Poly ethylene glycol (PEG) based microgels were synthesized and investigated. The PEG microgel has the same phase transition as the traditional poly N-isopropylacrylamide (PNIPAM). As a good substitute of PNIPAM, PEG microgel exhibits many advantages: it is easier to control the lower critical solution temperature (LCST) of the microgel by changing the component of copolymers; it has a more solid spherical core-shell structure to have a double thermo sensitivity; it is straightforward to add other sensitivities such as pH, magnetic field or organic functional groups; it readily forms a photonic crystal structure exhibiting Bragg diffraction; and, most importantly, the PEG microgel is biocompatible with human body and has been approved by FDA while PNIPAM has not. PEG microgels with core-shell structure are synthesized with a two-step free radical polymerization and characterized with DLS, SLS and UV–Vis. The dynamic mechanics of melting and recrystallizing of the PEG core-shell microgel are presented and discussed. Photonic crystals of PEG microgels were synthesized and characterized. The crystal can be isolated in a thin film or a bulk column. The phase transition of PEG microgel was simulated with the mean field theory. The enthalpy and entropy of phase transition can be estimated from the best fit to theoretical calculation with experimental data.

A 4 × 4 photonic switch matrix was designed, fabricated and characterized. The photonic switch matrix was based on microring resonator (MR) and was fabricated on relatively low-cost silicon-on-insulator (SOI). Independent wavelength channel switching was accomplished by thermo-optic tuning of the MRs through highly localized resistive micro-heaters. The device was fabricated using the relatively mature silicon fabrication technology. Waveguide patterns were defined with high definition eBeam lithography, etching was done in a reactive-ion etching chamber, and the top cladding SiO2 layer was deposited through plasma-enhanced chemical vapor deposition. Finally, resistive Nichrome micro-heaters were deposited locally directly above each MR to offer the dynamic tuning capability. The strong optical confinement offered by the high index contrast between silicon and SiO2 makes it possible to fabricate micrometer-sized MRs with acceptable optical power loss caused by the small bending radii. The MRs were designed with a uniform diameter of 10 µm to support a wide free spectral range. All waveguides have a design dimension of 450 nm × 250 nm to allow operation exclusively in the fundamental mode at the 1.55 µm wavelength. A FSR of 18 nm with a spectral linewidth of 0.1 nm were observed for the fabricated MRs offering high wavelength selectivity. The device exhibits virtually no thermal crosstalk between adjacent channels, showing no output peak wavelength shift at 0.01 nm wavelength measurement precision by thermally tuning an adjacent MR with electric current as high as 7 mA, which is equivalent to about 2.5 nm in resonance wavelength tuning. The device showed a tuning delay time of about 1 ms. The overall bare chip size of the device is 20 mm × 4 mm. We demonstrated through this work a wavelength selective photonic switch device using low-cost SOI technology that is compact and easy to fabricate. It shows high potential for further development into high port-count photonic switch matrix.

This study presents experimental works and finite element (FE) analyses for understanding nonlinear thermo-viscoelastic behaviors of multilayered (pultruded) composites under tension. Uniaxial isothermal creep tests in tension are conducted on Eglass/ Polyester pultruded composites of 0o, 45o and 90o off-axis fiber orientations subject to combined temperatures and stresses. The temperatures range from 0°F to 125°F, and stress levels range from 20% to 60% of the ultimate tensile strength of the composite specimen. The creep responses seem to accelerate with temperature for higher temperatures (75oF to 125oF) and do not behave in any particular manner for lower temperatures (0oF to 50oF). Isochronous curves of time-dependent material responses show that the nonlinearity increases with time and also temperature for higher temperatures while there is no particular trend seen at lower temperatures. Also, the creep responses of the axial specimens show negligible nonlinearity when compared to that of the transverse and 45o off-axis specimens. The Poisson’s effect is studied and orthotropic material symmetry conditions are satisfied. A nonlinear viscoelastic constitutive model, based on convolution integral equation, is presented for orthotropic materials. The nonlinear stress-temperature-dependent material parameters are coupled in the product form and are calibrated using the experimental data. Overall good predictions are shown but for a slight mismatch in the prediction of the responses at temperatures below 50 o F owing to the random behavior of the creep responses at lower temperatures. The numerical integration algorithm for the nonlinear viscoelastic model of orthotropic composite materials developed by Sawant and Muliana (2008) was used to integrate the constitutive material model to FE structural analyses. Sensitivity analysis is conducted to check for error in experiments by numerically simulating the testing procedure. A practical structural analysis is carried out on composite slabs using ABAQUS and our model is used to predict the responses of slabs under combined stress and temperature loading.

