Dissertations / Theses on the topic 'Young’s modulu'
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Holzer, Jakub. "Měření mechanických vlastností tenkých vrstev metodou bulge test." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-387730.
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Main objective of this diploma thesis is to finish a construction of the Bulge test apparatus for measurement of thin films, perform first tests on commercially available Si3N4 membranes and bilayer membrane with aluminium. First part of the thesis is focused mainly on literature review of current knowledge regarding this topic and other methods of thin films testing. Experimental part deals with construction of apparatus, methodology of data evaluation and results of the measurement. The thin films of interest are fabricated as amorphous silicon nitride or bilayer of mentioned nitride and either aluminium, titanium or Ta-B-C layer. The apparatus has been built in house in collaboration with Institute of Scientific Instruments of CAS. Both reliability and repeatability of this method has been tested on over 160 measurements of commercially available membrane. The results of measurements are compared with literature and nanoindentation test. More detailed data analysis is currently under development with colleagues at Institute of Physics of Materials. It has been proven beyond doubt that Bulge test method and constructed apparatus are suitable for the measurement of several mechanical properties of thin films.
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Valášek, Daniel. "Stanovení mechanických charakteristik povlaků impulsní excitační metodou." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-442844.
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This diploma thesis deals with the determination of the Young’s modulus of coatings using the impulse excitation technique (IET). The theoretical part of the thesis describes Cold and Thermal Spray technology, theoretical foundations of the impulse excitation technique and models of composite materials. The experimental part of the thesis deals with the determination of the tensile modulus of copper coating created by Cold Spray technology. The impulse excitation technique has been used to measure fifteen samples with coating thickness ranging approximately from 0,4 to 2 mm. Results from this measurement were evaluated using five composite models to establish the Young’s modulus of the applied coating. The best results were achieved by using the composite model based on rule of mixtures (ROM).
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POLITO, UMBERTO. "THE MENISCUS: BASIC SCIENCE TO IMPROVE KNOWLEDGE FOR TISSUE ENGINEERING." Doctoral thesis, Università degli Studi di Milano, 2020. http://hdl.handle.net/2434/707236.
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This thesis was thought with the intent to try to fill some lacunae in the knowledge of the anatomic-dependent features of the meniscus. In particular, the study of the effects of endogenous and exogenous factors upon the development of this structure will be outlined. Endogenous factors have been considered those factors that cannot be attributed to external or experimental factors: the effect of age and growth has been investigated focusing on the variation of the, matrix components (collagen types, GAGs and decorin), cellular phenotypic modifications and meniscal morpho-functional structure, with additional focus on possible differences presented in different animal models. On the other hand, exogenous factors have been considered those factors that are in any way attributable to the external interventions operated by the experimenter or by the application of forces upon meniscus. As exogenous factors, the effects of physiologic (compression and traction to which meniscus is naturally subjected) and non-physiologic (continuous compression without flexion) forces applied to meniscus during growth were evaluated. Furthermore, the effect of hypoxia in meniscal tissue-culture was also evaluated in a neonatal committed cell population in order to assess a faster maturation of the tissue. The importance of these investigations is linked to the possible application of these notions in the field of tissue engineering of the meniscus and may improve the current knowledge on the morpho-functional effect that external factors exercise on its structure.
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Fredriksson, Tore. "Carbon Nanotubes : A Theoretical study of Young's modulus." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-32351.
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Carbon nanotubes have extraordinary mechanical, electrical, thermal andoptical properties. They are harder than diamond yet exible, have betterelectrical conductor than copper, but can also be a semiconductor or evenan insulator. These ranges of properties of course make carbon nanotubeshighly interesting for many applications. Carbon nanotubes are already usedin products as hockey sticks and tennis rackets for improving strength and exibility. Soon there are mobile phones with exible screens made fromcarbon nanotubes. Also, car- and airplane bodies will probably be mademuch lighter and stronger, if carbon nanotubes are included in the construction.However, the real game changers are; nanoelectromechanical systems(NEMS) and computer processors based on graphene and carbon nanotubes.In this work, we study Young's modulus in the axial direction of carbonnanotubes. This has been done by performing density functional theorycalculations. The unit cell has been chosen as to accommodate for tubes ofdierent radii. This allows for modelling the eect of bending of the bondsbetween the carbon atoms in the carbon nanotubes of dierent radii. Theresults show that Young's modulus decreases as the radius decreases. Ineect, the Young's modulus declines from 1 to 0.8 TPa. This eect can beunderstood because the bending diminishes the pure sp^2 character of thebonds.These results are important and useful in construction, not only when usingcarbon nanotubes but also when using graphene. Our results point towardsa Young's modulus that is a material constant and, above a certain criticalvalue, only weakly dependent on the radius of the carbon nanotube.Graphene can be seen as a carbon nanotube with innite radius.
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Проценко, Олена Борисівна, Елена Борисовна Проценко, Olena Borysivna Protsenko, Вікторія Володимирівна Ємельяненко, Виктория Владимировна Емельяненко, and Viktoriia Volodymyrivna Yemelianenko. "The analysis of the elastic properties of armchair and zigzag single-walled carbon nanotubes." Thesis, Sumy State University, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20630.
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Computation simulation is a powerful tool for predictiong the mechanics models of elastic properties of armchair and zigzag single-walled nanotubes. The aim of this work is investigation and comparison of Young’s modulus, shear modulus and Poisson’s
ratio variations of armchair and zigzag tubes as functions of diameter. We obtained a set of concise, closed form expressions for the size-dependent elastic modulus, shear modulus and Poisson’s ratio of armchair (n, n) and zigzag (n, 0) nanotubes, which are basic for constructing mathematical models of elastic properties of SWNTs. We investigated armchair nanotubes with chirality (3, 3)–(40, 40) and zigzag (3, 0)–(40, 0) with diameters 4,2–54,2 Å and 2,4–31,3 Å respectively. We calculated Young’s modulus to be 0,26–2,95 TPa for armchair and 0,5–3,7 TPa for zigzag nanotubes. The shear modulus calculated for armchair nanotube appeared to be in the range of 0,2–2,0 TPa and for
zigzag one in the range of 0,2–2,7 TPa. Specifically, it was inverse dependences of Young’s modulus and shear modulus on diameter. The Poisson’s ratio was in range from 0,28 to 0,42 and from 0,27 to 0,39, respectively. Results of this research can be
used for design, analysis and evaluating of nanotubes unctioning and creating new materials based on CNTs.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20630
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CUPERTINO, LEANDRO FONTOURA. "MODELING YOUNGS MODULUS OF NANOCOMPOSITES THROUGH COMPUTATIONAL INTELLIGENCE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=15391@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
Materiais compósitos são a base de muitos produtos, devido à sua capacidade de aperfeiçoar certas propriedades. Recentemente, a utilização de nanocargas na fabricação de compósitos vem sendo amplamente estudada, pois a partir de concentrações baixas de nanocargas, as propriedades começam a melhorar, possibilitando a criação de materiais leves e com uma grande gama de propriedades. Uma das propriedades mecânicas mais estudadas é o módulo de Young, que mensura a rigidez de um material. Alguns dos modelos existentes para essa propriedade em nanocompósitos pecam na precisão ou são limitados em função da fração máxima de nanopartículas admissível no modelo. Outros se adequam apenas a uma determinada combina ção de matriz/carga preestabelecida. O objetivo deste trabalho é utilizar Redes Neurais Artificiais como um aproximador capaz de modelar tal propriedade para diversas matrizes/cargas, levando em consideração suas características, sem perder a precisão. A validação do aproximador é realizada comparando o resultado com outros modelos propostos na literatura. Uma vez validada, utiliza-se Algoritmos Genéticos em conjunto com tal rede para definir qual seria a configuração ideal para três casos de estudo: um que maximize o valor do módulo de Young, outro que maximize o módulo relativo e um terceiro que maximize o módulo relativo e minimize a quantidade de carga utilizada, diminuindo os custos de projeto. As técnicas de Inteligência Computacional empregadas na modelagem e síntese de materiais nanoestruturados se mostraram boas ferramentas, uma vez que geraram uma boa aproximação dos dados utilizados com erros inferiores a 5%, além de possibilitarem a determinação dos parâmetros de síntese de um material com o módulo de Young desejado.
Composite materials became very popular due to its improvements on certain properties achieved from the mixture of two different components. Recently, the use of nanofillers in the manufacture of composites has been widely studied due to the improvement of properties at low concentrations of nanofillers, enabling the creation of lightweight materials. Some of the existing models for the Young modulus of the nanocomposites have low accuracy or are limited in terms of the maximum filler fraction possible. Others are appropriate only for a given combination of matrix and filler. The objective of this work is to use Artificial Neural Networks as a function approximation method capable of modeling such property for various matrix/nanofillers, taking into account their characteristics, without losing accuracy. The validation of this approximator is performed comparing its results with other models proposed in the literature. Once validated, a Genetic Algorithm is used with the Neural Network to define which would be the ideal setting for three case studies: one that maximizes the value of composite’s Young’s modulus, other that maximizes the relative modulus and a third one that maximizes the relative modulus and minimizes the amount of load used, reducing the cost of project. Computational Intelligence techniques employed on the modeling and synthesis of nanostructured materials proved to be adequate tools, since it generated a good approximation of the data with errors lower than 5%, and determined the material’s parameters for synthesis with the desired Young’s modulus.
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Cheng, Kamyin. "Effective Young's Modulus of rigid particles in Gelatin composites." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59901.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 50).
In many biological systems, small rigid parts are embedded in deformable tissues to perform different biological functions. This study examines the effects of adding rigid filler particles inside deformable material. More specifically, a series of experiments led to eventual understanding of the relationship between effective Young's Modulus of material and volume fraction of rigid particles. The deformable material used in this study is gelatin, a readily available consumer product. It was found that the higher the volume fraction, the higher the Young's Modulus value for the composite material. In addition, it was found that cyclic loading with high strain and high volume fraction may cause stress stiffening or stress softening, while cyclic loading with small strain and small volume fraction yields linear elastic behavior. Furthermore, the effect of strain rate on material behavior was examined. Unfortunately the sample size was too small to draw definite conclusion. Finally, the reusability of particles was explored, and the results suggested that particles in composites are reusable so long as the composite did not undergo high strain compression.
by Kamyin Cheng.
S.B.
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Bodel, William. "The relationship between microstructure and Young's modulus of nuclear graphite." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/the-relationship-between-microstructure-and-youngs-modulus-of-nuclear-graphite(ac5fe868-cefb-4f0c-8b22-a8904bc97da5).html.
