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Talbert, Michael Lane. "A methodology for the measurement and evaluation of complex system designs." Diss., This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-10022007-145050/.
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Talbert, B. Allen. "The first year of an agriculture teacher : a case study of three beginning teachers /." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-05092009-040439/.
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Genkin, Jean-Marc P. (Jean-Marc Patrick). "Corrosion fatigue crack initiation in 2091-T351 Alclad." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/41792.
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Booth, Diccon Philip Paul. "Fatigue of friction stir welded AA2024-T351 plate." Thesis, University of Southampton, 2003. https://eprints.soton.ac.uk/363704/.
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The fatigue crack initiation and propagation characteristics of Friction Stir Welds (FSW) and 13mm gauge 2024-T351 A1 alloy have been studied. Two failure locations have been identified: outside the weld nugget region and over the nugget region. The study shows that when failure occurs outside the nugget, fatigue crack growth is essentially conventional (mode I dominated), with initiation from S-phase particles. For failures over the nugget region initiations were linked to coarse intermetallics associated with macroscopic discontinuities in the weld flow pattern; with subsequent crack growth being seen to follow the curve of the banded structure within the weld nuggets region. A variety of microstructural and micromechanical contributions to fatigue failure have been identified, including the roles of local matrix ageing characteristics, intermetallic particle size and distributions, local flow stress characteristics and the residual stress distributions. The effect of varying the welding parameters has also been studied in partial penetration 25mm gauge 2024-T351 Al alloy. Again, two failure locations have been identified: outside the weld nugget region and over the nugget region. Outside the nugget exhibited essentially conventional (mode I dominated) crack growth, with initiation occurring at S-phase particles. Failure over the nugget only occurred in samples from the slower of the two welding speeds, initiation was identified with linear defects at, or just below, the surface. Again a variety of microstructural and micromechanical facts were identified as having an influence on the subsequent growth, in particular the marked deflection from a conventional mode I path. The failure location however did not appear to significantly alter fatigue lives.
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Brzostek, Robson Cristiano. "Estudo da fratura em solda ponto por fricção em alumínio Alclad 2024-T351 e alumínio 2024-T351 : uma abordagem numérica experimental." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/72938.
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Friction Spot Welding (FSpW) é um processo de solda ponto por fricção, que opera na fase sólida do material e permite unir duas ou mais chapas de metal sobrepostas. Além de ser bastante usado para soldar materiais leves, ele também é aplicável a qualquer material que apresente boa plasticidade. Neste trabalho são analisados dois materiais: AA Alclad 2024-T351 e AA 2024-T351, diferindo entre si no uso, ou não, da camada de proteção contra a corrosão (Alclad). As uniões são feitas sob os mesmos parâmetros do processo, previamente estudados para o material com Alclad. Dois parâmetros são utilizados: um dito ótimo, capaz de produzir soldas com bom desempenho mecânico e reprodutibilidade e um segundo, dito insuficiente, por produzir soldas de baixo desempenho mecânico e baixa reprodutibilidade. Pretende-se, com este trabalho, avaliar os efeitos que a camada Alclad pode acarretar nas juntas soldadas, em seu desempenho mecânico, no modo de fratura, na microestrutura e na geometria da junta. Os resultados apresentam uma grande influência do Alclad, tendo em vista que durante o processo o recobrimento migra das superfícies das chapas para o centro da solda. Assim, uma interface deste material, que possui baixa resistência mecânica, é criada, influenciando negativamente o desempenho da junta e alterando o modo de fratura. O principal escopo desta dissertação é realizar uma análise da fratura do ensaio de cisalhamento, com o uso do método de elementos finitos. Portanto, fazse necessário estudar e desenvolver um modelo numérico capaz de representar a nucleação, coalescimento, formação de uma ou mais trincas e a consequente propagação até a fratura do corpo. Para a realização da análise utilizou-se o modelo numérico de fratura Johnson-Cook (JC), o qual expressa a tensão equivalente como uma função da deformação plástica, da taxa de deformação e da temperatura. Realizou-se, ainda, um estudo acerca das teorias do Continuum Damage Mechanics (CDM), bem como se fez necessário obter novos parâmetros para o modelo, que