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Lecieux, Yann. "Étude numérique et expérimentale des instabilités hors plan des films minces en tension : application aux structures spatiales." Nantes, 2010. http://www.theses.fr/2010NANT2042.
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Au cours des dernières années, de nombreux concepts de structures spatiales dépliables ou gonflables constituées de membranes de grande dimension ont vu le jour. Cependant, les films minces de faible épaisseur utilisés dans ces réalisations se plissent lorsqu’ils sont soumis à des contraintes de compression. L’existence de plis sur ces surfaces peut affecter la performance de certains dispositifs jusqu’à les rendre totalement inutilisables. C’est la raison pour laquelle la prédiction de l’apparition des zones plissées et de leur géométrie est un axe de recherche important pour les acteurs de l’industrie spatiale. L’objectif de ces travaux est de proposer un ensemble d’outils permettant la simulation du plissement des films minces avec la méthode des éléments finis. La robustesse de nos procédures de calcul devra être évaluée en confrontant nos résultats numériques avec des données d’essai. La première partie de l’étude est consacrée à la constitution d’une base de données expérimentale en procédant au relevé de la forme des ondulations sur des éprouvettes bi-axiales soumises à des trajets de chargement variés. Ces mesures sont destinées à l’évaluation des procédures de prédiction des plis par la méthode des éléments finis. La faible épaisseur des films utilisés engendre des difficultés numériques qui nous ont amené à discrétiser ces structures avec des éléments finis coque sans degrés de liberté en rotation. Pour la résolution du problème de lambement de ces films minces, deux techniques ont été testées : la méthode d’analyse post-bifurcatoire et la minimisation de l’énergie potentielle totale avec l’algorithme de gradient conjugué<br>Over the past years there has been a large number of new structural concepts for large spacecraft applications involving stretched membranes. However, the membranes used in gossamer structures cannot undergo compressive stress because of their small bending stiffness. The result of compressive stress is that buckling occurs leading to membrane wrinkling. This may affect the performance and the reliability of the flexible gossamer structures. Thus, the prediction of wrinkle patterns in membrane surfaces is one of the many current technological interests in the aerospace industry. The main purpose of this work is to propose a method able to predict wrinkling of thin structures. The ability of the wrinkling procedures to do it has to be compared to experimental results. Firstly we present an experimental study of the wrinkle patterns that appear on flat membranes. Experiments were carried out on cruciform specimens stretched under in-plane uncoupled biaxial loads. Experimental data are used as validation cases for numerical procedures of wrinkling simulation with the finite element method. Because of the small thickness of membranes, the shell element behavior can present numerical locking mechanism. To avoid it, thin structures are discretized with rotation free shell elements. Then, to predict films wrinkling, two numerical methods were tested : post buckling analysis and minimization of the total potential energy using the conjugate gradient algorithm
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Knowles, Kelsey. "Living Pedagogical Moments Between Curriculum as Lived and Curriculum as Plan: A Phenomenological Inquiry Into the Tensions of Teacher Education." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32573.
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This master’s research is a phenomenological inquiry into the pedagogical moment in teacher education. This phenomenon is explored through a conceptual lens that draws from the phenomenological pedagogical ideals that are intrinsic to the work of both Ted Aoki and Max van Manen. Following a comprehensive outline of the phenomenological methodology that guides this thesis, the pedagogical moment is described in terms of three phases: tension, opening and pulse. The phenomenon is further explored through several sub themes relating to the lifeworld existentials (time, body, space, relation to other). This research intertwines several phenomenological concepts (such as intentionality, embodiment, consciousness, pedagogy, and motion sensitive phenomenology), within the context of one “living” phenomenon as a way of shedding light on what it is like to experience a pedagogical moment from within the tensions of practicum teaching.
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Jecu, Cristian. "Système de protections novateur et distribué pour les réseaux Moyenne Tension du futur." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00862516.
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Ce travail est lié au système de protection des réseaux de distribution. Les réseaux radiaux dedistribution peuvent être protégés simplement par une protection placée en tête du départ. Maisl'exploitation future des réseaux de distribution, qui se transforment en réseaux intelligents,flexibles et adaptatifs, va sûrement nécessiter une protégeabilité plus complexe. Parconséquent, un nouveau plan de protection pourrait être nécessaire afin d'augmenter la fiabilitédu réseau de distribution et le taux de productions décentralisées. Il pourrait inclure plusieursprotections déployées sur un départ. Le but principal de ce travail est d'étudier comment lesprotections pourraient agir (sur quel genre de grandeurs les protections reposeront, quellecoordination faut-il choisir) et d'analyser les limites de ces nouvelles protections. En déployantplusieurs protections qui divisent le départ en des zones plus petites, le plan de protectionproposé, reposant sur une formulation modifié et optimisée, proche de celle des protections dedistance classiques, déconnectera ainsi moins de consommateurs et de producteurs lors del'apparition de défauts. Cela devrait réduire le temps de coupures brèves et de diminuerl'énergie non fournie. Ce manuscrit présente une solution pour les réseaux HTA radiaux faceaux défauts monophasés.
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Beroual, Abderrahmane. "Phénomènes de propagation et de génération des streamers dans les diélectriques liquides en géométrie pointe-plan sous créneau de tension." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376029350.
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Beroual, Abderrahmane. "Phénomènes de propagation et de génération des streamers dans les diélectriques liquides en géométrie pointe-plan sous créneau de tension." Grenoble INPG, 1987. https://hal.archives-ouvertes.fr/tel-01929451.
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Pour de tres nombreux liquides, il existe une relation etroite entre la forme du streamer, sa vitesse de propagation, les courants et la lumiere emise quelque soit la polarite. Les vitesses augmentent par addition de composes capteurs d'electrons ou a bas potentiel d'ionisation. Pour des pressions et des pentes de rampe de tension elevees, les champs harmoniques de generation des streamers sont suffisants pour produire une emission ou ionisation de champ. On montre que les processus gazeux interviennent dans les deux polarites. L'analyse du bilan energetique indique que les mecanismes dominants sont la vaporisation pour les streamers lents et la dissociation et l'ionisation pour les streamers rapides, ce qui est confirme par chromatographie et spectroscopie d'emission
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GILLMANN, GILBERT. "Dopage plan silicium dans l'arseniure de gallium." Paris 6, 1988. http://www.theses.fr/1988PA066256.
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Apres avoir rappele le principe de la technique de croissance d'epitaxie par jets moleculaires, presentation d'un ensemble de caracterisations magneto-electriques (effet hall a bas champ magnetique, magneto-resistance et effet a fort champ magnetique), mais aussi des resultats purement electriques de c(v). Analyses par spectroscopie de masse d'ions secondes et mesures de double diffraction x. Tres bon accord entre ces resultats experimentaux et les investigations theoriques sur ces structures. Application de la technique a l'elaboration de dopages intenses, de contact ohmiques non allies et de transistors a effet de champ dont le canal est constitue par un dopage plan. Les performances presentees montrent les potentialites des dopages plan dans l'application a des structures de plus en plus sophistiquees
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Knorst-Fouran, Auriane. "Contribution à l’étude de propriétés interfaciales d’alcanes confinés par simulation moléculaire de type Monte Carlo." Pau, 2010. http://www.theses.fr/2010PAUU3027.
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Ce travail concerne la modélisation de propriétés interfaciales d’alcanes linéaires confinés dans des pores plan/plan, telles que la quantité adsorbée ou la tension interfaciale par la simulation moléculaire de type Monte Carlo. Les calculs ont été réalisés dans les conditions thermodynamiques variées allant de pressions et températures très faibles jusqu’à des valeurs élevées rencontrées typiquement dans les réservoirs. Nous avons mené une étude de sensibilité concernant trois potentiels d’interaction classiquement utilisés, regardé l’influence du confinement géométrique et des conditions thermodynamiques sur le méthane confiné, calculé la chaleur isostérique d’adsorption et mis en évidence le phénomène de condensation capillaire. Les résultats d’isotherme d’adsorption obtenus par simulation ont été confrontés avec succès à des résultats expérimentaux. Cette comparaison a également permis de mettre en évidence l’importance de la caractérisation du milieu poreux lors de l’estimation de l’isotherme d’adsorption. Le comportement d’alcanes linéaires de plus longue chaine a également été étudié<br>This work concerns the modelling of interfacial properties of linear alkanes confined in slit pores, such as adsorbed quantities or interfacial tension by the Monte Carlo molecular simulation. The simulations were performed at various thermodynamic conditions ranging from very low pressures and temperatures to higher values typical of reservoirs. We have studied the influence of three classical interaction potentials, the effect of confinement and thermodynamic conditions on confined methane, the isosteric heat of adsorption and the phenomenon of capillary condensation. Adsorption isotherms obtained with Monte Carlo simulation were successfully compared with experimental results. This study has also underlined the impact of the porous media characterization on the estimation of adsorption. The behavior of alkanes with longer chains was also determined
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Szczepanski, Mateusz. "Development of methods allowing the test and the comparison of low-voltage motors insulation systems running under partial discharges (fed by inverter)." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30073.
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Depuis le développement des composants d'électronique de puissance qui ont permis la fabrication d'onduleurs fiables et efficaces, les entraînements à vitesse variable utilisant des moteurs asynchrones sont devenus de plus en plus populaires. La technique MLI s'est avérée être une méthode très efficace de contrôle de la vitesse de rotation. Cependant, les impulsions de tension, avec des pentes très raides (de l'ordre de quelques kV/µs), ont apporté de nouveaux risques pour le système d'isolation électrique des moteurs. La richesse harmonique de la tension MLI entraînera une surtension significative due à une différence d'impédance entre le câble et le moteur. En effet, la tension observée par certaines parties du système d'isolation peut dépasser la tension d'apparition des décharges partielles (ang. PDIV); ce qui amorcera une activité de décharges partielles localisée. Le système d'isolation des machines basse tension (appelé type I) est basé presque entièrement sur des matériaux polymères qui ne sont pas conçus pour supporter des décharges partielles tout au long de leur vie. En raison de l'utilisation de variateurs de fréquence, l'isolation primaire du fil émaillée est en danger par rapport aux machines alimentées par réseau. En conséquence, c'est souvent le point le plus faible du système d'isolation qui conduira à la panne prématurée d'une machine. Le but de cette thèse est d'étudier et d'analyser le processus de vieillissement du fil émaillé exposé aux différents facteurs et de proposer une méthode permettant de prédire les durées de vie dans des conditions fixées. Cette étude introduit une prédiction basée sur la méthode des plans d'expériences et la distribution statistique de Weibull. Grâce au modèle obtenu avec des tests de vieillissement courts multicontraintes (température, tension, fréquence) il est possible de prédire les résultats de tests significativement plus longs. De plus, la méthodologie proposée permet de prédire la dispersion des essais longs en se basant sur la dispersion des résultats à court terme. Les prédictions sont comparées avec les données expérimentales afin de prouver la précision du modèle<br>Since the development of power electronic components, which allowed the manufacturing of reliable and efficient inverters, variable speed drives using inductive motors have become more and more popular. The PWM technique has proven to be a very effective method of rotational speed control. However, the fast changing voltage pulses, with very steep slopes (in the order of a few kV/µs), has brought new hazards for the electrical insulation system of such motors. Very high frequency harmonic components of PWM voltage will result in significant overvoltage due to an impedance mismatch between the cable and the motor. As an effect, the voltage seen by some parts of the insulation system may exceed the Partial Discharge Inception Voltage (PDIV) stating localized partial discharges activity. The insulation system in low-voltage machines (called type I) is based almost entirely on polymer materials, which are not able to support partial discharge activity throughout their lives. Due to the use of frequency inverters especially the primary insulation of the magnet wire is endangered in comparison with system-powered machines. As a result this is often the weakest link of the insulation system leading to a premature breakdown of the machine. The aim of this thesis is to investigate and analyze the aging process of the enameled wire exposed to different factors and to propose a method allowing to predict their lifespans in given conditions. This study introduces a prediction based on the Design of Experiments method and the statistical Weibull distribution. Thanks to the model obtained with short multi-stress (temperature, voltage, frequency) aging tests, it is possible to predict the results of significantly longer ones. Moreover, the adapted methodology is proposed that allows to predict the scatter of the long tests basing on the short-time results dispersion. The predictions are compared with the experimental data in order to prove the model accuracy
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Emelin, Samuel. "Analyse et intercomparaison des choix techniques majeurs en terme de structures de réseau et de règles d'exploitation parmi les grands distributeurs d'électricité." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENT042.
