138 research outputs found
Structure-aware image denoising, super-resolution, and enhancement methods
Denoising, super-resolution and structure enhancement are classical image processing applications. The motive behind their existence is to aid our visual analysis of raw digital images. Despite tremendous progress in these fields, certain difficult problems are still open to research. For example, denoising and super-resolution techniques which possess all the following properties, are very scarce: They must preserve critical structures like corners, should be robust to the type of noise distribution, avoid undesirable artefacts, and also be fast. The area of structure enhancement also has an unresolved issue: Very little efforts have been put into designing models that can tackle anisotropic deformations in the image acquisition process. In this thesis, we design novel methods in the form of partial differential equations, patch-based approaches and variational models to overcome the aforementioned obstacles. In most cases, our methods outperform the existing approaches in both quality and speed, despite being applicable to a broader range of practical situations.Entrauschen, Superresolution und Strukturverbesserung sind klassische Anwendungen der Bildverarbeitung. Ihre Existenz bedingt sich in dem Bestreben, die visuelle Begutachtung digitaler Bildrohdaten zu unterstützen. Trotz erheblicher Fortschritte in diesen Feldern bedürfen bestimmte schwierige Probleme noch weiterer Forschung. So sind beispielsweise Entrauschungsund Superresolutionsverfahren, welche alle der folgenden Eingenschaften besitzen, sehr selten: die Erhaltung wichtiger Strukturen wie Ecken, Robustheit bezüglich der Rauschverteilung, Vermeidung unerwünschter Artefakte und niedrige Laufzeit. Auch im Gebiet der Strukturverbesserung liegt ein ungelöstes Problem vor: Bisher wurde nur sehr wenig Forschungsaufwand in die Entwicklung von Modellen investieret, welche anisotrope Deformationen in bildgebenden Verfahren bewältigen können. In dieser Arbeit entwerfen wir neue Methoden in Form von partiellen Differentialgleichungen, patch-basierten Ansätzen und Variationsmodellen um die oben erwähnten Hindernisse zu überwinden. In den meisten Fällen übertreffen unsere Methoden nicht nur qualitativ die bisher verwendeten Ansätze, sondern lösen die gestellten Aufgaben auch schneller. Zudem decken wir mit unseren Modellen einen breiteren Bereich praktischer Fragestellungen ab
Methodology for Shot-Peening Induced Intragranular Residual Stress Prediction
Résumé
Le grenaillage est un traitement mécanique des surfaces qui consiste à projeter des billes
à très haute vitesse à la surface d’une pièce. Ce traitement est utilisé depuis plus d’une
soixantaine d’année dans l’industrie pour améliorer la durée de vie en fatigue des matériaux
par l’introduction de contraintes résiduelles de compression et de gradients de duretés en
sous surface. Le procédé a longtemps été simplement considéré comme bénéfique sans réelle
quantification des bénéfices apportés sur la durée de vie en fatigue et les évolutions de microstructures.
En effet, modéliser le procédé a longtemps été un verrou car cela implique de
simuler un grand nombre d’impacts, de reproduire avec précision la cinétique des billes et de
prendre en compte un certain nombre de non-linéarités dues au contact et aux déformations
plastiques. Cependant les avancées de ces dix dernières années ont permis le développement
de modèles pouvant prédire avec précision le profil moyen de contraintes résiduelles en
profondeur ainsi que les gradients d’écrouissage résultants.
Peu d’études ont cependant tenté de prédire les contraintes résiduelles et l’écrouissage induits
à l’échelle d’un grain. Les variations intragranulaires des contraintes ont pourtant une influence
sur la durée de vie à grand nombre de cycle d’un matériau. Par ailleurs l’écrouissage
local constitue une donnée cruciale pour certains modèles de prédiction de durée de vie en
fatigue. Les verrous principaux à lever pour effectuer de telles prédictions sont l’identification
précise de modèles de plasticité cristalline à l’échelle de la surface et dans les conditions du
procédé, ainsi que le développement de méthodes expérimentales de validation des modèles
développés.
L’objectif de cette thèse est de développer une méthodologie pour la prédiction des contraintes résiduelles et de l’écrouissage intragranulaire à l’aide de modèles de plasticité cristalline par
éléments finis et de validations expérimentales.