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In addition to its role as moderator within British nuclear reactors, polycrystalline graphite is also a major structural component of the core, enabling access for control rods, coolant gas and fuel. Aging processes, primarily fast neutron irradiation and radiolytic oxidation lead to distortion of the graphite components and property changes which ultimately reduce the material's effectiveness and can lead to component failure.Despite much research into the material, graphite behaviour under irradiation conditions is not fully understood and has resulted in an overestimation of the extent of component failures in Magnox reactors, and a subsequent underestimation of component failures in the following generation Advanced Gas-cooled Reactors (AGRs). A greater understanding of the material is therefore required in order to make more informed evaluations as part of on-going safety cases. Young's modulus is one property which varies as a complex function of radiolytic oxidation and fast neutron irradiation dose; this work investigates investigate the Young's modulus behaviour of nuclear grade graphites through property measurement and microstructural characterisation. Physical properties are dependent on microstructure, which is in turn a result of the manufacturing processes and raw materials used in its fabrication. Because of this, this thesis begins with a microstructural study of AGR graphite artefacts from varying points during the manufacturing process and post-irradiation, utilising X-ray diffraction to observe changes in crystallinity, microscopy to directly observe the microstructure and pycnometry to gauge porosity variations. Increases in crystallinity towards graphitisation are seen, with a subsequent decrease after irradiation; and significant changes are observed from inspection of optical and scanning electron micrographs. Young's modulus property data are obtained using a combination of static and dynamic techniques to accumulate data from a variety of techniques. An experiment designed to track changes to the speed of sound under compressive load was carried out on Magnox and AGR graphite, showing different behaviour between the grades, and variation with irradiation.A final series of tests combine compressive testing with in-situ microscopy to try and better understand the reasons behind this varied in behaviour and relate microstructural changes to graphite behaviour under compressive loading.
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Nortemann, Markus. "Characterisation of Young's modulus and loss factor of damping materials." Thesis, Nelson Mandela Metropolitan University, 2014. http://hdl.handle.net/10948/d1021036.
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Given the importance of simulation techniques in automotive engineering, there is a lack of implementation regarding these techniques in the acoustics of damping materials for air-borne sound. Biot’s calculations have proven its abilities to simulate the acoustic characteristics of these damping materials. However, the characterisation of essential structural parameters, such as Young’s modulus and loss factor, in order to conduct Biot’s calculations have been inconclusive. Thus, the primary research objective of this study is to propose a new measurement system for the structural Biot parameters. After a comprehensive literature review has been undertaken on damping materials, as well as measurement apparatuses for Young’s modulus and loss factor of damping materials, two causes of measurement errors have been identified. Unknown stresses in measurement apparatuses and inhomogeneous, polytrophic and viscoelastic behaviour of specimens. A new measurement system that does not affect the specimens with unknown stresses and accounts for their complex behaviour required investigation. Non-contact ultrasound had been selected as a solution to determine the aforementioned parameters, since these methods do not necessarily touch or compress the specimen, which led to unknown stresses and neglection of the complex specimen behaviour with the aforementioned techniques. Although ultrasound had been used to determine structural parameters on various types of materials, it has never been used to measure soft porous damping materials. In order to find possible solutions, various sources using ultrasonics to investigate struc- tural parameters had been reviewed. In order to calculate structural parameters, the longitudinal and transversal wave velocity inside the specimen had to be determined. The main findings showed that non-contact ultrasound will be able to evaluate the Young’s modulus, loss factor as well as Poisson’s ratio. Consequently, it was shown that longitudinal velocity measurements could be conducted using well known transmission measurements. However, well known approaches would not be sufficient measuring the transversal wave velocity in soft damping materials. This problem was addressed with a special gas to be used, with lower sound speed velocity in the fluid than in the solid. Moreso, a new method determining the transversal wave velocity had been found, as it would enable the use of an even larger range of damping materials, especially ones with heavy frames and lower porosity. It will use refracted waves inside the specimen and the determination of the convertion position of the transversal to the longitudinal wave at the rear specimen surface. At the end of the study, hardware components were selected and a test rig was constructed, which should be able to prove that a determination of structural Biot parameters with non-contact ultrasound is possible with less errors instead of using mechanical transfer function systems. The development of measurement software as well as the testing of the measurement system and its validation was not under investigation in this dissertation. This study has expanded on the body of literature knowledge regarding non-contact ultrasound. Furthermore, a significant contribution has been made towards a new measurement system measuring Young’s modulus and loss factor which circumvents errors in mechanical transfer function systems. This will contribute to more precise simulations of damping materials and damped enclosures, which may ultimately result in enhanced efficiency of damping materials as well as the acoustic packaging of cars.
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Sampaio, Leonardo Fernandes. "Estudo de primeiros princípios de nanofios de inas submetidos a tensões extremas." Universidade Federal de Santa Maria, 2015. http://repositorio.ufsm.br/handle/1/9249.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThe ability to manipulate materials at the atomic scale turn it possible to look for materials at the nanoscale that can supersede the performance of their bulk counterparts in specific tasks. Nanowires, due to their unique structural characteristics, are natural candidates for electric or heat conducting devices. When these nanowires take part of a circuit, they can subjected to an external stress that can change their intrinsic properties. In this work, we will be studying the mechanical and electronic behavior of narrow InAs nanowires, with different diameters, when subjected to extreme external stress. Our calculations use the Density Functional Theory, and the local density approximation to the exchange and correlation potential, as implemented in the VASP code. Our results reveal that the InAs nanowires exhibit a mechanical behavior which depends on the external stress and the nanowire diameter. For the narrowest diameter, it shows an elastic behavior followed by the rupture of the wire. As the nanowires turn thicker, different responses to the external stress take place. When the first chemical bonds are broken, the nanowire changes between elastic behaviors with different Young modulus. When more and more chemical bonds are broken (for the thicker nanowires), the nanowires show a plastic behavior, before the rupture. For each of these mechanical regimes, the electronic band structure of the nanowires is also analysed.
Nanofios, devido às suas caracteristícas estruturais únicas, são candidatos naturais para dispositivos condutores de eletricidade e calor. Quando estes nanofios formam parte de um dispositivo, podem estar sujeitos a tensões externas que podem alterar as suas propriedades intrínsecas. Neste trabalho estudaremos o comportamento mecânico e eletrônico de nanofios de InAs com diferentes diâmetros quando sujeitos a tensões externas extremas. Nossos cálculos usam a Teoria do Funcional da Densidade dentro da aproximação da densidade local para o funcional de exchange e correlação, como implementado no código computacional VASP. Nossos resultados revelam que os nanofios de InAs exibem um comportamento mecânico que depende da tensão externa e do diâmetro do nanofio. Para o nanofio mais estreito, observa-se um comportamento elástico da curva de tensão vs elongação ( stress vs strain ), seguido de ruptura do fio. Quando os nanofios tornam-se mais espessos, diferentes respostas às tensões extremas são observadas. Quando as primeiras ligações químicas são quebradas, os nanofios mudam de regime elástico para outro, com diferentes valores de módulo de Young. Quando mais e mais ligações químicas são quebradas, sempre do centro para as bordas, os nanofios apresentam um comportamento plástico antes da ruptura. Para cada um destes regimes mecânicos estrutura de bandas dos nanofios é também analisada.
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Stewart, Robert L. Stewart. "EFFECTS OF POROSITY AND TEMPERATURE ON THE MECHANICALPROPERTIES OF HOLEY GRAPHENE SHEETS." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1533046679055161.
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Ткач, Геннадій Федорович, Геннадий Федорович Ткач, Hennadii Fedorovych Tkach, Віталій Зіновійович Сікора, Виталий Зиновьевич Сикора, Vitalii Zinoviiovych Sikora, Андрій Миколайович Буштрук, Андрей Николаевич Буштрук, and Andrii Mykolaiovych Bushtruk. "Зміни величини модуля Юнга та жорсткості поперечного перетину стегнової кістки в динаміці репаративного остеогенезу." Thesis, Сумський державний університет, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42223.
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Модуль Юнга, або модуль пружності є інтегрованим показником, який відображає
якість кісткової тканини та має переважне значення для показників еластичності органу, тобто
залежить в першу чергу від якості органічної складової. Проте, колагенові волокна у кісткові
тканині знаходяться у тісному зв’язку з мінералом гідроксиапатиту, тому зміна
співвідношення або якості зазначених складових мають значний вплив на величену модуля
Юнга. Жорсткість поперечного перетину кістки відображає здатність кісткової тканини до
супротиву та має більшу залежність від якості мінеральної складової. Не зважаючи на велику
кількість досліджень змін даних показників в процесі росту кісток, їх динаміка в процесі
репаративної регенерації в залежності від віку тварин вивчена недостатньо.
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Rivera, Constantino Rigoberto. "Détermination des propriétés mécaniques des sables et des argiles en régime dynamique et cyclique aux faibles déformations." Châtenay-Malabry, Ecole centrale de Paris, 1988. http://www.theses.fr/1988ECAP0075.
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Étude dans le domaine des faibles déformations (10**(-5) pour les essais dynamiques, et 10**(-6) a 10**(-3) pour les cycliques), a travers trois paramètres principaux: module de Young, coefficient de poisson et coefficient d'amortissement. Rôle de la contrainte moyenne, indice des vides, saturation, histoire des contraintes. Pour argiles remaniées normalement consolidées, corrélation entre module de Young, limite liquide, indice de plasticité et coefficient de compressibilité. Comparaison entre régime dynamique et cyclique
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Bizet, Laurent. "Caractérisation et modélisation du comportement thermomécanique des matériaux métalliques : vers la prise en compte des hétérogénéités micro-structurales intrinsèques." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAA001/document.
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La prédiction de la géométrie d'une pièce mise en forme par déformation plastique grâce à un logiciel de calcul par éléments finis (EF) s'effectue en suivant séquentiellement différentes étapes : la caractérisation thermo-mécanique du matériau, la modélisation de son comportement et son intégration dans un logiciel EF, puis la mise en données et la simulation de l'opération de formage. La phase de modélisation consiste entre autre à identifier quel type de modèle de comportement est le plus approprié pour prédire les réactions du matériau lors de l'opération de formage. Ces modèles sont essentiellement développés dans le cadre de la mécanique des milieux continus (MMC). L'hypothèse forte, si ce n'est centrale, de la MMC consiste à considérer que les variables qui servent à déterminer le comportement du matériau sont continues et dérivables. Cependant, les connaissances les plus élémentaires de métallurgie indiquent que les grandeurs locales dans les matériaux métalliques sont discontinues. La majorité des modèles de comportement mécanique des matériaux métalliques repose sur la définition d'un volume élémentaire représentatif dont la taille est assez grande pour permettre une homogénéisation de la description du comportement en gommant l'influence des hétérogénéités localesL'objet de ces travaux est de montrer que la prise en compte des hétérogénéités locales dans la modélisation du comportement des matériaux métalliques est pertinente et contribue à l'amélioration de la prédiction des simulations d'opérations de mise en forme en élargissant le potentiel prédictif des modèles ainsi construits. Un modèle élasto-plastique prenant en compte les hétérogénéités locales est alors proposéTo obtain a relevant shape of a formed part during its finite element simulation, several steps are needed: thermo-mechanical caracterization of the material, definition of the most relevant model and integration of this model in the FE software and finally after data converting and computing processes. The modelling step include, among other things, the identification of the most appropriate model to fit the experimental material behaviour. Those models are essentially developped within the framework of continuum mechanics (CM). A strong, if not the main assumption of the CM consists in considering that mechanical description variables are continuous and differentiable. However, the basic knowledge of metallurgy indicates that local data in metallic materials are discontinuous. For metallic materials, the majority of constitutive models are based on the definition of a representative elementary volume (REV). This REV is supposed to be large enough to erase the incidence of local heterogeneities. Then those constitutive models are assumed to be homogeneous.The aim of this work is to show that introducing local heterogeneities in the description of constitutive models is relevant and contribute to improve the simulation accuracy. Those models also provide an enlargement of the simulation predictive potential. Then an elasto-plastic model, based on local heterogeneities description, is proposed
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Oh, Jung Joo. "Determination of Young's modulus of carbon nanotube using molecular dynamics (MDSS) simulation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FOh.pdf.