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Confronté à un contexte de stagnation globale de la consommation d'électricité mais avec un potentiel important de développement de nouveaux usages, ainsi qu'à l'apparition d'unités de production dispersée sur le territoire, le principal gestionnaire de réseau de distribution français a besoin d'expliciter ce que sont ses grands choix de structure et de règles d'exploitation, et de les comparer avec les distributeurs étrangers. Les principes de construction du réseau ont un impact sur la capacité à intégrer les nouvelles installations de consommation ou de production à moindre cout, et à assurer les exigences sociétales,notamment pour ce qui concerne la continuité de fourniture. Cette thèse permet de comparer ces choix techniques majeurs avec les pratiques rencontrées à l'étranger, pour situer le réseau français et ses spécificités dans un environnement technique international.Après avoir arrêté une perspective de développement des usages et des productions en France sur la base notamment des textes législatifs, l'architecture du réseau de distribution français est décrite. Les différences fonctionnelles de choix de structure dans le monde sont alors analysés, en soulignant les conséquences dans le dimensionnement par rapport au cas français. Puis l'équilibre entre niveaux de tension est questionné, ainsi que les effet des caractéristiques du territoire sur le réseau. Enfin, des choix techniques nouveaux sont proposés après analyse des points forts et des points faibles des variantes existant dans le monde<br>Faced to a context of a global lack of growth in electricity consumption, but with many potential development of new uses, added with the appearance of more and more dispersed generation, the main French distribution grid utility needs to question and compare its choicesconcerning grid structure and exploitation practices. Grid building principles have a greatimpact over its capacity to integrate at low cost consumption and production facilities, whilemeeting society needs, mainly continuity of supply. This work allows to compare thosetechnical choices between France and other countries, to determine where French utilitystands and what are its specific features in a worldwide technical environment.After setting a perspective about uses and production development, mainly on the basis of French legislation, the overall distribution grid architecture is described. Functional differences in structure choices in the world are then analysed, their consequences in thesizing of equipments is underlined. Then the equilibrium between voltage levels is questioned,as the effect of territorial features on the grid. Finally, new technical choices are proposed after advantages and drawbacks analysis of existing world grids
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Köhn, André Oliveira. "Estudo analítico e numérico das tensões de Hertz em contato entre uma esfera/plano e um cilindro/plano /." Guaratinguetá, 2019. http://hdl.handle.net/11449/191208.
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Orientador: Fernando de Azevedo Silva<br>Banca: Edson Cocchieri Botelho<br>Banca: Antonio Carlos Ancelotti Filho<br>Resumo: Neste trabalho é apresentado um estudo analítico e numérico a respeito das tensões superficiais entre dois elementos. Quando uma força externa é aplicada a dois corpos em contato, verifica-se a existência de uma pequena deformação entre os elementos, causando um achatamento no plano de contato e criando uma zona de altas tensões de formato elíptico. Com a repetição cíclica destes carregamentos, pode ocorrer a perda progressiva de material superficial dos elementos envolvidos. De forma a investigar este fenômeno, esta dissertação realizou a análise detalhada de dois casos específicos encontrados na mecânica: o contato existente entra a esfera e a pista interna de um rolamento (contato esfera/plano), e o contato entre uma roda e um trilho ferroviário (contato cilindro/plano). Este estudo é essencial para a compreensão de como a aplicação de um carregamento externo pode influenciarna superfície de dois elementos. A análise foi realizada através de duas abordagens: uma analítica, através das equações oriundas da Teoria de Hertz, e outra numérica, através de programas computacionais de elementos finitos. Com os resultados verificados, foi feito uma série de gráficos que ilustram o comportamento das tensões ao longo dos eixos, além da análise da área afetada pela ação das tensões superficiais. Por fim, verificou-se a existência de tensões normais compressivas máximas encontradas no plano de contato entre os elementos, sendo a maior tensão localizada na direção do eixo de aplicação ... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: An analytical and numerical study regarding contact stresses between two elements is presented in this work. When an external force is applied to two bodies in contact, a small deformation between the elements appears, flattening the contact plane and creating high elliptical stresses. The cyclical repetition of these stresses can cause the progressive loss of surface material from the bodies. To verify this phenomenon, this work developed a detailed analysis of two specific cases found in many mechanical applications: the contact between a sphere and an inner ring of a bearing (sphere/plane contact) and the contact between a wheel and a rail track (cylinder/plane contact). This study is essential to the understanding of the influence in the surface of these two elements caused by an external load. The analysis was performed using two different approaches: one analytical, using Hertz equations, and one numerical, using computational simulations and finite element software. After the results were validated, a number of graphics were developed using the Hertz Equations for contact stresses to illustrate how the stresses behave along the axis, as well as the analysis of the area affected by the contact stresses. It was found that the maximum compressive stresses are located at the contact plane between the bodies, and the highest stress is found along the axis where the load was applied. When the depth is increased, all normal stresses tend to decrease until they became null. At... (Complete abstract click electronic access below)<br>Mestre
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Baig, Muhammad. "Extraction de composant de biomasse lignocellulosique oléagineuse en milieu eau et CO2 subcritique et fonctionnalisation enzymatique." Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20215/document.
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La thèse vise l'application du concept de bioraffinerie (extraction, fractionnement, séparation de composés à partir de biomasse avant transformation ultérieure), via le développement d'étapes de production destinées à être associées en un procédé continu. La complexité du solide nécessite une étape de prétraitement effectuée avec une technologie à faible impact environnemental et l'eau subcritique est déjà utilisée comme solvant d'extraction des produits naturels, en sus de leur hydrolyse. Ces travaux ont porté sur l'hydrolyse de polysaccharides (son de riz) et de triacylglycérols (TAG, huile de tournesol) choisis comme modèles. Les caractéristiques de l'eau subcritique (produit ionique, constante diélectrique) mise en œuvre en réacteurs à circulation construits dans ce but, ont permis l'hydrolyse quasi-totale de l'hémicellulose et des TAG. L'addition de CO2 et donc d'acide carbonique a eu un effet positif sur l'hydrolyse de l'hémicellulose. Les acides gras libres résultant de l'hydrolyse ont été estérifiés en ester éthyliques en présence d'une lipase en réacteur continu en milieu CO2 supercritique, avec un taux de synthèse de 95%. Les cinétiques des réactions ci-dessus d'hydrolyse et d'estérification ont été étudiées. La complexité des interactions entre les nombreux paramètres mis en jeu a conduit à appliquer des méthodes de plans d'expérience. Ces méthodes ont été validées avec succès avec les données expérimentales, montrant ainsi leur utilité dans le développement de procédés. La question importante de la solubilité des extractibles dans l'eau subcritique a été traitée et une méthode de prédiction mise au point et validée avec succès avec les données expérimentales. En conclusion, ce travail montre la possibilité d'appliquer le concept novateur de la Bioraffinerie Intégrée en réacteur continu avec des fluides sub- ou supercritique, contrairement à leur mise en œuvre actuelle en réacteur fermé, pour la production de composés commercialisables<br>This work addresses the integrated biorefining concept (extraction, fractionation, separation of compounds from biomass prior to further transformation) by developing discrete units with the ultimate objective of coupling them to enable a continuous flow configuration. Due to the complexity of solid, there is a need for a sustainable and environmentally friendly pre-treatment technology. Sub-critical water has been used as a solvent for extracting natural compounds in addition to hydrolysis. This work investigated the hydrolysis of carbohydrates (rice bran) and triacylglycerols (TAG; sunflower oil) chosen as models. The attribute of subcritical water (ion product and dielectric constant) in continuous flow reactors built for the purpose, allowed almost quantitative hydrolysis of hemicellulose and TAG. The effect of adding CO2 and therefore carbonic acid was positive on the hydrolysis of hemicellulose. Further, free fatty acids were transformed to ethyl esters using lipase within continuous flow super critical CO2 resulting in 95% yield. The hydrolysis and esterification reaction kinetics were studied. To address the complex interplay between multiple processing parameters response surface methodologies (RSM) were developed. Using the empirical data the models were successfully validated, therefore showing the utility of the RSM to assist process development. The important question of solubility of extractible in subcritical water was also addressed, through the development of a prediction method, validated with experimental data. In summary this work shows the possibility of applying the innovative Integrated Biorefining concept under continuous flow conditions -instead of the current application under batch conditions- for producing valuable compounds
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Guenther, Cristy Louise. "Evaluation of shear and diagonal tension in plain concrete." Laramie, Wyo. : University of Wyoming, 2007. http://proquest.umi.com/pqdweb?did=1400964851&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Diaz, Pulgar Luis Gerardo. "Lightning induced voltages in cables of power production centers." Thesis, Limoges, 2016. http://www.theses.fr/2016LIMO0093/document.
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Lorsqu’un bâtiment d’un centre de production d’électricité est frappé par la foudre, il se produit une dangereuse circulation de courants dans tous les composants connectés au bâtiment: les murs, le réseau de terre, et les câbles sortant du bâtiment. L’intérêt du présent travail est d’étudier les tensions transitoires aux extrémités de ces câbles, en particulier des câbles contrôle mesure, dans la mesure où ces câbles sont connectés à des équipements électroniques susceptibles d’être endommagés par des perturbations électromagnétiques engendrées par la foudre. Une approche basée sur la résolution numérique des équations de Maxwell via une méthode FDTD est adoptée. Notamment le formalisme de Holland et Simpson est utilisé pour modéliser toutes les structures constituées d’un réseau de fils minces: l’armature métallique du bâtiment, la grille en cuivre du réseau de terre, la galerie de béton et le câble coaxial de contrôle mesure. Une validation des modèles électromagnétiques développés pour chaque composant du site industriel est présentée. Une analyse de sensibilité est conduite pour déterminer l’influence des paramètres du système. En outre, la technique des plans d’expérience est utilisée pour générer un méta-modèle qui prédit la tension maximale induite aux extrémités du câble en fonction des paramètres les plus influents. Cela représentent un outil de calcul précis et informatiquement efficace pour évaluer la performance foudre des câbles de contrôle et de mesure<br>When lightning strikes a building in a Power Generation Center, dangerous currents propagates through all the components connected to the building structure: The walls, the grounding grid, and the cables leaving the building. It is the interest of this work to study the transient voltages at the terminations of these cables external to the building.Particularly, the Instrumentation and Measure (IM) cables, since they are connected to electronic equipment susceptible of damage or malfunctioning due to lightning ElectroMagnetic perturbations. A full wave approach based on the numerical solution of Maxwell’s equations through the FDTD algorithm is adopted. Notably, the formalism of Holland and Simpson is used to model all the structures composed of thin wires: the building steel structure, the grounding copper grid, the concrete cable ducts and the coaxial IM cables. A validation of the model developed for each component is presented. A sensitivity analysis is performed in order to the determine the main parameters that configure the problem. Also, the Design of Experiments (DoE) technique is used to generate a meta-model that predicts the peak induced voltages in the cable terminations, as a function of the main parameters that configure the industrial site. This represents an accurate, and computationally efficient tool to assess lightning performance of IM cables
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Gao, Sui. "In-plane stress analysis using tensor field photoelasticity." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/37059.
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Few experimental methods exist for evaluating all in-plane stress components in solid materials; because of the tensor nature of these quantities. Full field measurement of all three stress components is desirable, since plastic deformation or failure can result from any combination of the three. A new photoelastic stress measurement method is presented for evaluating all three in-plane stress components within a two-dimensional photoelastic material. The measurement method is based on the observation that the complex transmission factors that describe the optical phase changes due to stress-induced birefringence have a second order tensor character, similar to that of other tensor quantities such as stress and strain. The same transformation equations and Mohr’s circle construction can be applied to the rotation of optical axis. A Michelson type interferometer and phase shifting are used to quantify the phases of the complex transmission factors. Mohr’s circle calculation is applied to obtain the principal transmission factors and principal axis orientation. The principal stresses are then obtained from the principal transmission factors through the stresss optical relationship. The effectiveness of this technique is demonstrated by comparing the experimental and analytical results for a hollow circular ring under diametric compression.
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Almoughni, Hend Mohammed Aa. "Capillary flow of liquid water through plain knitted fabrics." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/capillary-flow-of-liquid-water-through-plain-knitted-fabrics(4cd71022-212f-4536-8a5f-532fcd0883d0).html.
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In extreme weather conditions and activity levels of human subjects evaporation of sweat is critical for maintaining the sensorial and thermal comfort. Fabrics, from which clothes worn next to the skin are made, play an important role in facilitating the transfer of body liquid perspiration away from the skin to the environment through the mechanisms of capillary flow and evaporation. This work is a theoretical and experimental investigation of water flow characteristics of plain knitted fabrics with relevance to their structure geometry and constituent fibre chemistry. Plain knitted fabrics were produced by systematically varying different production parameters including fibre type, fibre orientation, yarn folding, yarn twist, yarn linear density, and blend ratio. Cotton and polyester fibres were used. Some commercial fabrics were included in the study. The gravimetric absorbency test system (GATS) was adapted for testing the water areal flow and uptake rates through the fabrics. Yarns taken from the produced fabrics were also tested for horizontal linear flow of liquid water. A theoretical model to predict the capillary flow of liquid water through yarns was proposed. The model is based on the representation of the inter-fibre pores in terms of the hydraulic radius theory. It is established that the plain knitted fabric configuration as interlocking of loops plays an important role in facilitating the capillary flow of liquid water through the fabric. The yarn contact at the crossover points of the knitted loop enables a connected path for liquid flow which increases at higher contact pressure at the crossover points. If the contact pressure increases beyond a certain limit it starts to negatively affect the flow because the higher pressure reduces yarn porosity. When the number of yarns in contact with the liquid source per unit area of the fabric plane increases the capillary flow increases. Fabric compactness, which is controlled by yarn diameter and stitch length, is an important fabric parameter that determines these effects the fabric configuration have on the capillary flow. The experiments and the micro-structural analysis revealed that inter-fibre pores within the plain knitted fabric transfer the capillary driven liquid water through the structure at a faster rate. These pores hold the higher percentage of the fabric total air volume. It was also established that both fibre chemical nature and yarn fine structure geometry have critical effects on the apparent contact angle which is a critical factor controling capillary flow of liquid water. The smooth yarn surface made of filament polyester fibre gave a low apparent contact angle in contrast with the constituent filament which showed a high real contact angle. On the contrary, due to the more disorderly fibre arrangement on the yarn surface, yarns made of the staple polyester fibre showed a similar high contact angle to the constituent fibre. The experimental results of capillary flow of liquid water through yarns showed a strong correlation with the estimated results based on the theoretical model derived from the Kozeny-Carman equation. The model provides theoretical basis for understanding the effects of the geometric and material parameters on the capillary flow through the yarn. The model predicts that as the total fibre perimeter within the yarn cross section increases, or yarn porosity decreases, the velocity decreases, however, the eventual distance the water travels through the yarn increases.