descrevessem o fenômeno e o material. Nesse sentido, serão realizadas duas análises, sendo que a primeira considera o efeito da camada de Alclad e, a segunda, considera uma solda livre de defeitos. Espera-se identificar os locais em que trinca é nucleada e analisar a resposta da junta, passo a passo, durante a propagação da trinca, até a fratura completa do corpo. E, por fim, avaliar a interferência no modelo numérico da presença da camada contra a corrosão Alclad.Friction Spot Welding (FSpW) is a friction spot weld process, it operates in the solid-state of the material and allows joining two or more sheets in overlap configuration. It is used to join light weight materials, also is suitable to any material that shows good ductility. In this work two different materials are analyzed AA Alclad 2024-T351 e AA 2024-T351, between them the use, or not, of the corrosion protection layer Alclad. The welds are made under the same process parameters previously studied to the material with Alclad. Two parameters are utilized: the first one is the optimum parameter capable to produce welds with good mechanical performance and reproducibility, and another one inadequate because it produces joins with poor mechanical response and reproducibility. It is intended with this work, to evaluate the effects that the Alclad layer can cause in the welds, in its mechanical performance, fracture mode, microstructure and geometry of the join. The results showed a considerable influence of the Alclad, considering that during the process, it migrates from the sheet surface to the center of the weld. Thus, an interface of this material, that has a very low hardness, is created, influencing negatively the performance of the weld and changing the fracture mode. The aim of this dissertation is to perform an analysis of the fracture from the lap shear test, using the finite element method. Therefore, becomes necessary study and develop a numerical model capable to represent the nucleation, coalescence, formation of one or more cracks and, the consequent propagation until the fracture of the body. To perform the analysis it was used the numerical model of fracture called Johnson-Cook (JC), which expresses the equivalent stress as a function of the plastic deformation, the strain rate and the temperature. It was also made a study about the Continuum Damage Mechanics (CDM) theories, and it was necessary to obtain new parameters for the model, that describe the phenomenon and the material. In this sense, it will be performed two analyses, and the first considers the Alclad layer and, the second, considers a weld without defects. It is expected to identify the places where the crack nucleated, and analyze the behavior of the weld, step by step, during the crack propagation, until the complete fracture of the component. And, finally, evaluate the interference in the numerical model of the presence of the protection corrosion layer Alclad.
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Rodrigues, Camila Fernanda. "Rebitagem por fricçao de alumínio 2024-T351 em policarbonato." Universidade Federal de São Carlos, 2014. https://repositorio.ufscar.br/handle/ufscar/937.
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Previous issue date: 2014-10-24Universidade Federal de Minas Gerais
This dissertation addressed the feasibility study of Friction Riveting technique on polycarbonate and 2024-T351 aluminum alloy spot joints. Design of experiments and Artificial Neural Network modelling were used to investigate the influence of process parameters on mechanical and microstructural properties of joints. These joints were produced at the Institute for Research Helmholtz Zentrum Geesthacht (HZG), in Germany, during the undergraduate years of the applicant. Process temperature was measured using an infrared camera. The mechanical properties of the joints were determined by tensile testing. The macro and microstructural characterization were carried out by light optical microscopy (LOM) and Vickers microhardness tests. The fracture mechanisms were investigated by optical and scanning electron microscopy (SEM). The level of PC degradation in the joining area was obtained by viscometry and Fourier transform infrared spectroscopy (FTIR). The average peak temperatures meausured during joining varied between 52% and 72% of the melting point interval of AA 2024 aluminium alloy. Strong joints with high anchoring efficiency were achieved, with ultimate tensile strength of approximately 90% of metallic rivet, and non-catastrophic ductile fracture at the metallic rivet outside the joined area. This is desirable failure type in riveted polymeric structures and an indication of high-strenght joints. The viscometry and FTIR analysis showed the absence of thermal degradation of the PC in the riveted joint. Statistical and Artificial Neural Networks modeling process showed good repeatability and reproducibility within the conditions studied. These results demonstrated the feasibility of producing spot joints of rivets 2024-T351 and PC by using the FricRiveting process.