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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2003.Thesis advisor(s): Young W. Kwon, James H. Luscombe. Includes bibliographical references (p. 53-57). Also available online.
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Geyin, Mertcan. "Micro-Scale Characterization of Quartzitic and Carbonate Sand Grains Using Nanoindentation." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/81274.
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Many offshore energy infrastructures are built on carbonate sands which are skeletal remains of marine organisms. Carbonate sands have a porous grain structure and are more compressible compared to quartzitic sand grains which are abundant in alluvial depositional environments. Consequently, there is a stark difference in material behavior of carbonate sands and it is difficult to characterize this distinct behavior with conventional methods. This study focuses on micro-scale characterization of carbonate and quartzitic sands to overcome this challenge. Experimental studies consist of nanoindentation tests performed on 17 different sands; 7 quartzitic and 10 carbonate sand samples. Mechanical properties of individual sand grains with different mineralogies are determined using nanoindentation. A force is applied by the nanoindenter on the grain surface and the load-displacement curve is developed. Modulus and hardness of individual sand grains are evaluated. Nanoindentation test results show that modulus and hardness of carbonate sands are significantly lower than quartzitic sands. For quartzitic grains, mechanical properties are relatively independent of indentation depth; whereas, for carbonate grains there is a considerable decrease in both Young's modulus and hardness values with increasing indentation depth. Results from this study can further be used for the evaluation of compressibility and strength characteristics of these two types of sands as part of a multi-scale analysis framework.Master of Science
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Crocker, Janina. "Measurement of the Young's modulus of Hexoloy silicon carbide thin films using nanoindentation." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18414.
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Thin films of metals and ceramics are commonly used as the structural materials for microelectromechanical systems (MEMS). These systems are used for a wide range of applications that include sensors, displays, and portable power generators. Accurate measurement of the mechanical properties of these thin films is essential for the robust design of high-performance and reliable MEMS. In this thesis, the method of nanoindentation is used to characterize the elastic properties of thin films of Hexoloy-SG silicon carbide. This material is of particular interest for MEMS operating in harsh, hightemperature environments. Nanoindentation was performed using a commercial Hysitron TriboIndenter® equipped with a diamond Berkovich nanoindenter tip. During each nanoindentation test, the indenter was forced into the specimen by a calibrated load, while the indentation depth was recorded continuously with nanometer resolution. The first part of this thesis describes a detailed protocol for nanoindentation testing using the TriboIndenter® and discusses the calibration of the instrument using a quartz standard. The identification of errors due to drift, vibrations, and surface inhomogeneities is described in detail. This protocol was then used to test a 2.1 µm thick film of Hexoloy-SG silicon carbide film deposited on a 500 µm thick single-crystal silicon substrate. The film was tested with loads varying from 1,000 µN to 13,000 µN, such that the maximum indentation was always less than 10% of the film thickness. The nanoindentation load-displacement curves from a total of 155 individual indents were analyzed using three different methods to extract the value of the Young's modulus of the Hexoloy film. The first method, developed by Oliver and Pharr, is widely used in nanoindentation analysis, but does not account explicitly for the effects of the underlying substrate. It is valid strictly for monolithic materials. Therefore, refinements of the Oliver-Pharr method by King aDes structures formées de couches minces métalliques et céramiques sont couramment utilisées dans la conception de microsystèmes électromécaniques (MEMS). Ces derniers se retrouvent dans plusieurs domaines, tels que les capteurs, les vidéoprojecteurs et les systèmes de génération d'énergie portable. Pour concevoir des MEMS fiables, les propriétés mécaniques de ces couches minces doivent êtres connues précisément. Le but de cette thèse est d'utiliser la méthode de nanoindentation pour déterminer les propriétés mécaniques des couches minces de carbure de silicium Hexoloy-SG. Ce matériel à été développé pour des microsystèmes opérant dans des conditions thermiques et chimiques extrêmes. La nanoindentation a été réalisée par le système TriboIndenter® de Hysitron équipé d'une pointe Berkovich en diamant, de forme pyramidale à base triangulaire. Chaque indentation comprend un cycle charge/décharge durant lequel la pointe indentatrice est enfoncée et retirée du matériel par une force calibrée, tandis que la profondeur de l'indentation est surveillée continuellement au nanomètre près. La première partie de cette thèse décrit une procédure détaillée pour la nanoindentation avec le système TriboIndenter®, incluant la calibration de l'instrument utilisant une norme en quartz monolithique. Également, l'identification d'erreurs expérimentales reliées au système de nanoindentation dues à la dérive, aux vibrations et à la rugosité de l'échantillon et leurs mesures correctrices sont présentées. Par après, cette méthodologie a été utilisée pour tester les propriétés mécaniques d'une couche mince de Hexoloy-SG mesurant 2.1 µm d'épaisseur, déposée sur un substrat de silicium monocristallin comptant 500 µm d'épaisseur. La force exercée par l'indentateur sur l'échantillon varie de 1,000 µN à 11,000 µN, pour que la profondeur de l'indentation demeure en deçà de 10% de l'épaisseur totale de la co
18
Chan, Wing Kin. "Intrinsic and extrinsic effects on Young's modulus of nanowire measured in nanobridge tests /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MECH%202009%20CHANW.
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Bester, E. J. "Multidrug sedation for dental procedures in children younger than eight." Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_1512_1181913752.
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In this case study research project I have determined that multidrug sedation in children younger than eight years are possible.
Conscious sedation [or sedation where verbal contact with the patient is possible] can be used successfully to decrease anxiety and fear for unpleasant experiences, like dental procedures.
Behaviour therapy in conjunction with one or more drugs can be used to depress the central nervous system in order to decrease the patient&rsquo
s awareness of unpleasant stimuli. This enables treatment to be carried out without patient interference. Extensive literature surveys were done to determine the ideal drugs as well as the ideal route for conscious sedation in dental treatment for children. In this study project drugs like midazolam, propofol, alfentanyl and ketamine were titrated intravenously to achieve conscious sedation.
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Gemmiti, Christopher V. "Effect of Fluid Flow on Tissue-Engineered Cartilage in a Novel Bioreactor." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/13963.
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Due to its relative avascularity, low cellularity and lack of an undifferentiated cell reservoir, articular cartilage has a limited capacity for self-repair when damaged through trauma or disease. Articular cartilage impairment and the resultant reduced joint function affects millions of people at a substantial cost. In the U.S. alone, over 20 million adults are afflicted with osteoarthritis, costing more than $65 billion per year in health care and lost wages. Surgical techniques have been developed to address small, focal lesions, but more critical sized defects remain without a viable solution. Tissue engineering strategies produce cartilage-like constructs in vitro containing living cells in the hope of replacing damaged cartilage and restoring joint function. However, these constructs lack both sufficient integration into the surrounding tissue following implantation and the mechanical properties capable of withstanding the demanding and complex in vivo loading environment.
Our central hypothesis is that exposure of engineered cartilage to fluid-induced shear stress increases the collagen content and mechanical properties (tensile and compressive). The overall objective of this project is to modulate the matrix composition and mechanical properties of engineered cartilage to be more like native tissue using a novel bioreactor. Improving the matrix components and mechanical stability of the tissue to be more similar to that of native tissue may aid in integration into a defect in vivo.
The central hypothesis was proven in that shear stress potently altered the matrix composition, gene expression and mechanical properties of both thick and thin engineered cartilage. Modulation was found to be highly dependent on shear stress magnitude, duration, and waveform and affected different matrix constituents and mechanical properties in disparate ways. Our overall objective was satisfied on the basis that the bioreactor created stronger engineered tissues, but with the caveat that the tissues showed an increase in presence of type I collagen. Such an effect would be undesirable for articular cartilage engineered tissues, but could be very beneficial in fibrocartilaginous tissues such as that found in the temporomandibular joint. In conclusion, the novel bioreactor system provides a flexible platform technology for the study of three-dimensional engineered tissues, not just articular cartilage.
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Vautrot, Mathieu. "Étude du comportement mécanique des matériaux dans des conditions étendues de vitesses et de températures : application à l'acier C68 dans le cas d'une opération de formage incrémental." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00795973.
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L'objectif de ce travail de thèse est la caractérisation et la modélisation du comportement thermo-mécanique d'un acier à haut taux de carbone dans des conditions de chargement identiques à celles d'un procédé de formage incrémental à 720°C. Le regain d'intérêt des industriels pour ce type de procédé provient du fait qu'ils sont moins énergivores et permettent un ratio matière valorisée sur matière brute intéressant pour des propriétés mécaniques améliorées de la pièce formée. Le recours à l'outil numérique devient aujourd'hui une solution intéressante pour optimiser au mieux la mise au point du procédé. Son application demande, entre autres, une description fine du comportement du matériau dans les conditions de sollicitations de celui-ci, c'est-à-dire sur une large plage de vitesses de déformation et de températures. Pour cela, une caractérisation du matériau est nécessaire dans ces conditions. Le comportement mécanique d'un acier à haut taux de carbone a été étudié au travers d'essais de traction quasi-statiques et dynamiques afin de déterminer la sensibilité du matériau à la température et à la vitesse de déformation. Cette caractérisation repose sur la combinaison novatrice d'un système de chauffage par induction contrôlé par pyrométrie et d'un système d'acquisition d'images numériques. Ce dernier est utilisé pour la détermination des déformations à partir des champs de déplacement obtenus par corrélation d'images. En particulier, les effets de la température sur le module d'élasticité, l'anisotropie et l'écrouissage isotrope ont été étudiés. Les résultats de ces essais ont ensuite constitué une base de données expérimentales pour l'identification des paramètres de divers modèles de comportement thermo-élasto-visco-plastique. Ces derniers sont plus ou moins complets selon le nombre de paramètres utilisés pour décrire le comportement du matériau sur l'ensemble du domaine étudié. Cela permet d'identifier le modèle avec le meilleur ratio qualité/coût-délai pour une application donnée. Chacun des modèles étudiés dispose donc d'un domaine de définition propre.
