Ce travail de thèse s’est attaché à investiguer, d’une part, le mécanisme d’érosion interne par suffusion dans les ouvrages hydrauliques en terre, et d’autre part, les conséquences qu’il pourrait avoir sur le comportement mécanique du sol, l’objectif principal étant d’améliorer notre compréhension de ce processus et du comportement des sols érodés. La démarche adoptée est principalement expérimentale, réalisée à différentes échelles : du macroscopique, à l’échelle du matériau, au microscopique, à l’échelle des grains constitutifs. A l’échelle macroscopique, des essais de suffusion ont été réalisés sur des échantillons de sol à l’aide d’un nouveau dispositif d’essai d’érosion, appelé perméamètre de suffusion, développé dans le cadre de cette thèse. Après érosion dans le perméamètre, les échantillons érodés sont transférés par une procédure de congélation / décongélation dans un dispositif d’essai triaxial afin d’étudier leur comportement sous chargement mécanique. Les résultats obtenus à cette échelle ont permis de donner un aperçu général du mécanisme de suffusion et de mettre en évidence son impact sur les propriétés de résistance au cisaillement du sol. A l’échelle microscopique, une analyse fine a pu être menée en réalisant un essai de suffusion des mesures in-operando de tomographie à rayons X et de la visualisation locale par techniques optiques sur un sol artificiel. La caractérisation du sol à cette échelle microstructurale a permis de mieux comprendre le processus de suffusion, notamment en mettant en évidence l’apparition et le développement de fortes hétérogénéités qui semblent avoir une influence importante sur la réponse mécanique des sols érodés / This thesis work has investigated, on the one hand, the mechanism of internal erosion by suffusion in earthen hydraulic structures, and, on the other hand, the consequences suffusion can cause on the mechanical behavior of soils, the main objective being to improve our understanding of both the suffusion process and the behavior of eroded soils. The approach adopted was mainly experimental, by a multi-scale scope: from macroscopic, at the material scale, to microscopic, at the grain scale. At the macroscopic scale, suffusion experiments were performed on gap-graded cohesionless soil samples using a newly developed testing device, called the suffusion permeameter. Then, the eroded samples are transferred by a freeze/thaw procedure to a triaxial device to study their behavior under mechanical loading. The achieved results provide a general overview of the suffusion mechanism at the sample scale and highlight its impact on soil shear resistance properties. At the microscopic scale, the suffusion mechanism has been studied by performing a suffusion test with in-operando x-ray tomography and using local visualization based on optical techniques in an artificial soil. Subsequent grain-scale analysis has provided a deeper understanding of suffusion process through the characterization of the eroded soil microstructure, particularly highlighting the occurrence and development of strong heterogeneities, which appear to play a key role in the macroscopic mechanical behavior of eroded soils

La reproduction expérimentale de transitoires thermiques accidentels de type Accident par Perte de Réfrigérant Primaire (APRP) en laboratoire a permis d’observer la fragmentation du combustible fortement irradié lorsque la gaine se déforme sous l’augmentation de la température. Ces fragments de petites tailles peuvent se relocaliser dans le ballon voire être éjectés hors du crayon cas de rupture de gaine. La zone High Burnup Structure (HBS) des combustibles fortement irradiés est la plus susceptible de se fragmenter et d’être relocalisée par sa position en périphérie de pastille. Pour expliquer ce phénomène, l’hypothèse retenue est que le transitoire provoque une surpression dans les bulles HBS ce qui mène à la décohésion des joints de grains et à la fragmentation. Cette thèse a pour but de développer un critère de fissuration mécanique du combustible pour mieux comprendre le comportement des bulles HBS lors des conditions thermiques APRP. Ce travail se base sur une méthode une méthode micromécanique en trois étapes : i) la représentation qui permet de caractériser la microstructure de la zone HBS (leurs dimensions, leur fraction volumique, et la pression interne). Deux sources d’informations seront utilisées : les observations expérimentales provenant de disques ou de pastilles de combustible irradiés à fort taux de combustion et d’outils numériques(avec Alcyone-Caracas [JSB+14]) / Under Loss Of Coolant Accident(LOCA) transients conditions, the high irradiated fuel is fragmented in small sizes fragments who can be relocated in the balloon, or being ejected out of the fuel rod if the latter burst. This work focuses on the pellet rim, where bubbles density increases owing to a higher irradiation level. Usually the hypothesis used to explain fuel fragmentation during transient is grain cleavage induced by over pressurized fission gas bubbles, located at the grain boundary. The aim of this study is to define a macroscopic fragmentation model based on a micro mechanical approach to have a better understanding of the fuel mechanical behaviour at lower scale : size and volume fraction of fragments. This PhD introduces a stepwise micromechanical method based on three steps : i) firstly, we detail how to model the HBS microstructure including pressurized porosities, based on experimental or numerical data and define a representative volume element (RVE)

The methods of MSD are applied to the design of functionally graded materials. Analysis models are presented to allow the design of compliant derailleur for a case study and constraints are placed on the design. Several methods are presented for relating elements of the microstructure to the properties of the material, including Taylor yield theory, Hill elastic bounds, and precipitation hardening. Applying n-point statistics to the MSD framework is also discussed. Some results are presented for the information content of the 2-point correlation statistics that follow from the methods used to integrate functionally graded materials into MSD. For the compliant beam case study, the best design (98%Al-2%Li) was a 97% improvement over the worst (100%Al). The improvements were primarily due to the precipitation hardening, although anisotropy also significantly impacted the design. Under the constraints for the design, allowing the beam to be functionally graded had little effect on the overall design, unless there was significant stiffening occurring along with particulate formation.

