite construit. Il permet de prendre en compte la géométrie exacte des pièces ainsi que les contacts entre les pièces. Ce modèle mécanique est développé grâce à la corrélation avec des mesures et porte principalement sur trois parties de l’alternateur : le paquet de tôles du stator, le bobinage du stator et l’assemblage stator-paliers. Enfin, les simulations acoustiques avec les modèles numériques sont comparées aux mesures et permettent de retrouver les principaux pics de bruit des alternateurs. Dans la quatrième partie, des études de sensibilités sont menées afin de déterminer les paramètres les plus influents sur le bruit acoustique d’origine magnétique des machines à griffes. Ces études montrent l’influence importante de la géométrie du rotor, du bobinage stator et de la température sur le bruit. Les modifications de la structure ainsi que les imperfections étudiées (i.e. défauts de forme et excentricité) ont une influence moindre. Les caractéristiques des forces magnétiques ainsi que les influences des forces radiales et tangentielles sont ensuite exposées. Finalement, des exemples d’optimisation du rotor sont traités avec les deux modèles électromagnétiques (numérique et hybride). Un prototype est réalisé pour valider expérimentalement les résultats des simulations et un gain de 10 dB est obtenu sur la puissance acoustique. / This thesis aims at simulating and reducing the acoustic noise due to magnetic forces of claw-pole automotive alternators. It also aims at improving the understanding of the noise generation mechanisms. In the first part, the assembly of the claw-pole alternator and its different parts are described. The particularities of the acoustic noise of the alternator are also given. Then, the problem as well as the global approach, based on the vibro-acoustic simulation, are explained. The second part is a review of the studies on the acoustic noise from a magnetic origin of electrical machines. The models used to study these machines as well as the main noise reduction solutions are detailed. In the third part, new electromagnetic and vibro-acoustic models are developed. Two electromagnetic models are considered : a finite element model and a hybrid model which couples the finite element model with an analytical model. This analytical model computes the airgap magnetic flux density as the product of a permeance and a magnetomotive force functions. Each function takes the variations of the claw-pole geometry along the axial direction into account. Saturation and tangential forces are taken into account thanks to the finite element model. Then, a finite element mechanical model is developed. Three unknown parameters of the model are determined thanks to the correlation between the model and experimental data, namely : the equivalent materials of the stator stack and the windings and the contact conditions between the stator and the brackets. Finally, acoustic simulations are compared with measurements. A good correlation is achieved between simulated and measured noise peaks. In the fourth part, sensitivity studies are carried out in order to determine the most influential parameters on the acoustic noise of claw-pole alternators. These studies show the significant influence of the claw-pole geometry, the stator windings and the temperature on the acoustic noise. Structural modifications and studied faults have a smaller influence. Characteristics of the magnetic forces as well as the influences of radial and tangential forces are then detailed. In the end, optimizations with the finite element and the hybrid models are presented. A prototype is built and acoustic measurements show a 10 dB decrease of the sound power level.

Light-frame shearwall assemblies have been successfully used to resist gravity and lateral loads, such as earthquake and wind, for many decades. However, there is a need for maintaining the structural integrity of such buildings even when large openings in walls are introduced. Wood portal frame systems have been identified as a potential alternative to meet some aspects of this construction demand. The overarching goal of the research is to develop wood portal frame bracing systems, which can be used as an alternative or in combination with light-frame wood shearwalls. This is done through investigating the behavior of wood portal frames using the MIDPLY shearwall framing technique. A total of 21 MIDPLY corner joint tests were conducted with varying bracing details. Also, a finite element model was developed and compared with test results from the current study as well as studies by others. It was concluded from the corner joint tests that the maximum moment resistance increased with the addition of metal straps or exterior sheathings. The test results also showed a significant increase in the moment capacity and rotational stiffness by replacing the Spruce-Pine Fir (SPF), header with the Laminated Veneer Lumber (LVL) header. The addition of the FRP to the standard wall configuration also resulted in a significant increase in the moment capacity. However, no significant effect was observed on the stiffness properties of the corner joint. The FE model was capable of predicting the behavior of the corner joints and the full-scale portal frames with realistic end-conditions. The model closely predicted the ultimate lateral capacity for all the configurations but more uncertainty was found in predicting the initial stiffness.The FE model used to estimate the behavior of the full-scale portal frames constructed using the MIDPLY framing techniques showed a significant increase in the lateral load carrying capacity when compared with the traditional portal frame. It was also predicted using the full-scale FE model that the lateral load carrying capacity of the MIDPLY portal frame would increase with the addition of the metal straps on exterior faces. A parametric study showed that using a Laminated Strand Lumber (LSL) header increased the lateral load carrying capacity and the initial stiffness of the frames relative to the SPF header. The study also showed that there was an increase in the capacity if high strength metal straps were used. Doubling of the nail spacing at header and braced wall segment had a considerable effect on the lateral capacity of portal frame. Also, the initial stiffness was reduced for all the configurations with the doubling of the nail spacing at the header and braced wall segment in comparison with the reference frame.