Nesta dissertação de mestrado foi realizado um estudo da viabilidade de fabricação de juntas híbridas de Policarbonato (PC) e Alumínio 2024-T351 através do processo de rebitagem por fricção ( Friction Riveting ). Técnicas de planejamento de experimentos aliadas à modelagem por redes neurais foram utilizadas na investigação da influência dos parâmetros de processo, nas propriedades mecânicas e microestruturais das juntas. As juntas foram produzidas no Instituto de Pesquisa Helmholtz Zentrum Geesthacht (HZG), na Alemanha, durante o período de estágio da proponente. A temperatura dos materiais durante o processamento foi medida utilizando-se uma câmera de infravermelho. As propriedades mecânicas das juntas foram determinadas por meio de ensaios de tração. As características macro e microestruturais foram avaliadas por meio de microscopia ótica e ensaios de microdureza Vickers. Os mecanismos de fratura foram investigados por análises em microscópico ótico e de varredura (MEV). O nível de degradação do PC na região da solda foi investigado por viscosimetria e espectroscopia no infravermelho por transformada de Fourier (FTIR). As temperaturas médias atingidas na área friccionada estiveram entre 56% a 72% do intervalo de ponto de fusão da liga AA 2024. Foram produzidas juntas com alta eficiência de ancoramento do rebite metálico, com limites de resistência à tração de aproximadamente 90% da resistência mecânica do rebite, e falha dúctil não catastrófica, ocorrendo no rebite na região externa à placa de PC. As análises de viscosimetria e FTIR demonstraram a ausência de degradação térmica do PC na área de união. A modelagem estatística e via redes neurais do processo demonstraram boa repetitividade e reprodutibilidade dentro das condições estudadas. Tais resultados permitiram demonstrar a viabilidade de produzir juntas de qualidade, com rebites de 2024-T351 e placas de PC, utilizando o processo de Rebitagem por Fricção.
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Tabaddor, Mahmood M. "Nonlinear vibration of beam and multibeam systems." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/40463.
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Tang, Ming. "The effect of an urban growth boundary on property prices : the case of Virginia Beach, Virginia /." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-12172008-063712/.
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Tarazi, Ghassan John. "National survey of school board members' perceived religious and political leanings and their attitudes on selected education issues." Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-10022007-144639/.
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Younes, Yousif Younes Abo. "Corrosion control of friction stir welded AA2024-T351 aluminium alloys." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/corrosion-control-of-friction-stir-welded-aa2024t351-aluminium-alloys(ae2c342d-4cfb-4bbb-a6b4-f62c688b92c6).html.