Des essais d’indentation sphérique sur des monocristaux de cuivre sont présentés afin d’estimer
le champ de contrainte induit en sous surface expérimentalement et numériquement.
Les résultats révèlent que l’anisotropie de la plasticité cristalline peut induire des contraintes
résiduelles de tension en sous surface. La comparaison des champs numériques et expérimentaux
confirme aussi la possibilitĂ© de comparer des champs de contraintes estimĂ©s par EBSD Ă
haute résolution à ceux prédits par des modèles de plasticité cristalline de façon suffisament
quantitative pour permettre la validation de modèle.
Les évolutions microstructurales induites par le grenaillage d’un coin sont ensuite étudiées
par des estimations EBSD de densités de dislocations géométriquement nécessaires à l’aide
de nouvelles méthodes d’indexation alternatives. Les différences d’écrouissage relevées démontrent
l’importance de modéliser le procédé à l’échelle du grain.
Une méthodologie pour l’identification de loi de plasticité cristalline à haute vitesse basée
sur des essais de microcompression est détaillée. Une attention particulière à été portée sur
le caractère bien posé du problème d’identification, à l’aide d’indice d’identifiabilités. Un
canon a grenailler capable de projeter des billes isolées avec une large gamme de vitesse
et une haute précision a été développé pour valider le modèle. Un code a été implémenté
pour estimer la trajectoire de la bille en trois dimensions avec une précision de 200 μm pour
servir d’entré aux modèles éléments finis. La validation du modèle précédent est effectuée
par comparaison du déplacement de la bille, de la topologie de l’empreinte d’impact et du
champ de désorientation sous l’empreinte estimés expérimentalement et numériquement.
Enfin la possibilité d’utiliser le déplacement de la bille et le champ de contraintes résiduelles
induit par un impact est explorée par une étude d’identifiabilité détaillée. Ces travaux offrent
de nouveaux outils et méthodologies pour l’identification de paramètres et la validation de
modèles à l’échelle du grain et à haute vitesse.
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Abstract
Shot peening is a mechanical surface treatment which consist in projecting several spherical
particles onto a material’s surface. The process have been widely used in the industry
over more than sixty years to enhance material’s fatigue properties by introduction of subsurface
compressive stresses and hardening gradients. It has been long used as a ’nice to
have’ without any quantification of its benefits as its modeling involved a large number of
impacts, complex shot kinematics and non linearities induced by contact and plastic deformations.
Nonetheless, advances over the past twenty years provided models that successfully
reproduced experimentally measured average residual stress profiles and hardening gradients.
However, only few attempts to predict the residual stress and hardening variations at the
grain scale have yet been reported. Intragranular stress variations could influence a structure
high cycle fatigue behaviour and local hardening could be a crucial input for fatigue life
predictions models. The main barriers to achieve such predictions are mainly the difficulty
to identify accurate crystal plasticity models in the process conditions as well as defining
relevant validation procedures to assess the ability of the models to predict residual stress
variations.
The objective of this thesis is to develop a methodology for shot peening induced intragranular
residual stress and hardening prediction using crystal plasticity finite element simulations and
experimental validations.
Indentation on single crystal copper are first presented to assess the residual stress variations
in a single grain under the indent both experimentally and numerically. The results reveal
that crystal plasticity anisotropy could induce subsurface tensile residual stresses under a spherical contact. It also demonstrates that experimental residual stress fields estimated by
high angular resolution electron backscattered diffraction could be quantitatively compared
to finite element models. This finding makes it a relevant tool for constitutive behaviour
validation.
The microstructural evolutions induced by shot peening of a corner are investigated using
electron backscatter diffraction geometrically necessary dislocation estimations with recently
developed alternative indexation methods. The differences in hardening gradient close to
the corner compared with a reference shot peened material evidences that accurately predict
microstructural evolutions induced by the process at the grain scale is necessary to predict
the induced hardening distribution. These works provides new evidences of the relevance of
modeling the process at the crystal scale.