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Hakoon, Sagy. "Material characterization of Li-ion battery segments subjected to lateral compression and an in-plane tension loads." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108925.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (page 40).<br>In the last two decades, Lithium-ion (Li-ion) batteries have become an inherent part of day-to-day life thanks to their widespread use in many consumer products and electric vehicles. While these batteries possess great advantages, they also carry an inherent safety liability: In case of a crash event, short-circuit failure of the battery may develop, leading to thermal runaway, fires and even explosions. Hence, a comprehensive study is required, aimed to modulate these batteries and optimize their testing standard. The objective of this research was to characterize the effect of lateral compression on the in-plane tensile failure load of Li-ion battery segments. A new experimental system was developed, which allows fine control of the compression load, and decouples the out-of-plain compression load and the in-plain tension load. Then, measurements were conducted with single-layer, 4-layers and 11-layers specimens, producing characterizing graphs of the tensile load versus displacement. For all types of specimens, results show an observable decrease in the failure load for increasing pre-compression load, as expected. Furthermore, measurements confirmed that the relation between the tensile load and the displacement does not change for different compression loads. For the multi-layer specimens (4 layers), the failure sequence was studied. It was found that the sequence may alter for different pre-compression loads. Nevertheless, on all cases, the cathode failed first, and the anode failed second. Throughout all experiments, failures were located on the edge of the compression area of the specimen. Several methods were used to encourage emergence of failure at the center, but with no success. A hypothesis to explain the development of this mode of failure is suggested at the end of this work.<br>by Sagy Hakoon.<br>S.M.
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Stuhlen, Birgit. "The mechanical design of turgid plant tissues." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312582.
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Torrens, Amanda E. "The Story of Storytellers: Navigating the Dialectical Tensions of a New Church." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1462208550.
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Marcadet, Stephane (Stephane Jean Marie). "Effect of non-linear loading paths on sheet metal fracture : large strain in-plane compression followed by uniaxial tension." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/70442.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 70-73).<br>Advanced high strength steel sheets are rapidly entering the transport industry, as their high strength to weight ratio helps improving fuel and costs efficiency. The early ductile fracture of these materials limits their formability and crash-worthiness. A phenomenological criterion to predict ductile fracture has been developed based on a law of damage accumulation weighted by the stress state. The calibration of such a model requires accurate measurements of the history of stress and strain state up to the onset of fracture. The phenomenon of localized necking occurs prior to ductile fracture in most types of loading of sheet metal. In order to measure the local state of stress and strain, a hybrid experimental and numerical method is tested. The Finite Element model can accurately predict the load displacement relation using a quadratic Hill 48 yield surface and an associated flow rule. The evolution of the local stresses and strains in the material are found to be non linear after necking. Results of such a method to calibrate the fracture criterion provide a validation of the model in a large range of loadings, including uniaxial, biaxial and shear. The effect of a reverse loading is then explored by developing an innovative experimental procedure to adapt the hybrid method for in plane compression followed by uniaxial tension of sheet metal. An Anti Buckling Device (ABD) and special grips are developed to delay buckling of the sheet. The hybrid method requires an accurate constitutive model of the material in the case of reverse loading for the Finite Element model. A modified Yoshida hardening called IH + LK + LNK combining isotropic hardening, linear and non linear kinematic hardening provides good prediction of the load displacement relation. An analysis of the history of local stresses and strains up to the onset of fracture suggests that limited damage is accumulated during the compression phase, validating the phenomenological model.<br>by Stephane Marcadet.<br>S.M.
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Hagman, Anton. "Influence of inhomogeneities on the tensile and compressive mechanical properties of paperboard." Doctoral thesis, KTH, Hållfasthetslära (Avd.), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-185917.
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The in-plane properties of paperboard have always been of interest to paper scientists. Tensile properties are crucial when the board is fed through converting machines at high speeds. Compressive properties are essential in the later use. Inhomogeneities affect both the compressive and tensile properties. For the tensile properties, it is the inherent heterogeneity of the paperboard that might cause problems for the board-maker. Varying material properties, through the thickness of the paperboard, are on the other hand used to achieve high bending stiffness with low fiber usage. It is of interest to know how this practice affects the local compressive properties. Papers A and B aims to address this, while C, D and E focus on in-plane heterogeneities. Paper A investigates the mechanism that causes failure in the short span compression test (SCT). It was concluded that the main mechanism for failure in SCT is delamination due to shear damage. In paper B the effect of the through-thickness profiles on the local compression strength was examined. It was concluded that the local compression is governed by in-plane stiffness and through thickness delamination. The latter was in turn dependent on the local shear strength and in-plane stiffness gradients. In paper C the tensile test is investigated with focus on sample size and strain distributions. The strain behavior was dependent on the length to width ratio of the sample and was caused by activation of local zones with high strainability. Paper D focuses on the strain zones seen in C. The thermal response in paper was studied. It was observed that an inhomogeneous deformation pattern arose in the paper samples during tensile testing. It was concluded that the heat patterns observed coincided with the deformation patterns. It could be shown that the formation was the cause of the inhomogeneous deformation. In final paper, E, the virtual field method was applied on data from C.<br>Egenskaperna hos ett kartongark kan grovt delas upp i två kategorier: i-planet egenskaper och ut-ur-planet egenskaper. I-planet egenskaperna har länge varit ett område som pappersmekanister och andra pappersforskare visat intresse för. Anledningen till detta är att de är avgörande för hur väl det går att konvertera kartongen till färdiga förpackningar, samt hur väl de förpackningarna klarar sin uppgift. Dragegenskaperna prövas när kartongen dras genom tryck- och konverteringsmaskiner i hög hastighet. Tryckegenskaperna spelar stor roll för hur väl en förpackning klarar att staplas och hålla sitt innehåll intakt. Inhomogeniteter påverkar både drag och tryckegenskaper. Papprets naturliga variation påverkar dragegenskaperna hos kartongen och kan orsaka problem för kartongmakarna. Särskilt när utvecklingen går mot mer avancerade kartong utseenden. Å andra sidan så använder sig kartongmakare flitigt av egenskapsvariationer genom tjockleken på kartongen, när dom vill åstadkomma böjstyva kartonger utan att slösa med fibrer. I detta fall är det intressant att veta hur de lokala kompressionsegenskaperna påverkas av kartongens ut-ur-planet profil. Det första två uppsatserna i denna avhandling, A och B, handlar om just detta. Uppsatserna C, D och E avhandlar hur i-planet variationer påverkar kartongens egenskaper. I Artikel A undersöks vilka skademekanismer som aktiveras under ett kortspannskompressionstest (SCT). Tre flerskiktskartonger undersöktes. De hade valts så att de hade distinkt olika skjuvstyrkeprofiler. Kartongerna karakteriserades och datan användes som materialdata i en finit element modell av SCT-testet. Modellen bestod av skikt, betraktade som kontinuum, mellan vilka det fanns kohesiva ytor. Huvudmekanismen i SCT var att kartongen delaminerade på grund av skjuvskador. Den andra uppsatsen, Artikel B, var en fortsättning på den första. Denna gång undersöktes fem flerskiktskartonger framtagna så att de hade olika skjuvstyrka beroende på positionen i tjockleksled. Det konstaterades att kompressionsegenskaperna lokalt styrs av skjuvstyrkeprofilen och styvhetsgradienter. Vidare konstaterades det att mekanismerna innan kartongen delaminerar är, i huvudsak, elastiska. Den tredje artikeln, Artikel C, fokuserade på hur dragprov på kartong påverkas av provstorleken och töjningsvariationen. Tre olika flerskiktskartonger användes som provmaterial och provbitar med olika storlek analyserades. Förutom dragprov så användes digital image correlation (DIC) för analysen. Det visade sig att den globala töjbarheten varierade med storleken på provet beroende på kvoten mellan längd och bredd. DIC visade att detta i sin tur berodde på att zoner med hög töjbarhet aktiverades i provet. Dessa zoner hade samma storlek oberoende av provstorlek och påverkade därför den totala töjbarheten olika mycket. Artikel D undersöker töjningszonerna som sågs i Artikel C samt hur de påverkas av kreppning. Vidare undersöktes pappersproverna med hjälp av termografi. Termografin visade att varma zoner uppstod i proven när det töjdes. Zonerna blev synliga när provet töjdes plastiskt. Termografi kördes parallellt med DIC på några prover. Det visade sig att de varma zonerna överenstämde med zoner med hög lokal töjning. Vidare kunde det visas att dessa zoner övenstämde med papperets mikrostruktur, formationen. En finit element analys av hur papper med olika formation töjs gjordes. Delar av provningen gjordes på kreppade papper som har högre töjbarhet. Det visades sig att någon form av skada hade överlagrats på papprets mikrostruktur under kreppningen, och att den deformationen återtogs när pappret töjdes. I den sista artikeln, Artikel E, behandlas hur VFM (Virtual Field Method) kan användas på DIC-data från kartong. DIC-datan som användes hämtades från Artikel C. Detta gjordes för att visa på hur olika VFM-formuleringar kan användas för att karakterisera styvhetsvariationen hos kartong. Provet delades upp i tre subregioner baserat på den axiella töjningsgraden. VFM-analysen visade att dessa subregioners styvhet och tvärkontraktionstal sjönk monotont, men att skillnaden mellan regionerna ökade med ökande spänning. även om endast ett prov undersöktes, så indikerade resultaten att områden med hög styvhet endast förbättrar de mekaniska egenskaperna marginellt. Analysen visade också att även om subregionerna inte är sammanhängande, så har dom liknande mekaniska egenskaper.<br><p>QC 20160429</p>
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Teiga, André Filipe Silva. "Análise de tensões em tubos curvos sob flexão no plano de curvatura." Master's thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/2520.
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Mestrado em Engenharia Mecânica<br>Os tubos curvos representam elementos estruturais de uma vasta e enorme aplicação em quase todo o género de indústrias. Geralmente é uma função
extremamente complicada a obtenção do seu estado de tensão quando aplicados num sistema de tubagens.
Este trabalho teve como principal objectivo o conhecimento da distribuição axial de tensões, num tubo circular curvo a 90º, em torno da circunferência central. Para tal necessitou-se de um método prático e funcional que permitisse a medição de deformações axiais provenientes de carregamentos externos. De modo a confrontar valores obtidos através de ensaios práticos
efectuou-se a modelação num programa de elementos finitos, SolidWorks. Após o estudo e desenvolvimento do artifício de medição, utilizou-se um tubo curvo, fabricado em aço AISI 304, disponibilizado pelo Departamento de Engenharia Mecânica da Universidade de Aveiro.
ABSTRACT: Curved pipes represent a type of structural elements of a vast and enormous application in almost all fields of industries. It is complicated obtaining their stress state when inserted in a pipe system.
This work has as main objective the development of a practical and functional method that allows the measurement of longitudinal deformations resulting of external loads in tubes of circular section. For confrontation of the strain values obtained by an experimental practical method, a numerical modeling with finite element techniques was performed. The obtained results were graphically
processed with SoliWorks so that a better visualization of the deformed structures could be observed.
In addition to this resume about procedures followed, it is reported that the experimental step of the work consisted in the in-plane bending of a curved pipe made with AISI 304 stainless steel with rigid endflanges, having applied a transverse force at one end. Results were then used to be compared with the finite element modeling.
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Faria, Alex de Mello. "Estudo sobre métodos para cálculo da amplitude de tensão cisalhante em modelos de plano crítico." reponame:Repositório Institucional da UnB, 2018. http://repositorio.unb.br/handle/10482/32079.