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Friction stir welding (FSW) is a modern solid state welding technique developed at the welding institute (TWI) in 1991. The joining is achieved by heat generation, material softening and plastic deformation following the travelling of non-consumable pin through the gap between the two work pieces to be joined. In present study, joining of AA 2024-T3 aluminium alloy, is achieved by FSW. The influence of the FSW on the alloy microstructure and corrosion behaviour is determined. The effect of laser surface melting (LSM) treatment on the improvement of corrosion resistance of friction stir welded alloys is investigated. Further, heat treatments to simulate the welding process with controlled cooling rate are performed to assess the effect of cooling rate on the microstructure, consequently, the corrosion performance of the welds. It is revealed that FSW process introduces elevated temperatures at the weldment, resulting in distinct regions with modified microstructures. The regions are named as the TMAZ (thermomechanically affected zone) and the HAZ (heat affected zone). TMAZ, positioned at the weldment centre, is featured by a central nugget with dynamically recrystallised fine, equiaxid grains, that is surrounded by heavily deformed grains. HAZ, positioned as narrow bands just outside TMAZ, has grain size similar to parent alloy. Corrosion testing shows that the as-welded alloy is highly susceptible to corrosion, particularly at the bands just outside the TMAZ (i.e. HAZ). Welding process resulted in the preferential precipitation of copper and magnesium rich particles at the grain boundaries within the HAZ, which reduces the corrosion resistance as a result of the galvanic coupling of the sensitised grain boundaries and the adjacent matrix. Laser treatment resulted in a melted near-surface layer, up to 6 μm thick, where normal constituent particles are absent. Corrosion testing showed that laser treatment reduces the degree of localized corrosion due to the removal constituent particles. However, scrutiny of the melted near-surface layer revealed continuous segregation bands, approximately 10nm thick, containing mainly copper. The presence of such segregation bands promoted localised corrosion of the laser melting layer due to microgalvanic action. From the areas where melting layer is corroded, localised corrosion propagated further into the weld intergranularly. The severe intergranular corrosion beneath the laser melting layer undermines the laser melting layer, resulting delamination of the surface layer from theunderlying bulk alloy. The simulated heat treatments show that the cooling cycle of the welding process has a significant influence on the alloy's microstructure and corrosion behaviour. Slow cooling can result in formation of a continuous network of second phase particles at the grains boundaries, leading to significantly reduced corrosion resistance. Rapid cooling tends to prevent the formation of second phase particles at grains boundaries, resulting in improved corrosion resistance.
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Tatarka, Bernadette. "Relationships among body-self relations, exercise involvement, and exercise clothing attitude for women in regular exercise programs." Diss., This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-06062008-162917/.
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Neumann, Tomasz. "Friction stir welding of Al 2024-T351 using a self-reacting bobbin tool." Aachen Mainz, 2009. http://d-nb.info/997950617/04.
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Asquith, David Thomas. "Residual stress and fatigue in cold-worked, hard-coated 2024-T351 aluminium alloy." Thesis, University of Sheffield, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486777.
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Due to the continued demand for high performance, light-weight components in many areas of engineering, researchers strive to enhance characteristics to satisfy these needs. A synergistic approach to performance enhancement. of aluminium alloys has been investigated through combined cold-work and hard coating thereby affording increased performance in teIflls of both fatigue and surface hardness. With an' emphasis on coldwork processing, two different methods of introducing surface compressive residual stresses in this manner have been used. This leads to an interest in the influence of residual stress in the hard coated aluminium on its behaviour. In particular, the characterisation of residual stress states in the modified materials with specific-interest in the evolution of triaxial stresses with the treatment process steps has been studied. This is combined with materials characterisation in form of microstructure, micro-hardness, phase composition and corrosion behaviour to complete the evaluation of duplex treatments.
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Mann, Philip. "Evaluation of surface modifications introduced by shot peening of aluminum alloy 2024-T351." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123117.