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Ståhl, Martin. "Numerical modeling to complement wood tests." Thesis, Uppsala universitet, Tillämpad mekanik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-207269.
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Pressure tests on wood have been conducted to determine its properties. The resultswere not as expected, and it is therefore difficult to obtain the parameters of thewood. This project examines how a specific defect in the wood sample affects theresult.The pressure test is simulated with numerical modeling. In the numerical model thecube’s top side is non-parallel with the bottom side, it is in other words somewhattilted.The results from the model agreed with the findings from some pressure tests. Withthose we can easily calculate the wood's properties. For other pressure tests, otherfactors might need to be examined before we can draw any conclusions.Tryckprover på trä har utförts för att ta reda dess egenskaper. Resultaten blev intevad som förväntades, och det blir därför svårt att få fram träets egenskaper. Dettaprojekt undersöker hur en viss defekt i träprovet påverkar resultatet.Tryckprovet simuleras med numerisk modellering. I modellen är kubens toppsida inteparallell med bottensidan, den är med andra ord något sned.Resultatet från modellen stämde med resultat från vissa tryckprover. Då kan man fåfram träets egenskaper. För andra tryckprover kan andra faktorer behöva undersökasinnan man kan dra några slutsatser.
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Luyken, Lewis. "Using intercalation to simulate irradiation damage of nuclear graphite." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/using-intercalation-to-simulate-irradiation-damage-of-nuclear-graphite(85ce1ebb-2981-4807-8cf8-4aedc4acea97).html.
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This thesis investigates the use of bromine intercalation of graphite as a method to simulate and investigate irradiation damage. In particular this study investigates the effects of intercalation on dimensional change on the macro and micro scales and how these changes combine to affect Young’s modulus. Highly Orientated Pyrolytic Graphite has been used to gather data as a close approximation to single crystal graphite. Three different grades of polycrystalline nuclear graphite have been used to investigate the effect of different microstructure on intercalation and subsequent property changes. The graphites have been characterized by optical microscopy, pycnometry and x-ray powder diffraction and texture measurements. A number of bespoke rigs were designed and manufactured to carry out sorption, tomography and laser vibrometry experiments.The results indicate that the rate of dimensional change for polycrystalline graphites is significantly lower than for single crystal graphites. Modelling of dimensional change suggests that the difference in expansion is due to closure of porosity. Closer investigation of the dimensional change within the microstructure shows that the majority of the dimensional change is driven by expansion of filler particles.The young’s modulus results show an initial increase in modulus followed by a decrease, which corresponds with empirical evidence for irradiated samples. It is postulated that the initial increase in modulus is due to crystal expansion and that the subsequent decrease is due to crack growth. After experimentation some samples show significant cracking which would appear to support this assertion.
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Ali, S. "Dynamic effect of Young's modulus on attachment and differentiation of mouse embryonic stem cells." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1467252/.
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Embryonic stem cells have generated much interest due to their ability to differentiate into any cell type within the body. This ability could potentially allow for scientists and engineers to develop a number of therapies for diseases, which currently have no cure such as Parkinson’s disease, Alzheimer’s disease and diabetes. However, the differentiation process itself is one of the major bottlenecks in developing potential therapies. Currently protocols involve the use of mixtures of growth factors in order to create a suitable soluble microenvironment for differentiation. These growth factors are often expensive, thereby limiting the potential for scale-up of cell bioprocesses. Much interest has thus been generated into other elements of the microenvironment that could improve differentiation efficiency. The field of mechanobiology in particular, has developed rapidly in recent years. The aim of this thesis was to investigate the effect of Young’s modulus on neuronal differentiation of mouse embryonic stem cells (mESC’s). Instead of treating differentiation as one long process, the decision was made to split the process into three stages. The first, involved the formation of neural precursors from mESC’s. This was followed by the formation of immature neurons from neural precursors. The final stage was to allow the immature neurons to develop into a mature neuronal subtype. The impact of Young’s modulus was split into three effects. One was the initial attachment of cells. The second was the expansion of cells into colonies. The third was the effect of Young’s modulus on enrichment of neuronal cells. It was found that physiologically soft materials favoured the formation of all three neuronal cell types (precursor, immature and mature). However, the exact effect of differentiation varied over the course of differentiation. Over the first and second stages, soft substrates favoured the initial attachment of cells without affecting enrichment. Over the final stage, however, soft substrates directly favoured maturation of immature neurons, without having a significant effect upon their attachment. Thus the effect of Young’s modulus on neuronal differentiation changes according to the level of cellular maturity. There have not been any previous studies, which have tried to characterise the effect of the mechanical microenvironment on differentiation in a stage-by-stage manner. These findings have many important implications in terms of regenerative medicine bioprocessing. Firstly the optimal conditions for cellular attachment are not always the same as the optimal conditions for increasing cell enrichment. By carefully fine-tuning the mechanical properties at each stage of differentiation, both cell yields and final enrichment could be increased substantially. Furthermore, different cell types will require different optimisation strategies. Finally, by better understanding the interaction between cells and their mechanical environment, these findings could allow for better future design of tissue engineering biomaterials for implantation of cells into target areas for cell therapies.
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Ahmed, Tabassum. "Computing Wall Thickness and Young's Modulus of Carbon Nanotubes with Atomistic Molecular Dynamics Simulations." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/103647.
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Carbon nanotubes (CNTs) are tubular structure of a layer or layers of carbon atoms. CNTs serve as a prototypical nanomaterial holding great promises for various basic and applied research applications in the fields of electrical, thermal, and structural materials owing to their superlative mechanical, thermal, electrical, optical, and chemical properties. Since the discovery of CNTs by Iijima in 1991, numerous researches have been conducted to quantify and understand the atomic origin of their high strength, exceptional thermal conductivity, and unique electrical properties. CNTs are also widely used as nanofillers in composite materials to enhance their mechanical properties such as fracture toughness and to serve as sensing agents. There is thus an imperative need to deeply understand the physical properties of CNTs and their responses to various models of deformations such as stretching, bending, twisting, and combinations thereof. In this thesis, we apply all-atom molecular dynamics simulations to study in detail the behavior of several single-walled, armchair CNTs under stretching and bending deformations, realized by imposing appropriate boundary conditions on the CNTs. The simulation results reveal unique scaling properties of the stretching and bending stiffness with respect to the CNT radius and length, which indicate that a single-walled CNT is best modeled as a thin cylindrical shell with a cross-sectional radius equal to the CNT radius and a constant wall thickness much smaller than the CNT radius. By studying the thermal fluctuations of carbon atoms on the CNT wall, the wall thickness is determined to be about 0.45~AA~for all the single-walled CNTs studied in this thesis and correspondingly, Young's modulus is estimated to be about 8.78 TPa for these CNTs.Master of Science
Carbon atoms are magic building blocks of our world and the basis of life on the earth, and likely in the universe too. They can also form amazing materials with dimensionalities ranging from 0 to 3. For example, carbon atoms can form soccer-ball like spherical structures called fullerenes, with 0 dimensionality. They can also form 1-dimensional tubular structures with only one wall (i.e., one layer of carbon atoms) or multiple walls, called carbon nanotubes (CNTs) that have diameters typically in the nanometer range and lengths as long as 0.5 meter. Carbon atoms also form graphene sheets, which can be regarded as 2-dimensional structures, and 3-dimensional materials including graphite and diamond. In this work, we model CNTs using the molecular dynamics simulation method, where the motion of each atom is resolved and controlled if needed. Specifically, we study CNTs under stretching by fixing one end while pulling the other end in the axial direction, or bending by pulling the middle of a CNT along the radial direction in its cross-section while fixing its two ends. By fitting the simulation results to the continuum mechanics models, we show that a CNT is best described as a thin cylindrical shell with a radius equal to the CNT radius and a wall thickness much smaller than the radius. At the end, the wall thickness of all the CNTs studied here is determined to be about $0.45times 10^{-10}$ meter and their Young's modulus is estimated to be about $8.78times 10^{12}$ Pa, confirming that CNTs are one of the strongest and stiffest materials.
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Benjamin, Louis. "The development and evaluation of a metacognitive programme for young learners in the South African context." Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&.
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The Basic Concepts Mediated Learning Programme (BCMLP) was developed to enhance the cognitive and scholastic functioning of learners who experience barriers to learning in the early years of schooling in the South African context. The study aimed to initiate a process of evaluation of the efficacy of this metacognitive programme with Grade 2 learners from the &lsquoCape Flats&rsquo
, an historically disadvantaged community in Cape Town. The study was conducted simultaneously in two local education authorities by independent teams of fieldworkers in each of the education authorities. This quantitative, quasi-experimental, non-equivalent comparison group design study was implemented with learners who were equally assigned to an Experimental group (N=54) or Comparison group (N=55). English home-language and Bilingual (English and Afrikaans) learners made up a majority of the study sample. The study was conducted in English.
Extensive pre-test and post-test batteries consisting of cognitive (information-processing), cognitive modifiability (dynamic assessment), and scholastic tests were used to collect data. A number of structured interview schedules including post-intervention teacher rating scales were also used for the purpose of data gathering. The results from the parametric and non-parametric methods of data analysis selected, revealed a pattern of significant pre- to post-study cognitive and scholastic gains in scores for learners in both the Experimental and Comparison groups (p<
0.05). In addition, it was found that the study participants, irrespective of their designation to the Experimental or Comparison group became more modifiable and demonstrated enhanced information-processing abilities at the end of the study. Significantly greater gains were, however, attained by learners in the Experimental group in a majority of the areas assessed (7 out of 12) (p<
0.05). Learners in the Experimental group were also found to be more responsive to instruction and modifiable than learners in the Comparison group.
Learners who participated in the BCMLP were found to benefit with respect to their knowledge of basic concepts, cognitive and scholastic functioning. However, it was not possible to infer from the current study that findings were attributable to any one specific procedure (mediational teaching, concept teaching, vocabulary teaching and teaching to enhance information-processing) or process (Basic Concept Teaching Model) of this metacognitive programme. Furthermore, the study had a number of limitations and findings should be regarded with some caution until replication studies can be completed and the long-term effects of the study can be evaluated.
The study provides some evidence for the efficacy of short-term, small group intervention programmes implemented by Learning Support Teachers within disadvantaged communities. The study also provides some initial evidence for the efficacy of the BCMLP (a specially designed metacognitive programme). The BCMLP was found to be both appropriate and manageable for Learning Support Teachers to implement in the South African context.
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Garcia, Giseli Cristina Ribeiro. "Estudo do comportamento ao dano por choque térmico de um concreto refratário, contendo agregados de andaluzita, sinterizado em diferentes temperaturas." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-27092012-122818/.