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Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2018.<br>Submitted by Robson Amaral (robsonamaral@bce.unb.br) on 2018-05-09T20:13:33Z
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Previous issue date: 2018-06-07<br>A presente dissertação avalia três métodos para cálculo da amplitude de tensão cisalhante equivalente utilizada em modelos de fadiga multiaxial baseados na abordagem do plano crítico. Avaliou-se o Método da Mínima Circunferência Circunscrita (MCC), o Método da Caixa (MRH) e o Método do Momento de Inércia (MOI). Com os resultados desses métodos foram aplicados três critérios de fadiga multiaxial: o critério de Susmel e Lazzarin (2002), o critério de Findley (1956) e o critério de Matake (1977). O objetivo foi a avaliação de quais métodos aplicados aos critérios resultam em melhores estimativas de resistência à fadiga multiaxial. Para a validação da análise, foram utilizados dados disponíveis na literatura para espécimes fabricados em ligas de aço submetidos a carregamentos combinados de flexão e torção em iminência de falha por fadiga. Um Índice de Erro (IE), que fornece uma medida da distância entre a previsão dos modelos e os dados experimentais foi utilizado como medida da acurácia nesta análise. Conclui-se que, em um contexto geral, para os dados sob carregamentos síncronos em fase ou fora de fase, os melhores resultados foram obtidos pelo Método MRH aplicado conjuntamente com o modelo de Findley (1956) e, para os dados sob assíncronos, as melhores estimativas foram obtidas quando o MRH foi utilizado juntamente com o modelo de Susmel e Lazzarin (2002).<br>This thesis evaluate three different methods that calculate the equivalent shear stress amplitude using Multiaxial Fatigue models based on the Critical Plane approach. It was evaluated the Minimum Circumscribed Circle (MCC), the Maximum Rectangular Hull (MRH) and the Moment of Inertia (MOI). With the result of these methods on hands, it was applied three multiaxial fatigue criteria: Susmel and Lazzarin (2002), the Findley (1956) criteria and the Matake (1977) criteria. The aim of this was to evaluate which of these methods applied in these criteria result in the closest estimated of multiaxial fatigue resistance. In order to validate the analysis, it was used available data base to different types of steel loaded to combined torsion and bending at the limit of fatigue failure. In this way, a percentual error index was used to measure how distant the prediction of the criteria was to the empirical result. Therefore, it was showed that the best results were obtained by using the MRH method when applied to the Findley criteria for synchronous loadings and, for asynchronous loadings, the same method using the Susmel and Lazzarin (2002).
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Tomasino, Alfred P. "The effects of porosity on the out-of-plane tensile strength of laminated composites." Thesis, Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53192.
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The objective of this study was to investigate the out-of-plane tensile strength of graphite/epoxy laminates as a function of porosity. An experimental test program was designed to apply tension to the faces of circular graphite/epoxy specimens in a direction perpendicular to the laminate mid-plane. The specimens were removed from the webs of angle sections fabricated by Lockheed Georgia Company using (AS4/1806 and AS4/3501-6 graphite/epoxy material systems with a stacking sequence of (±45/90₂/ ±45/0₂)<sub>S</sub> or (±45/0₂/ +̅ 45/90₂)<sub>S</sub>. The specimen porosities were the result of four distinct processing methods: a baseline hand lay-up, low pressure cure-cycle, a solvent wipe of pre-preg to remove resin, and the addition of water between pre-pregs. The experimental results have shown a significant reduction in the out-of-plane tensile strength as a function of increasing void content.
The volume fraction of pores, pore geometry, size, and orientation were determined for a representative number of specimens by metallography and optical analysis methods. This data was combined with the out-of-plane tensile data and used in the theoretical model, prepared by Brown et al, to predict the out-of-plane strength as a function of porosity. The predicted strength values compared very well with the experimental data when the pores were found to be uniformly distributed throughout the laminate.<br>Master of Science
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Song, Xiao. "Identification of forming limits of sheet metals with an in-plane biaxial tensile test." Thesis, Rennes, INSA, 2018. http://www.theses.fr/2018ISAR0002/document.
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Les procédés de mise en forme des tôles minces sont largement utilisés dans l'industrie. L’utilisation optimale des alliages légers ou des aciers à haute résistance, propices à des économies d’énergie dans le domaine des transports, nécessite une connaissance approfondie de leurs limites de formabilité. Classiquement, la formabilité d’une tôle est caractérisée par l’apparition d’une striction localisée. Cependant, pour des chargements spécifiques (chemins de déformation complexes ...), la rupture caractérise la formabilité du matériau, la courbe limite de formage à rupture (CLFR) plutôt que celle à striction (CLFS) doit alors être considérée. Pour identifier la CLFS et la CLFR pour des chemins de déformation linéaires et non-linéaires, les méthodes conventionnelles requièrent différents dispositifs expérimentaux et différentes formes d'éprouvette pour atteindre une large gamme de chemins de déformation. L'essai de traction biaxiale, associé à une éprouvette cruciforme, est possible pour la réaliser. De plus, le changement de chemin est activé au cours de l’essai, sans déchargement. Le premier objectif de cette étude est de montrer que l'essai de traction biaxiale, associé à une forme unique d'éprouvette cruciforme, permet de tracer la CLFS et la CLFR pour plusieurs chemins de déformation, qu’ils soient linéaires ou non-linéaires. En premier lieu, des essais ont été réalisés sur des tôles d’alliage d’aluminium 5086 (épaisseur initiale de 4 mm) à partir d’une forme d’éprouvette déjà proposée au laboratoire. Une nouvelle forme d'éprouvette cruciforme a été proposée pour des tôles moins épaisses (2 mm), plus répandues. Cet éprouvette a été validée pour étudier la formabilité d’un acier dual phase DP600 pour plusieurs chemins de déformation. Le deuxième objectif est de discuter la validité de critères classiques de rupture ductile. Pour les deux matériaux, un critère a finalement été identifié pour prédire assez précisément les résultats expérimentaux<br>Sheet metal forming is very common in industry for producing various components. The optimal use of light alloys or high strength steels in transportation for energy economy, requires in-depth analysis of their formability. Usually, the formability of sheet metal is controlled by the onset of localized necking. However, under specific loadings (complex strain paths...), fracture characterizes the formability and the forming limit curve at fracture (FLCF) instead of the forming limit curve at necking (FLCN) should be considered. For identifying FLCN and FLCF under linear and non-linear strain paths, conventional methods require different experimental devices and geometrical specifications of specimen to cover a wide range of strain paths. However, using the in-plane biaxial tensile test with just one shape of cruciform is sufficient for that, even changes of strain path without unloading can be made during the test. The first objective of this study is to show that the in-plane biaxial tensile test with a single type of cruciform specimen permits to investigate the FLCN and FLCF of sheet metals under different linear and non-linear strain paths. Firstly, the forming limit strains at fracture of AA5086 sheet (t=4 mm) under linear and non-linear strain paths have been characterized, by testing an existed dedicated cruciform specimen. Thinner sheet metals are often used in industry, so a new shape of cruciform specimen with an original thickness of 2 mm was proposed. This specimen is successfully used to investigate the formability of DP600 sheet under linear and two types of non-linear strain paths. The second objective is to discuss the validity of commonly used ductile fracture criteria to predict the onset of fracture. Some ductile fracture criteria were used to produce numerical FLCFs for AA5086 and DP600 sheet. Finally, for the two tested materials, it is possible to find a criterion to predict the experimental FLCFs for either linear or non-linear strain paths
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CARMONA, João Victor Costa. "Análise e desempenho de tráfego triple play em redes PLC de baixa tensão." Universidade Federal do Pará, 2011. http://repositorio.ufpa.br/jspui/handle/2011/3025.
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Previous issue date: 2011-12<br>CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico<br>Este trabalho faz uma análise de desempenho de aplicações triple play através da tecnologia Power Line Communication, fazendo uma abordagem direcionada para qualidade de serviço e qualidade de experiência. Apresenta resultados obtidos em cenários residenciais onde o uso desta tecnologia como última milha mostra-se uma solução passível de implementação diante dos testes realizados com transmissões de chamadas VoIP, transmissões de vídeo em alta definição e dados. O conceito de rede doméstica, interligando todos os pontos de uma casa, vem representando um novo rumo na definição de um padrão global, no qual a transmissão de dados por meio da fiação
elétrica será uma das tecnologias empregadas e de maior destaque. Também será mostrado o desempenho das métricas avaliadas como jitter, largura de banda, perda de pacotes, PSNR, MOS, VQM, SSIM e suas correlações.<br>This work is a performance analysis of triple play applications using Power Line Communication technology, making a targeted approach to quality of service and quality of experience. Presents results obtained in residential settings where the use of this technology as a last mile solution proves capable of implementation before the tests with transmission of VoIP calls, streaming high definition video and data. The concept of home network, connecting all the points of a house, has represented a new direction in defining a global standard, in which the transmission of data via the electrical wiring will be one of the technologies employed and the spotlight. Also shown will be
evaluated performance metrics such as jitter, bandwidth, packet loss, PSNR, MOS, VQM, SSIM and their correlation.
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Li, Richard Ph D. Massachusetts Institute of Technology. "Hierarchical carbon fiber composites with radially aligned carbon nanotubes : preservation of in-plane tensile properties." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/85806.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2013.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 89-94).<br>Hierarchical carbon-nanotube (CNT)-based composites have significant potential to expand the performance and functionality of aerospace composite structures. Notably, circumferentially aligned CNT arrays have previously been grown on woven alumina filaments to form a "fuzzy fiber" reinforced plastic (FFRP) architecture with demonstrated improvements in inter- and intra-ply mechanical properties as well as multifunctional enhancement via tailorable electrical and thermal conductivities. However, thus far, the development of fuzzy carbon fiber reinforced plastics (fuzzy CFRP) with all-around enhanced mechanical properties has been elusive. In particular, prior work attaining growth of CNTs on carbon fibers (CF) have resulted in drastic reductions in fiber tensile strength (e.g., 55% loss), thereby compromising in-plane tensile properties of the resultant fuzzy CFRP. In this thesis, a novel method for high-yield growth of carbon nanotubes on carbon fiber is refined and implemented in the fabrication of unidirectional fuzzy CFRP plies with preserved tensile properties: Non-covalent functionalization of the CF surface coupled with a low temperature thermal chemical vapor deposition process enable high density catalyst adhesion and CNT growth below critical temperatures that would result in fiber strength loss. Successful scale-up to unidirectional fuzzy CFRP specimens with high (67%) and low (32%) CF volume fractions is presented. Testing results indicate that longitudinal elastic properties are retained for all fuzzy CFRP samples consistent with micromechanical analyses. Unexpectedly, the high fiber volume fraction fuzzy CFRP specimens show a 12% decrease in mean tensile strength that was hypothesized to be due to fiber damage introduced through transverse compression during processing of the fuzzy carbon fiber tows. As such, lower fiber volume fraction fuzzy CFRP specimens were subsequently tested and observed to retain strength. These advances pave the way for scale-up to fuzzy CFRP laminates with integrated multifunctionality and improved interlaminar performance without compromising in-plane mechanical properties critical to aerospace-grade composite materials.<br>by Richard Li.<br>S.M.
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Dolphyn, Bradley P. "Laminar cracking in post-tensioned concrete nuclear containment buildings." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55017.
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As a critical public safety-related structure, the long-term integrity of post-tensioned concrete containment buildings (PCCs) is necessary for continued operation of the reactors they house. In 2009, during preparations for a steam generator replacement, extensive subsurface laminar cracking was identified in a portion of the Crystal River 3 (CR3) PCC in Florida, and the plant was permanently shut down in 2013. This study investigates potential contributing factors to the identified cracking with particular focus on the effects of high early-age temperatures on the cracking risk of the concrete, on the development of the concrete properties, and on the late-age structural behavior of the concrete. Two planar, full-scale mock-ups of a portion of the CR3 PCC were constructed and instrumented with temperature and strain gauges to monitor the thermal and mechanical behavior during representative concrete curing and post-tensioning loading. Standard- and match-cured concrete specimens were tested for determination of the time- and temperature-dependent development of thermal and mechanical concrete properties, and hydration parameters were determined for the mock-up cement paste for modeling the heat generation in the concrete. These properties and parameters were utilized in 3D finite element analysis of the mock-ups in COMSOL Multiphysics and compared with experimental results. Non-destructive evaluation via shear wave tomography was conducted on the mock-ups to identify flaws and determine the effectiveness of the methods for identifying delaminations between post-tensioning ducts approximately 10 inches beneath the concrete surface. Though early-age thermal stresses were determined not to have caused cracking in the mock-ups, the high early-age concrete temperatures resulted in decreased late-age mechanical properties that were shown to contribute to greater concrete cracking risk when the mock-up was post-tensioned. Tensile stresses exceeding the tensile strength of the concrete were identified along the post-tensioning ducts when biaxial post-tensioning loads were applied in finite element analysis, but the stresses decreased rapidly with increased distance from the ducts. Through parametric modeling, increasing the tensile strength of the concrete was identified as an effective means of reducing the cracking risk in PCCs. Additionally, relationships between the mechanical properties for the standard- and match-cured specimens were identified that could enable prediction of in-place or match-cured concrete properties based only on the results of tests on fog-cured specimens.
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Friday, Brian Matthew. "VANISHING LOCAL SCALAR INVARIANTS ON GENERALIZED PLANE WAVE MANIFOLDS." CSUSB ScholarWorks, 2019. https://scholarworks.lib.csusb.edu/etd/884.
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Characterizing a manifold up to isometry is a challenging task. A manifold is a topological space. One may equip a manifold with a metric, and generally speaking, this metric determines how the manifold “looks". An example of this would be the unit sphere in R3. While we typically envision the standard metric on this sphere to give it its familiar shape, one could define a different metric on this set of points, distorting distances within this set to make it seem perhaps more ellipsoidal, something not isometric to the standard round sphere. In an effort to distinguish manifolds up to isometry, we wish to compute meaningful invariants. For example, the Riemann curvature tensor and its surrogates are examples of invariants one could construct. Since these objects are generally too complicated to compare and are not real valued, we construct scalar invariants from these objects instead. This thesis will explore these invariants and exhibit a special family of manifolds that are not flat on which all of these invariants vanish.
