Dissertations / Theses on the topic 'In situ micropillar compression'
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Jonsson, Åsa, and Grim Skarsgård. "Synchrotron tomography of pressboard during in-situ compression loading : Construction of compression rig, image acquisition procedure and methods for image processing." Thesis, Uppsala universitet, Tillämpad mekanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-257276.
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Pressboard, a high density cellulose-based material used for insulation in high voltage power transformers, exhibits stress relaxation during compressive loading. Investigating the micro-mechanical mechanisms responsible for the relaxation can lead to modifications of the production process to control the behaviour of the material. This investigation can be done using Synchrotron X-ray micro Computed Tomography which provides sufficient temporal and spatial resolutions to capture the stress relaxation process. In the present thesis, a compression rig for in-situ mechanical loading during X-ray micro Computed Tomography was designed and constructed. Local tomography scans with sub-micrometre resolution were obtained at the TOMCAT beamline at the Swiss Light Source, Paul Scherrer Institut, Switzerland. Several fibre segmentation techniques are analysed, together with Optical Flow and Digital Volume Correlation (DVC), methods used for estimating displacement, strain and velocity vector fields. Suitability of the tested methods is evaluated, and it is found that segmentation of individual fibres in a cellulose material of such a high density is probably not possible using currently available segmentation techniques. The movements during relaxation are measurable at the used resolution, and can be estimated using Optical Flow. Further work into correction of image shift due to rig movement between scans, as well as image artefact reduction should allow for measurement and comparisons of displacement during relaxation as well as DVC-computed strain measurements during compression, recreating earlier results.
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Li, Shaomeng. "Wavelet Compression for Visualization and Analysis on High Performance Computers." Thesis, University of Oregon, 2018. http://hdl.handle.net/1794/23905.
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As HPC systems move towards exascale, the discrepancy between computational power and I/O transfer rate is only growing larger. Lossy in situ compression is a promising solution to address this gap, since it alleviates I/O constraints while still enabling traditional post hoc analysis. This dissertation explores the viability of such a solution with respect to a specific kind of compressor — wavelets. We especially examine three aspects of concern regarding the viability of wavelets: 1) information loss after compression, 2) its capability to fit within in situ constraints, and 3) the compressor’s capability to adapt to HPC architectural changes. Findings from this dissertation inform in situ use of wavelet compressors on HPC systems, demonstrate its viabilities, and argue that its viability will only increase as exascale computing becomes a reality.
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Carpenter, John Stuart. "Estimates of Interfacial Properties in Cu/Ni Multilayer Thin Films using Hardness and Internal Stress Data." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1285006915.
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Saïghi, Ali. "Comparaison des essais au laboratoire et in situ : exemple du triaxial et du pressiomètre." Châtenay-Malabry, Ecole centrale de Paris, 1998. http://www.theses.fr/1998ECAP0689.
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Le modèle hyperbolique de Duncan tient compte de la non-linéarité de la relation contrainte-déformation due à la pression moyenne sous une forme du type Hertz ou le module sécant s'exprime sous la forme E=&Pn. Il tient compte aussi de la courbure de q(E) mais pas de la dilatance du matériau. Les essais triaxiaux sur le sable d'Hostun effectués par trois chercheurs : Mohkam, Flavigny et Colliat ont été étudiés à l'aide de ce modèle. On obtient en première approximation des résultats analogues comparativement à l'erreur due au non prise en compte de la dilatance. Une analyse détaillée met en évidence les différences dues aux difficultés expérimentales. Les essais pressiométriques présentent aussi des difficultés dues en particulier à leur mise en place. La validation de ce modèle sur un chemin pressiométrique a été précédée par une analyse des courbes pressiométriques en chambre de calibration effectues par Foray et Mokrani afin de déceler d'éventuelles anomalies. Cette analyse nous a permis de mieux appréhender la phase de validation de ces paramètres. Le regroupement des essais pressiométriques sous la forme pp0/ v(v/v 0) met bien en évidence le rôle de la dilatance dans le cas des sables denses pour les déformations v/v 0>5%. La loi élastique plastique parfait avec dilatance limitée permet donc de pallier la limitation de la loi précédente. Pour les sols in situ, nous avons compare les résultats obtenus à l'aide du pressiomètre autoforeur paf du laboratoire central des ponts et chaussées à ceux obtenus a l'aide de l'essai Ménard et du triaxial. Le pressiomètre menard donne des modules beaucoup plus petits à cause des grandes déformations du trou de forage, mais des cohésions du même ordre de grandeur que celles du paf. Les valeurs des cohésions et des modules donnes par la méthode de la dérivation de la courbe pressiométrique de Jezequel permettent un calcul elastique plastique parfait en très bon accord avec les essais du paf.
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Kharaghani, Saeed. "Localisation des grandes déformations au laboratoire et in situ." Châtenay-Malabry, Ecole centrale de Paris, 1994. http://www.theses.fr/1994ECAP0373.
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La localisation des déformations est un phénomène qui apparait dans une large classe de matériaux. Elle fait apparaitre brutalement, dans un champ de déformation homogène, une structure connue sous le nom de bande de cisaillement, caractérisée par des déformations beaucoup plus grandes que dans le reste du matériau. Au laboratoire, c'est au cours des essais triaxiaux, voulus homogènes, que surgit la localisation ; celle-ci vient traverser l'échantillon testé suivant une certaine inclinaison par rapport à la direction de la contrainte principale majeure. Le calcul par la méthode des éléments finis, nécessite la connaissance des lois de comportement et la comparaison des calculs à des modeles et des réalités. Nous avons cherché à montrer que certaines difficultés, en particulier la localisation des grandes déformations dans les essais triaxiaux conduisent à des résultats erronés qu'il faut pouvoir déceler et essayer de corriger. L'indice des vides critique (l'état de plasticité parfaite) est très souvent perturbé. Une méthode de contrôle est proposée avec une première approximation. In situ, l'origine des failles et les causes de leur apparition sont liées à ce phénomène de la localisation. Les vitesses de déformation sont très différentes pour la tectonique et pour l'essai triaxial ; néanmoins on observe des failles directes et inverses qui font avec la contrainte principale majeure un angle analogue à celui observé dans un essai triaxial. L'autre objectif de notre travail est donc l'étude de l'origine de l'apparition des différents types de failles dans le cadre de l'approche théorique de ce type d'accident géologique. Pour cette partie de notre travail, l'existence d'un siècle de mesures topographiques des veines de charbons nous a conduit à choisir le bassin houiller du nord-pas de calais. Ces mesures nous donnent une base numérique pour étudier les grandes déformations et les failles existants dans cette région. En analysant les données retraçant les déformations tectoniques provoquées durant les différentes périodes géologiques, nous proposons une base de comparaison pour le calcul avec éléments finis destiné à visualiser la localisation des grandes déformations tectoniques
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Issa, Inas. "In situ TEM nanocompression and mechanical analysis of ceramic nanoparticles." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI008/document.