A methodology for identification of crystal plasticity parameters at high strain rates using
micropillar compression is then detailed. Particular attention is paid to the identification
problem well-posedness using identifiability indicators provided by the literature. A shotpeening
canon that can propel single shot over a wide velocity range with high aiming precision
is developed. An in-house code that can estimate the shot trajectory within 200 ÎĽm
is implemented to provide input for finite element analyses. The setup is used for validation
of the previously identified model by comparison of the shot displacement impact dent
topography and in-depth crystal misorientation field.
Finally, the possibility to use the shot displacement curve and residual stress field under the
dent produced by the setup is investigated through a detailed identifiability analyses. These
works provide new tools and methodologies for crystal plasticity parameters identification
and validation at the grain scale and at high strain rates
Experimental studies on the formation of pyrite and marcasite and the mechanisms of arsenic incorporation
Iron disulfide (FeS2) has two polymorphs, pyrite and marcasite. Pyrite is the most abundant sulfide in the Earth's crust. Both minerals can host economic amount of gold and environmentally hazardous arsenic and are found to coexist in hydrothermal mineralization. With time, thermodynamically metastable marcasite can transform to pyrite. However, the kinetics of the marcasite to pyrite transformation, and the mechanisms of arsenic incorporation during growth of pyrite are not well-constrained. This thesis presents experimental results and discussions on: (i) the formation of pyrite and marcasite under dry and hydrothermal conditions (Chapter 2 and 3), and (ii) incorporation of arsenic into pyrite during the growth of pyrite on pyrite seeds (Chapter 4).
In Chapter 2, the transformation from marcasite to pyrite was studied by in situ synchrotron powder X-ray diffraction (PXRD) at 520 °C and 540 °C, and ex situ anneal/quench experiments at 400 °C, 462 °C, and 520 °C. It was found that the mechanism and kinetics of this transformation depend not only on temperature, but also on particle size, the presence of water vapor, and the presence of pyrite inclusions in marcasite. Under dry conditions, the transformation is limited by surface nucleation and occurs via epitaxial nucleation of pyrite on marcasite, with {100}pyrite//{101}marcasite and {001}pyrite//{010}marcasite. In contrast, in the presence of water vapor, there is little crystallographic orientation relationship between the two phases; the transformation is limited by surface nucleation, but modification of the surface properties by water vapor results in a different nucleation mechanism, and consequently different kinetics. Kinetic analysis estimates a half-life of 1.5 Ma at 300 °C for the transformation under dry conditions with pyrite-free marcasite grains (<38 μm), but this estimation should be used with extreme caution due to the complexity of the process. From synchrotron X-ray fluorescence elemental mapping, trace elements (As and Pb) play an insignificant role in the transformation. However, the presence of a fluid phase changes the behavior of Pb. Under dry conditions randomly oriented particles of galena formed in pyrite, while under water vapor conditions arrays of nano-to-microparticles of galena precipitated in pores. This chapter highlights that although the natural occurrence of marcasite can indicate low temperature environments, precise estimation of temperature should not be made without considering the influences from various reaction parameters.
In Chapter 3, combined in-situ synchrotron PXRD and ex situ experiments were conducted under hydrothermal conditions at 190 °C and 210 °C and pH 1, aiming to study the controls on the precipitation of pyrite and marcasite from supersaturated hydrothermal solutions and the kinetics of hydrothermal transformation from marcasite to pyrite. In situ PXRD experiments show the important role of saturation index on the precipitation of pyrite and marcasite; at 190 °C, hydrothermal fluids rich in ΣS(-II) (0.9 mM) favors the precipitation of nanocrystalline pyrite (23 nm) due to high saturation index, while S(-II)-free fluids produce a mixture of marcasite and pyrite nanocrystals (21-46 nm) due to low saturation index. Fluid/rock ratio (70 and 120 g/g at 210 °C) can affect saturation index of the fluids, resulting in complex nucleation and crystal growth dynamics such as the evolution of crystallite size, phase abundance, and pyrite/marcasite ratio. Ex situ experiments show the rapid transformation from marcasite to pyrite at 210 °C; around 83% marcasite is transformed to pyrite in just 3 weeks, compared to 4.3 million years or 6.3 trillion years at 210 °C based on extrapolation using the kinetic models reported in early studies under dry conditions. These results suggest that saturation index influences the dynamics of precipitation under hydrothermal conditions and controls the phase selection between pyrite and marcasite, and that marcasite may not survive over geological time in low temperature environments in the presence of acidic hydrothermal fluids.