We will go on to properly define, and gives examples of, manifolds, metrics, tangent vector fields, and connections. We will show how to compute the Christoffel symbols that define the Levi-Civita connection, how to compute curvature, and how to raise and lower indices so that we can produce scalar invariants. In order to construct the curvature operator and curvature tensor, we use the miracle of pseudo-Riemannian geometry, i.e., the Levi-Civita connection, the unique torsion free and metric compatible connection on a manifold. Finally, we examine Generalized Plane Wave Manifolds, and show that all scalar invariants of Weyl type on these manifolds vanish, despite the fact that many of these manifolds are not flat.
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Čermáková, Klára. "Úprava závěsu bočních dveří osobního automobilu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-254288.
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This thesis introduces issues of passenger car side-door hinges. Practical part of this thesis deals with modifying the current low-cost side-door hinge for Edscha Automotive Kamenice s.r.o. First, material was chosen to decrease weight while maintaining the required mechanical properties. Then follows the detail design of the hinge model, which was created in the software program Catia. Heat and surface treatments are described. Both treatments ensures the hinge's final features. To verify the strength of the hinge, tensile and sag test was simulated in Ansys. Subsequently, record from the consultation of the hinge's manufacturability in series and the hinge’s cutting plans are provided. At the end of the thesis, the assembling procedure is suggested. Final part of the thesis compares the developed low-cost hinge against two similar side door hinges.
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Itocazu, Vitor Tatsuo. "Influência da tensão de substrato em transistores SOI de camada de silício ultrafina em estruturas planares (UTBB) e de nanofio (NW)." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-13072018-105203/.
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Esse trabalho tem como objetivo estudar o comportamento de transistores de camada de silício e óxido enterrado ultrafinos (UTBB SOI nMOSFET) e transistores de nanofios horizontais com porta ômega ? (?G NW SOI MOSFET) com ênfase na variação da tensão aplicada no substrato (VGB). As análises foram feitas através de medidas experimentais e simulações numéricas. Nos dispositivos UTBB SOI nMOSFET foram estudados dispositivos com e sem implantação de plano de terra (GP), de três diferentes tecnologias, e com diferentes comprimentos de canal. A partir do modelo analítico de tensão de limiar desenvolvido por Martino et al. foram definidos os valores de VGB. A tecnologia referência possui 6 nm de camada de silício (tSi) e no óxido de porta uma camada de 5 nm de SiO2. A segunda tecnologia tem um tSi maior (14 nm) em relação a referência e a terceira tecnologia tem no óxido de porta um material de alta constante dielétrica, HfSiO. Na tecnologia de referência, os dispositivos com GP mostraram melhores resultados para transcondutância na região de saturação (gmSAT) devido ao forte acoplamento eletrostático entre a região da porta e do substrato. Porém os dispositivos com GP apresentam uma maior influência do campo elétrico longitudinal do dreno no canal, assim os parâmetros condutância de saída (gD) e tensão Early (VEA) são degradados, consequentemente o ganho de tensão intrínseco (AV) também. Na tecnologia com tSi de 14 nm, a influência do acoplamento eletrostático entre porta e substrato é menor em relação a referência, devido à maior espessura de tSi. Como a penetração do campo elétrico do dreno é maior em dispositivos com GP, todos os parâmetros analógicos estudados são degradados em dispositivos com GP. A última tecnologia estudada, não apresenta grande variação nos resultados quando comparadodispositivos com e sem GP. O AV, por exemplo, tem uma variação entre 1% e 3% comparando os dispositivos com e sem GP. Foram feitas análises em dispositivos das três tecnologias com comprimento de canal de 70 nm, e todos os parâmetros degradaram com a diminuição do comprimento de canal, como esperado. O fato de ter um comprimento de canal menor faz com que a influência do campo elétrico longitudinal do dreno seja mais relevante, degradando assim todos os parâmetros analógicos nos dispositivos com GP. Nos dispositivos ?G NW SOI MOSFET foram feitas análises em dispositivos pMOS e nMOS com diferentes larguras de canal (WNW = 220 nm, 40 nm e 10 nm) para diferentes VGB. Através de simulações viu-se que dispositivos com largura de canal de 40 nm possuem uma condução de corrente pela segunda interface para polarizações muito altas (VGB = +20 V para nMOS e VGB -20 V para pMOS). Todavia essa condução de corrente na segunda interface ocorre ao mesmo tempo que na primeira interface, impossibilitando fazer a separação dos efeitos de cada interface.A medida que a polarização no substrato faz com que haja uma condução na segunda interface, todos os parâmetros degradam devido a essa condução parasitária. Dispositivos estreitos sofrem menor influência de VGB e, portanto, tem os parâmetros menos degradados, diferente dos dispositivos largos que tem uma grande influência de VGB no comportamento elétrico do transistor. Quando a polarização no substrato é feita a fim de que não haja condução na segunda interface, a variação da inclinação de sublimiar entre dispositivos com WNW = 220 nm e 10 nm é menor que 2 mV/déc. Porém a corrente de dreno de estado ligado do transistor (ION) apresenta melhores resultados em dispositivos largos chegando a 6 vezes maior para nMOS e 4 vezes maior para pMOS que em dispositivos estreitos. Os parâmetros analógicos sofrem pouca influência da variação de VGB. Os dispositivos estreitos (WNW = 10 nm) praticamente têm resultados constantes para gmSAT, VEA e AV. Já os dispositivos largos (WNW = 220 nm) possuem uma pequena degradação de gmSAT para os nMOS, o que degrada levemente o AV em cerca de 10 dB. A eficiência do transistor (gm/ID) apresentou grande variação com a variação de VGB, piorando-a a medida que a segunda interface ia do estado de não condução para o estado de condução. Porém analisando os dados para a tensão que não há condução na segunda interface observou-se que, em inversão forte, a eficiência do transistor apresentou uma variação de 1,1 V-1 entre dispositivos largos (WNW = 220 nm) e estreitos (WNW = 10 nm). Com o aumento do comprimento do canal, esse valor de variação tende a diminuir e dispositivos largos passam a ser uma alternativa válida para aplicação nessa região de operação.<br>This work aims to study the behavior of the ultrathin body and buried oxide SOI nMOSFET (UTBB SOI nMOSFET) and the horizontal ?-gate nanowire SOI MOSFET (?G NW SOI MOSFET) with the variation of the back gate bias (VGB). The analysis were made through experimental measures and numerical simulation. In the UTBB SOI nMOSFET devices, devices with and without ground plane (GP) implantation of three different technologies were studied. Based on analytical model developed by Martino et al. the values VGB were defined. The reference technology has silicon film thickness (tSi) of 6 nm and 5 nm of SiO2 in the front oxide. The second technology has a thicker tSi of 14 nm comparing to the reference and the third technology has a high-? material in the front oxide, HfSiO. In the reference technology, the devices with GP shows better result for transconductance on saturation region (gmSAT) due to the strong coupling between front gate and substrate. However, devices with GP have major influence of the drain electrical field penetration, then the output conductance (gD) and Early voltage (VEA) are degraded, consequently the intrinsic voltage gain (AV) as well. In the technology with tSi of 14 nm, the influence of the coupling between front gate and substrate is lower because of the thicker tSi. Once the drain electrical field penetration is higher in devices with GP, all analog parameters are degraded in devices with GP. The third technology, presents results very close between devices with and without GP. The AV has a variation from 1% to 3% comparing devices with and withoutGP. Devices with channel length of 70 nm were analyzed and all parameters degraded with the decrease of the channel length, as expected. Due to the shorter channel length, the influence of the drain electrical field penetration is more relevant, degrading all the analog parameters in devices with GP. In the ?G NW SOI MOSFET devices, the analysis were done in nMOS and pMOS devices with different channel width (WNW = 220 nm, 40 nm and 10 nm) for different VGB. By the simulations, devices with channel width of 40 nm have a conduction though the back interface for very high biases (+20 V for nMOS and -20 V for pMOS). However, this conduction occurs at the same time as in the front interface, so it is not possible to separate de effects of each interface. As the substrate bias voltage induces a back gate current, all the parameters are degraded due to this parasitic current. Narrow devices are less affected by VGB and thus its parameters are less degraded, different from wider devices, in which VGB has a greater influence on their behavior. When the back gate is biased in order to avoid the conduction in back interface, the subthreshold swing variation between devices with WNW = 220 nm and 10 nm is lower than 2 mV/déc. However, the on state current (ION) has better results in wide devices reaching 6 times bigger for nMOS and 4 times bigger for pMOS The analog parameterssuffer little influence of the back gate bias variation. The narrow devices (WNW = 10 nm) have practically constant results gmSAT, VEA and AV. On the other hand, wide devices (WNW = 220 nm) have a small degradation in the gmSAT for nMOS, which slightly degrades de AV. The transistor efficiency showed great variation with the back gate bias variation, worsening as the back interface went from non-conduction state to conduction state. However, when the back gate is biased avoiding the conduction in back interface, the transistor efficiency for strong inversion region has a small variation of 1,1 V-1 between wide (WNW = 220 nm) and narrow (WNW = 10 nm) devices. As the channel length increases, this value of variation tends to decrease and wide devices become a valid alternative for applications in this region of operation.
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Krämer, Thorsten. "Deposit characteristics, penetration and biological efficacy of selected agrochemicals as affected by surfactants and plant micromorphology." Göttingen Cuvillier, 2008. http://d-nb.info/992749697/04.
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Nguyen, Bao Quoc. "Internationalization at Jesuit Colleges and Universities in the United States: Tensions between the Jesuit Mission and Internationalization in Strategic Plans." Thesis, Boston College, 2018. http://hdl.handle.net/2345/bc-ir:107905.
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Thesis advisor: Johannes de Wit<br>While internationalization in higher education is widely documented, little research has been conducted on how internationalization efforts at the 28 Jesuit colleges and universities in the United States have been operated. Through three exploratory case studies at Boston College, Saint Louis University, and the University of San Francisco, administrators, faculty members, and students were interviewed to address questions of rationales, strategies, outcomes with respect to internationalization, in relation to the Jesuit mission. Information from institutional websites and Jesuit documents served to round out the analysis of global engagement at Jesuit higher education institutions in the United States. Informed by the literature, the study draws on data collected from the 24 semi-structured interviews including individual and focus groups of international and study-abroad students. The study employs the conceptual framework of three pillars of internationalization at home, abroad, and through partnerships, provided by De Wit, Howard, Egron-Polak, & Hunter (2015). The findings show the growth of Jesuit institutions in the United States in the number of their internationals students, more concentration on global curricula, more opportunities for study abroad, and promotion of international partnerships. However, the study illustrates that Jesuit colleges and universities in the United States are still more regional or national institutions and are involved in internationalization at a preliminary stage of the process with ad hoc and fragmented strategic plans. The thesis ends with recommendations for more global collaboration and frequent assessment among Jesuit entities in order to sustain their operation and continually pursue the international mission of their Jesuit tradition, for a more balanced approach between the business/reputation model and the mission model, for more faculty and international students support, and for more attention to international alumni<br>Thesis (PhD) — Boston College, 2018<br>Submitted to: Boston College. Lynch School of Education<br>Discipline: Educational Leadership and Higher Education
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Lopes, Laerte Venâncio. "Influência das propriedades plásticas na resistência à propagação de trinca sob "estado plano de tensão"." Instituto Tecnológico de Aeronáutica, 1988. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=1516.
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Face à importância do conhecimento da tenacidade à fratura dos materiais metálicos sob estado plano de tensão, este trabalho analisa a influência do comportamento plástico na força de resistência à propagação de trinca destes materiais, permitindo estimar a curva R através de propriedades plásticas obtidas com ensaio de tração simples. Este estudo é feito através do equacionamento da taxa de energia dissipada com deformação plástica durante crescimento estável da trinca, considerando que o comportamento plástico do material é representado pela expressão constitutiva de Swift. Visto que as propriedades plásticas assumem uma importência significativa nesta análise, é desenvolvido um método que determina computacionalmente, a partir dos dados obtidos com o ensaio de tração, o coeficiente resistência (A), o coeficiente de encruamento (n) e o encruamento inicial (e0). O parâmetro (e0) é introduzido neste estudo com o propósito de levar em consideração o efeito do estado mecânico-metalúrgico do material. Fica caracterizado que a força de resistência à propagação de trinca é dependente do parâmetro de crescimento estável (D), que representa a taxa de extensão da zona plástica que se desenvolve na vizinhança da extremidade da trinca, durante o estágio de crescimento estável. Fica caracterizado também que a previsão da curva R do material a partir do conhecimento das propriedades plásticas, depende da determinação da extensão da zona plástica do início da propagação, e de um fator de correção, que considera o efeito da espessura sobre a forma da região deformada plasticamente.
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Murta, Yvan Bovolenta. "Comportamento pós-crítico de um painel plano em cisalhamento uniforme." Instituto Tecnológico de Aeronáutica, 2006. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=3217.
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O perfeito entendimento do comportamento pós-crítico de placas sob cisalhamento é de interesse prático em diversos ramos da engenharia. A solução analítica das equações diferenciais que descrevem o problema é de difícil tratamento devido à presença de não linearidade geométrica. Tenta-se contornar as dificuldades por meio de procedimentos simplificados como o oferecido pela teoria do campo de tração diagonal, amplamente difundida no meio aeronáutico. Resultados dessa teoria são aqui comparados com a solução rigorosa da teoria de placas de Kirchhoff, sob as relações deformação-deslocamento de von Kármán, e com a solução numérica do modelo não-linear de elementos finitos.