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Dans cette étude, nous proposons d’utiliser la compression in situ dans le MET afin de caractériser les propriétés mécaniques de nanoparticules céramiques dont la taille caractéristique est de l’ordre de quelques dizaines de nanomètres. Nous appliquerons cette méthode à des nanocubes monocristallins de MgO, une céramique modèle dont la plasticité est bien connue dans le matériau massif. Les essais de nanocompression montrent que les nanocubes de MgO se déforment de façon homogène jusqu’à de grandes déformations (>50%) sans fissure apparente. L’analyse des résultats est assistée par des méthodes de corrélation d’images numériques et simulations de type dynamique moléculaire. Le mécanisme de déformation et l'effet de taille sur la limite élastique sont identifiés. Dans une deuxième partie de la thèse, nous présentons une étude sur des nanoparticules d’alumine de transition compactée en CED (Cellule à Enclumes en Diamant) à température ambiante, sous plusieurs pressions (5 GPa, 15 GPa et 20 GPa). Des lames minces préparées par FIB ont été étudiées en MET. Des images HRTEM montrent une texture cristallographique qui devient plus importante à des pressions plus élevées. Une orientation cristallographique préférentielle est observée, avec les plans {220} de la phase gamma de l’alumine la plupart du temps parallèles à la surface de contact avec une particule voisine. Ce comportement mécanique est cohérent avec un système de glissement, connu pour les structures spinelles. Une corrélation de ce comportement avec les tests in situ MET réalisés sur des nanoparticules similaires, par Emilie Calvié lors de sa thèse, est présentée. Enfin, des clichés de diffraction de type Debye Scherrer sont réalisés sur ces lames minces de nanoparticules d’alumine de transition compactées en CED à différentes pressions. L’analyse quantitative de ces clichés montre une transformation de phase de ces nanoparticules d’alumine de phase gamma en phase delta, de manière croissante avec la pressionIn this study, we propose an innovative mechanical observation protocol of ceramics nanoparticles in the 100nm size range. This Protocol consists of in situ TEM nanocompression tests of isolated nanoparticles. Load–real displacements curves, obtained by Digital Image Correlation, are analyzed and these analyses are correlated with Molecular Dynamics simulations. By this protocol a constitutive law with its mechanical parameters (Young modulus, Yield stress...) of the studied material at the nano-scale can be obtained. In situ TEM nano-compression tests on magnesium oxide nanocubes are performed. Magnesium oxide is a model material and its plasticity is very well known at bulk. The MgO nanocubes show large plastic deformation, more than 50% of plastic strain without any fracture. The TEM results are correlated to MD simulations and the deformation mechanism can be identified.The size effect and the electron beam effect on the yield strength are investigated. In a second part of the dissertation, we present a study on transition alumina nanoparticles compacted in a Diamond Anvil Cell at different uniaxial pressures. Thin Foils of these compacted nanoparticles are prepared by FIB for HRTEM Observations. Their analysis reveals the plastic deformation of the nanoparticles. The crystallographic texture observed inthese compacted nanoparticles in DAC shows a preferred orientation of the {110} lattice planes, orientated perpendicular to the compression direction. This is compatible with the slip system. This argument was reinforced with a preferred orientation of slip bands observed during in situ TEM nano-compression tests. Moreover, electron diffraction patterns (Debye Scherrer) analysis on these compacted transition alumina nanoparticles reveals the decrease of the presence of gamma-alumina and the increase of delta-alumina with increasing pressure. This reveals the phase transformation with increasing pressure from gamma to delta* alumina
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Liebaert, Philippe. "Etude de la forgeabilité des aciers à haute température : mise en oeuvre d'essais de criquabilité." Valenciennes, 1991. https://ged.uphf.fr/nuxeo/site/esupversions/91ceec35-dd8b-40dd-85f0-c5e0c2f054ae.
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En dépit du développement remarquable des techniques de coulée continue les caractéristiques thermomécaniques des aciers restent encore très mal connues à haute température, immédiatement après solidification. Cette lacune s'avère particulièrement grave, d'autant que les produits élaborés par coulée continue subissent généralement des sollicitations thermomécaniques diverses durant leur refroidissement pouvant localement induire des défauts en peu de produit criques superficielles ou a coeur - criques internes. L'étude des mécanismes de formation de ces défauts est corrélée a la conception d'un essai de caractérisation thermomécanique apte à simuler l'état des aciers résultant de leur solidification et de leur refroidissement jusqu'a une température typiquement comprise entre le solidus et 800c, c'est-à-dire un essai capable de reproduire au mieux l'histoire thermomécanique réelle de l'acier. Ainsi, l'échantillon sera mis en fusion, puis refroidi selon des schémas similaires a ceux des sites de fabrication, et enfin soumis à un essai mécanique objectif sans retour intermédiaire à la température ambiante. L'étude des chemins de déformation et des courbes contrainte moyenne réduite. Déformation équivalente obtenus, complétée par des observations métallurgiques et géométriques montrent l'apport de ces nouveaux essais et leur nécessité si l'on veut approcher de façon optimale le comportement réel de l'acier.
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Lehmann, Henry [Verfasser], Bernhard [Akademischer Betreuer] Jung, Bernhard [Gutachter] Jung, and Gerik [Gutachter] Scheuermann. "Temporal Lossy In-Situ Compression for Computational Fluid Dynamics Simulations / Henry Lehmann ; Gutachter: Bernhard Jung, Gerik Scheuermann ; Betreuer: Bernhard Jung." Freiberg : Technische Universität Bergakademie Freiberg, 2018. http://d-nb.info/1226100805/34.
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Guérin, Jean-Dominique. "Analyse des essais de compression et de traction des aciers après solidification in situ et des essais d'indentation des aciers phosphatés." Valenciennes, 1993. https://ged.uphf.fr/nuxeo/site/esupversions/b769f69b-4777-454d-94ad-c3bac6b6fab1.
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La mise en forme à chaud et à froid des aciers est étudiée avec deux types d'expérimentations : les essais à hautes températures des aciers juste après leur solidification et les essais à température ambiante des aciers phosphates. Le premier type d'expérimentation consiste à mener un essai de compression ou de traction à vitesse de traverse constante sur des éprouvettes, cylindriques pour l'essai de compression et axisymétriques à entaille circulaire pour l'essai de traction, en acier solidifie in situ. Il s'agit a partir des données expérimentales de caractériser le comportement de l'acier solidifie in situ teste. Une procédure d'essai est donc proposée et des modélisations analytiques permettent, d'une part, de déterminer le comportement élasto-thermo-viscoplastique de l'acier solidifie et, d'autre part, d'évaluer les contraintes et déformations caractéristiques dans les zones de l'éprouvette d'essai propices a l'apparition de criques. La comparaison des résultats obtenus analytiquement et par éléments finis, pour des essais de référence sur deux types d'acier, montre que les analyses proposées sont suffisamment précises pour identifier efficacement le comportement de l'acier solidifie situ. Le deuxième type d'expérimentation consiste à mener un essai d'indentation rotation sur une éprouvette cylindrique revêtue d'une ou plusieurs couches de frottement en phosphate ou stéarate de zinc. La spécificité du contact indenteur éprouvette durant la phase d'indentation de l'essai requiert une modélisation adéquate pour étudier le comportement de l'éprouvette sous la zone de contact. Un modèle par éléments finis local au contact est donc construit et des calculs sont menés pour des cas typiques de revêtements phosphates. Ce modèle par éléments finis s'avère apte à déterminer efficacement les répartitions de contraintes et de déformations dans l'éprouvette et il est ainsi opérationnel pour prédire l'efficacité du revêtement sans procéder à l'expérimentation.
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Devillard, Julie. "Lien entre microstructure et résistance à la compression du gypse moussé." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI043.
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La présente étude porte sur la caractérisation microstructurale et mécanique du gypse moussé, matériau de cœur des plaques de plâtre allégées, présentant une forte porosité (75%) multi-échelle. L'objectif de ce travail est de déterminer l'influence de la microstructure du gypse moussé sur la dureté mesurée en indentation sphérique et d'analyser les mécanismes d'endommagement pour différentes microstructures. Des essais d’indentation sphérique ont été conduits sur des échantillons présentant des variations des différentes caractéristiques microstructurales du gypse moussé. Ces essais montrent que la masse a une influence du premier ordre sur la dureté et que la dispersion des mesures de dureté en indentation sphérique peut être reliée à l’hétérogénéité de la macroporosité. Des essais d'indentation in situ ont également été effectués, avec un suivi en tomographie aux rayons X et une analyse par corrélation d’images volumiques, afin d’étudier avec précision les mécanismes d'endommagement. Deux modes d'endommagement différents ont été déterminés selon les densités considérées (fraction de macropores variable). Les résultats de ces essais ont été utilisés pour alimenter un modèle analytique, basé sur un critère énergétique qui relie la force d'indentation à la zone endommagée sous l’indenteur. Cela permet de prédire la courbe force-déplacement d'indentation propre à une microstructure avec comme seule donnée d'entrée un scan de la microstructure initiale. Une modélisation numérique a également été effectuée grâce à la méthode des éléments finis avec la prise en compte de la microstructure réelle, à deux échelles. L’utilisation de différents modèles de comportement, basés sur des critères de plasticité, a permis de prévoir les régions impactées par la densificationThis study focuses on the microstructural and mechanical characterization of foamed gypsum, the core material of lightweight gypsum boards, with a high (75%) multi-scale porosity. The objective of this work is to determine the influence of the microstructure of foamed gypsum on the hardness measured in spherical indentation and to analyze the damage mechanisms for different microstructures. Spherical indentation tests were conducted on samples showing variations in microstructural features of foamed gypsum. The results of these tests show that density has a first-order influence on hardness and that the dispersion of hardness measurements in spherical indentation can be related to heterogeneity in macroporosity. In situ indentation tests were also carried out, with X-ray tomography and digital volume correlation (DVC) analysis, in order to accurately study the damage mechanisms. Two different modes of damage were determined according to the densities considered (variable macropore fraction). The results of these tests were used to feed an analytical model, based on an energy criterion that links the indentation force to the damaged area under the indenter. This provides the prediction of the indentation force-displacement curve specific to a microstructure with a scan of the initial microstructure as the only input data. Numerical modelling was also carried out using the finite element method with consideration of the actual microstructure, at two scales. The densified areas were properly predicted by different behaviour models based on plasticity criteria
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Foscan, Tiziana. "Mechanical characterization of double-wythe masonry walls with a view to in-situ testing methods." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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Unreinforced masonry is one of the most commonly used structure typologies for the construction of residential buildings, which is why the estimation of its mechanical parameters is of primary importance. The main techniques to acquire them are based on destructive methods, however less invasive tests have been studied in the past years in order to obtain the same parameters in-situ: the core testing method is one of those. While monotonic compression tests on single-wythe cores provided good results, tests performed on double-wythe cores have given a significant overestimation of the compressive strength, supposedly due to the excessive stiffness of the high strength mortar cap used to perform the tests, that doesn’t allow the opening of the collar joint. An experimental campaign was conducted at Delft University of Technology in order to identify a new configuration of the cap suitable to use in moderately destructive tests to retrieve the mechanical properties of masonry under compression. An initial Finite Element Analysis is performed to anticipate the behaviour of the different configurations in order to choose the right prototypes. Four different models are developed, and the most significant ones are implemented and tested in the laboratory. In particular, a configuration with high strength mortar cap is tested as a comparison with previous tests on double-wythe cores, while a configuration with a high strength mortar cap separated from the core by a neoprene sheet is chosen in an attempt to reduce the confinement in the direction perpendicular to the collar joint. Finally the results obtained from the monotonic compression tests on cores are compared with the results from destructive tests on companion wallets, which were carried out in a previous experimental campaign on the same masonry.