In Chapter 4, the formation of zoned arsenian pyrite was studied by growing pyrite on pyrite seeds in O2-free, As-enriched fluids at 200 °C and pH 7. The distribution and concentrations of As in pyrite, as well as the morphology of the zoning are influenced by sulfur source; i.e., native sulfur or Na2S2O3·5H2O. For experiments with native sulfur, up to four concentric alternate zones of As-rich (first zone on pyrite seed) and As-free pyrite grow on pyrite seeds. For experiments with Na2S2O3·5H2O, an aggregate of concentrically zoned pyrite microparticles (~1 µm) precipitate on the surface of pyrite seeds. Based on EMPA, the maximum concentration of As is 4.3 wt. %. However, the TEM-EDS analyses reveal ≤5.8 wt. % of As. HRTEM and selected area electron diffraction (SAED) pattern combined with EBSD analyses document epitaxial growth of As-pyrite on pyrite seed in the presence of native sulfur, but aggregation of randomly oriented aggregates of pyrite microparticles in the presence of thiosulfate. High-angle annular dark-field scanning TEM (HAADF-STEM), HRTEM observations, and EDS mapping show a sharp boundary and trails of pores between the pyrite seed and the product and between the growth zones. In the presence of native sulfur, the thickness of the As-pyrite growth zones is ~ 50 nm, while the subsequently formed growth zones of “barren” pyrite are ~5000 nm thick. X-ray absorption near edge structure (XANES) analyses reveal that speciation of As in pyrite depends on the S-source: (i) anionic As(-I) substitutes for S in pyrite as As2 pair when native S is used, and (ii) cationic As(II)/As(III) substitutes for Fe when thiosulfate is used. Our experiments show that the incorporation of As into pyrite and the formation and morphology of pyrite growth zones are controlled by the source of sulfur in hydrothermal fluids.
This thesis highlights the factors that control the mechanisms of the formation and transformation of pyrite and marcasite and the dependence of As incorporation into arsenian pyrite structure as a function of S and As source in the presence of pyrite seeds. These outcomes should benefit our understanding of the formation and alteration of Carlin-type, epithermal, volcanic-hosted massive sulfide (VMS), and orogenic Au deposits
Evaporation and dissolution of droplets in ternary systems
The evaporation and dissolution of droplets in multi-component systems are omnipresent in nature, science, and many advanced technologies. However, these droplets have much less been studied than droplets consisting of a pure liquid only. The two-way interactions between the fluid properties and hydrodynamics make the dynamical behavior of the droplet complicated. In this thesis, we give our contributions to this field by studying the evaporation and dissolution of Ouzo droplets. Ouzo is an anise-flavored aperitif, primarily consisting of water, ethanol and a small amount of anise oil. The Ouzo droplet may be seen as a model system for any ternary mixture of liquids with different volatilities and mutual solubilities. In Part I, we explored the evaporating and dissolving processes of “ouzo” (water, ethanol, and anise oil) droplets on surfaces. Through a series of studies, we revealed microdroplet nucleation processes triggered by the evaporation or dissolution of the droplets in ternary systems and consequently induced dynamical behaviors of the droplets. In Part II, we performed exploratory research on the application of the evaporating multicomponent droplets. Inspired by the interesting phenomenon observed in Part I, we proposed a method for evaporation-driven particles assembly. Through this method, the evaporating colloid ouzo droplets acquire a “self-lubrication” ability, which improves the supraparticle fabrication technique. In the last Part III, our attention focused on the nucleated nanodroplets on the surface induced by the “ouzo effect.” We used the solvent exchange method to form the surface nanodroplets in a narrow channel with controlled flow conditions. A comprehensive three-dimensional (3D) spherical cap fitting procedure was developed for the accurate extraction of the morphologic characteristics of complete or truncated spherical caps from atomic force microscopy (AFM) images
Polymer Processing and Surfaces
This book focuses on fundamental and applied research on polymer processing and its effect on the final surface as the optimization of polymer surface properties results in the unique applicability of these over other materials. The development and testing of the next generation of polymeric and composite materials is of particular interest. Special attention is given to polymer surface modification, external stimuli-responsive surfaces, coatings, adhesion, polymer and composites fatigue analysis, evaluation of the surface quality and microhardness, processing parameter optimization, characterization techniques, among others
Surfaces and interfaces in thin-film and conventional li-ion batteries
El capĂtulo 4 está sujeto a confidencialidad por el autor.