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O conhecimento da resistência ao dano por choque térmico de materiais refratários é uma das características mais importantes para determinar seu desempenho em muitas aplicações, pois quando os refratários são submetidos a abruptas e severas variações de temperatura, estes podem sofrer danos. A resistência ao dano por choque térmico de um material pode variar com o tamanho de grão, com o tipo e valor da tensão, com a taxa de carregamento e com outras condições de aplicação da tensão, ou seja, não é uma propriedade intrínseca do material. Os métodos correntemente utilizados para prever o comportamento da resistência ao dano por choque térmico são baseados nos trabalhos de Hasselman, responsável pelo estudo da determinação dos parâmetros de resistência ao choque térmico, R (oC), o parâmetro de resistência ao dano por choque térmico R\'\'\'\' (m), e o parâmetro de estabilidade da trinca sob tensão térmica Rst (m1/2.oC). As equações previstas por ele levam em consideração o módulo de Young, o módulo de ruptura, a energia de fratura e o coeficiente de expansão térmica do material a ser analisado. A resistência ao dano por choque térmico pode ser avaliada por meio de ciclos térmicos, isto é, sucessivos testes de aquecimento e subseqüente resfriamento, com análise da queda do módulo de Young a cada ciclo. Para prever e avaliar a resistência ao dano por choque térmico, amostras de um concreto refratário comercial fornecido pela IBAR (Indústrias Brasileiras de Artigos Refratários), foram sinterizadas a 1000ºC e 1450ºC por cinco horas. Essas temperaturas foram definidas em virtude de o concreto em questão apresentar agregados de andaluzita, que sofrem mulitização após 1280ºC. Logo esse concreto exibe um comportamento distinto em função da temperatura de tratamento térmico, pois seu agregado pode se transformar em mulita e sílica. Para esse estudo, amostras prismáticas sinterizadas a 1000ºC e 1450ºC, foram submetidas a ciclos de choque térmico, permanecendo 20 minutos no forno com temperatura de 1000ºC e subseqüente resfriamento em água circulante a 25ºC. Também foram realizadas análises de porosidade aparente, de absorção de água, de massa específica aparente, de difração de raios X e microscopia eletrônica de varredura. Foi verificado que os parâmetros de Hasselman previram que o refratário sinterizado a 1450ºC apresentaria menor resistência ao choque térmico, previsão esta confirmada pelos testes experimentais. Sendo assim é importante avaliar o comportamento do concreto refratário desde a temperatura ambiente até a temperatura de trabalho, a fim de que se conheçam todas as mudanças envolvidas, e que sejam evitados problemas que possam gerar prejuízos na instalação industrial e ao processo pertinente à sua aplicação.The thermal shock resistance of refractory materials is one of the most important characteristics that determine their performance in many applications, since abrupt and drastic differences in temperature can damage them. A material1s thermal shock resistance may vary according to grain size, the type and intensity of the stress to which it is subjected, the loading rate, and other loading conditions; hence, this resistance is not an intrinsic property of the material. The method currently employed to predict thermal shock behavior is based on the work of Hasselman, whose studies involved the determination of the parameters of thermal shock resistance, R (ºC), thermal shock damage resistance, R\"\" (m), and thermal stress crack stability, Rst (m1/2.ºC). Hasselman\'s equations take into consideration Young\'s modulus, the modulus of rupture, the energy at fracture and the coefficient of thermal expansion of the material under analysis. Resistance to thermal shock damage can be evaluated based on thermal cycles, i.e., successive heating and cooling cycles followed by an analysis of the drop in Young\'s modulus occurring in each cycle. In the present study, samples of a commercial refractory produced by IBAR (Indústrias Brasileiras de Artigos Refratários) were sintered at 1000ºC and 1450ºC for 5 hours to predict and evaluate their thermal shock resistance. These temperatures were chosen because this refractory contains andalusite aggregates that become mullitized at temperatures above 1280ºC. Therefore, this castable displays a particular behavior as a function of the heat treatment temperature, since its aggregates can transform into mullite and silica. In this study, prismatic samples from each sintering temperature were subjected to thermal shock cycles, soaking in the furnace for 20 minutes at a temperature of 1000ºC, and subsequent cooling in circulating water at 25ºC. Apparent porosity, water absorption, apparent density, X-ray diffraction and scanning electron microscopy analyses were also performed. It was found that Hasselman\'s parameters predicted that the refractory sintered at 1450ºC would show lower thermal shock resistance than the refractory sintered at 1000ºC, a prediction that was confirmed by the results of the thermal shock tests. Hence, is important to evaluate the behavior of refractory castables from ambient temperature to working temperature in order to be aware of all the changes that occur, thus avoiding problems leading to losses in industrial installations and in the processes involved in the specific applications of these refractories.
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Bakenne, Adetokunboh. "Deformation and modulus changes of nuclear graphite due to hydrostatic pressure loading." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/deformation-and-modulus-changes-of-nuclear-graphite-due-to-hydrostatic-pressure-loading(aa6b8fd6-1c9f-4e71-b0dc-b5150b67223d).html.
Full textAbstract:
Graphite is used within a reactor as a moderator and a reflector material. During fast neutron irradiation, the physical properties and dimensions of nuclear graphite are changed significantly. Graphite shrinkage could lead to disengagement of individual component and loss of core geometry; differential shrinkage in the graphite component could lead to the generation of internal stresses and component failure by cracking. The latter behaviour is complicated by the irradiation induced changes in Young's modulus and strength. These dimensional and modulus change have been associated with the irradiation-induced closure of many thousands of micro-cracks associated with the graphite crystallites due to crystal dimensional change. Closure of microcracks in nuclear graphite was simulated by external pressure (hydrostatic loading, deviatory stress and dynamic loading) and not by irradiation, whilst Young's modulus was measured to check if there was any correlation between the two mechanisms. A study of the deformation behaviour of polycrystalline graphite hydrostatically loaded up to 200MPa are reported. Gilsocarbon specimens (isotropic) and Pile Grade A (PGA) specimens are (anisotropic in nature) were investigated. Strain measurements were made in the axial and circumferential directions of cylindrical samples by using strain gauges. Dynamic Young's modulus was also investigated from the propagation velocity of an ultrasonic wave. Porosity measurements are made to determine the change in the porosity before and after deformation and also their contribution towards the compression and dilatation of graphite under pressure. Graphite crystal orientation during loading was also investigated by using XRD (X-ray diffraction) pole figures. Effective medium models were also investigated to describe the effect of porosity on graphite elastic modulus. All the graphite specimens investigated exhibited non-linear pressure- volumetric strain behaviour in both direction (axial and circumferencial). In most of the experiments, the deformation was closing porosity despite new porosity being generated. Under hydrostatic loading, PGA graphite initially stiff then it became less stiff after a few percent of volume strain and then after about ~20% volumetric strain they stiffen up again, whist Gilsocarbon showed similar behaviour at lower volumetric strain (~10-13%). Gilsocarbon was stiff than PGA; this behaviour is due to the fact that Gilsocarbon has higher density and lower porosity than PGA. During unloading, a large hysteresis was formed. The stressed grains are relieved; the initial closed pores began to reopen. It is suggested that during this stage, the volume of pore re-opening superseded the volume of pores closing, the graphite sample volume almost fully recovered. In the axial compression test, PGA perpendicular to the extrusion direction (PGA-AG) was less stiff than PGA parallel to the extrusion direction (PGA-WG); in the hydrostatic compaction test, the PGA-WG sample deformed more because it had to undergo a less complicated shape change. This is because the symmetry of their anisotropy is parallel to the symmetry of the sample. The Pole figures showed an evidence of slight crystal reorientation after hydrostatic loaded up to 200MPa. The effective medium model revealed the importance of porosity interaction in graphite during loading.
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Brunetti, Carlotta. "Frequency-dependent response of snow in uniaxial compression and comparison with numerical simulation." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7820/.
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La determinazione del modulo di Young è fondamentale nello studio della propagazione di fratture prima del rilascio di una valanga e per lo sviluppo di affidabili modelli di stabilità della neve. Il confronto tra simulazioni numeriche del modulo di Young e i valori sperimentali mostra che questi ultimi sono tre ordini di grandezza inferiori a quelli simulati (Reuter et al. 2013). Lo scopo di questo lavoro è stimare il modulo di elasticità studiando la dipendenza dalla frequenza della risposta di diversi tipi di neve a bassa densità, 140-280 kg m-3. Ciò è stato fatto applicando una compressione dinamica uniassiale a -15°C nel range 1-250 Hz utilizzando il Young's modulus device (YMD), prototipo di cycling loading device progettato all'Istituto per lo studio della neve e delle valanghe (SLF). Una risposta viscoelastica della neve è stata identificata a tutte le frequenze considerate, la teoria della viscoelasticità è stata applicata assumendo valida l'ipotesi di risposta lineare della neve. Il valore dello storage modulus, E', a 100 Hz è stato identificato come ragionevolmente rappresentativo del modulo di Young di ciascun campione neve. Il comportamento viscoso è stato valutato considerando la loss tangent e la viscosità ricavata dai modelli di Voigt e Maxwell. Il passaggio da un comportamento più viscoso ad uno più elastico è stato trovato a 40 Hz (~1.1•10-2 s-1). Il maggior contributo alla dissipazione è nel range 1-10 Hz. Infine, le simulazioni numeriche del modulo di Young sono state ottenute nello stesso modo di Reuter et al.. La differenza tra le simulazioni ed i valori sperimentali di E' sono, al massimo, di un fattore 5; invece, in Reuter et al., era di 3 ordini di grandezza. Pertanto, i nostri valori sperimentali e numerici corrispondono meglio, indicando che il metodo qui utilizzato ha portato ad un miglioramento significativo.
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Oumarou, Noura. "La caractérisation mécanique de systèmes film-substrat par indentation instrumentée (nanoindentation) en géométrie sphère-plan." Thesis, Vandoeuvre-les-Nancy, INPL, 2009. http://www.theses.fr/2009INPL001N/document.