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Sylvain, Wilgens. "Étude de la plasticité du monocristal de phase MAX par déformation aux petites échelles." Thesis, Poitiers, 2016. http://www.theses.fr/2016POIT2307/document.
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L'objectif de cette thèse est l'étude de la déformation, à l'échelle microscopique, de la phase MAX Ti2AlN, synthétisée par métallurgie des poudres. Ce travail se divise en trois parties : une première dans laquelle l'accent a été mis sur l'hystérèse mécanique des phases MAX via des essais cyclés, en nanoindentation sphérique et compression ex-situ de micro-piliers, sur des grains d'orientations différentes déterminées par l'EBSD. Dans la deuxième nous nous sommes intéressés à la déformation de micropiliers via des essais de compression cyclés in-situ couplés à la micro-diffraction Laue. L'objectif a été d'analyser les taches diffraction au cours de la déformation du pilier afin de mettre en évidence les mécanismes de déformation élémentaires mis en jeu et d'observer les structures finales via des images MEB post-mortem des piliers. Enfin, une dernière dans laquelle l'objectif a été l'étude des mécanismes de déformation en température à l'échelle microscopique via des essais de nano-indentation allant jusqu'à 800°C. La caractérisation des lignes de glissement en surface et des configurations microstructurales sous l'empreinte a été réalisée par AFM et MET respectivement. Toutes les données recueillies par ces divers essais aux petites échelles, ont permis d'affiner notre compréhension des mécanismes de déformation du monocristal de phase MAX, notamment vis à vis des modèles usuellement proposés dans la littératureThe thesis's goal is to study the deformation, at microscopic scale, of the MAX phase Ti2AlN synthesized by powder metallurgy. This work is divided into three parts: in the first part, the interest has been put on the hysteretic behavior of the MAX phases via cyclic mechanical solicitations, during spherical indentation tests and ex-situ compression of micro-pillars, on differently orientated grains beforehand determined by EBSD. In the second part, we were interested into the micro-pillar's deformation via insitu cyclic compression tests coupled with Laue micro-diffraction. The goal was to analyse the evolution diffraction lines during the pillar's deformation in order to highlight the elementary deformation mechanisms and to observe the finale structures via the post-mortem SEM imaging of the pillars. Finally, a last part was devoted to study the deformation mechanisms in temperature at microscopic scale via nano-indentation tests up to 800°C. The characterization of the slip lines on the surface has been revealed by AFM and that of t he microstructural configurations (dislocations) under the indent has been done by TEM. All data collected by these various tests at the small scales have refined our understanding of the deformation mechanisms of crystal MAX phase, particularly with respect to the models usually proposed in the literature
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Capolo, Laura. "Contribution à l'étude des hétérogénéités de déformation viscoplastique de la glace Ih mono et multi cristalline : essais de compression in-situ sous rayonnement X." Phd thesis, Université Joseph Fourier (Grenoble), 2007. http://tel.archives-ouvertes.fr/tel-00175271.
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Le cristal de glace est un matériau particulièrement anisotrope dans le domaine viscoplastique, qui se déforme principalement par glissement des dislocations dans le plan de base. Cette très forte anisotropie viscoplastique engendre une importante hétérogénéité de déformation à l'origine d'hétérogénéités inter-granulaires. Pour mieux comprendre les mécanismes impliqués dans cette déformation, des expériences de fluage ont été réalisées sous diffraction X (topogaphie X et X durs refocalisés) ainsi qu'en chalbre froide, sur des monocristaux et des tricristaux de glace. La déformation a été suivie in-situ à l'aide d'un dispositif spécialement mis au point au LGGE. Une attention particulière a été portée sur l'évolution de la microstructure (évolution des dislocations individuelles, densités de dislocations, distorsions cristallographiques) notamment au niveau des joints de grains et du point triple.
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Hauss, Grégory. "Microtomographie X de matériaux à comportement pseudo-fragile : Identification du réseau de fissures." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2012. http://tel.archives-ouvertes.fr/tel-00789670.
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L'étude de l'endommagement des matériaux à comportement pseudo-fragile fait l'objet denombreuses études et la caractérisation du réseau de fissures constitue une étape nécessairepour une meilleure compréhension de leur comportement. L'objectif principal est ici d'identifierde manière la plus fine possible cet espace fissuré en trois dimensions grâce à la techniqued'imagerie nommée microtomographie X. Pour ce faire, une machine d'essai in-situ a étédéveloppée et une procédure d'analyse des images 3D a été validée. L'objectif du dispositif insituest de maintenir l'échantillon dans différents états fissurés pour rendre possible lesacquisitions microtomographiques. Une fois les images 3D reconstruites, la procédure detraitement est appliquée et l'espace fissuré est identifié. Des mesures sont alors réalisées surl'évolution du réseau de fissures au cours de l'endommagement. Ce travail constitue la premièreétape d'un traitement plus général qui a pour objectif de simuler numériquement lecomportement mécanique de ces matériaux en se basant sur leur géométrie réelle.
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Warner, Wyatt Young. "Characterization of Local Void Content in Carbon Fiber Reinforced Plastic Parts Utilizing Observation of In Situ Fluorescent Dye Within Epoxy." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7772.
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Experimentation exploring the movement of voids within carbon fiber reinforced plastics was performed using fluorescent dye infused into the laminates observed through a transparent mold under ultraviolet light. In situ photography was used as an inspection method for void content during Resin Transfer Molding for these laminates. This in situ inspection method for determining the void content of composite laminates was compared to more common ex-situ quality inspection methods i.e. ultrasonic inspection and cross-section microscopy. Results for localized and total void count in each of these methods were directly compared to test samples and linear correlations between the three test methods were sought. Test coupons were then cut from these laminates and were used to calculate the interlaminar shear strength at certain locations throughout the laminates. Although this research did not adequately observe correlations between results obtained from ultrasonic C-scans, cross-sectional microscopy and in situ photography of the surface, it was seen that the fluid dynamics of the thermosetting epoxy used in this experimentation correlated to results obtained from previous experimentation performed by students at Brigham Young University using vegetable oil as a substitute for resin.
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Khosravani, Ali. "Application of High Resolution Electron Backscatter Diffraction(HR-EBSD) Techniques to Twinning Deformation Mechanism in AZ31 Magnesium Alloy." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3432.
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The application of high resolution electron backscatter diffraction (HR-EBSD) techniques has been used in order to study the evolution of geometrically necessary dislocation (GND). The tested materials were taken from AZ31 magnesium sheet which had strong basal texture. Because of low symmetry of the magnesium crystal lattice, the von Mises criteria cannot be satisfied by the three independent, easily activated, basal slips. The strain along the c-axis of the crystal must be accommodated by either twinning and/or slip systems. HR-EBSD data was taken in order to investigate these phenomena. The HR-EBSD results were post processed in order to resolve total GND density onto the observed possible slip systems. The first chapter of the investigation focused on the correlation between resolved GNDs with tensile twin nucleation, and the subsequent propagation path in the microstructure. For this purpose, 2.5 % strain was applied in a uniaxial compression test along the transverse direction (TD). Several fine scan were done at the boundaries where twin formed. The results show that in order for a twin to nucleate spontaneously at the grain boundaries, two criteria should generally be met: high angle grain boundaries (35-45°) and pile ups of basal slip system in neighboring grain at the other side of the boundary. Furthermore, once nucleation has initiated, twin propagation can occur through low angle grain boundaries (15-25°); if a twin reaches a high angle boundary, it will generally terminate at the boundary at low strain levels. A twin may pass through high angle boundaries with further deformation. In the second chapter, deformation of the AZ31 magnesium alloy was study for different strain paths. For this purpose, compression and tension in-situ tests were done and the texture and GND evolutions were investigated. The results show that the load paths, compression and tension, evolve the microstructure in different ways. Massive twin fractions were formed in compression, and higher GND contents were observed in tension tests. It was observed that at higher strain levels GND contents are roughly independent of the initial texture but the activation of slip systems at low strain strongly depends on initial structure. If the samples were loaded along RD, GND density increased sharply at low strain. In contrast, for the samples loaded along TD, GND increased moderately. A small amount of repetition is apparent in the two parts of the thesis due to them being formatted for individual publication as journal papers.