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Shot peening is a cold working mechanical deformation process consisting of bombarding a metallic surface with small spherical media, called shots, at velocities commonly in the range of 10 to 100 m/s. Upon impact, the shots generate a near-surface deformed layer containing local hardening as well as compressive residual stresses, resulting in an improved fatigue resistance. However, the dependence of shot velocity and percentage of the total area covered by shot impacts on the surface modification introduced by shot peening are not well understood.The hardness and residual stress profiles beneath shot peened surfaces were investigated using nanoindentation experiments for the situations of three different average shot velocities, corresponding to 35 m/s, 54 m/s and 66 m/s, and two surface coverages, corresponding to a single shot peening impingement and full coverage (100%). For the situation (i) of a single impingement, a new polishing procedure was developed allowing locating an isolated single impingement, verifying that the impingement was produced by a shot that impacted at normal incidence, as well as preparing the surface such that nanoindentation could be performed on the impingement's cross-section. It was demonstrated that both hardness and compressive residual stresses increased with an increase in shot velocity. The experimental residual stress results were compared to those from numerical simulations that utilized the same peening parameters as the experiments. It was observed that the experimental results demonstrated similar behavior and were of the same order of magnitude as those predicted numerically. The main difference was that the experimental results demonstrated a maximum compressive residual stress that was independent of shot velocity.For the situation (ii) of full coverage, channelling contrast imaging in a scanning electron microscope revealed that there were recrystallized grains adjacent to the shot peened edge. Additionally, the hardness and compressive residual stresses were observed to increase with an increase in shot velocity. Similarly to the single impingement, the location of maximum compressive residual stress was independent of shot velocity.Le grenaillage est un procédé de déformation mécanique consistant à bombarder une surface métallique ductile avec de petits billes sphériques à des vitesses élevées (10 à 100 m/s). Lors de l'impact, les billes génèrent l'apparition d'une zone déformée en surface, caractérisée par un durcissement relativement important ainsi qu'un champ de contraintes résiduelles de compression, ce qui entraîne une meilleure résistance à la fatigue. Cependant, l'effet de la vitesse d'impact de la bille et de la couverture de surface sur la modification des propriétés de surface induit par le grenaillage ne sont pas bien compris.Dans cette étude, la dureté et les contraintes résiduelles ont été étudiées en utilisant des expériences de nanoindentation pour les situations suivantes: trois vitesses de billes différentes correspondant à 35 m/s, 54 m/s et 66 m/s, ainsi que deux couvertures de surface correspondant à un seul impact et à une couverture complète (100%). Pour la situation (i) de l'étude d'un unique impact, une nouvelle procédure de polissage a été développée permettant de localiser un impact isolé. Cette procédure permet de préparer la surface de telle sorte que la nanoindentation peut être effectuée sur la section transversale de l'impact et permet de vérifier que l'impact a été produit par une bille frappant la surface avec une incidence normale. Il a été observé que la dureté et les contraintes résiduelles de compression augmentent avec une augmentation de la vitesse de la bille. Les résultats expérimentaux de contraintes résiduelles ont été comparés à ceux d'une simulation numérique en utilisant les mêmes paramètres expérimentaux de grenaillages. Il a été observé que les résultats expérimentaux montrent un comportement similaire et sont du même ordre de grandeur que ceux obtenus par simulation numérique. La principale différence est que les résultats expérimentaux ont montré une contrainte résiduelle de compression maximale étant indépendante de la vitesse de la bille.Pour la situation (ii) d'une couverture complète et à l'aide du procédé de microscopie électronique à balayage, nous avons observé un raffinement des grains adjacents à la surface grenaillée. En outre, nous avons observé que la dureté et les contraintes résiduelles de compression augmentaient avec une augmentation de la vitesse de la bille. De même que pour l'impact isolé, la localisation des contraintes résiduelles de compression maximale était indépendante de la vitesse de la bille.
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Seidt, Jeremy Daniel. "Plastic Deformation and Ductile Fracture of 2024-T351 Aluminum under Various Loading Conditions." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1268148067.
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Aburas, Zakria Moh. "Microstructural characterisation and corrosion studies of excimer laser-treated aluminium alloy AA2024-T351." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/microstructural-characterisation-and-corrosion-studies-of-excimer-lasertreated-aluminium-alloy-aa2024t351(d517d02a-ca18-4b08-8131-699a4426fd92).html.