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Kljuno, Elvedin. "Elastic Cable-Driven Bipedal Walking Robot: Design, Modeling, Dynamics and Controls." Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1354708727.
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Fields, Jeb Stuart. "Soilless Substrate Hydrology and Subsequent Impacts on Plant-Water Relations of Containerized Crops." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/74925.
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Freshwater is a finite resource that is rapidly becoming more scrutinized in agricultural consumption. Specialty crop producers, especially ornamental crop producers, must continually improve production sustainability, with regards to water resource management, in order to continue to stay economically viable. Soilless substrates were initially developed to have increased porosity and relatively low water holding capacity to ensure container crops would not remain overhydrated after irrigations or rain events. As a result, substrates were selected that are now considered to be in efficient in regards to water resource management. Therefore, to provide growers with additional means to improve production sustainability, soilless substrate hydrology needs be innovated to provide increased water availability while continuing to provide ample air filled porosity to ensure productive and efficient water interactions. Historically, soilless substrates have been characterized using "static" physical properties (i.e. maximum water holding capacity and minimum air-filled porosity). The research herein involves integrating dynamic soilless substrate hydraulic properties to understand how substrate hydrology can be manipulated to design sustainable substrates. This task involved adapting new technologies to analyze hydrological properties of peat and pine bark substrates by employing evaporative moisture characteristic measurements, which were originally designed for mineral soils, for soilless substrate analyses. Utilizing these evaporative measurements provide more accurate measures of substrate water potentials between -10 and -800 hPa than traditional pressure plate measurements. Soilless substrates were engineered, utilizing only three common substrate components [stabilized pine bark (Pinus taedea L.), Sphagnum peatmoss, and coconut coir fiber], via particle fractionation and fibrous additions. The engineering process yielded substrates with increased unsaturated hydraulic conductivity, pore connectivity, and more uniform pore size distributions. These substrates were tested in a greenhouse with irrigation systems designed to hold substrates at (-100 to -300 hPa) or approaching (-50 to -100 hPa) water potentials associated with drought stress. Substrate-water dynamics were monitored, as were plant morphology and drought stress indicators. It was determined that increased substrate unsaturated hydraulic conductivity within the production water potentials, allowed for increased crop growth, reduction in drought stress indicators, while producing marketable plants. Furthermore, individual plants were produced using as low as 5.3 L per plant. Increased production range substrate hydraulic conductivity was able to maintain necessary levels of air-filled porosity due to reduced irrigation volumes, while providing water for plants when needed. The substrates were able to conduct water from throughout the container volume to the plant roots for uptake when roots reduced substrate water potential. Furthermore, increased substrate hydraulic conductivity allowed plants within the substrate to continue absorbing water at much lower water potentials than those in unaltered (control) pine bark. Finally, HYDRUS models were utilized to simulate water flux through containerized substrates. These models allowed for better understanding of how individual hydraulic properties influence substrate water flux, and provided insight towards proportions of inaccessible pores, which do not maintain sufficient levels of available water. With the models, researchers will be able to simulate new substrates, and utilize model predictions to provide insight toward new substrates prior to implementing production tests. It has been determined, that increasing substrate hydraulic conductivity, which can be done with just commonly used components, water requirements for production can be reduced, to produce crops with minimal wasted water resources. Concluding, that re-engineering substrate hydrology can ameliorate production sustainability and decrease environmental impact.<br>Ph. D.
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El, Golli Rami Ben Salem. "Etude de stabilité et modélisation des détendeurs de gaz." Paris, ENMP, 2003. http://www.theses.fr/2003ENMP1210.
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Vasoya, Manishkumar Laxmanbhai. "Study on Tensile Failure of Highly Heterogeneous Brittle Materials." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066650.
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Le développement d’outils prédictifs qui relient l’échelle microscopique à l’échelle macroscopique dans le cadre de la rupture fragile est le défi majeur de cette thése. Dans le cas d’une fissure plane se propageant de façon quasistatique, en mode I, dans un matériau faiblement hétérogène et invariant dans la direction de propagation, on peut montrer à l’aide d’une approche perturbative utilisant les fonctions de poids, que le seuil de rupture de Griffith est toujours atteint en tout point du front et que par conséquent la ténacité effective est simplement égale à la moyenne des valeurs locales. Nous abordons ici le même problème mais avec des hétérogénéités de ténaciteé plus élevées. Dans la première partie, nous considérons une fissure semi-infinie dans un corps infini ou dans une plaque d’épaisseur finie et nous étendons analytiquement l’approche du premier au second ordre. Nous montrons que, même si le critère de Griffith est atteint partout, les déformations du front peuvent induire une déviation de la ténacité efficace de sa valeur moyenne. Nous effectuoès de plus des expériences de peeling afin de préciser le domaine de validité des approches. Dans la deuxième partie, nous considérons une fissure circulaire se propageant dans un motif de ténacité axisymétrique et résolvons le problème numériquement, quelquesoit le contraste de ténacité et la taille des hétéogénéités, en itérant sur les formules du premier ordre. Pour un contraste d’hétérogénéité suffisamment grand, le critére de la Griffith ne peut plus être atteint partout: certains points du front sont piégés par les zones plus tenaces, tandis que d’autres parties avancent indéfiniment. De ce fait, la ténacité diminue avec la taille et le contraste, à partir de sa valeur moyenne locale jusqu à son minimum<br>The development of predictive tools that bridge microscopic to macroscopic scales in brittle fracture is the key challenge of this thesis. In the context of quasi-static planar crack propagation under mode I loading, it has been shown, using first-order weight-function perturbation approaches that, for weak heterogeneities, when the material is homogeneous in the propagation direction, the Griffith’s threshold is always reached for all points of the crack front so that the effective toughness is simply equal to the average of the local toughness. Here, we address the same problem but with stronger toughness heterogeneities. In the first part, we consider a half-plane crack embedded in an infinite body or in a finite thickness plate and we extend analytically the first-order approaches to the second-order. We show that even if Griffith’s criterion is reached all over the front, the deformations of the front may induce some second-order deviation of the effective toughness from its mean value. We also perform peeling experiments that define their range of applicability. In the second part, we consider a circular crack propagating in an axisymmetric toughness map and solved the problem numerically, for any toughness contrast and heterogeneity size, by iterating the first-order formulas. For large enough heterogeneity contrast, the Griffith’s criterion can no more be reached everywhere: some points of the front are pinned by strong impurities, while some other parts advances continuously. Correspondingly, the effective toughness is shown to decrease with size and strength of heterogeneity from the average value of the local toughness down to its minimum one
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Cezar, Vinicius Oiring de Castro. "Contribution au renvoi de tension et à la reconstitution du réseau. Estimation des flux rémanents dans un transformateur." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAT046/document.
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Lors de la réalimentation des auxiliaires d'une tranche nucléaire ou hydraulique, l'étape la plus à risque est la remise sous tension brusque du transformateur à cause des surtensions et courants d'appels générés. Ces phénomènes transitoires engendrent des effets très indésirables autant pour le réseau comme pour le transformateur (efforts électrodynamiques sous les bobinages, vibration du circuit magnétique, bruit et vieillissement prématuré du transformateur.) Le but de ces travaux de thèse est de proposer de nouvelles méthodologies permettant d'évaluer les paramètres mal connus (les valeurs des flux rémanents présents dans le circuit magnétique du transformateur avant sa mise sous tension). Face aux problèmes actuelles pour l'estimer (méthode non directe, dérive, imprécision de la mesure de la tension, etc.), deux nouvelles méthodes basées sur la magnétisation préalable du circuit magnétique (méthode de prefluxing) et sur la mesure des flux de fuites du circuit magnétique (méthode de mesure directe de flux par mesure de l’induction magnétique) sont proposées<br>During the re-energization of the auxiliaries of a nuclear or hydraulic power plant, the most dangerous step is the re-energization of the power transformer, because of the temporary overvoltage and inrush currents. These transients phenomenon causes undesirable effects for both network and for the power transformer (electrodynamic forces over the windings, the magnetic circuit’s vibration, noise and the premature aging of the transformer). The goal of these thesis is to suggest new methodologies allowing us to evaluate unknown parameters (the residual flux’s values in the magnetic circuit before transformer’s energization). According to the latest problems in order to evaluate it (no direct method, derivation, voltage measurement error, etc) two new methods based on the previous magnetization of the magnetic circuit (prefluxing method) and on the leakage flux measurement of the magnetic circuit (direct measurement of the flux by measuring the magnetic induction method) are proposed
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Tung, David C. "Welding Metallurgy of Nickel-Based Superalloys for Power Plant Construction." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1449164834.
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Real, Mauro de Vasconcellos. "Análise probabilística de estruturas de concreto armado, sob estado plano de tensão, através do método dos elementos finitos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2000. http://hdl.handle.net/10183/119135.
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O objetivo deste trabalho é apresentar um modelo para análise probabilística de estruturas de concreto armado, sob estado plano de tensão, através do método dos elementos finitos. O modelo permite mostrar como as incertezas presentes nos principais parâmetros do comportamento de vigas e pilares afetam a variabilidade da resposta destas estruturas. Inicialmente é desenvolvida, através do Princípio dos Trabalhos Virtuais, uma formulação para análise não-linear física e geométrica de estruturas, submetidas a um estado plano de tensão, utilizando-se a formulação Lagrangeana Total. É apresentado um modelo para análise não-linear de estruturas de concreto através do método dos elementos finitos. O concreto é modelado através de elementos isoparamétricos bidimensionais, quadráticos, de oito nós, com dois graus de liberdade por nó. A armadura é representada através do modelo incorporado. Para resolver o sistema de equações não-lineares resultante, emprega-se o método BFGS, com o uso de “line-searches”. O modelo constitutivo bidimensional para o concreto é baseado naquele proposto por DARWIN, empregando-se o conceito de deformação uniaxial equivalente e o critério de ruptura bidimensional de KUPFER e GERSTLE. Após a fissuração, o modelo inclui o efeito de tension-stiffening e a rigidez ao corte no plano da fissura. O aço é modelado como um material elasto-plástico perfeito ou com um endurecimento linear, após o escoamento. É feita a comprovação experimental do modelo de elementos finitos, comparando-se análises numéricas com os resultados de ensaios de vigas, de pilares, e de uma viga-parede. Para a análise probabilística de estruturas, através do método de Monte Carlo, as propriedades do concreto têm a sua variabilidade modelada através de um campo estocástico bidimensional, gerado através do método da representação espectral. As propriedades da armadura e as dimensões da estrutura são consideradas como variáveis aleatórias de distribuição normal. São realizados testes paramétricos para vigas e pilares de concreto armado. O efeito da variação dos parâmetros estatísticos do concreto, da armadura e da geometria na resposta da estrutura é verificado. Após a definição do índice de confiabilidade β, é feita uma análise probabilística de vigas e de pilares projetados de acordo com as prescrições da NBR-6118/1980. Estas estruturas têm o seu nível de segurança avaliado, para uma determinada distribuição de carregamento, tanto em relação aos Estados Limites de Serviço, como em relação aos Estados Limites Últimos.<br>The objective of this work is to present a model for probabilistic analysis of reinforced concrete structures, under a plane stress state, through the finite element method. This model allows to show how the uncertainties that appear in the main parameters of the behavior of beams and columns affect the variability of the mechanical response of these structures. Initially, it is developed, through the Principle of the Virtual Work, a formulation for physical and geometric nonlinear analysis of plane structures, submitted to a plane stress state, using the Total Lagrangean formulation. A model is presented for nonlinear analysis of concrete structures through the finite element method . The concrete is modeled through two-dimensional isoparametric quadratic elements, with two degrees of freedom per node. The reinforcement is represented through the embedded model. To solve the resultant nonlinear system of equations, the BFGS technique is used, with additional line-searches. The two-dimensional constitutive model for concrete is based on that proposed by DARWIN, using the concept of equivalent uniaxial strain and the two-dimensional failure criterion of KUPFER and GERSTLE. After the cracking of concrete, the model includes the tension-stiffening effect and the shear stiffness in the plane of the crack. The steel is modeled as a perfect elasto-plastic material or with a linear hardening after yielding. The experimental validation of the finite element model is made, comparing the numerical analysis with tests results of beams, columns, and a shear-wall. For the probabilistic analysis of structures, through Monte Carlo's method, the concrete properties have their variability modeled through a two-dimensional stochastic field, generated through the spectral representation method. Reinforcement properties and structure dimensions are considered as normal distribution random variables. Parametric tests are accomplished for beams and columns of reinforced concrete. The effect of the variation of the statistical parameters of concrete, steel and dimensions in the structure response is verified. After the definition of the reliability index β, a probabilistic analysis of beams and columns, designed in agreement with the prescriptions of NBR-6118/1980, is made. These structures have their level of safety evaluated for a fixed load distribution, for both Service and Ultimate Limit States.
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Harsan, Horea. "Analyse cyclique de sécurité : approche temps réel et intégration dans la gestion prévisionnelle." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0166.