Low-temperature waste heat recovery is an important component of generating a more efficient, cost-effective and environmentally-friendly energy source. To meet this goal, thermo-electrochemical cells (TECs) are cost-effective electrochemical devices that produce a steady electric current under an applied temperature difference between their electrodes. However, current TECs have low conversion efficiencies. On this project, I developed a comprehensive multiscale model that couples the governing equations in TECs. The model was used to understand the fundamental principles and limitations in TECs, and to find the optimum cell thickness, aspect ratio and number of cells in a series stack. Doped multiwall carbon nanotubes (MWCNTs) were then explored as alternative electrodes for TECs. One of the main objectives of this dissertation is to study multiwall carbon nanotube/ionic liquid (MWCNT/IL) mixtures as alternative electrolytes for TECs. Previous authors showed that the addition of carbon nanotubes (CNTs) to a solvent-free IL electrolyte improves the efficiency of dye solar cells by 300%. My research plan involved a spectroscopy analysis of imidazolium-based ionic liquids (IILs) mixed with MWCNTs using impedance spectroscopy and nuclear magnetic resonance. The results show that the combination of interfacial polarization and ion pair dissociation effects reduces mass transfer resistances and enhances the power of TECs at low wt% of MWCNTs. This happens in spite of reduced open circuit voltage due to percolated networks.

Magma chambers are a fundamental component of crustal magma transport modulating erupted volumes, compositions, and timing of eruptions. However, we understand little about how eruption episodicity relates to magma chamber evolution. A sizable amount of research has been done on the thermo-mechanical and chemical evolution of a chamber, but little has been done in combining the two. The many influences on composition make inference of crustal processes from erupted compositions dicult, but there are patterns of eruptive evolution in well- characterized systems that suggest something systematic is occurring. We have developed a coupled thermo-mechanical-chemical model in order to characterize melt evolution through cycles of chamber filling, rupture, and drainage in a thermally evolving, viscoelastic crust. We consider a deeply seated oblate spheroidal chamber, calculating pressure, temperature, volume, elemental concentration, partitioning between crystals and melt, and crustal temperature through time. We characterize the time dependence of chamber failure, thermal longevity, and melt elemental concentrations on mechanical parameters and influx rates, exploring the dependence on depth, primary and crustal compositions. These results should be important for constraining physical controls on eruption episodicity and predictions of instability at magmatic centers.

No description available.