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Guitton, Antoine. "Mécanismes de déformation des phases MAX : une approche expérimentale multi-échelle." Thesis, Poitiers, 2013. http://www.theses.fr/2013POIT2280/document.
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Il est couramment admis que la déformation plastique des phases MAX est dueau glissement de dislocations dans les plans de base s'organisant en empilements et murs. Cesderniers peuvent former des zones de désorientation locale appelées kink bands. Cependant, lesmécanismes élémentaires et le rôle exact des défauts microstructuraux sont encore mal connus. Cemanuscrit présente une étude expérimentale multi-échelle des mécanismes de déformation de laphase MAX Ti2AlN. A l'échelle macroscopique, deux types d'expériences ont été menés. Des essaisde compression in-situ à température et pression ambiantes couplés à la diffraction neutroniqueont permis de mieux comprendre le comportement des différentes familles de grains dans le Ti2AlNpolycristallin. Des essais de compression sous pression de confinement ont également été réalisés dela température ambiante jusqu'à 900 °C. À l'échelle mésoscopique, les microstructures des surfacesdéformées ont été observées par MEB et AFM. Ces observations complétées par des essais denanoindentation ont montré que la forme des grains et leur orientation par rapport à la directionde sollicitation gouvernent l'apparition de déformations intra- et inter-granulaires ainsi que lalocalisation de la plasticité. Finalement à l'échelle microscopique, une étude détaillée par METdes échantillons déformés sous pression de confinement a révélé la présence de configurations dedislocations inédites dans les phases MAX, telles que des réactions entre dislocations, des dipôleset des dislocations hors plan de base. À la vue de ces résultats nouveaux, les propriétés mécaniquesdes phases MAX sont rediscutéesIt is commonly believed that plastic deformation mechanisms of MAX phases consistin basal dislocation glide, thus forming pile-ups and walls. The latter can form local disorientationareas, known as kink bands. Nevertheless, the elementary mechanisms and the exact role ofmicrostructural defects are not fully understood yet. This thesis report presents a multi-scale experimentalstudy of deformation mechanisms of the Ti2AlN MAX phase. At the macroscopic scale,two kinds of experiments were performed. In-situ compression tests at room temperature coupledwith neutron diffraction brought new insight into the deformation behavior of the different grainfamilies in the polycrystalline Ti2AlN. Compression tests from the room temperature to 900 °Cunder confining pressure were also performed. At the mesoscopic scale, deformed surface microstructureswere observed by SEM and AFM. These observations associated with nanoindentationtests showed that grain shape and orientation relative to the stress direction control formationof intra- and inter- granular strains and plasticity localization. Finally, at the microscopic scale,a detailed dislocation study of samples deformed under confining pressure revealed the presenceof dislocation configurations never observed before in MAX phases, such as dislocation reactions,dislocation dipoles and out-of-basal plane dislocations. In the light of these new results, mechanicalproperties of MAX phases are discussed
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Pour, Shahid Saeed Abadi Parisa. "Mechanical behavior of carbon nanotube forests under compressive loading." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47699.
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Carbon nanotube (CNT) forests are an important class of nanomaterials with many potential applications due to their unique properties such as mechanical compliance, thermal and electrical conductance, etc. Their deformation and failure in compression loading is critical in any application involving contact because the deformation changes the nature of the contact and thus impacts the transfer of load, heat, and charge carriers across the interface. The micro- and nano-structure of the CNT forest can vary along their height and from sample to sample due to different growth parameters. The morphology of CNTs and their interaction contribute to their mechanical behavior with change of load distribution in the CNT forest. However, the relationship is complicated due to involvement of many factors such as density, orientation, and entanglement of CNTs. None of these effects, however, are well understood. This dissertation aims to advance the knowledge of the structure-property relation in CNT forests and find methodologies for tuning their mechanical behavior. The mechanical behavior of CNT forests grown with different methodologies is studied. Furthermore, the effects of coating and wetting of CNT forests are investigated as methods to tailor the degree of interaction between CNTs. In situ micro-indentation of uncoated CNT forests with distinct growth-induced structures are performed to elucidate the effects of change of morphology along the height of CNT forests on their deformation mechanism. CNT aerial density and tortuosity are found to dictate the location of incipient deformation along height of CNT forests. Macro-compression testing of uncoated CNT forests reveals mechanical failure of CNT forests by delamination at the CNT-growth substrate. Tensile loading of CNT roots due to post-buckling bending of CNTs is proposed to be the cause of this failure and simple bending theory is shown to estimate the failure load to be on the same order of magnitude as experimental measurements. Furthermore, delamination is observed to occur in the in situ micro-indentation of CNT forests coated with aluminum on the top surface, which demonstrates the role of the mechanical constraints within the CNT forest in the occurrence of delamination at the CNT-substrate interface. In addition, this dissertation explores the mechanical behavior of CNT forests coated conformally (from top to bottom) with alumina by atomic layer deposition. In situ micro-indentation testing demonstrates that the deformation mechanism of CNT forests does not change with a thin coating (2 nm) but does change with a sufficiently thick coating (10 nm) that causes fracturing of the hybrid nanotubes. Ex situ flat punch and Berkovich indentations reveal an increase in stiffness of the CNT forests that are in range with those predicted by compression and bending theories. An increase in the recoverability of the CNTs is also detected. Finally, solvent infiltration is proposed as a method of decreasing stiffness of CNT forests and changing the deformation mechanism from local to global deformations (i.e., buckling in the entire height). Presence of solvents between CNTs decreases the van der Waals forces between them and produces CNT forests with lower stiffness. The results demonstrate the effect of interaction between CNTs on the mechanical behavior. This dissertation reveals important information on the mechanical behavior of CNT forests as it relates to CNT morphology and tube-to-tube interactions. In addition, it provides a framework for future systematic experimental and theoretical investigations of the structure-property relationship in CNT forests, as well as a framework for tuning the properties of CNT forests for diverse applications.
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Lahouij, Imène. "Mécanismes de lubrification des nanoparticules à structure Fullerène : approche multi-échelle." Phd thesis, Ecole Centrale de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00790813.
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Les fullerènes de bisulfure métallique de type ( M eS2 , où Me= Mo et W) rencontrent un intérêt croissant du fait de leurs pouvoirs anti usure et réducteur de frottement en régime de lubrification limite. Les propriétés tribologiques de ces nanoparticules, dépendent à la fois de leurs caractéristiques intrinsèques (structure, morphologie, taille, ... ), des conditions de sollicitations (nature des surfaces, pression, température, ... ) ainsi que du cocktail d'additifs présent dans une formulation d'huile moteur. La compréhension de l'origine de ces propriétés passe obligatoirement par une parfaite connaissance du mode d'action des nanoparticules. L'objectif de ce travail de thèse est d'identifier les paramètres pouvant avoir une influence sur le comportement des nanoparticules à l'échelle nanométrique et de faire le lien entre ce comportement, les mécanismes de lubrification des nanoparticules, et leurs propriétés tribologiques. Afin de répondre à cet objectif nous avons adopté une approche multi échelle qui consiste dans un premier temps à étudier le comportement de fullerènes individuels (IF - M eS2 , ou Me= Mo et W) en cours de sollicitation. Ainsi grâce à une méthodologie expérimentale originale couplant la technique de nano indentation à une observation in situ dans un microscope électronique à transmission haute résolution (HRMET), nous avons visualisé pour la toute première fois et en temps réelle comportement de nanoparticules individuelles d'if- M eS2 (Me= Mo et W) sollicitées en compression et/ou en cisaillement dans un contact dynamique. Cette étude a permis d'identifier l'influence des caractéristiques intrinsèques des fullerènes sur leur réponse à l'échelle nanométrique et d'estimer des pressions de contact pour lesquelles le fullerène s'exfolie, roule ou glisse dans le contact. Nous nous sommes ensuite intéressés aux mécanismes de lubrification des fullerènes en dispersion dans une base lubrifiante, en condition de lubrification limite. En se basant sur des analyses XPS et des observations MEB et MET des tribofilms et des débris d'usure générés à l'issu d'essais de frottement réalisés dans trois contacts de nature différente (acier, alumine et DLC), nous avons clairement montré que les propriétés lubrifiantes des nanoparticules d'IF - M eS2 (Me= Mo et W) dépendaient à la fois de leurs caractéristiques intrinsèques et de la nature des surfaces frottantes. Ainsi un lien a été établi entre le comportement des fullerènes à l'échelle nanométrique et leur mode d'action dans un contact tribologique. Enfin, l'influence de la mise en dispersion des nanoparticules sur leurs propriétés tribologiques a été étudiée. Les propriétés tribologiques des nanoparticules dans une huile moteur ont été également évaluées. Deux approches expérimentales de type 'Bottom up' et 'Top dawn'ont été adoptées afin d'évaluer les interactions entre les nanoparticules et l'ensemble des additifs présents dans une huile complétement formulée. L'influence de la température sur les propriétés tribologiques des nanoparticules a été également abordée.