L'Orogène de l'Ungava correspond à la branche nord-est de l'Orogène Trans-Hudsonien et est situé sur la péninsule de l'Ungava dans le nord du Québec. La présence d'une éclogite de 1,8 Ga au sein du Domaine de Kovik dans l'Orogène de l'Ungava a été utilisée pour proposer une tectonique des plaques moderne active au Paléoprotérozoïque. Cette étude vise à contraindre la cinématique, la température et la chronologie de la déformation associée à une structure interprétée comme ayant permis l'exhumation de cette éclogite, la zone de cisaillement séparant le Domaine de Kovik du Domaine Nord. Nous avons combiné les observations de terrain le long de transects à travers le contact entre le Domaine de Kovik et le Domaine Nord, l'analyse microstructurale du quartz et de la titanite et des datations U-Pb sur titanite. Deux zones de cisaillement, localisées dans les orthogneiss du domaine de Kovik, ont été identifiées. La zone de cisaillement principale, distale au contact, est caractérisée par une cinématique de sommet-vers-le-sud et des fabriques d'axes-c du quartz associées à une déformation en aplatissement. La zone de cisaillement secondaire, proximale au contact, est caractérisée par une cinématique de sommet-vers-le-nord et des fabriques d'axes-c du quartz associées à une déformation plane. La température de déformation est contrainte à 627 et 580 ± 50°C pour les zones de cisaillement principale et secondaire, respectivement. La géochronologie U-Pb sur titanite a permis de définir deux populations de titanite. La vielle population, contrainte à ~1890 Ma, est contemporaine de la mise en place de la grande province ignée du Circum-Supérieur. La jeune population, contrainte à ~1740 Ma, est interprétée comme représentant la réinitialisation de la vieille population pendant un épisode de déformation tardive possiblement relié à l'effondrement de l'orogène. Nous interprétons que le contact entre le Domaine de Kovik et le Domaine Nord représente un détachement.

This study aims to improve the Additive Manufacturing (AM) design space for the popular multi-component Ni alloy Inconel 625 (IN625) thorough investigating the microstructural evolution, namely the solidification microstructure and the solid-state phase transformations during the Laser Powder Bed Fusion (LPBF) process. Highly non-equilibrium solidification and the complex reheating conditions during the LPBF process result in the formation of various types of solidification microstructures and grain morphologies which consequently lead to a wide range of mechanical properties. Understanding the melt’s thermal conditions, alloy chemistry, and thermodynamics during the rapid solidification and solid-state phase transformation in AM process will help to control material properties and even produce a material with specific microstructural features suited to a given application. This research helps to better understand the process-microstructure-property relationships of LPBF IN625. First, a set of simple but effective analytical solidification models were employed to evaluate their ability to predict the solidification microstructure in AM applications. As a case study, Solidification Microstructure Selection (SMS) maps were created to predict the solidification growth mode and grain morphology of a ternary Al-10Si-0.5Mg alloy manufactured by the LPBF process. The resulting SMS maps were validated against the experimentally obtained LPBF microstructure available in the literature for this alloy. The challenges, limitations, and potential of the SMS map method to predict the microstructural features in AM were comprehensively discussed. Second, The SMS map method was implemented to predict the solidification microstructure and grain morphology in an LPBF-built multi-component IN625 alloy. A single-track LPBF experiment was performed utilizing the EOSINT M280 machine to evaluate the SMS map predictions. The resulting microstructure was characterized both qualitatively and quantitatively in terms of the solidification microstructure, grain morphology, and Primary Dendrite Arm Spacing (PDAS). Comparing the experimentally obtained solidification microstructure to the SMS map prediction, it was found that the solidification mode and grain morphology were correctly predicted by the SMS maps. Although the formation of precipitates was predicted using the CALculation of PHAse Diagrams (CALPHAD) approach, it was not anticipated from the analytical solution results. Third, to further investigate the microsegregation and precipitation in IN625, Scanning Transmission Electron Microscopy (STEM) using Energy-Dispersive X-ray Spectroscopy (EDS), High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM), Scheil-Gulliver (with solute trapping) model, and DIffusion-Controlled TRAnsformations (DICTRA) method were employed. It was found that the microstructural morphology mainly consists of the Nickel-Chromium (gamma-FCC) dendrites and a small volume fraction of precipitates embedded into the interdendritic regions. The precipitates predicted with the computational method were compared with the precipitates identified via HAADF-STEM analysis inside the interdendritic region. The level of elemental microsegregation was overestimated in DICTRA simulations compared to the STEM-EDS results; however, a good agreement was observed between the Scheil and STEM-EDS microsegregation estimations. Finally, the spatial variations in mechanical properties and the underlying microstructural heterogeneity of a multi-layer as-built LPBF part were investigated to complete the process-structure-properties relationships loop of LPBF IN625. Towards this end, numerical thermal simulation, electron microscopy, nano hardness test, and a CALPHAD approach were utilized to investigate the mechanical and microstructural heterogeneity in terms of grain size and morphology, PDAS, microsegregation pattern, precipitation, and hardness along the build direction. It was found that the as-built microstructure contained mostly columnar (Nickel–Chromium) dendrites were growing epitaxially from the substrate along the build direction. The hardness was found to be minimum in the middle and maximum in the bottom layers of the build’s height. Smaller melt pools, grains, and PDAS and higher thermal gradients and cooling rates were observed in the bottom layers compared to the top layers. Microsegregation patterns in multiple layers were also simulated using DICTRA, and the results were compared with the STEM-EDS results. The mechanism of the formation of precipitates in different regions along the build direction and the precipitates’ corresponding effects on the mechanical properties were also discussed. / Thesis / Doctor of Philosophy (PhD)