Ce travail a pour objet le développement d’un système combinant un algorithme génétique d’optimisation multiobjectifs avec des outils de thermodynamique prédictive de type calphad (calcul des diagrammes de phases) et de fouille de données permettant l’estimation des propriétés thermochimiques et thermomécaniques d’alliages multicomposants. L’intégration de ces techniques permet l’optimisation quasi-autonome de la composition d’alliages complexes vis-à-vis de plusieurs critères antagonistes telles les résistances mécaniques et chimiques, la stabilité microstructurelle à haute température et le coût. La méthode est complétée d’une technique d’analyse décisionnelle multicritères pour assister la sélection d’alliages. L’approche est illustrée par l’optimisation de la chimie de deux familles d’alliages multicomposants. Le premier cas d’étude porte sur les superalliages à base de nickel polycristallins corroyés renforcés par précipitation de la phase 0 destinés à la fabrication de disques de turbines dans l’aéronautique ou de tuyauteries de centrales thermiques. L’optimisation résulte en la conception d’alliages moins onéreux et prédits plus résistants que l’Inconel 740H et le Haynes 282, deux superalliages de dernière génération. Le second cas d’étude concerne les alliages dits « à forte entropie » dont la métallurgie singulière est emblématique des problèmes combinatoires. À l’issue de l’optimisation, quelques alliages à forte entropie ont été sélectionnés et fabriqués ; leur caractérisation expérimentale préliminaire met en évidence des propriétés attrayantes tel un ratio dureté sur masse volumique inédit. / The present work revolves around the development of an integrated system combining a multi-objective genetic algorithm with calphad-type computational thermodynamics (calculations of phase diagrams) and data mining techniques enabling the estimation of thermochemical and thermomechanical properties of multicomponent alloys. This integration allows the quasiautonomous chemistry optimisation of complex alloys against antagonistic criteria such as mechanical and chemical resistance, high-temperature microstructural stability, and cost. Further alloy selection capability is provided by a multi-criteria decision analysis technique. The proposed design methodology is illustrated on two multicomponent alloy families. The first case study relates to the design of wrought, polycrystalline 0-hardened nickel-base superalloys intended for aerospace turbine disks or tubing applications in the energy industry. The optimisation leads to the discovery of novel superalloys featuring lower costs and higher predicted strength than Inconel 740H and Haynes 282, two state-of-the-art superalloys. The second case study concerns the so-called “high-entropy alloys” whose singular metallurgy embodies typical combinatorial issues. Following the optimisation, several high-entropy alloys are produced; preliminary experimental characterisation highlights attractive properties such as an unprecedented hardness to density ratio.

Dans ce travail de recherche, on aborde une étude expérimentale et numérique du comportement mécanique des roches argileuses soumis à des chargements mécaniques et à des sollicitations thermiques. L’esprit de cette étude provient de la pratique de l’exploitation des huiles lourdes avec la technique d’injection de vapeur à haute température où les roches de réservoir sont soumises à des sollicitations thermiques et hydromécaniques couplées. L’enjeu est d’étudier le comportement hydromécanique de ces matériaux soumis à des variations importantes de température afin d’évaluer la stabilité mécanique des réservoirs. L’étude expérimentale contient des modifications d'une cellule triaxiale autonome et auto compensé à haute température (250 C°) ainsi que le système de pilotage, le système de mesure et d’étalonnage de déformations. Ces modifications sont importantes pour effectuer des tests hydrostatiques, uniaxiaux et triaxiaux servaient à obtenir une base des données expérimentales, cette base caractérise l’effet thermique sur le comportement mécanique des roches argileuse.Le cadre général de la modélisation est d’abord proposé pour décrire le comportement mécanique d’argilite dans le cas isotrope. Après une analyse détaillée des données expérimentales, un modèle spécifique élastoplastique couplé à l’endommagement est élaboré pour décrire le comportement mécanique. Ensuite l’effet de la température est pris en compte. Les comparaisons entre les simulations numériques et les données expérimentales ont montré la capacité du modèle proposé pour la description du couplage hydromécanique et thermique. Afin de décrire le comportement des roches anisotrope, nous avons proposé une extension du modèle en y introduisant une formulation de tenseur de fabrique Cette formulation est exprimée en termes d'invariants couplé aux tenseurs de contraintes et d’orientation de chargement. Des essais en laboratoire sous différents chemins de sollicitations ont été modélisés, le modèle proposé semble décrire correctement les principales réponses mécaniques des matériaux. / We proposed, in this work, an experimental and numerical study of mechanical behavior of shale rocks subjected to mechanical and thermal loads.In the petroleum industry, during the production of heavy oil with the technique of steam water injection at high temperature, the cap rocks are subjected to coupled thermal and hydro-mechanical solicitations. The challenge is to study the hydro-mechanical behavior of these materials subject to large variations in temperature in order to assess the mechanical stability of the reservoir. The experimental study includes the modifications in a triaxial cell in ordre to support a high temperature (250° C). These modifications are very important for hydrostatic, uniaxial and triaxial tests, all these tests are used to obtain an experimental data base characterizing the thermal effect on the mechanical behavior of shale rocks.The modeling framework is proposed at first to describe the mechanical behavior of shale rock in isotropic case. After a detailed analysis of experimental data obtained in the experimental section, a specific coupled elastoplastic-damage model has been developed to describe the mechanical behavior of these shale materials. The effect of temperature is taken into account and a comparison between numerical simulations and experimental data have shown the ability of the proposed model for the description of thermo mechanical coupling. To describe the behavior of anisotropic rocks, we have proposed an extension of the fabric tensor model to present the initial anisotropy of shale rock. This formulation is expressed in terms of invariant stress tensor coupled with loading orientation. Laboratory tests under different stress paths were modeled, the proposed model seems able to describe correctly the main mechanical responses of shale materials.