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Laser surface melting (LSM) of aluminium alloys with high power continuous wave (CW) CO2 and Nd:YAG lasers has been shown to produce dendritic/cellular microstructures with refined second-phase particles distributed along the dendritic boundaries. Although refinement of the microstructure and extension of the solute solubility in the matrix can be achieved, the refined second-phase particles still act as preferential sites to initiate localized corrosion. In contrast to a CW laser, an excimer laser with a UV wavelength and pulses width in the range of nanoseconds, resulting in extremely high cooling rate up to 1011 K/s, is expected to generate a further refining of the near-surface microstructure and hence, improved corrosion performance. In this project, a Lumonics IPEX 848 KrF excimer laser, with a wavelength of 248 nm and pulse width of 13 ns, has been used for surface melting of an AA2024-T351 alloy. The aim is to investigate the microstructure and the resultant corrosion behaviour of the laser treated surface, and its contribution to alloy performance. The laser fluence was fixed at 7 J/cm2 and the number of pulses per unit area was varied as 10, 25 and 50 pulses respectively. Microstructural characterisation and compositional analysis have been performed by SEM/EDX, TEM/EDX and XRD to disclose solidification phenomena and phase transformations. The results show that the melted layers, with a melt depth from 3 to 7 µm, have been achieved, that is far more chemically uniform than the bulk alloy. In particular, the relatively fine precipitates and dispersoids in the matrix have been dissolved, while large constituent intermetallic particles at the melted layer/matrix interface have been partially melted. In addition, solute-rich bands, containing particularly copper, were formed within the melted layers, especially at the melted layer/matrix interface. SKPFM also reveals that the laser-melted layers exhibit a uniform surface potential distribution. The corrosion performance of AA2024-T351 alloy before and after LSM has been evaluated by anodic polarisation in deaerated and aerated 0.1 M NaCl solution, and immersion tests in 0.1 NaCl solutions. Exfoliation corrosion immersion test ASTM G34- 01 (EXCO test) was also carried out to evaluate the intergranular corrosion (IGC)/exfoliation resistance of the alloy. The results show that the untreated alloy exhibits severe pitting corrosion and IGC. After LSM, significant improvement of corrosion resistance has been achieved. However, delamination of the laser melted layer from the matrix was evident after an EXCO test for 6 hours. The absence of significant corrosion product may suggest a stress-related mechanism. In order to investigate the effect of LSM on anodising of AA2024-T351 alloy and its influence on the corrosion resistance, excimer LSM has been applied as a pre-treatment method prior to anodising in 0.46 M H2SO4 solution. The results show that LSM significantly improved the corrosion performance following anodising compared with the alloy anodised without LSM and LSM alone.
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Taylor, Karen. "William Thomas Sutherlin, patriarch of Danville." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/88585.
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William Thomas Sutherlin was born on April 7, 1822 in Pittsylvania County, Virginia. He worked in tobacco on his father's farm until 1843. He then moved to Danville and embarked on a career in tobacco manufacturing. Sutherlin's ventures in the tobacco industry allowed him to become the second wealthiest man in the state of Virginia.
In 1849, Sutherlin married Jane Erwin Patrick of Greensboro, N. C. Seven years later the couple moved to their newly built country manor which has been preserved as a museum today.
Sutherlin generously supported numerous industries in his hometown and constantly strove to protect the interests of his fellow Danvillians.
In 1851, he began his illustrious career as a public servant. He served on the Danville Council from 1851-1855 and as Danville's mayor from 1855 to 1861. The year 1861 found Sutherlin expanding his political interests. He was one of Pittsylvania County's two delegates to the Virginia State Convention of that year.Master of Arts
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Pilli, Srinivas. "Effects of ultrasonic impact treatment on fatigue life of pre-exfoliated AA-2024-T351." Thesis, Sheffield Hallam University, 2008. http://shura.shu.ac.uk/20229/.