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Ghazi, Arash. "Microstructural computational modeling of the mechanical behaviour of closed-cell foams: from tessellation-based to CT scan-based modeling." Doctoral thesis, Universite Libre de Bruxelles, 2020. https://dipot.ulb.ac.be/dspace/bitstream/2013/306841/3/Thesis.pdf.
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The mechanical behavior of closed cell metallic foams strongly depends on their geometry at the scale of cells and cell walls. Two approaches are proposed in this work to address this computationally:(i) a controlled geometrical description of foam morphology features by exploiting an advanced tessellation-based procedure, allowing to generate realistic microstructural geometry,(ii) a procedure allowing to extract geometrical features of a foam morphology based on image-based modelling using CT scans. The first approach proposes a methodology that allows the automated generation of RVEs with a detailed control of the microstructure, including of cell geometries. It is primarily based on an inclusions packing algorithm assisted by distance fields control. Such distance fields can subsequently be used to morph inclusions, producing generalized tessellations with the possibility of incorporating curved and irregular boundaries. 3D morphologies of closed cell foams are produced by extracting the geometry from a proper combination of distance field functions. The procedure allows controlling the cell size distribution, spatial cell wall thickness distribution (correlated or not with the cell size distribution), wall curvatures and/or defects. An automated 3D meshing tool for implicit geometries was exploited to produce high quality tetrahedral meshes from the generated implicit foam geometries. Representative volume element based simulations were performed using this approach to assess the different morphological features relative importance on the mechanical behaviour of ALPORAS. An original extension of this tool was incorporating the transformation of 3D geometry into a shell-based finite element model. This resulted in a significant gain in computation time and allowed for simulating compression test up to densification (being out of reach with 3D solid finite element models) showing a good qualitative match with experimental results from the literature.The second approach proposes a robust methodology for the automated generation of shell-based finite element models directly from X-ray Computed Tomography (CT) scans.An in situ X-ray CT compression test of the sample was performed to serve as basis of comparison to the computations. As first steps, raw CT images are segmented using various image processing techniques and an implicit 3D geometry is reconstructed for each cell by using a Euclidean distance field computation technique. An automated geometrical procedure is used next to extract a (surface) shell geometry from this implicit 3D geometry, followed by subsequent meshing step. A direct comparison of the performed simulations with raw experimental data is performed. The detailed deformation and failure mechanisms of closed-cell foams under quasi static uniaxial compressive loading are investigated numerically and compared directly with the result of the in situ experimental measurement.Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished
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Soler, Maxime. "Réduction et comparaison de structures d'intérêt dans des jeux de données massifs par analyse topologique." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS364.
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Dans cette thèse, nous proposons différentes méthodes, basées sur l'analyse topologique de données, afin de répondre aux problématiques modernes concernant l'analyse de données scientifiques. Dans le cas de données scalaires, extraire un savoir pertinent à partir de données statiques, de données qui varient dans le temps, ou données d'ensembles s'avère de plus en plus difficile. Nos approches pour la réduction et l'analyse de telles données reposent sur l'idée de définir des structures d'intérêt dans les champs scalaires à l’aide d’abstractions topologiques. Dans un premier temps, nous proposons un nouvel algorithme de compression avec pertes offrant de fortes garanties topologiques, afin de préserver les structures topologiques tout au long de la compression. Des extensions sont proposées pour offrir un contrôle supplémentaire sur l'erreur géométrique. Nous ciblons ensuite les données variables dans le temps en proposant une nouvelle méthode de suivi des structures topologiques, basée sur des métriques topologiques. Ces métriques sont étendues pour être plus robustes. Nous proposons un nouvel algorithme efficace pour les calculer, obtenant des accélérations de plusieurs ordres de grandeur par rapport aux approches de pointe. Enfin, nous appliquons et adaptons nos méthodes aux données d'ensemble relatives à la simulation de réservoir, dans un cas de digitation visqueuse en milieu poreux. Nous adaptons les métriques topologiques pour quantifier l’écart entre les simulations et la vérité terrain, évaluons les métriques proposées avec le retour d’experts, puis implémentons une méthode de classement in-situ pour évaluer la fidélité des simulationsIn this thesis, we propose different methods, based on topological data analysis, in order to address modern problematics concerning the increasing difficulty in the analysis of scientific data. In the case of scalar data defined on geometrical domains, extracting meaningful knowledge from static data, then time-varying data, then ensembles of time-varying data proves increasingly challenging. Our approaches for the reduction and analysis of such data are based on the idea of defining structures of interest in scalar fields as topological features. In a first effort to address data volume growth, we propose a new lossy compression scheme which offers strong topological guarantees, allowing topological features to be preserved throughout compression. The approach is shown to yield high compression factors in practice. Extensions are proposed to offer additional control over the geometrical error. We then target time-varying data by designing a new method for tracking topological features over time, based on topological metrics. We extend the metrics in order to overcome robustness and performance limitations. We propose a new efficient way to compute them, gaining orders of magnitude speedups over state-of-the-art approaches. Finally, we apply and adapt our methods to ensemble data related to reservoir simulation, for modeling viscous fingering in porous media. We show how to capture viscous fingers with topological features, adapt topological metrics for capturing discrepancies between simulation runs and a ground truth, evaluate the proposed metrics with feedback from experts, then implement an in-situ ranking framework for rating the fidelity of simulation runs
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Lamb, Juliano Rodrigo. "Sistema de informação para ajuste dos dados de tensão-deformação nos ensaios de compactação do solo." Universidade Estadual do Oeste do Parana, 2006. http://tede.unioeste.br:8080/tede/handle/tede/181.
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Previous issue date: 2006-12-13The soil compaction is a harmful phenomenon to the agricultural sector, intensified with the current model of culture adoption though the use of machines weighed in the culture systems, where these can exert superior pressures to the soil load support capacity. With the soil compaction and compression there is a reduction of the void ratios face to the air and water expulsion, that composes the system, harming the water absorption and minerals for the plants roots, as well as increasing the resistance of the ground to the penetration. By the way, it is formed becomes important the accomplishment of trials of compression for determination of the compaction levels, either in field through assays in situ or laboratory trials. The difficulty presented in trials of this nature, this related with the analysis of the gotten data and with the determination of the compression curves and stress point. Face this conjuncture one utilized the systems of information with the development of application of data base for the adjustment of the data of tension-deformation in trials in situ and laboratory. The system was developed using the environment of development Borland© Delphi© with data base Firebird and methodologies Oriented Objects and to 3Tier. With data proceeding from carried through trials, the software have demonstrated to efficiency in the reading and filtering of in situ trials data, security in the storage of all the referring data to the trials, as well as agility and precision in the determination of the curves of compression of the ground and in the esteem of the stress point. The results still allow concluding that, the traffic of machines in the activities in field intensify the phenomenon of the compaction, and that sinkage plate and oedometer are important in the accomplishment of trials of soil compression.
A compactação do solo é um fenômeno danoso ao setor agrícola, intensificado com a adoção do modelo de produção atual que utiliza nos sistemas de cultivo. máquinas pesadas que podem exercer pressões superiores à capacidade de suporte do solo. Com a compactação e compressão do solo ocorre uma redução do índice de vazios, face à expulsão do ar e da água que compõem o sistema, prejudicando a absorção de água e minerais pelas raízes das plantas e aumentando a resistência do solo à penetração. Dessa forma, torna-se importante a realização de ensaios de compressão para determinação dos índices de compactação, seja em campo por meio de ensaios in situ ou em ensaios laboratoriais. A dificuldade apresentada em ensaios desta natureza, está relacionada à análise dos dados obtidos e com a determinação das curvas de compressão e índice de pré-consolidação. Face a essa conjuntura procurou-se a utilização de sistemas de informação com o desenvolvimento de um aplicativo de banco de dados para o ajuste dos dados de tensão-deformação em ensaios in situ e em laboratório. O sistema foi desenvolvido usando o ambiente de desenvolvimento Borland© Delphi© com banco de dados Firebird e metodologias Orientada a Objetos e 3Tier. Alimentado com dados provenientes de ensaios realizados, o software demonstrou eficiência na leitura e filtragem dos dados de ensaios in situ, segurança no armazenamento de todos os dados referentes aos ensaios, bem como agilidade e precisão na determinação das curvas de compressão do solo e na estimação do ponto de pré-consolidação. Os resultados ainda permitem concluir que o tráfego de máquinas, nas atividades em campo, intensifica o fenômeno da compactação e que o penetrômetro e o oedômetro são importantes na realização de ensaios de compressão do solo.