In this study, a typical mat foundation and structural loading pattern is considered. Three dimensional finite element analyses, PLAXIS 3D, is performed to determine the soil / foundation contact stress distribution, settlement distribution, distribution of modulus of subgrade reaction as a function of column spacing, stiffness of the soil and thickness of the foundation. A parametric study is performed to demonstrate the dependence of those distributions on various parameters. Moreover, a relationship between size of the foundation, deformation modulus of foundation soil and modulus of subgrade reaction is proposed. Depending on the variations in those parameters, obtained shear force and bending moment distributions are compared. Consistency between the resulting shear forces and bending moments of a typical foundation, modeled in two different three dimensional finite element programs, PLAXIS 3D and SAP 2000, is discussed. It is found that the variation in the aforementioned parameters cause different influences on contact stress distribution, settlement distribution, distribution of modulus of subgrade reaction. The importance of those variations in beforementioned parameters, under different situations is discussed. A relationship between modulus of subgrade reaction and deformation modulus of foundation soil is proposed.

Virtual crack closure technique (VCCT) is commonly used to analyze debonding/delamination onset and growth in fiber reinforced composite assemblies. VCCT is a computational fracture mechanics based approach, and is based on Irwin&rsquo / s crack closure integral. In this study, the debonding/delamination onset and growth potential in a bonded fiber reinforced composite skin-flange assembly is investigated using the VCCT. A parametric finite element analyses is conducted. The finite element analyses results are compared with coupon level experimental results available in the literature. The effects of different finite element modeling techniques are investigated. The bonded flange-assembly is modeled with pure solid (3D) elements, plane stress (2D) shell elements and plane strain (2D) shell elements. In addition, mesh density, element order and geometric non-linearity parameters are investigated as well. The accuracy and performance of these different modeling techniques are assessed. Finally, effect of initial defect location on delamination growth potential is investigated. The results presented in this study are expected to provide an insight to practicing engineers in the aerospace industry.

Hemodynamic monitoring is extremely important in the accurate measurement of vital parameters. Current methods are highly invasive or noncontinuous, and require direct access to the patient’s skin. This study intends to explore the modulated magnetic signature of blood method (MMSB) to attain blood flow information. This method uses an applied magnetic field to magnetize the iron in the red blood cells and measures the disturbance to the field with a magnetic sensor [1]. Exploration will be done by experimentally studying in-vitro, as well as simulating in COMSOL the alteration of magnetic fields induced by the flow of a magnetic solution. It was found that the variation in magnetic field is due to a high magnetization of blood during slow flow and low magnetization during rapid flow. The understanding of this phenomenon can be used in order to create a portable, non-invasive, continuous, and accurate sensor to monitor the cardiovascular system.

No description available.

A numerical formulation for two-dimensional electro-osmotic consolidation in soft clays was derived from the basic equations of fluid flow, current flow and virtual work law. And, a well known elasto-plastic soil model, Modified Cam Clay was embedded into the formulation and implemented into the finite element program AFENA. The formulation was evaluated by comparing the predicted settlement and pore water pressure response with the values obtained from laboratory tests. The tests were conducted in an electro-osmotic triaxial apparatus, which was modified from a standard triaxial apparatus to facilitate electro-osmotic consolidation and required measurements. A series of electro-osmotic consolidation tests under different initial stress conditions were conducted to evaluate the finite element model and very good agreements between the observed and predicted results were observed. Another set of electro-osmotic tests were conducted with the similar initial stress, but different boundary conditions to examine the effects of electrochemical changes during the electro-osmosis. The study showed an apparent increase in the preconsolidation pressure and alteration in the coefficient of consolidation as a result of the electrochemical changes. A one-dimensional electro-osmotic consolidation problem was simulated and analysed, and the settlement and pore water pressure responses were compared with the solutions obtained from Esrig's (1968) one-dimensional theory. Another problem involving combined electro-osmotic and direct loading consolidation was also analysed and the results were compared with the solutions obtained from Wan and Mitchell's (1976) theory. Excellent matches were observed in both cases mentioned above for constant values of electro-osmotic and hydraulic permeabilities. However, the effects of varying electro-osmotic and hydraulic permeabilities, which are practically far more significant and not adopted in the theories mentioned above, were also analysed and the results presented. An attempt was made to simulate and analyse one of the successful field trial of electro-osmotic stabilisation conducted by Bjerrum et al (1967) on Norwegian quick clay. Good agreement between the predicted and reported settlement was observed for the first 50days of the treatment period. However, the model over-predicted the settlement after this period and the possible causes for this variation are discussed.