L’objectif de ce travail est d’étudier l’effet des fissures de dessiccation sur le comportement thermo-hydro-mécanique des sols argileux sensibles au phénomène de retrait. Ce travail inclut une étude expérimentale caractérisant l’influence des fissures sur le séchage des sols fins ainsi qu’une étude numérique comprenant une modélisation du processus dans le but de présenter l’impact des fissures sur le comportement thermo-hydrique d’un milieu argileux non saturé. L’étude expérimentale comprend des expériences de séchage réalisée en laboratoire sur des échantillons de sol intacts et fissurés où l’évolution de la teneur en eau a été suivie. Les processus liés la formation de nouvelles fissures ainsi qu’à la propagation des fissures sont aussi discutés.Une modélisation numérique du processus de fissuration des sols fins est ensuite présentée. Dans cette étude, une analyse détaillée de l’influence des fissures sur l’interaction sol-atmosphère est présentée. Un modèle numérique bidimensionnel de l’interaction sol- atmosphère tenant compte de la présence des fissures a été développé. Ce modèle prend en compte le couplage thermo-hydrique d’un milieu argileux non saturé. Dans cette étude, on a montré l’impact des fissures sur le développement de la succion, sur la variation de la teneur en eau ainsi que sur la valeur d’entrée de l’air. L’influence des fissures sur l’évolution du tassement du sol est également présentée. Cette étude propose aussi une approche simple pour la prise en compte des fissures dans l’interaction sol-atmosphère.Dans la dernière partie de ce travail, l’influence des fissures sur le comportement mécanique des sols fins est présentée et discutée. / The objective of this work is to study the effect of desiccation cracks on the thermo-hydro-mechanical behavior of clayey soils.The study includes an experimental study to characterize the influence of cracks on the drying process of clay samples and a numerical study in order to present the impact of cracks on the soil-atmosphere interaction.In the first phase of this study, an experimental work performed in the laboratory to characterize the influence of cracks on drying soil was conducted. Drying tests were conducted on samples of intact and cracked soil where the evolution of the water content and cracking due to drying were monitored. In the second phase of this study, the influence of cracks on the thermo-hydro-mechanical behaviour of clayey soil is presented. A two-dimensional numerical model of soil-atmosphere interaction has been developed considering the presence of cracks. The model takes into account the thermo- fluid coupling of an unsaturated clay soil.The model is used to simulate the evolution of evaporation during the drying process. It shows the impact of cracks on the suction development and water content evolution as well as the air entry value. This study also proposes a simple approach to the consideration of cracks in the soil-atmosphere interaction. In the last part of this work, the influence of cracks on the mechanical behaviour of fine soils is presented and discussed.

The research presented herein describes the coupling of acoustic and heat release fluctuations in a perfectly-premixed swirl-stabilized combustor by analysis of simultaneous high-repetition-rate laser diagnostics data. Nine cases are studied, varying the thermal power and the equivalence ratio. Proper orthogonal decomposition (POD) of the velocity data shows that cases with higher amplitude thermoacoustic oscillations have flow fields containing helical vortex cores (HVC); these cases are further analysed to determine the driving mechanisms of the oscillations. Flow and flame statistics are compiled as a function of both the phase in the thermoacoustic cycle and a phase representing the azimuthal position of the HVC relative to the measurement plane. These data are used to spatially map the thermoacoustic energy transfer field, as described by the Rayleigh integral. It is found that periodic deformations of the HVC cause large-scale flame motions, resulting in regions of positive and negative energy transfer.