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L’indentation instrumentée (nanoindentation) est une technique d’analyse des données expérimentales utilisées pour atteindre les propriétés mécaniques de matériaux (dureté H, module de Young E) pour lesquels les techniques classiques sont difficilement applicables voire non envisageables. Ces paramètres mécaniques sont issus de l’exploitation de la seule courbe expérimentale charge-décharge. L’analyse de cette dernière repose sur des nombreux modèles reportés dans la littérature (Oliver et pharr, Field et Swain, Doener et Nix, Loubet et al.) qui considèrent la décharge purement élastique. De nombreuses expériences que nous avons menées, sur divers types de matériaux massifs (aciers inoxydables AISI304, AISI316, AISI430; aciers rapides HSS652; verre de silice SiO2) et revêtus de films minces de TiN et TiO2 ont montré que les propriétés mécaniques (E et H), déduites de la méthode de Oliver et Pharr, dépendent du pourcentage de la courbe de décharge considéré, de la charge appliquée et du rayon de la pointe. De plus, pour un système film-substrat, la technique est en général utilisée pour atteindre les propriétés in-situ du film ou du substrat, alors que la méthode de dépouillement fournit des paramètres composites qu’il faut ensuite déconvoluer. Dans la recherche d’une stratégie simple, permettant d’accéder au module élastique d’un film « dur » pour les applications mécaniques, nous avons fait appel à la simulation numérique. Le code de simulation numérique utilisé, est basé sur la méthode des éléments de frontière. Nos investigations numériques utilisant l’indentation sphérique nous ont permis de mettre en évidence un certain nombre de résultats utiles pour l’analyse des données expérimentales. Nous avons commencé par montrer que aussi bien pour un matériau massif homogène élastoplastique que pour un système film dur – substrat élastoplastique, la relation [delta]=a2/R demeure valable (R étant le rayon de l’indenteur, a le rayon de l’aire projetée de contact). Cela permet de représenter les résultats de l’essai d’indentation sphérique par la courbe pression moyenne F/[pi]a2- déformation a/R . Au début du chargement, la pente cette courbe est proportionnelle au module de Young du film tandis que la pente initiale de la courbe de décharge est proportionnelle au module d’élasticité du substrat. Une relation entre le déplacement de l’indenteur et [delta] , puis une méthode d’analyse d’indentation ont été établies. Enfin, la procédure a été validée numériquement et expérimentalement sur les données issues de l’indentation de divers combinaisons film-substrat (TiN/AISI430, TiN/HSS652 et TiO2/HSS652) avec succèsDepth sensing Indentation (nanoindentation) is an experimental technique increasing retained for the assessment of the mechanical properties of materials (hardness H, Young's modulus E) for which common homogeneous mechanical tests can not be performed or are extremely difficult to perform. The mechanical parameters are obtained from the indentation curve (the plot of the load vs penetration depth during both load and unload). Usually, some methodology reported in the literature (Oliver and pharr, Field and Swain, Doener and Nix, Loubet and al.) are used in order to assess E and H. We have performed a number of experiments on homogeneous materials (stainless steel AISI304, AISI316, AISI430; high-speed steel HSS652; glass SiO2) as well as a film-substrate system (TiN/AISI430, TiN/HSS652, TiO2/HSS652). Applying the Oliver and Pharr methodology, E end H vary with the applied load as well as the percentage of used unload curve retained for the analysis, as reported in the literature. Besides, in the case of the film-substrate system, only composite parameters are obtained instead of the in-situ films properties. In order to establish a simple strategy for the determination of the elastic modulus of a hard coating, we have carried out many simulations using a boundary element based numerical tool. Then a number of useful results have been identified. The well known elastic relation [delta]=a2/R between the relative approach [delta], the projected contact radius a and the punch radius R, remain valid in the plastic range for homogeneous as well as film-substrate specimens. This allows data indentation to be represented in term of mean pressure F/[pi]a2 vs indentation strain a/R . The initial slope of the loading part of the latter curve is proportional to the elastic modulus of the film, while the slope of the initial part of the unloading curve is proportional to the substrate elastic modulus. Our indentation procedure anlysis has been validated experimentally on a number of samples (TiN/AISI430, TiN/HSS652, TiO2/HSS652) after having established a relation between the punch displacement and the relative approach [delta]
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Farbos, Baptiste. "Structure et propriétés de carbones anisotropes par une approche couplant analyse d’image et simulation atomistique." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0331/document.
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Des techniques combinées d'analyse/synthèse d'images et de simulation atomistique ont permis d’étudier la nanostructure/-texture de matériaux carbonés anisotropes et denses de type pyrocarbone (PyC) laminaire hautement texturé. Des représentations atomiques d’un PyC laminaire rugueux tel que préparé (AP) ainsi que d’un PyC laminaire régénéré AP et après plusieurs traitements thermiques (HT) ont été reconstruites pour mieux caractériser ces matériaux. Ces modèles comportent des domaines graphéniques de quelques nanomètres, joints entre eux par des lignes de défauts formées de paires de cycles à 5 et 7 carbones dans le plan et par des dislocations vis et des atomes tétravalents entre les plans. Les modèles les plus ordonnés ont des domaines plus étendus et un plus faible taux de connexions inter-plan. Les propriétés mécaniques et thermiques prédites à partir de ces modèles sont proches de celles du graphite et augmentent avec la cohérence intra-plan et la densité de connexions inter-plans. Des modèles de graphène polycristallins ont aussi été générés. Ils sont apparus, du point de vue structural et des propriétés mécaniques, très proches des feuillets de carbones des PyCs. Ils ont permis d'étudier la réorganisation structurale se produisant au cours du HT : formation de lignes de défauts, réparation de lacunes, … Il s'agit d'un premier pas vers l'étude de la graphitation des PyCs. La méthode de reconstruction a enfin été adaptée à l'étude de l'évolution structurale d'un graphite au cours de son irradiation par les électrons. Cela a permis d'observer à l'échelle atomique la création et la propagation des défauts au cours de l'irradiationCombined images analysis/synthesis techniques and atomistic simulation methods have allowed studying the nanostructure/-texture of anisotropic dense carbons of the highly textured laminar pyrocarbon (PyC) type.Atomic representations of an as-prepared (AP) rough laminar PyC as well as a regenerative laminar PyC AP and after several heat treatments (HT) were reconstructed to better characterize these materials.The models contain nanosized graphene domains connected between them by line defects formed by pairs of rings with 5 and 7 carbons inside layers and by screw dislocations and fourfold atoms between layers. The most ordered models have larger domains and a lower percentage of connections between the layers.Mechanical and thermal properties predicted from these models are close to those of graphite and increase with the coherence inside layers and the density of connections between layers.Models of polycrystalline graphene were also generated, showing structure and mechanical properties very close to those of the carbon layers extracted from PyCs. The structural reorganization occurring during the HT of such materials was studied: thinning of line defects and vacancy healing were observed. This represents a first step towards the study of the graphitization of PyCs.The reconstruction method was eventually adapted to study the structural evolution of a nuclear-grade graphite during its irradiation by electrons, allowing us to observe how defects are created and propagate during irradiation
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Fintland, Trygve Westlye. "Measurements of Young's Modulus on Rock Samples at Small Amplitude and Low Frequency : RockHard Deformations." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13580.
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This thesis describes a new instrumental approach designed to measure the complex Young’s modulus on cylindrical samples 1 inch in diameter 2 inch long and typically in the range of 1-70 GPa. Excitation frequencies are from 11 Hz to 167 Hz. The setup is based on the Forced Deformation Method (Batzle et al., 2006) and is capable of measuring phase and magnitude of the dynamic stress and strain. An actuator provides an oscillating force from one end of the plug. Strain is measured on the cylindrical side with three strain gages evenly spaced around the circumference. The lowest recordable magnitude of strain is in the order of 10E-8. Force is measured by a piezoelectric transducer. Values are < 10 N. Plug sample measurements of the Young’s modulus values for Berea sandstone, Castlegate sandstone, Pierre shale, PEEK, and aluminium alloys (ALU-7075 and ALU-6061) are included. Reference material results are in accordance with published values. Some of the instrumentation needed is also given in detail in the previous work (Fintland, 2010).
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Kubavat, Harshal A. "The influence of crystallization on the mechanical and interfacial properties of active pharmaceutical ingredients." Thesis, University of Bath, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548090.
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Karlsson, Tomas, and Johan Fromell. "Förstärkta strävor i trätakstolar för ökad tryckkapacitet : En laborativ undersökning." Thesis, Växjö University, School of Technology and Design, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:vxu:diva-1545.
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I vissa takstolskonstruktioner kan det ibland uppstå stora tryckkrafter i diagonala reglar. I Sverige löser man oftast detta med hjälp av stagning tvärs diagonalen för att hindra utböjning i veka riktningen. Ibland när det är svårt att på plats trä in strävor på grund av utrymmesbrist och dylikt kan man spika eller skruva på en regel för att på så sätt förstärka den diagonala strävan. Detta examensarbete har undersökt två olika förstärkningsalternativ, rektangulärt- och T-tvärsnitt, med hjälp av reglar med dimension 45x95 mm2 vilka skruvas respektive spikas ihop. Detta har gjorts laborativt genom att trycka provkroppar i en provningsram och undersöka hur mycket den axiala kapaciteten ökar med förstärkning. De två olika förstärkningslösningarna bygger på att man på plats kan förstärka strävor med enkla medel.
Testbitarna har levererats till Växjö universitet och är av oklassat virke. Provbitarnas E-modul har undersökts för att på teoretisk väg undersöka hur stor axialkraftskapacitet den primära strävan har utan förstärkning. Provkroppar tillverkades och konditionerades i klimatrum, med temperaturen 20°C och 65 % RF, i ca tre veckor före provtryckning.
De laborativa värdena visar att den axiella kapaciteten ökar med 1,9 – 2,7 ggr för de rektangulära tvärsnitten och 2,5 – 4,0 ggr för T-tvärsnitten. Förstärkningsfaktorn är beroende av längd, förstärkningsalternativ och sammanfogning. Förstärkningseffektiviteten är högst för de längre strävorna.
In wooden roof trusses there sometimes may occur buckling in compressed web members. In most cases in Sweden this is solved by bracing between two webs to prevent buckling of the minor axis. Sometimes it is hard to brace between webs because of lack of space. Then it is possible to nail or screw a side member on the compressed web to increase the capacity. This diploma work has examined two different ways of bracing, rectangular cross section and T-bracing, with webs 45x95 mm2. Experimental tests have been made on compression webs and examine the bracing efficiency. It is important that the bracing alternatives are easy to use with simple tools.
Ungraded lumber were delivered to Växjö University. The Youngs modulus of the test pieces has been examined so the critical buckling load of the main member without bracing could be calculated theoretically. The lumber was conditioned to equilibrium moisture content of approximately 12 percent in a room maintained at 65 percent relative humidity and 20°C in three weeks before testing the critical buckling load.
The experimental results show that the critical buckling load increases with a factor of 1,9 – 2,7 for the rectangular cross sections and with a factor of 2,5 – 4,0 for the T-bracing. The bracing efficiency is dependent on length, bracing alternative and type of connectors.. The bracing efficiency increases for longer webs.
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Stevens, Mildrett Elizabeth. "Resilience of young people exposed to parental alcohol abuse." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_2618_1308728030.