No description available.

No description available.

No description available.

L'Orogène de l'Ungava correspond à la branche nord-est de l'Orogène Trans-Hudsonien et est situé sur la péninsule de l'Ungava dans le nord du Québec. La présence d'une éclogite de 1,8 Ga au sein du Domaine de Kovik dans l'Orogène de l'Ungava a été utilisée pour proposer une tectonique des plaques moderne active au Paléoprotérozoïque. Cette étude vise à contraindre la cinématique, la température et la chronologie de la déformation associée à une structure interprétée comme ayant permis l'exhumation de cette éclogite, la zone de cisaillement séparant le Domaine de Kovik du Domaine Nord. Nous avons combiné les observations de terrain le long de transects à travers le contact entre le Domaine de Kovik et le Domaine Nord, l'analyse microstructurale du quartz et de la titanite et des datations U-Pb sur titanite. Deux zones de cisaillement, localisées dans les orthogneiss du domaine de Kovik, ont été identifiées. La zone de cisaillement principale, distale au contact, est caractérisée par une cinématique de sommet-vers-le-sud et des fabriques d'axes-c du quartz associées à une déformation en aplatissement. La zone de cisaillement secondaire, proximale au contact, est caractérisée par une cinématique de sommet-vers-le-nord et des fabriques d'axes-c du quartz associées à une déformation plane. La température de déformation est contrainte à 627 et 580 ± 50°C pour les zones de cisaillement principale et secondaire, respectivement. La géochronologie U-Pb sur titanite a permis de définir deux populations de titanite. La vielle population, contrainte à ~1890 Ma, est contemporaine de la mise en place de la grande province ignée du Circum-Supérieur. La jeune population, contrainte à ~1740 Ma, est interprétée comme représentant la réinitialisation de la vieille population pendant un épisode de déformation tardive possiblement relié à l'effondrement de l'orogène. Nous interprétons que le contact entre le Domaine de Kovik et le Domaine Nord représente un détachement.

Doctor of Philosophy / Department of Grain Science and Industry / Hulya Dogan / Jon Faubion / Bread quality and final crumb grain are reflective of the ability for wheat flour dough to retain and stabilize gas cells during the baking process. The visco-elastic properties of dough allow for the incorporation of air cells and expansion during fermentation and baking. The gluten-starch matrix provides the backbone support. However, following the end of proofing and during the beginning of baking, the structure weakens due to over-extension and expansion and the matrix begins to separate and eventually break down. Native wheat lipids, which are found in small quantities in wheat flour, provide a secondary support for gas cell stabilization because of their amphiphilic characteristics and ability to move to the interface and form condensed monolayers. The objectives of this research were to evaluate the influence of native wheat lipids on the rheological properties of dough and the microstructure of bread. Native wheat lipids were extracted from straight-grade flour and separated into total, free, bound, nonpolar, glycolipids, and phospholipids using solid-phase extraction (SPE) with polar and nonpolar solvents. Defatted flour was reconstituted using each lipid fraction at a range of levels between 0.2% and 2.8%. Dough and bread were made following AACC Method 10-10.03. Rheological testing of the dough and evaluation of the microstructure of the bread was conducted using small and large deformation testing, C-Cell imaging, and x-ray microtomography analysis to determine changes in visco-elastic properties and gas cell structure and distribution. Rheological assessment through small amplitude oscillatory measurements demonstrated that nonpolar, phospholipids, and glycolipid fractions had a greater interaction with both proteins and starch in the matrix, creating weaker dough. Nonpolar, phospholipids, and glycolipids, varied in their ability to stabilize gas cells as determined by strain hardening index. C-Cell imaging and x-ray microtomograpy testing found that treatments containing higher concentrations of polar lipids (glycolipids and phospholipids) had a greater effect on overall loaf volume, cell size, and distribution. This illustrates that level and type of native wheat lipids influence the visco-elastic properties of dough and gas cell size, distribution, cell wall thickness, and cell stability in bread.