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L'un des aspects important de la conception et de l'exploitation des grands réseaux de transport et d'interconnexion est le maintien de la sécurité du système. Cette sécurité concerne aussi bien les limites thermiques sur les ouvrages de transport que les limites de tension aux noeuds du réseau (contraintes d'isolation et de stabilité). A cet effet, le développement de méthodes nouvelles qui permettront à l'opérateur d'exploiter le réseau de façon à ce qu'aucun incident ne puisse causer les dépassements de limites de sécurité du système, est de plus en plus une nécessité. Cette thèse présente un algorithme général pour rendre plus efficace l'naisse de sécurité et donc permettre une analyse réellement systématique des incidents. Cet outil est basé sur l'utilisation des informations intrinsèquement contenues dans les résultats d'une analyse de sécurité systématique. Ces dernières peuvent être utilisées à des instants suivants en temps réel ou pour construire la carte des contraintes sur un horizon journalier. Une partie importante de cette thèse est consacrée à l'intégration de l'analyse de sécurité cyclique dans la réalisation du couplage production-réseau (introduction de la sécurité réseau dans la gestion prévisionnelle). Les résultats obtenus sur des données de planification issues du dispatching national montrent un gain de temps considérable acquit grâce à l'analyse cyclique. Elle se prête également bien aux analyses successives utilisées dans les optimisations du plan de tension en sécurité N et N-1. Un des chapitres de cette thèse traite l'analyse cyclique de sécurité en parallèle. La validation de la stratégie de parallélisation choisie a été faite sur un ordinateur parallèle CRAY
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Thornberg, Fredrik. "Lärares lärande om bedömning : En aktionsforskningsstudie om konsten att ta reda på vad elever kan." Thesis, Högskolan i Halmstad, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-15071.
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Studiens övergripande syfte är att kartlägga lärares syn på bedömningskompetens. En långsiktig intention är även att synliggöra lärares kompetensutvecklingsbehov inom bedömningsområdet. Processen vägleddes av en frågeställning gällande de kunskapsbehov som synliggörs i lärares diskussioner. Forskning har visat att elever lär sig det som de blir bedömda på vilket kan innebära att bedömningen snarare än styrdokument bestämmer vad och hur elever lär. Detta betyder att kunskap om bedömningsprocesser är viktigt och studien relaterar klassrumsbedömning till forskning samt politiskt genomförda reformer. Studien ämnar fylla det hål som Vetenskapsrådets kartläggning om svensk forskning om bedömning efterlyser; projekt i skärningspunkten mellan forskning, politik och praktik. Ansatsen är baserad på aktionsforskning som ett medel att frigöra kunskap inifrån. Studien utgick därför från ett skolutvecklingsprojekt med lärarnas autentiska frågor och deras vardagsarbete i centrum. Data som analyserades synliggjorde ett behov för lärarna av att reflektera över kunskapssyn samt olika bedömningsmetoder för att våga ge sig ut på den tunna is de beskrev som lärande. Med reflektionsprotokoll, fokusgruppsintervjuer och individuella intervjuer som grund visade resultet att lärarna ansåg sig behöva kunna: tolka och konkretisera, visa progression samt involvera eleverna. Vidare diskuteras resultatet i relation till tre olika spänningsfält som lärarna tvingades hantera för att betraktas som bedömningskompetenta.<br>The overall aim is to identify teachers' views of assessment skills. A long-term intention is also to draw attention to teachers' professional development needs within the assessment area. The process was guided by a question regarding the need for knowledge, which is made visible in the teachers' discussions. Research has shown that students learn what they are assessed on which may mean that the assessment rather than policy documents determines what and how students learn. This means that knowledge of assessment processes is important and the study relates classroom assessment to research and political reforms. The study intends to fill the gap the research council´s survey about Swedish research on assessment defines as; projects at the intersection between research, policy and practice. The approach is based on action research as a mean to free knowledge from within. The study therefore relates to a school development project where the teachers' authentic questions and everyday work was in focus. Data were analyzed and made visible a need for teachers to reflect on epistemological beliefs and different assessment methods in order to dare to venture out on the thin ice they described as learning. With reflection protocols, focus group interviews and individual interviews as a basis the results showed that teachers felt the need to be able to: interpret and concretize, show progression and involve students. The result is also discussed in relation to three tensions the teachers needed to manage in order to be considered as assessment literate.
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Dantas, Alberto Pinheiro. "Proposta alternativa para amplitude da tensão cisalhante e uso de algoritmos genéticos para determinação do plano crítico em fadiga multiaxial." reponame:Repositório Institucional da UnB, 2009. http://repositorio.unb.br/handle/10482/7766.
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Tese(doutorado)-Universidade de Brasília, Departamento de Engenharia Mecânica, 2009.<br>Submitted by Jaqueline Ferreira de Souza (jaquefs.braz@gmail.com) on 2011-05-14T00:55:37Z
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2009_AlbertoPinheiroDantas.pdf: 15007432 bytes, checksum: 000a9081d281fe643ad5224199c24aab (MD5)<br>Esta tese apresenta uma nova alternativa para calcular a amplitude da tensão cisalhante em critérios de fadiga multiaxial baseados na abordagem de plano crítico. Essa nova medida foi aplicada aos critérios de Findley e de Susmel & Lazzarin e os resultados comparados com dados experimentais sob carregamentos combinados disponíveis na literatura para condições limite de fadiga. Os resultados obtidos pela nova medida denominada de Máximo Retângulo Circunscrito (MRC) foram também comparados com os resultados obtidos pelo Método do Mínimo Círculo Circunscrito (MCC), mostrando que o MRC é mais eficiente e mais preciso que o MCC. Uma nova definição para o plano crítico foi proposta, pois observou-se que a definição clássica não possui unicidade e não considera explicitamente a influência da tensão normal máxima na localização do plano crítico. Aplicou-se algoritmos genéticos, um método de otimização, para reduzir o custo computacional tornando viável o uso de critérios de fadiga multiaxial baseados em abordagens plano críticos no âmbito da engenharia. _______________________________________________________________________________ ABSTRACT<br>The aim of this thesis is to propose a new alternative to compute the amplitude of the shear stress on critical plane based multiaxial fatigue approaches. This new measure was applied to Findley and Susmel & Lazzarin criteria and compared with 42 experimental data taken from the literature. The estimates provided by this measure, here on denominated the Maximum Circumscribed Rectangle (MCR) were also compared with results obtained by the celebrated Minimum Circumscribed Circle (MCC) method. Results showed that the MCR is more efficient and more accurate than the MCC to estimate multiaxial fatigue strength. A new definition of critical plane is presented as the classic one proved to be an ill posed problem and does not take in account the influence of the maximum normal stress on the critical plane localization. It was applied genetic algorithms, an optimization method, to reduce the computational cost associated with the material search process. The use of genetic algorithms turns feasible the use of multiaxial fatigue criteria based on critical plane approaches in the engineering framework, where real components are usually modeled by means of Finite Element Methods (FEM).
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Pinheiro, Paulo Arthur Batista. "Análise crítica de modelos de fadiga de plano crítico e proposta de uma nova medida de amplitude da tensão cisalhante." reponame:Repositório Institucional da UnB, 2012. http://repositorio.unb.br/handle/10482/11394.
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Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2012.<br>Submitted by Albânia Cézar de Melo (albania@bce.unb.br) on 2012-10-10T14:51:23Z
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2012_PauloArthurBatistaPinheiro.pdf: 1682565 bytes, checksum: cce207577a61fdfef055f163221c6f4a (MD5)<br>Embora existam inúmeros modelos de fadiga disponíveis na literatura, ainda são necessárias pesquisas para melhorar a capacidade de predição dos mesmos, sobretudo na presença de carregamentos multiaxiais não-proporcionais e tensões médias superpostas. O tempo de processamento de análises de fadiga baseadas em modelos de elementos finitos também é um aspecto que precisa ser aprimorado. O objetivo deste trabalho é propor uma nova medida de amplitude da tensão cisalhante para modelos de fadiga de plano crítico. Essa medida é calculada a partir dos lados de uma única envoltória
retangular associada à trajetória do vetor tensão cisalhante em um plano material. Essa definição é capaz de distinguir trajetórias proporcionais das não-proporcionais. Para avaliar a capacidade de predição da medida proposta, a mesma foi incorporada a um modelo modificado de Findley. A modificação consiste na introdução de um novo parâmetro que quantifica a sensibilidade do material à
presença de tensões médias. As predições do modelo foram comparadas com aproximadamente 350 limites de resistência à fadiga de diferentes metais, sob vários tipos de carregamentos multiaxiais (fora-de-fase, assíncrono e não-harmônico) e níveis de tensão média superposta. Os erros do modelo
ficaram dentro do intervalo (-39,9, 19,7)%. Verificou-se que a tensão de Mises era superior à tensão do escoamento em aproximadamente 15% dos ensaios. Quando esses ensaios foram excluídos da análise, os erros do modelo passaram a ficar dentro do intervalo (-18,2, 19,8)%. O custo computacional da nova medida é significativamente menor que o de outras propostas da literatura, e.g. Menor Circunferência Circunscrita (MCC), tornando viável a utilização de modelos de plano crítico em análises de fadiga baseadas no Método dos Elementos Finitos, mesmo quando a varredura dos planos materiais é realizada com incrementos de rotação pequenos. ______________________________________________________________________________ ABSTRACT<br>Although there are many fatigue models available in the literature, further research
is still needed to improve their accuracy, mainly in the presence of non-proportional
multiaxial loadings and superimposed mean stresses. The computational time of a
nite element-based fatigue analysis also needs to be reduced. The aim of this work is to propose a new measure of shear stress amplitude for critical plane based fatigue models. Such a measure is de ned by means of a unique rectangular hull enclosing the shear stress vector path, and is capable to distinguish a proportional from a non-proportional path. To assess the proposed measure, it was incorporated into
a modi ed Findley model. The modi cation consists in the introduction of a new pa-
rameter which quanti es the material sensitivity to mean stresses. Model's predictions were compared with approximately 350 fatigue limits, generated under di erent types of multiaxial loadings (out-of-phase, asynchronous and non-harmonic) and levels of superimposed mean stress. Errors were found to lie within the interval (-39,9, 19,7)%. An additional analysis was carried out, where tests having Mises equivalent stress greater than the yield stress were excluded. In this case, errors fell within the interval (-18,2, 19,8)%. The processing time to compute the proposed measure is signi can-
tly faster than the ones of others proposals available in the literature, e.g. Minimum
Circumscribed Circle (MCC). This feature allows nite element-based fatigue analyses
with critical plane models to be carried out with low computation e ort, even when
the critical plane search is performed with small rotation increments.
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Liu, Wei. "Identification of strainrate dependent hardening sensitivity of metallic sheets under in-plane biaxial loading." Thesis, Rennes, INSA, 2015. http://www.theses.fr/2015ISAR0005/document.
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Les procédés de mise en forme des tôles métalliques sont largement utilisés dans l’industrie mécanique. La simulation numérique des opérations de mise en forme nécessite une caractérisation précise des modèles de comportement rhéologique des matériaux. Dans de nombreuses opérations de mise en forme des tôles métalliques telle que l’emboutissage, l’hydroformage, …, de grandes déformations et des vitesses de déformations dites intermédiaires peuvent être atteintes sous des états biaxiaux de déformation ou de contrainte. L’objectif de ce travail est de montrer le potentiel de l’essai de traction bi-axiale pour caractériser l’écrouissage des tôles métalliques pour de grandes déformations et dans une gamme de vitesse de déformation dite intermédiaire. A partir de simulations numériques, une forme optimale d’éprouvette en croix, permettant d’atteindre 30% de déformation plastique équivalente dans la zone centrale de l’éprouvette sous un chargement équibiaxial, a été proposée. Par la suite, des essais quasi-statiques et dynamiques de traction bi-axiale ont été réalisés sur la forme d’éprouvette proposée à partir d’une machine dédiée d’essais servo-hydraulique à quatre vérins. Dans un premier temps, le matériau choisi est un alliage d’aluminium AA5086 ne présentant pas de dépendance à la vitesse de déformation. Les déformations expérimentales sont déterminées à partir de la technique de corrélation d’images. L’écrouissage isotrope de différents modèles est identifié à partir d’une procédure inverse basée sur une modélisation éléments finis de l’essai de traction biaxiale. Trois critères de plasticité (Mises, Hill 48 et Bron et Besson) ont été successivement utilisés pour l’identification des paramètres des lois d’écrouissage. Les résultats obtenus montrent d’une part que la modélisation est très sensible au critère de plasticité choisi, et d’autre part que le critère de Bron et Besson permet d’obtenir une très bonne corrélation entre les courbes d’écrouissage identifiées à partir de l’essai bi-axial et de l’essai uni-axial. Pour les tests dynamiques bi-axiaux, les phénomènes de résonance du dispositif mécanique, générés à l’impact initial de début d’essai et matérialisés par de fortes oscillations du signal d’effort, sont atténués par l’interposition d’un élément en élastomère dans le système d’ancrage de chaque bras de l’éprouvette. Pour finir, la méthodologie d’identification proposée est appliquée à la caractérisation du comportement viscoplastique d’un acier dual phase DP600. Les courbes d’écrouissage identifiées à partir des essais bi-axiaux ont été comparées à celles obtenues par des essais uni-axiaux pour une gamme de vitesse de déformation allant de 10- 3s-1 à 101s-1. Le DP600 présente une même sensibilité à la vitesse de déformation quelque soit la sollicitation, uni-axiale ou bi-axiale. Les lois d’écrouissage de Ludwick et de Voce, identifiées jusqu’à 30% de déformation plastique équivalente sur la base de données expérimentales constituées des essais bi-axiaux, sont relativement proches. Les différences observées entre ces courbes d’écrouissage et celles identifiées à partir des essais de traction uni-axiaux montrent tout l’intérêt de l’essai de traction bi-axiale sur éprouvette en croix<br>Sheet metal forming processes are widely adopted to produce panels, tubes, profiled parts in manufacturing industry. The numerical simulation of the forming processes requires accurate constitutive models of material. In many sheet metal working operations such as stamping, hydroforming, …, large strains and intermediate strain rates can be reached under biaxial strain or stress states. The objective of this work is to show the potential of the biaxial in-plane tensile test to characterize the hardening behaviour of metal sheets up to large strain levels. By numerical investigation, an optimal cruciform shape is designed to obtain large equivalent plastic strain, up to 30%, at the central zone under equi-biaxial strain path. As expected, the initial cracks of tested specimens are always observed at the central zone. Then, quasi-static and dynamic biaxial tensile tests on in-plane cross specimens have been performed on a dedicated servo-hydraulic machine. These biaxial tensile tests have been carried out on aluminium alloy AA5086 to validate the identification methodology of hardening behaviour under biaxial loading. This alloy has been chosen since its hardening behaviour is not dependent on the strain rate. Digital Image Correlation (DIC) technique is used for strain measurement. The parameters of isotropic hardening models are identified by inverse analysis based on the finite element model of the biaxial tensile test. Three yield criteria of Mises, Hill48 and Bron and Besson are compared for the parameter identification of different hardening laws. It is shown that the hardening law identified by biaxial test is precise only if an appropriate yield function is preliminarily determined. The biaxial flow stress curve identified with Bron and Besson yield function have been found in good agreement with the experimental flow stress curve obtained from uniaxial tensile tests. For biaxial tests at intermediate strain rates, damping layers are adopted to reduce oscillations on force versus time curves. The comparison of flow stress curves, identified from quasi-static and dynamic biaxial in-plane tensile tests on the non strain rate-dependent material AA5086, validates the identification methodology of strain-rate dependent hardening models. Finally, the proposed methodology is applied to the hardening characterization of a strain-rate dependent Dual Phase steel DP600 at room temperature. Identified biaxial flow stress curves have been compared with uniaxial ones for different strain rates ( . = 10-3s-1, 10-1s-1 and 101s-1). DP600 steel exhibits the same positive strain rate sensitivity for uniaxial and biaxial strain states. The biaxial flow stress curves identified on the basis of Ludwick and Voce hardening models are close, up to equivalent plastic strains of 30%. The benefits of the proposed methodology, based on a biaxial in-plane tensile test carried out on cross specimen, are clearly shown since the hardening behaviour identified in this case for large strains (up to 30%) is very different from the one identified from uniaxial tensile test on a smaller strain range
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Leidermark, Daniel. "Crystal plasticity and crack initiation in a single-crystal nickel-base superalloy : Modelling, evaluation and appliations." Doctoral thesis, Linköpings universitet, Hållfasthetslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-72093.