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This study explores the possible resilient factors which prevent young people who have been exposed to parental alcohol abuse from abusing alcohol themselves. Additionally, this study explores the coping mechanisms of young people living with a (n) alcohol abusing parent(s). This study uses a qualitative methodological design. The initial plan was purposive sampling. However it became evident that this type of sampling is not possible as no suitable candidates were found. One participant volunteered to participate in the study and suggested a few other suitable candidates. The candidates were contacted and invited to become part of the study. Individual interviews were conducted with the participants, using an interview guide and a voice recorder. The researcher ended up using snowball sampling as the candidates suggested other possible candidates. The findings suggest that the participants experienced an array of emotional, developmental and socio-economical difficulties. Feelings of shame, fear, anxiety and a deep sense of unhappiness about the situation was shared by all the participants. The family, friends and some teachers were instrumental in helping to find coping mechanisms during this challenging time of growing up with an alcohol abusing parent. Religion, academics, and positive role-modelling were contributing factors to their resilience in not using alcohol themselves even though they were exposed to alcohol-abusing parents.
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Petracovschi, Elena. "Vitrocéramiques infrarouges pour application à la vision nocturne." Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S058/document.
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Les verres de chalcogénures sont utilisés en tant qu'optiques pour les caméras IR grâce à leur transparence dans les deux fenêtres atmosphériques [3 – 5 µm] et [8 – 12 µm]. Afin de diminuer leur prix et d'augmenter la gamme des compositions qui pourraient être produites, une nouvelle méthode de synthèse a été élaborée au laboratoire Verres et Céramiques. Les travaux présentés dans ce manuscrit ont ainsi porté sur le développement de la technique de synthèse des verres et vitrocéramiques de chalcogénures par mécanosynthèse et frittage flash, ainsi que sur l'étude de la structure et des propriétés mécaniques des vitrocéramiques. Les différents paramètres de broyage et frittage ont été étudiés et la possibilité de produire des matériaux massifs, avec une structure et des propriétés similaires à celles des verres obtenus par voie classique de fusion-trempe, a été démontrée. Egalement, il a été constaté que la génération des particules cristallines dans la matrice vitreuse permet d'améliorer les propriétés mécaniques sans altérer la transmission optique des échantillons. Finalement, une étude théorique, basée sur la méthode DFT, a été initié pour accéder à des informations plus précises concernant la structure et les propriétés mécaniques des verres et vitrocéramiques de chalcogénuresChalcogenide glasses are used as optics for the IR cameras thanks to their transparence in the two atmospheric windows [3 – 5 µm] and [8 – 12 µm]. In order to reduce their price and to increase the panel of compositions which may be produced, a new method of synthesis has been elaborated in the Glass and Ceramics group. Thus, this manuscript presents the development of the new way of synthesis of chalcogenide glasses and glass-ceramics by mechanical milling and SPS sintering, and the study of the structure and mechanical properties of glass-ceramics. The different milling and sintering parameters have been studied and the possibility to produce bulk samples with a structure and properties similar to those of glasses synthesized by melt-quenching method has been demonstrated. Also, it has been shown that the generation of crystalline particles in the glassy matrix increases mechanical properties of the samples without spoiling their optical transmission. Finally, a theoretical study, based on the DFT method, has been initiated in order to access more precise information concerning glass and glass-ceramic structure and mechanical properties
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Hittel, Jonathan Erwin. "Effect of Surface Chemistry and Young's Modulus on the Surface Motility of the Bacterium Pseudomonas Aeruginosa." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/96635.
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This study demonstrates that the surface motility of the bacterium Pseudomonas aeruginosa is dependent on the surface chemistry of the underlying substrate. In particular, cells on hydrophobic polydimethylsiloxane (PDMS) have a speed that is on average 38% greater than on hydrophilic PDMS. These results were obtained using time-lapse microscopy of bacteria exposed to continuously flowing tryptic soy broth growth medium at 37 ⁰C. Not only are the mean speeds different, the distributions of speeds are also different: on the hydrophobic substrate, a smaller proportion of bacteria move by less than about one body-length (~3 µm) in 60 minutes. In addition, the surface chemistry affects the orientation of the cells: there is a greater fraction of "walking" bacteria on the hydrophobic surface. Sensitivity to the substrate surface chemistry occurs despite the presence of a complex mix of substances in the growth medium and offers hope that surface chemistry can be used to tune motility and the progression to biofilm formation. Additionally, the effect of reducing the near-surface Young's modulus of the PDMS from 7000 to 70 kPA is investigated. For the lower modulus material, there is an increase in the likelihood of a bacterium executing sudden, high angle turns. This is evident in images with a framerate of one frame per 0.22s. However, the impact of these turns is averaged out over longer times such that the mean speed over periods of more than about one minute is the same for bacteria on both the high and the low modulus materials. Consequently, except over very short time intervals, Young's modulus in the surface region is not effective as a means of modulating motile behavior.Master of Science
This study demonstrates that the ability of the bacterium Pseudomonas aeruginosa to move on a solid surface is dependent on the surface chemistry of the underlying substrate. In particular, cells on hydrophobic polydimethylsiloxane (PDMS) have a speed that is on average 38% greater than on hydrophilic PDMS. These results were obtained using time-lapse microscopy of bacteria exposed to continuously flowing growth medium at 37 ⁰C. Not only are the mean speeds different, the distributions of speeds are also different: on the hydrophobic substrate, a smaller proportion of bacteria move by less than about one body-length (~3 µm) in 60 minutes. In addition, the surface chemistry affects the orientation of the cells: there is a greater fraction of vertically-oriented bacteria on the hydrophobic surface. Additionally, the effect of reducing the stiffness of the PDMS from 7000 to 70 kPA is investigated. For the less stiff material, there is an increase in the likelihood of a bacterium executing sudden, high angle turns. This is evident in images with a framerate of one frame per 0.22s. However, the impact of these turns is averaged out over longer times such that the mean speed over periods of more than about one minute is the same for bacteria on both the high and the low stiffness materials. Consequently, except over very short time intervals, stiffness in the surface region is not effective as a means of changing patterns of surface-bound P. aeruginosa movement.
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Yamaguchi, M., Y. Yamada, Y. Goto, M. Shikida, and K. Sato. "Mechanical Properties of Silicon-Based Membrane Windows Applied for a Miniature Electron Beam Radiation System." IEEE, 2007. http://hdl.handle.net/2237/9570.
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Sun, Li. "Complex Unloading Model for Springback Prediction." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1298656444.
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RAMACHANDRAN, RAHUL. "A nonlinear stress sensitivity study on role of Coil-thrombus complex in reduction of idealized cerebral aneurysm wall stresses." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1202193853.
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Yescas, Jorge Arturo. "Vibrational study of agarose spheres of millimetric and micrometric size." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/vibrational-study-of-agarose-spheres-of-millimetric-and-micrometric-size(c4bf7877-f6cf-48b8-bed2-ece48e230c5d).html.
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This PhD thesis is concerned with developing a methodology for early diagnosis of cancer by comparing the resonant frequencies in the amplitude spectra obtained during a vibration test using the AFM or, by comparing the stiffness properties of single cancerous and normal cells obtained using a resonant technique. As there is no reliable data in the literature to prove the existence of resonant frequencies of single cells, this work pioneers the search for resonant frequencies of related microspherical soft bodies using the AFM. Experiments to investigate the resonant behaviour of single cells depends on various parameters which are difficult to control; for example, the cell type, deciding at what stage the cell should be tested during the culturing process, determining the nucleus size, determining the cytoskeleton integrity and designing an appropriate vibration test setup among others. For this reason, agarose microspheres were selected to carry out preliminary work as these samples have similar properties to human cells and their resonances are affected by fewer variables. Although these micrometric spheres were tested under different conditions, no clear resonant behaviour was found at frequencies below 20 kHz and, only wide curves (interpreted as highly damped peaks of resonance) in the interval ranging from 20 kHz to 100 kHz were observed. By considering those curves as the quadrupole (Qp) vibration mode, approximate stiffness values for the agarose microspheres were found to be in between 37 kPa and 72 kPa. These values are similar to those obtained during an indentation test performed on the same samples whic¬¬h gave Young’s modulus values ranging from 10 kPa to 200 kPa. In order to gain a greater insight into the vibration test performed on microscopic samples, the research was extended to include agarose spheres of millimetric size. The characterization of these samples was carried out using an innovative purpose-built experimental setup. For the vibration test, a PZT based excitation device and a vibro-acoustic sensor were designed and constructed. The amplitude spectra of the vibration tests performed on millimetric samples consistently showed at least three peaks of resonance from which after the numerical simulation of the vibration test were interpreted as the quadrupole (Qp) and octupole (Op) vibration modes. Using this information, stiffness values for the samples ranging from 100 kPa to 700 kPa were calculated. In order to obtain the stiffness of the millimetric samples using a different technique, an experimental setup was constructed to perform a compression test. However, due to high viscoleasticity of the samples, it was not possible to obtain a standard compression curve necessary for their mechanical characterization. The results obtained from the tests on millimetric agarose samples demonstrate that spheres made of this material are able to provide measurable vibrational characteristics. Consequently, this methodology can be further implemented on micrometric samples and possibly on human cells to detect their resonant frequencies and equivalent stiffness values which can be used as a cancer marker. From the vibrational experiments on millimetric samples, it was noticed that the excitation mechanism plays an important role and for this reason future work is proposed to continue in this direction.
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Saheli, Massih. "Elastic Modulus Determination of Krouse Specimens through Resonance using Simple Beam Theory." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1555140817600694.
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Ceglia, Gaétane. "Élaboration et caractérisation de matériaux polymères poreux modèles à base d’émulsions contrôlées." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14462/document.
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Des mousses de polymères modèles sont élaborées à partir d’émulsions afin d’en étudier les propriétés. De telles mousses sont intéressantes dans des applications variées d’amortisseurs (sécurité passive), de filtres ou d’isolation. Les objectifs de cette étude sont de comprendre l’origine des propriétés mécaniques des mousses et d’identifier les paramètres structuraux les plus pertinents. Pour cela, la première étape consiste en la fabrication de mousses de morphologies contrôlées à partir d’émulsions monodisperses très concentrées. Par polymérisation de la phase continue des émulsions, des mousses solides modèles à taille de cellules contrôlées et de porosité ouverte sont obtenues. Ensuite la structure de ces matériaux poreux est analysée et comparée à celle des émulsions initiales. Enfin, ces mousses sont caractérisées mécaniquement en compression. Nous présentons les résultats obtenus en variant de manière contrôlée la taille des pores et leur fraction volumique et les confrontons aux modèles existantsPolymer foams are cellular materials commonly used for safety applications in many industrial sectors (aeronautic, passive safety, gears…). To even improve their performances, the link between their structural parameters (cell sizes, density...) and their mechanical behaviour should be better understood and modelled. A way of producing such foams is to polymerize the continuous phase of highly concentrated emulsions. The advantage of such an emulsion-based strategy is that it becomes possible to take advantage of the good control over emulsion parameters (drop size, dispersed phase volume fraction, continuous phase composition) to elaborate model foams with cells and pores having narrow size distributions. The production of model foams makes it possible to determine independently the influence of each parameter on the compression modulus and to compare the results with existing models
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Wang, Hanqing [Verfasser]. "Ligand Receptor Interaction on Soft Scaffolds: the Influence of Young's Modulus, Ligand Concentration, and Type / Hanqing Wang." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1136608796/34.