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RATHOD, CHANDRASEN. "DIFFRACTION STUDIES OF DEFORMATION IN SHAPE MEMORY ALLOYS AND SELECTED ENGINEERING COMPONENTS." Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2892.
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Deformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and exhibiting the shape memory effect. Ni rich compositions on the other hand can exist near room temperature in the austenitic phase and undergo a reversible martensitic transformation on application of stress. Associated with this reversible martensitic transformation are macroscopic strains, again as large as 8%, which are also recovered and resulting in superelasticity. This work primarily focuses on neutron diffraction measurements during loading at the Los Alamos Neutron Science Center at Los Alamos National Laboratory. Three phenomena were investigated: First, the phenomena of hysteresis reduction and increase in linearity with increasing plastic deformation in superelastic NiTi. There is usually a hysteresis associated with the forward and reverse transformations in superelastic NiTi which translates to a hysteresis in the stress-strain curve during loading and unloading. This hysteresis is reduced in cold-worked NiTi and the macroscopic stress-strain response is more linear. This work reports on measurements during loading and unloading in plastically deformed (up to 11%) and cycled NiTi. Second, the tension-compression stress-strain asymmetry in martensitic NiTi. This work reports on measurements during tensile and compressive loading of polycrystalline shape-memory martensitic NiTi with no starting texture. Third, a heterogeneous stress-induced phase transformation in superelastic NiTi. Measurements were performed on a NiTi disc specimen loaded laterally in compression and associated with a macroscopically heterogeneous stress state. For the case of superelastic NiTi, the experiments related the macroscopic stress-strain behavior (from an extensometer or an analytical approach) with the texture, phase volume fraction and strain evolution (from neutron diffraction spectra). For the case of shape memory NiTi, the macroscopic connection was made with the texture and strain evolution due to twinning and elastic deformation in martensitic NiTi. In all cases, this work provided for the first time insight into atomic-scale phenomena such as mismatch accommodation and martensite variant selection. The aforementioned technique of neutron diffraction for mechanical characterization was also extended to engineering components and focused mainly on the determination of residual strains. Two samples were investigated and presented in this work; first, a welded INCONEL 718 NASA space shuttle flow liner was studied at 135 K and second, Ti-6Al-4V turbine blade components were investigated for Siemens Westinghouse Power Corporation. Lastly, also reported in this dissertation is a refinement of the methodology established in the author's masters thesis at UCF that used synchrotron x-ray diffraction during loading to study superelastic NiTi. The Los Alamos Neutron Science Center is a national user facility funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36. The work reported here was made possible by grants to UCF from NASA (NAG3-2751), NSF CAREER (DMR-0239512), Siemens Westinghouse Power Corporation and the Space Research Initiative.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering
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MAYEUR, BERTRAND. "Mesure et modelisation des contraintes naturelles dans un massif rocheux alpin : effets de la topographie, de l'anisotropie et des contraintes tectoniques ; application au projet de tunnel maurienne-ambin." Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10198.
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Le projet de tunnel de base maurienne-ambin, qui traversera les alpes sur plus de 50 km de longueur et sous un recouvrement de terrain atteignant au maximum 2500 m, pose le probleme de la prevision des etats de contraintes naturelles dans les massifs rocheux ; le comportement du rocher pendant l'excavation aussi bien que la stabilite de l'ouvrage en dependent. Pour etudier cette question complexe, nous avons eu recours a plusieurs approches complementaires. Il s'agit tout d'abord d'une etude en laboratoire du comportement mecanique du gneiss d'ambin, visant en particulier a quantifier precisement son anisotropie elastique ; c'est dans cette roche que le recouvrement sera maximal, et donc la prevision de contraintes particulierement importante. Nous avons ensuite interprete une serie de mesures de contraintes in-situ realisees dans quinze forages de reconnaissance a la cote du futur tunnel, essentiellement par la methode des tests hydrauliques sur fractures preexistantes (methode htpf). Nous avons enfin evalue, avec l'aide de la modelisation numerique, le poids relatif des differents parametres influant sur l'etat de contraintes naturel : la topographie, l'anisotropie elastique des roches et la tectonique. Il ressort de cette etude que dans le secteur concerne par le tunnel maurienne-ambin, la tectonique combinee a la topographie semble etre le facteur predominant, qui explique une bonne partie des observations de terrain. L'anisotropie des roches comme le gneiss d'ambin, dont le rapport des modules elastiques est proche de 1. 5, n'est qu'un parametre de second ordre, mais il influe tout de meme sur les valeurs et les orientations des contraintes principales.
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LIN, KAI-PENG, and 林凱鵬. "Mechanical Properties of Micropillars Using In Situ Transmission Electron Microscope Compression And Indentation." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/65z5pu.
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博士國立高雄應用科技大學
機械工程系
106
In this study, the mechanical properties of micropillars were analyzed by in situ transmission electron microscopy compression and indentation. The results show that the stress wave propagation and structural variations of the material can be found during in situ compression. After compression process, because of the internal structure of the material defects and damage, the micropillar will be bended and broken. The Young's modulus of NaCl, Al2O3, NiAl and NiTi alloy micropillaby in situ compression test were 10.4-23.9 GPa, 25.5-347.5 GPa, 32.7-44.9 GPa and 5.9-24.4 GPa, respectively. Vickers hardness values of NaCl, Al2O3, Cu, NiAl and NiTi alloy were found to be 196-260 MPa, 14.0-20.2 GPa, 1.1-1.2 GPa, 2.9-4.5 GPa and 7.4-7.7GPa, respectively. In the study, it was found that the phenomenon of dislocation and dislocation loop appeared in the internal structure of the Al2O3 by high-resolution transmission electron microscopy after the Vickers hardness test. The mechanical behavior and deformation mechanism of Cu micropillar structures through molecular dynamics simulation after compressed were also investigated in this study. As can be seen from the research results, Cu pillars have dislocation and stress wave transmission phenomenon during the compression process, and the diameter of the Cu pillar has increased with the increase of the compression displacement. Finally, through theoretical exploration and simulation analysis, the mechanical properties of micropillar should establish the important properties and the mechanism of structures and theory.
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Wu, Jui-Yang, and 吳瑞洋. "Mechanical Behaviors of Cu6Sn5 in 3D IC Micro JointsUsing Micropillar Compression." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/hvvnmy.
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博士國立臺灣大學
材料科學與工程學研究所
107
As semiconductor industry is confronted with the challenge of physical limit in scaling down transistor size, three dimensional integrated circuits (3D ICs) serve as one of the most promising technologies to extend Moore’s law (More-Moore) or even go More-than-Moore. Yet, the miniaturization of micro solder joints, an essential joining structure in 3D IC technology, leads to quick transformation from solders into intermetallic compounds (IMCs) in the joint. When a large portion of micro joints is occupied by IMCs, the mechanical properties and deformation behaviors of micro joints are no longer dominated by solder as in conventional flip-chip joints and ball grid array (BGA) joints, and instead intermetallics are anticipated to shoulder primary responsibility of mechanical reliability of micro joints. In light of this, this study puts emphasis on mechanical reliability assessment of single crystalline IMCs and IMC-based multiphase structures by means of nanoindentation and micropillar compression. In order to eliminate the influence of indenter, substrate, misalignment and gravity effect under tilt condition, a calibration approach for micropillar compression is firstly established such that Young’s moduli measured from micropillar compression tests are in good agreement with those from nanoindentation. Also, the stress-strain curves show that Cu6Sn5 exhibited one or more strain bursts prior to brittle fracture, and the post-mortem transmission electron microscopy (TEM) analysis suggests that dislocation gliding inside micropillars is involved in strain jumps. Besides, a statistical analysis of the anisotropy in hexagonal Cu6Sn5 is also carried out based on micro-compression as well as nanoindentation results, where Cu6Sn5 exhibits a higher value of Young’s modulus when the loading direction is closer to c-axis. Furthermore, Ni addition into Cu6Sn5 can notably enhance mechanical strength and stabilize the hexagonal structure. Last but not least, multilayered micropillars (Cu6Sn5/Sn/Cu6Sn5 and Cu6Sn5/Cu3Sn/Cu) containing heterogeneous phase interfaces provide insight into overall deformation behaviors in real Cu-Sn interconnects. On one hand, Cu6Sn5/Sn/Cu6Sn5 cylinders exhibit remarkable plasticity in the manner of interface sliding at around 100 MPa, accommodating at least 10% strain and retaining its integrity without any void formation at the interface. On the other hand, multilayered Cu6Sn5/Cu3Sn/Cu micropillars undergo plastic deformation through slip deformation at Cu substrate, suggesting sufficient strength of intermetallic compounds and the interfaces. These results are beneficial in evaluation of validity and reliability of 3D IC micro-joints for chip-stacking applications.