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In this dissertation the work done in the projects KME-410/502 will be presented.The overall objective in these projects is to evaluate and develop tools for designingagainst fatigue in single-crystal nickel-base superalloys in gas turbines. Experimentshave been done on single-crystal nickel-base superalloy specimens in order toinvestigate the mechanical and fatigue behaviour of the material. The constitutivebehaviour has been modelled and veried by FE-simulations of the experiments.Furthermore, the microstructural degradation during long-time ageing has been investigatedwith respect to the material's yield limit. The eect has been includedin the constitutive model by lowering the resulting yield limit. Moreover, the fatiguecrack initiation of a component has been analysed and modelled by using acritical plane approach in combination with a critical distance method. Finally, asan application, the derived single-crystal model was applied to all the individualgrains in a coarse grained specimen to predict the dispersion in fatigue crack initiationlife depending on random grain distributions. This thesis is divided into three parts. In the rst part the theoretical framework,based upon continuum mechanics, crystal plasticity, the critical plane approachand the critical distance method, is derived. This framework is then used in thesecond part, which consists of six included papers. Finally, in the third part, detailsof the used numerical procedures are presented.
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Panini, Rafael Luiz. "Velocidade das gotas geradas por pontas de jato plano de faixa ampliada em função da tensão superficial e da viscosidade da calda /." Botucatu, 2019. http://hdl.handle.net/11449/181319.
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Orientador: Ulisses Rocha Antuniassi<br>Banca: Kléber Pereira Lanças<br>Banca: Rone Batista de Oliveira<br>Resumo: O objetivo do presente trabalho foi determinar a velocidade das gotas geradas por uma ponta de jato plano de faixa ampliada (XR11003) em função de variações na tensão superficial e da viscosidade de caldas compostas por diluições de um surfactante e um óleo vegetal. Os adjuvantes utilizados foram o surfactante Agral e o óleo vegetal Natur'óleo, além de uma calda padrão (testemunha) composta apenas por água. Os ensaios foram conduzidos em delineamento inteiramente casualizado com 5 repetições. Para isso foram determinadas as viscosidades e tensão superficial para diferentes concentrações dos adjuvantes, bem como velocidade de gotas. As caldas pulverizadas foram amostradas em condições operacionais idênticas de pressão (2,8 bar), buscando a quantificação das velocidades de forma homogênea, em diferentes diâmetros de gota: 50, 100, 150, 200, 250, 300 e 350 µm. Os experimentos foram conduzidos para coleta na altura de pulverização de 30 cm em relação ao analisador de partículas em tempo real VisiSize Portable (Oxford Lasers Ltd / UK). Foram ajustados modelos para os dados de velocidade e tamanho de gotas, viscosidade e tensão superficial, assim como realizou-se a Análise de Variância para significância do modelo e o coeficiente de determinação múltipla. A análise de correlação foi empregada para verificar o efeito da viscosidade e tensão superficial sobre a velocidade de gotas. Os resultados mostraram que os modelos tridimensionais indicam a formação de gradiente ascendente da ve... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: The objective of the present work was to determine the velocity of the droplets generated by a wide band plane jet (XR11003) as a function of variations in surface tension and viscosity of syrups composed of dilutions of a surfactant and vegetable oil. The adjuvants used were the Agral surfactant and the Natur'óleo vegetable oil, besides a standard syringe (control) composed only of water. The trials were conducted in a completely randomized design with 5 replicates. For this, the viscosities and surface tension were determined for different concentrations of the adjuvants, as well as droplet velocity. The pulverized samples were sampled under identical operating pressure conditions (2.8 bar), aiming at the quantification of the homogeneous velocities in different drop diameters: 50, 100, 150, 200, 250, 300 and 350 μm. The experiments were conducted at the 30 cm spray height in relation to the VisiSize Portable (Oxford Lasers Ltd / UK) real-time particle analyzer. Models for the velocity and droplet size, viscosity and surface tension data were adjusted, as well as the Analysis of Variance for model significance and the multiple determination coefficient. Correlation analysis was used to verify the effect of viscosity and surface tension on the droplet velocity. The results showed that the three-dimensional models indicate the formation of an upward velocity gradient as a function of viscosity, that is, a trend of higher velocities was observed for higher viscosity values. The inverse occurred for surface tension (downward velocity gradient as a function of surface tension), that is, a trend of lower velocities was observed for higher values of surface tension. However, no significant correlations were observed between surface tension or viscosity and velocities for each droplet size (p> 0.05). It is concluded, therefore, that for the spray tip XR 11003 at a pressure of 2.8 bar, the droplet ...<br>Mestre
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Leidermark, Daniel. "Modelling of constitutive and fatigue behaviour of a single-crystal nickel-base superalloy." Licentiate thesis, Linköping University, Linköping University, Solid Mechanics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-56288.
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<p>In this licentiate thesis the work done in the project KME410 will be presented. The overall objective of this project is to evaluate and develop tools for designing against fatigue in single-crystal nickel-base superalloys in gas turbines. Experiments have been done on single-crystal nickel-base superalloy specimens in order to investigate the mechanical behaviour of the material. The constitutive behaviour has been modelled and verified by simulations of the experiments. Furthermore, the microstructural degradation during long-time ageing has been investigated with respect to the component’s yield limit. The effect has been included in the constitutive model by lowering the resulting yield limit. Finally, the fatigue crack initiation of a component has been analysed and modelled by using a critical plane approach.</p><p>This thesis is divided into three parts. In the first part the theoretical framework, based upon continuum mechanics, crystal plasticity and the critical plane approach, is derived. This framework is then used in the second part, which consists of three included papers. Finally, in the third part, details are presented of the used numerical procedures.</p>
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Douar, Adnane. "Recherche de matériaux isolants pour la conception d'une nouvelle génération de connecteurs électriques haute tension : influence de la pollution sur les phénomènes de décharges partielles du contournement et de claquage." Thesis, Ecully, Ecole centrale de Lyon, 2014. http://www.theses.fr/2014ECDL0046/document.
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Dans le présent travail, nous abordons une problématique essentielle liée aux accessoires des lignes électriques et plus particulièrement au connecteur à perforation d’isolant (TTDC 45501 FA), commercialisé par la société Sicame située à Arnac-Pompadour (Corrèze). Ce produit permet d’effectuer des dérivations de courant en moyenne tension gainé HTA entre 15 et 25kV. Cependant, il devient nécessaire de concevoir une nouvelle génération de connecteurs capable de fonctionner à une tension de 52 kV en raison de la constante augmentation des besoins en électricité. En réalité, le principal souci concernant ces produits réside dans l’apparition de décharges partielles dans le volume constitué par la matière isolante (polyamide 6 chargée à 50% en poids de fibres de verre). Ces décharges engendrent un vieillissement prématuré du produit sous l’action conjuguée d’une atmosphère corrosive (brouillard salin) et d’un champ électrique. Ainsi, l’objectif de la présente thèse est de faire, dans un premier temps, un choix approprié de matériaux isolants parmi des polymères thermoplastiques, thermodurcissables époxydes ou élastomères en EPDM, capables de résister à plusieurs contraintes : thermique, électrique, mécanique, chimique et climatique. La partie expérimentale concerne, tout d’abord, la mesure de la tension de contournement, de l’activité des décharges partielles se propageant à la surface des matériaux isolants et de la tension de claquage, en tension alternative (A.C.). Pour cela, des échantillons polymères qui comportent des surfaces planes ou des surfaces pourvues de protubérances ont été moulés en vue de comparer leur comportement diélectrique en présence d’atmosphères polluées de type brouillard salin; ces mesures sont nécessaires pour effectuer un choix approprié du matériau à intégrer dans le connecteur. Par la suite, l’étude et la caractérisation optique et électrique de décharges glissantes, se propageant en surface de divers matériaux polymères, en tension impulsionnelle (L.I.) pour les deux polarités (positive et négative) et pour deux types de champ électrique (normal et tangentiel) sont présentées pour le cas d’une interface solide/air. La mesure de la longueur finale des décharges glissantes et la visualisation de l’onde de courant sont les deux paramètres principaux pour différencier les caractéristiques des matériaux utilisés. L’ensemble des résultats de mesures a permis de sélectionner les résines époxydes cyclo-aliphatiques (CEP) comme candidates potentielles pour la conception d’une nouvelle génération de connecteurs. De plus, la simulation du champ électrique, à l’aide du logiciel Flux 2D/3D, sur le connecteur électrique (TTDC 45501FA) a permis d’aboutir à la proposition d’un prototype de connecteur présentant une nouvelle géométrie et pouvant fonctionner à 52kV<br>In the present study, we deal with an essential problem related to electrical lines accessories and more particularly to piercing connectors (TTDC 45501FA) commercialized by a private company named Sicame and which is located in Arnac-Pompadour (Corrèze, France). This product/accessory is designed to provide power diversions on medium voltage live lines HVA operating between 15 and 25kV. However, it becomes required to design a new generation of piercing connectors able to operate on 52kV live lines because of the electrical power demands that are steadily increasing. Actually, the main concerns about these products are the occurrence of partial discharges within the insulating material volume (polyamide 6 containing 50%wt of glass fibers). Most of the time, these discharges induce an early ageing process of the accessory under the combined effects of a corrosive environment (as salt fog) and an electric field threshold. Thus, the main objective of the present Ph.D. thesis is to carry out an appropriate choice of insulating materials among several tested polymers such as thermoplastics and thermosetting epoxy resins and EPDM elastomers that are capable of withstanding several constraints: thermal and electrical and mechanical and chemical conditions. The experimental section is focusing on the measurements of flashover voltage and partial discharges activity propagating on polymeric surfaces and breakdown voltage within material bulks under A.C voltage. That is why polymeric samples with plane surfaces and textured surfaces are molded to compare their resistance to partial discharges when being subjected to polluted environments such as salt fog; these measurements are necessary to choose the suitable materials for the required application to be integrated in the new generation of connectors. Then, the optical and electrical characterization results of creeping discharges propagating on several polymeric surfaces under lightning impulse (L.I.) voltage with its both polarities (positive and negative) and for two kinds of applied electric field (normal and tangential) are presented in the case of solid/air interfaces. Final length measurements of creepage discharges are the main parameter for distinguishing material properties. The whole obtained results (under AC and LI voltages) allow us to point out the cycloaliphatic epoxy resins as potential candidates to the conception of a new generation of piercing connectors. In addition, the electric field simulation and modelling of the TTDC 45501FA connector by using the Flux 2D/3D software seems to be helpful to design a connector prototype which exhibits a new geometry and is able to reach a voltage level that equals 52kV