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Werner, Jörn. "The influence of composition, processing and temperature on the Young's modulus of elasticity of carbon-bonded refractories." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2014. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-155296.
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Thermal shock resistance is a key property of refractory materials. Its determination and prediction is essential for the design of structural refractories as well as lining materials. Young’s modulus of elasticity (E) is a crucial parameter for the calculation of thermal shock resistance.
For all investigated carbon-bonded alumina composition a significant increase of E was observed. This increase was attributed to a mismatch of the coefficient of thermal expansion of the composite constituents. Besides others, the graphite content as well as the maximum alumina particle size were identified as crucial factors influencing E(T). Furthermore, the influence of the porosity on E was shown and existing models were fitted to the experimental data for future predictions of E. Finally a metal melt filter structure was investigated to investigate the relationship between its strut Young’s modulus and the structures’ E at high temperatures. Further research should address the filter topic since it was uncertain how to find the normal modes of those structures.
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Breton, Fabienne Knauss Wolfgang Gustav Knauss Wolfgang Gustav. "A large deformation analysis of plates or membranes for the determination of Young's modulus and Poisson's ratio /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-03292007-093444.
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Tarabeux, Justine. "Prédiction de la polymération et des propriétés mécaniques de pièces céramiques élaborées par stéréolithographie - Optimisation du procédé." Thesis, Limoges, 2019. http://www.theses.fr/2019LIMO0111.
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Ces travaux de thèse portent sur la maîtrise des caractéristiques dimensionnelles et mécaniques de pièces céramiques obtenues par stéréolithographie. L’objectif est d’être capable de prédire ces caractéristiques afin d’obtenir des pièces conformes dès la première fabrication. La stratégie a été de développer un modèle de simulation numérique capable de prédire l’exposition, la profondeur et la demi-largeur de polymérisation, ainsi que le module d’Young des pièces crues obtenues en fonction des paramètres du procédé. Ce modèle numérique intègre le phénomène de diffusion et est calibré pour chaque système à l’aide d’essais expérimentaux. Afin de pouvoir accéder aux propriétés élastiques effectives des pièces crues, un modèle de simulation par calculs éléments finis couplé à la technique d’homogénéisation a été développé. Ce modèle a été validé en comparant les résultats obtenus par simulation et les valeurs de module d’Young déterminées expérimentalement. Le caractère isotrope des propriétés élastiques dans le plan perpendiculaire à la direction de construction des pièces a ainsi été démontré. Sur la base des données fournies par les modèles numériques, une approche d’optimisation du procédé a été mise en oeuvre pour l’obtention de pièces crues conformes. Ainsi, des expositions élevées sont à privilégier pour assurer la faisabilité de la fabrication, des expositions faibles pour assurer la haute qualité dimensionnelle des pièces et des expositions intermédiaires pour assurer une grande productivité. Les pièces denses ont ensuite été considérées. Les propriétés élastiques et la contrainte à la rupture ont été déterminées avec des mesures ultrasonores et des essais de flexion bi-axiale. Une tendance similaire entre l’exposition maximale globale et les propriétés mécaniques a été mise en évidence, i.e. plus l’exposition maximale globale est élevée, plus les valeurs de module d’Young et de contrainte à la rupture sont élevées. Le travail d’optimisation pour l’obtention de pièces frittées en alumine montre que les expositions élevées sont à privilégier pour assurer de bonnes propriétés mécaniquesThis thesis work focuses on the control of the dimensional and mechanical characteristics of ceramic parts produced by stereolithography. The goal is to be able to predict these characteristics using a numerical model in order to manufacture parts in accordance with specifications, from the first production. The strategy was to develop a numerical simulation model capable of predicting exposure, cure depth and half width of polymerization, as well as Young's modulus of the green parts obtained, according to process parameters. This numerical model integrates the diffusion phenomenon and is calibrated for each system using experimental tests. In order to access the effective elastic properties of the green parts, a finite element simulation model, coupled with the homogenization technique, has been developed. This model was validated by comparing the results obtained by simulation and the experimentally determined Young's modulus values. The isotropic nature of the elastic properties in the plane perpendicular to the direction of construction of the pieces has thus been demonstrated. On the basis of data provided by the numerical models, an optimization approach has been performed to obtain compliant green parts. Thus, high exposures are preferred to ensure feasibility of manufacturing, low exposures to ensure high dimensional quality of parts and intermediate exposures to ensure high productivity. The elastic properties and the tensile stress of dense parts were determined by ultrasonic measurements and biaxial flexion tests. A similar trend between the overall maximum exposure and mechanical properties has been demonstrated, i.e. higher overall maximum exposure leads to higher Young's modulus and tensile strength values. The optimization work on sintered alumina parts showed that high exposures are preferred to ensure good mechanical properties
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Zhuravleva, Ksenia. "Porous ß-type Ti-Nb alloy for biomedical applications." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-147426.
Full textAbstract:
One of the most important factors for a successful performance of a load-bearing implant for hard tissue replacement is its mechanical compatibility with human bone. That implies that the stiffness should be close to that of a bone and the strength of the implant material must be high enough to bear the load applied under physiological conditions. The Young´s modulus of most of the commonly used biomedical alloys is larger than that of a human bone (around 100 GPa for cp Ti, 112 GPa for Ti-6Al-4V versus 10-30 GPa for cortical human bone). A stiffness reduction of Ti alloys can be achieved by two approaches: (i) selecting an alloy composition with low Young´s modulus i.e. a ß-type alloy and (ii) introducing a reasonable amount of porosity. The composition of Ti-40Nb was chosen for the present work, as it allows to stabilize a single ß-type phase with low Young´s modulus at room temperature.
The samples were produced by a powder metallurgical approach. The Ti-40Nb alloy powder was obtained by ball-milling of elemental Ti and Nb powders. The influence of the milling parameters on the oxygen content in the milled powder was studied. Powders with a lowest oxygen content of 0.4 wt.-% had an almost single ß-type phase after heat treatment and quenching.
Porous samples were produced by loose powder sintering, hot-pressing and sintering with NaCl as a space-holder. The influence of the different processing routes and different porosities on the mechanical properties of the alloy was studied. The samples produced by loose powder sintering had mechanical properties close to those of cortical human bone (Young´s modulus 20 GPa, compression strength 150 MPa) and the samples produced by loose sintering with space-holder materials had mechanical properties close to those of human spongy bone (Young´s modulus 0.2-2 GPa, compression strength 50 MPa). Porous Ti-40Nb samples were coated with bone-like hydroxyapatite by an electrochemical deposition method in order to improve the osseointegration of the samples with bone tissue. The experiments were carried out with samples produced by different routes and a correlation between the deposition parameters and the morphology of the hydroxyapatite needles was found.
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Ševc, Jan. "Studené asfaltové směsi s R-materiálem." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2016. http://www.nusl.cz/ntk/nusl-240090.
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The thesis is focused on the use of R-material into cold asphalt mixtures. It deals with cold recycling and with input materials for this technology. It verifies properties of R-material and residues of bituminous binder. It also verifies properties of designed cold asphalt mixtures by the probative controls (indirect tensile strenght and water resistance). Furthermore is focused on the experimental measurement of selected mixtures to ensure more characteristics. The amount of homogenity of R-material, quantity and quality of residues bituminous binder is essential for positive results.
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Li, Ye. "Propagation and reflection of pulse waves in flexible tubes and relation to wall properties." Thesis, Brunel University, 2011. http://bura.brunel.ac.uk/handle/2438/6554.
Full textAbstract:
The wall properties of the arteries play an important role in cardiovascular function. Stiffness of large artery is predictive of cardiovascular events. To understand the function of the cardiovascular system, special attention should be paid to the understanding of pulse wave propagation, because pulse waves carry information of the cardiovascular function, and provide information which can be useful for the prevention and diagnosis of diseases. This thesis presents a series of in vitro experimental studies of wave propagation, wave reflection and determination of mechanical properties of flexible vessels. In this thesis, several studies have been included: 1) applied and compared foot-to-foot, PU-loop and lnDU-loop methods for determination of wave speed in flexible tubes and calf aortas; 2) investigated the variation of local wave speed determined by PU-loop with proximity to the reflection site; 3) investigated using wave intensity analysis (WIA) as the analytical technique to determine the reflection coefficient; 4) developed a new technique which based on one-point simultaneous measurements of diameter and velocity to determine the mechanical properties of flexible tubes and calf aortas. In the first study, it is found wave speeds determined by PU-loop and lnDU-loop methods are very similar, and smaller than those determined by foot-to-foot method. The timing of arrival time of reflected wave based on diameter and velocity technique highly agreed with the corresponding timing based on pressure and velocity technique. The shapes of forward and backward non-invasive wave intensities based on diameter and velocity are very similar with the corresponding shapes based on pressure and velocity. Although the density term is not part of the equation, the lnDU-loop method for determining local wave speed is sensitive to the fluid density. In the second study, it is found wave speed measured by PU-loop is varied with proximity to the reflection site. The closer the measurement site to the reflection site, the greater the effect upon measured wave speed; a positive reflection caused an increase in measured wave speed; a negative reflection caused a decrease in measured wave speed. Correction iteration process was also considered to correct the affected measured wave speed. In the third study, it is found, reflection coefficient determined by pressure, square roots of wave intensity and wave energy are very close, but they are different from reflection coefficient determined by wave intensity and wave energy. Due to wave dissipation, the closer the measurement site to the reflection site, the greater is the value of the local reflection coefficient. The local reflection coefficient near the reflection site determined by wave intensity and wave energy are very close to the theoretical value of reflection coefficient. In the last study I found that distensibility determined by the new technique which utilising lnDU-loop is in agreement with that determined from the pressure and area which obtained from tensile test in flexible tubes; distensibility determined by the new technique is similar to those determined in the static and dynamic distensibility tests in calf aortas; Young’s modulus determined by the new technique are in agreement with that those determined by tensile tests in both flexible tubes and calf aortas. In conclusion, wave speed determined by PU-loop and lnDU-loop methods are very similar, the new technique lnDU-loop provides an integrated noninvasive system for studying wave propagation; wave speed determined by PU-loop is affected by the reflection, the closer the measurement site to the reflection site, the greater the change in measured wave speed; WIA could be used to determine local reflection coefficient when the measurement site is close to the reflection site; the new technique using measurements of diameter and velocity at one point for determination of mechanical properties of arterial wall could potentially be non-invasive and hence may have advantage in the clinical setting.