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Jia-ShiunChen and 陳家勛. "Simulation by the finite element method for the compression of bulk metallic glass micropillar." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/63053818792571702611.
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Chou, Hung-Sheng, and 周鴻昇. "Strengthening and Toughening of Zr-Based Thin Film Metallic Glasses and Composites under Nanoindentation and Micropillar Compression." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/14392610155375909609.
Full textAbstract:
博士國立中山大學
材料與光電科學學系研究所
99
Since the first discovery of amorphous alloys in 1960, researchers have explored many unique mechanical, magnetic, and optical characteristics of such materials for potential applications. Up to now, well-developed processes, such as rapid quenching, sputtering, evaporation, pulse laser deposition, etc, have been applied for different applications in micro-electro-mechanical systems (MEMS). Due to the lack of ordered structure, amorphous alloys can bear a high stress in the elastic region. Their plastic deformation stability is also of interest and has been widely studied. The shear-band characteristic, a kind of inhomogeneous deformation mechanism, dominates the deformation after yielding at room temperature. While a shear band nucleate, its propagation usually cannot be arrested or stopped. In other words, the occurrence of matured shear bands needs to be prevented. There are two major approaches in this aspect. The first is to increase the material yield strength so as to delay the shear band nucleation. Another is to incorporate intrinsic or extrinsic particles so as to absorb the kinetic energy of shear bands in the amorphous matrix. In this study, we utilize three strategies to control the propagation of shear bands in thin film metallic glasses (TFMGs): sub-Tg annealing, the addition of strong element in solute form, and the introduction of strong nanocrystalline layers. For sub-Tg annealing, the base alloy system is Zr69Cu31, with a base film hardness of 5.1 GPa measured by nanoindentation. After annealing, the hardness exhibits ~30% increase. Without the occurrence of the phase transformation, as confirmed by X-ray diffraction, the possible reaction during sub-Tg annealing is attributed to structural relaxation, not crystallization. The full width at half maximum of the X-ray peak exhibits a decreasing trend in the using X-ray and transmission electron microscopy diffraction, meaning the excess free volumes forming during vapor-to-solid deposition process would be annihilated by localized atomic re-arrangement. Moreover, the formation of medium-ordering-range clusters was confirmed utilizing high-resolution transmission electronic microscopy. The denser amorphous structure leads to the increment of hardness. For the addition of Ta in Zr55Cu31Ti14, sputtering provides a wide glass forming range with solubility of Ta approaching ~75 at%. With increasing Ta content, the elastic modulus and hardness increase slowly. A steep rise occurs at ~50 at% of Ta. Up to 75 at% of Ta, the elastic modulus and hardness approaches 140 GPa and 10.0 GPa, respectively (100% increment). Up to now, Ta-rich TFMGs exhibit the highest elastic modulus and hardness among all amorphous alloys fabricated using vapor deposition techniques. The irregular increase is attributed to the formation of Ta-Ta bonding. A large quantity of Ta bonds would lead to the formation of Ta-rich nanoclusters, drastically decreasing the strain rate while shear band propagates under nanoindentation and microcompression tests. The introduction of nanocrystalline Ta layers can not only effectively enhance the yield strength but also serve as the absorber for the kinetic energy of shear bands, revealing ductility in the microcompression test.
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Lehmann, Henry. "Temporal Lossy In-Situ Compression for Computational Fluid Dynamics Simulations." Doctoral thesis, 2017. https://tubaf.qucosa.de/id/qucosa%3A31413.
Full textAbstract:
Während CFD Simulationen für Metallschmelze im Rahmen des SFB920 fallen auf dem Taurus HPC Cluster in Dresden sehr große Datenmengen an, deren Handhabung den wissenschaftlichen Arbeitsablauf stark verlangsamen. Zum einen ist der Transfer in Visualisierungssysteme nur unter hohem Zeitaufwand möglich. Zum anderen ist interaktive Analyse von zeitlich abhängigen Prozessen auf Grund des Speicherflaschenhalses nahezu unmöglich. Aus diesen Gründen beschäftigt sich die vorliegende Dissertation mit der Entwicklung sog. Temporaler In-Situ Kompression für wissenschaftliche Daten direkt innerhalb von CFD Simulationen. Dabei werden mittels neuer Quantisierungsverfahren die Daten auf ~10% komprimiert, wobei dekomprimierte Daten einen Fehler von maximal 1% aufweisen. Im Gegensatz zu nicht-temporaler Kompression, wird bei temporaler Kompression der Unterschied zwischen Zeitschritten komprimiert, um den Kompressionsgrad zu erhöhen. Da die Datenmenge um ein Vielfaches kleiner ist, werden Kosten für die Speicherung und die Übertragung gesenkt. Da Kompression, Transfer und Dekompression bis zu 4 mal schneller ablaufen als der Transfer von unkomprimierten Daten, wird der wissenschaftliche Arbeitsablauf beschleunigt.
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(6635129), Kayla Haruko Yano. "In Situ TEM Mechanical Testing of Irradiated Oxide Dispersion Strengthened Alloys." Thesis, 2019.
Find full textAbstract:
The objective of this dissertation is to demonstrate the use of in situ TEM mechanical testing to find mechanical properties of as received, self-ion, and proton irradiated Fe-9%Cr ODS. The desire to work at small scale in the characterization of irradiated materials to reduce costs and improve throughput, require the development of novel methods to assess mechanical properties in volume-limited irradiation damage layers. Yet at these micrometer or nanometer scales, the mechanical properties can begin to be impacted by size effects. In this work micropillar compression, cantilever bending, lamellae indentation, and clamped beam fracture testing is conducted on ion-irradiated Fe-9%Cr ODS to find yield stress, elastic modulus, flow stress, and fracture toughness. Micropillars in compression allow us to define a minimum sample dimension, which approaches the obstacle spacing of the material, at which size effects are observed. This relationship between sample dimension and obstacle spacing defined through micropillar compression is extended to a new testing geometry, cantilever bending, and material property, flow stress. Lessons learned during the cantilever bending informed the clamped beam design for conducting fracture testing on a ductile engineering alloy at micrometer scales. Finally, lamellae indentation was conducted to link qualitative observations of the microstructure under load with literature strength of obstacle values. By combining an understanding of the microstructure of irradiated Fe-9%Cr ODS and the in situ TEM technique, one can find the bulk-like mechanical properties of ion irradiated Fe-9%Cr ODS.
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(7036280), Cuncai Fan. "Radiation Response of Nanostructured Cu." Thesis, 2019.
Find full textAbstract:
Irradiation of metals with energetic particles causes heavy damage effects in microstructure and
mechanical properties, which is closely associated with irradiation conditions, presence of
impurities, and microstructural features. It has been proposed that the radiation tolerance of a
certain material can be enhanced by introducing a high density of interfaces, acting as ‘sinks’ that
can frequently involve in attracting, absorbing and annihilating defects. Nanostructured materials
with large volume fraction of interfaces, therefore, are assumed to be more radiation tolerant than
conventional materials. This thesis focuses on the radiation damage effects in nanostructured Cu
via the methods of in-situ TEM (transmission electron microscope) radiation experiments, postirradiation TEM analyses, small-mechanical tests (nanoindentation and micro-pillar compression),
and computer simulations (molecular dynamics and phase-field modeling).
We design and fabricate nanostructured Cu using direct current (DC) magnetron sputtering
deposition technique, a typica physical vapor deposition (PVD) method and a bottom-up way to
construct various nanostructured metals. High-density twin boundaries (TBs) and nanovoids (NVs)
are introduced into two distinct nanostructured Cu films, including nanovoid-nanotwinned (NVNT) Cu (111) and nanovoid (NV) Cu (110). The in-situ high-energy Kr++ (1 MeV) and ex-situ
low energy He+
(< 200 keV) irradiations are subsequently preformed on the as-deposited Cu
samples. On the one hand, the in-situ TEM observations suggest that TBs and NVs can influence
the formation, distribution and stability of radiation-induced defects. Meanwhile, the preexisting
microstructures also undergo structural change through void shrinkage and twin boundary
migration. On the other hand, the ex-situ micro-pillar compression tests reveal that the Heirradiated NV-NT Cu contains less defect clusters but experiences more radiation-induced
hardening. The underlying mechanisms of void shrinkage, twin boundary migration, and radiationinduced hardening are fully discussed based on post-irradiation analyses and computer simulations.