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In this study investigations were made into the effects of Ultrasonic Impact Treatment (UIT) on pre-exfoliated AA 2024 T351. Electrochemical tests were conducted to determine any changes in electrochemical behaviour of the alloys due to UIT condition. Uniaxial monotonic, cyclic and fatigue crack propagation (FCG) tests were conducted on material in As-Received (AR) condition and UIT condition in air and in a corrosive environment by pre-exfoliating the test specimens at pre-defined set of time periods and temperature range (20 °C). It was clear that the fatigue performance was severely reduced by the introduction of the corrosion environment for AR specimens. SEM analysis suggests that UIT conditioned AA 2024-T351 exhibits resistance to exfoliation corrosion at ambient and temperatures ranging between 20°C to 40°C when compared to AR specimens. However, these results are not supported by potentiodynamic polarisation curves which show a decrease in corrosion resistance of UIT specimens. Also it is understood that there is a considerable amount of Cu refinement and enrichment near the surface when the AA 2024-T351 is subjected to exfoliation corrosion tests. Whilst hydrogen is in an atomic state, it can be adsorbed onto the metal surface and consequently diffuses into the matrix and can have serious detrimental effects. A reference line for minimal pre-existing hydrogen in the alloy is identified and the magnitude of hydrogen is found to be 180 Arbitrary Hydrogen Units (AHU). It is also found that in corrosion environment, the hydrogen ingress and further charging is prominent at ambient temperatures for AR samples, and showed damage over the full width of cross-section. The following conclusions were drawn: 1. UIT surface treatments, followed by exfoliation corrosion have shown increased resistance to a reduction in mechanical properties, notably tensile and yield strength. Fractographic analysis further supported this finding by showing smaller average brittle failure depths for UIT specimens when compared to AR specimens. SEM analysis of AR samples (without exfoliation) showed a crystallographic contribution to the mode of failure where high density slip bands are formed and the initial failure exhibits a step format. 2. It is observed that during exfoliation, hydrogen ingress and adsorption is more prominent at ambient temperatures for AR samples. 3. A slight improvement In Low Cycle Fatigue (LCF) life is observed for pre-exfoliated and UIT conditioned sample but not for UIT conditioned samples only. Little effect is observed for either treatment in the High Cycle Fatigue (HCF) region. 4. Fatigue crack initiation occurred from the edges for all samples. 5. Fatigue crack propagation of exfoliated specimens exhibited faster crack propagation than As-Received specimens. UIT caused retardation in crack propagation rate in AR samples but not in corroded samples. Failure of pre-exfoliated, UIT treated samples failed within the treated strip. It is also noted that crack deviation can occur when the crack tip reaches a secondary phase particle. 6. Nanocrystallisation generates uniformity of the surface which refines the secondary phase particles and helps mitigate crack initiation sites.
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Tavakkoli, Shahriar. "Shape design using intrinsic geometry." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/39421.
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Taylor, Helen Wilson. "An investigation of factors associated with the implementation of mandatory staff development training." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54439.
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This descriptive study investigated those factors associated with mandatory staff development training that teachers reported as being conducive to the implementation of the content presented. To obtain the necessary data for this study, 24 elementary teachers from Portsmouth, Virginia Public Schools were interviewed. The interview guide sought answers to questions relating to 1) mandatory staff development participation, 2) school based support of staff development training, 3) relevancy of content presented, 4) factors that motivate teachers in wanting to attend staff development training programs, and 5) demographic information.
The major findings were that there is no clear distinction between responses of those teachers who implemented and those that did not implement the mandatory staff development training. The majority of the responses toward mandatory staff development training were positive, even though the impact of the content presented was not as great on some teachers as it was on others. Most of the teachers saw staff development training as being very important and did tend to use some or most of the content presented.
School based support by the principal was revealed as being helpful when teachers sought their assistance. Teachers' colleagues and central administration were reported as being positive and enthusiastic, thus enhancing the implementation of the content presented. Also, motivational status of the teachers was a primary factor in affecting the implementation of staff development training. Lastly, the demographic variable, currently enrolled in graduate work, was found to be the predictor variable in whether or not a teacher would tend to be an implementor of staff development training.Ed. D.
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Busquim, Thaís de Paula. "Avaliação da resistência à corrosão da liga 2024-T351 soldada por FSW Friction Stir Welding." Universidade Federal de São Carlos, 2007. https://repositorio.ufscar.br/handle/ufscar/764.