194 p.En esta tesis doctoral titulada "Surfaces and Interfaces in Thin-Film and Conventional Li-ion Batteries" se presentan los resultados del trabajo experimental realizado en relaciĂłn a materiales del estado del arte en baterĂas Ăon-litio. En particular, en una primera parte se describen los resultados obtenidos al estudiar la superficie de electrodos formados por el material Titanato de Litio (Li4Ti5O12, LTO). En esta primera parte el estudio se centra en la evoluciĂłn de las fases presentes en la superficie del electrodo a lo largo del ciclado electroquĂmico. En una segunda parte, continuando con los electrodos basados en el material LTO, se estudia el efecto de capas protectoras depositadas en electrodos convencionales mediante la tĂ©cnica de sputtering. En esta parte se describe el efecto positivo que dichas capas protectoras tienes en el comportamiento electroquĂmico de los electrodos, al mismo tiempo que se estudia el origen de dicha mejora. Finalmente, en un Ăşltimo capĂtulo se describe la deposiciĂłn, caracterizaciĂłn y optimizaciĂłn de electrodos de capa fina del material LiMn1.5Ni0.5O4. Además de una caracterizaciĂłn composicional, morfolĂłgica, estructural y electroquĂmica de los electrodos, se dedica especial atenciĂłn a las intercaras, tanto la del colector de corriente-electrodo como la del electrodo-electrolito sĂłlido
Super-Flexible Sensors and Advanced 3D Morphing Actuators based on Elastic Instability
Super-flexible devices based on soft materials have the potential to sustain large mechanical deformations, enabling advanced applications such as flexible electronics, soft robots, artificial skin, and biomedical transducers. Subject to a large compression, materials may undergo different types of elastic instabilities such as wrinkles, creases, and folds. Despite recent growing interests in turning this usually unwanted phenomenon into useful engineering applications (e.g. tactile sensing), this topic remains relatively under-researched.
Therefore, this thesis focuses on developing the control mechanisms of elastic instabilities, and their applications in sensing and actuation systems.
Elastic instabilities induced strain-gated logic sensing technology is developed by research into micro structured metal-elastomer tri-layer system. The test structures are designed to study the deformation behaviour and to exploit the large strain sensing mechanism. The stepwise electrical signals are achieved (from ~1010 to ~120 Ω at first switching stage and then to ~50 Ω at second switching stage) that survived much higher than usual compressive strains of up to 60%.
On the other hand, elastic instabilities induced topo-optical sensing strategy is created by patterning microstructure arrays within the tri-layer system. Two unwanted phenomena (creases/folds and oxygen quenching effect) are turned into a responsive and programmable 'fold to glitter' function through micro engineering, which can light up areas of an object or material by creating microscopic creases/folds within its surface. The signal-Noise-Ratio (SNR) contrast in optical pattern generation is improved by 6 folds due to the oxygen quenching effect. The numerical analysis by ABAQUS provides the fundamental theory on the mechanism of generating targeted folding through simulating the in-plane and out-of-plane strain energy localization.
Different luminescent optical patterns are demonstrated under in-plane uniaxial or equi-biaxial compression.
Apart from the surface deformation, the bulk deformation of heterogeneous layered structures of soft functional hydrogel is also developed to generate the controllable and reconfigurable 3D morphing device. The initial configurations with various shapes (“S”, “W” and “C”) are demonstrated due to the swelling ratio mismatch. The developed sensing and actuation technologies provide opportunities for future applications in flexible electronics, tuneable optics, soft robotics and bio-medical systems
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