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Chun-WeiTang and 湯君偉. "Effects of Diabetes Mellitus on Mechanical Behavior of Peripheral Nerve Tissues and Vasa Nervora under In Situ Circular Compression." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/03082780865605227003.
Full textAbstract:
碩士國立成功大學
機械工程學系
104
Ischemia of vasa nervora in peripheral nerves may be the main cause of diabetic neuropathies. Diabetic neuropathies are also related to clinical morbidity of carpal tunnel syndrome. Thus, from biomechanics perspective, study of mechanical behavior of peripheral nerve tissues and vasa nervora under compression and diabetic circumstances may help understanding mechanisms of retarded blood flow in nerve. In this study, in situ compress-and-hold experiments were implemented by circular compression on sciatic nerve of rats and blood flow within vasa nervorum was observed by using Doppler optical coherence tomography (D-OCT) simultaneously. Mechanical property of nerves was determined by fitting the data from the experiments with a quasi-linear viscoelasticity (QLV) model. Cross sectional area and morphology of vasa nervorum and their variations with time were estimated from D-OCT image data using new methods. The finite element method (FEM) was utilized to simulate stress distribution and morphology changes of substructures in the nerve. Results of this study suggested diabetic nerves are more viscous in mechanical property and their vasa nervora are more vulnerable to circular compression. Results from FEM suggested that the perineurium could sustain more stress while the epineurium served as cushion under circular compression. The results also indicated there are specific regions in epineurium which sustained less stress and blood vessels in such regions had less tendency to collapse. The large blood vessels in nerve are most likely to be settled on these regions according to tissue slices. Comparison between D-OCT data and FEM results suggested that vasa nervora have auto-regulation ability.
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EricChia and 謝博弈. "In situ Circular Compression and Doppler Optical Coherence Tomography Studies on Effects of Diabetic Mellitus on Vesa Nervonum of Sciatic Nerve." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/45862378173555611749.
Full textAbstract:
碩士國立成功大學
機械工程學系
102
Diabetes mellitus is one of the most common diseases in the world and can cause many types of neuropathies, and even mortality. It is therefore important to understand how diabetes mellitus alters the mechanical properties of nerve tissues and their blood vessels. This study is to examine the dilatation of vasa nervorum inside the nerve trunk by using circular compression test and Doppler OCT, then proposes a biomechanical model to explain how vasa nervorum interact with the compression force and compare the simulated results with images captured by Doppler OCT. In this study, in situ compression-and-hold circular compression tests were applied to the sciatic nerves of both diabetic rats and normal rats. Doppler optical coherence tomography (Doppler OCT) was then utilized to monitor the configuration of the vasa nervorum in two groups of rats. The force data acquired in the compression tests were fitted by using Fung’s quasi-linear viscoelastic model (QLV) to determine the viscoelasticity of the nerves. The results show that the nerves in the diabetic group had a longer relaxation time but lower stress responses than those in the normal group. Consequently, the Doppler OCT observations reveal that in contrast to the normal vasa nervorum, the diabetic vasa nervorum did not dilate in the relaxation phase. This study also provides that the biomechanical properties of vasa nervorum may be described as shell model and confirms the autoregulatory responses of blood vessels. In summary, the diabetic nerve is friable and its vasa nerverom is fragile and may explain why the diabetic patients are more prone to carpal tunnel syndrome.
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"Deformation Behavior of adidas BOOST(TM) Foams Using In Situ X-ray Tomography and Correlative Microscopy." Doctoral diss., 2020. http://hdl.handle.net/2286/R.I.62793.
Full textAbstract:
abstract: Energy return in footwear is associated with the damping behavior of midsole foams, which stems from the combination of cellular structure and polymeric material behavior. Recently, traditional ethyl vinyl acetate (EVA) foams have been replaced by BOOST(TM) foams, thereby reducing the energetic cost of running. These are bead foams made from expanded thermoplastic polyurethane (eTPU), which have a multi-scale structure consisting of fused porous beads, at the meso-scale, and thousands of small closed cells within the beads at the micro-scale. Existing predictive models coarsely describe the macroscopic behavior but do not take into account strain localizations and microstructural heterogeneities. Thus, enhancement in material performance and optimization requires a comprehensive understanding of the foam’s cellular structure at all length scales and its influence on mechanical response.
This dissertation focused on characterization and deformation behavior of eTPU bead foams with a unique graded cell structure at the micro and meso-scale. The evolution of the foam structure during compression was studied using a combination of in situ lab scale and synchrotron x-ray tomography using a four-dimensional (4D, deformation + time) approach. A digital volume correlation (DVC) method was developed to elucidate the role of cell structure on local deformation mechanisms. The overall mechanical response was also studied ex situ to probe the effect of cell size distribution on the force-deflection behavior. The radial variation in porosity and ligament thickness profoundly influenced the global mechanical behavior. The correlation of changes in void size and shape helped in identifying potentially weak regions in the microstructure. Strain maps showed the initiation of failure in cell structure and it was found to be influenced by the heterogeneities around the immediate neighbors in a cluster of voids. Poisson’s ratio evaluated from DVC was related to the microstructure of the bead foams. The 4D approach taken here provided an in depth and mechanistic understanding of the material behavior, both at the bead and plate levels, that will be invaluable in designing the next generation of high-performance footwear.Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2020
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Grave, Douglas Marcus Hadley. "Determination of the factors affecting the performance of grout packs." Thesis, 2007. http://hdl.handle.net/10539/2138.
Full textAbstract:
Student Number : 7439270 -
MSc research report -
School of Mining -
Faculty of Engineering and the Built EnvironmentIn tabular mining, common in South African gold and platinum mines, the removal of the tabular ore body by mining operations leaves behind excavations known as stopes. These stopes form the production areas of a mine and have to be supported in order that a safe working environment is created. Stopes generally have widths of close to a metre but, in some areas and on certain reefs, may be much wider. Prior to the 1980s, a combination of in-stope pillars and timber was used to support these stopes, but innovations from the 1970s have produced grout packs as a viable support option. These packs are cast in situ through the use of cemented classified tailings gravitated from surface and placed in reinforced geotextile bags at the stope face. As these packs cure and become rigid they are able to bear load when compressed by stope closure. In this way, the packs keep the working areas open. To quantify the load-bearing capacity of grout packs, a range of sizes and designs was tested in a laboratory press and, thereafter, a select few were tested underground. Initially, two aspects of grout packs that had not been adequately quantified previously were addressed. These were: the in situ load / compression characteristics of different forms of grout packs; and the relationship between laboratory test results and in situ performance. The laboratory test programme was extended to allow for an investigation into methods of improving the yieldability of grout packs and the possibility of using them to replace in-stope pillars. It was found that the factors that most affect the initial strength and post-failure characteristics of a grout pack are: the grout strength; the amount and type of steel reinforcement; the inclusion of ancillary columnar support; and the height and diameter of the pack. It was also found that grout packs could be used to replace in-stope pillars, but that pack strength and spacing should be conservatively calculated before implementation. A provisional relationship between the behaviour of packs tested in a press and those placed underground was determined.
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Englmaierová, Martina. "Mechanické vlastnosti zemin z pískovny Kolný v třeboňské pánvi." Master's thesis, 2010. http://www.nusl.cz/ntk/nusl-295820.
Full textAbstract:
This thesis originated as a part of the PhD research carried out by Mgr. Radek Suchomel. To calibrate a hypoplastic model for granular materials a large number of laboratory tests was needed and a part of the testing constitutes the present thesis. The hypoplastic model by von Wolffersdorff (1996) has eight materials parameters. The critical state fiction angle φc', which was obtained directly by the measurement of the angle of repose, is one of the eight parameters. Other parameters are determined form the results of experiments and empirically. Aim of this thesis was to carry out field and laboratory tests, to determine selected soil properties and to interpret them with regard to the variability of the soil in the selected face of the sand pit. The material for investigation comes from the south part of the Cretaceous Třeboň Basin in the South Bohemia from the Kolný sand pit. The pit is located in the upper part of the Klikov layers. The fluvial layers are characterised by rhythmical variation of gravely sands, sands and sands with dark grey clayey inclusion. Samples were taken in the face of the sand pit with the dimensions of 9 x 36 m. The following tests were performed: drained triaxial compression test (38 samples), oedometric compression test (38 samples), measurement of the angle of repose...