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Previous issue date: 2007-09-14Universidade Federal de Sao Carlos
The corrosion resistance of aluminum alloy can be impaired due to intermetallic precipitation during thermal treatment to improve mechanical properties. This work investigates the corrosion resistance of aluminum alloy 2024-T351 and the joint welded by FSW. Microstructural analysis and microhardness tests were made. Intergranular corrosion tests according to ASTM G110-97, exfoliation corrosion tests according to ASTM G 34-01 and stress corrosion cracking in 3.5% NaCl according to ASTM G 129-00, were carried out. Anodic behavior was evaluated by potentiodynamic polarization measurements in 3.5% NaCl solution. It was not detected intermetallic precipitates by electron and optical microscopy. It was also detected that the joint was more severe attacked than the base metal by intergranular corrosion and exfoliation tests. The welded joint was susceptible to stress corrosion cracking in tests carried out with low nominal strain rate of 10-7 s-1. Base metal and the joint in tests carried out in air and in 3.5% NaCl at strain rate of 10-6 s-1 showed ductile behavior, while the joint with strain rate of 10-7 s-1 showed fragile behavior. The polarization test in chloride medium of aluminum alloys didn t show passive breakdown what make difficult to determinate the pitting potential. Polarization curves indicated that the welded joint had lower current density and higher potential than the base metal. In lower potentials pitting was formed majoritary at grain boundaries
A resistência à corrosão de ligas de alumínio pode ser degradada devido à precipitação de intermetálicos quando submetidas a tratamentos térmicos para elevar a resistência mecânica. Este trabalho investiga a resistência à corrosão da liga de alumínio 2024-T351 e também da junta soldada por FSW. Foram feitos análise microestrutural e microdureza. Foram realizados ensaios de corrosão intergranular segundo a norma ASTM G110-97, corrosão por esfoliação de acordo com a norma ASTM G34-01 e também ensaio de corrosão sob tensão em solução de NaCl 3,5% com taxa de deformação de 10- 6 e 10-7 s-1, segundo a norma ASTM G129-00. O comportamento anódico foi avaliado por testes potenciodinâmicos em solução de NaCl 3,5%. Os precipitados intermetálicos não foram observados por microscopias ótica e eletrônica. Nos ensaios de corrosão intergranular e esfoliação foi observado que a junta soldada sofreu corrosão mais acentuada do que o metal base. A junta soldada foi suscetível a corrosão sob tensão, somente em ensaios realizados com taxa de deformação baixa, de 10-7 s-1. O metal base e a junta ensaiada ao ar e em NaCl 3,5% com taxa de deformação de 10-6 s-1 apresentaram comportamento dútil, enquanto a junta com taxa de deformação 10-7 s-1, apresentou comportamento frágil. Nos ensaios de polarização em meio de cloretos a liga 2024-T351 não foi observado patamar de passivação o que dificultou a determinação do potencial de pite. As curvas de polarização mostraram que a junta soldada possui densidade de corrente menor e maiores potenciais do que o metal base. Em baixos potenciais os pites foram formados preferencialmente nos contornos dos grãos
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Taraban, Ronald H. "Isolation and characterization of carbofuran and dicamba degrading bacteria." Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40115.
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Tate, Andrew E. "Maturation, spawning and fertility of hybrid striped bass (Morone chrysops x Morone saxatilis) exposed to 6- and 9-month photothermal cycles." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-02132009-170956/.
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Larignon, Céline. "Mécanismes d'endommagement par corrosion et vieillissement microstructural d'éléments de structure d'aéronef en alliage d'aluminium 2024-T351." Phd thesis, Toulouse, INPT, 2011. http://oatao.univ-toulouse.fr/6994/1/larignon_partie_1_sur_2.pdf.
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Cette thèse s'inscrit dans le cadre d'une collaboration avec EADS Innovation Works et AIRBUS. L'objectif des travaux est d'identifier les modes d'endommagements possibles d'éléments de structure métalliques d'aéronefs développés en service et d'en comprendre les mécanismes et les effets sur les propriétés des matériaux afin de contribuer au développement d'une méthode de contrôle non destructif innovante. Le matériau sélectionné est un alliage d'aluminium 2024-T351, l'un des matériaux constitutifs de la voilure et du fuselage d'avions civils. Les modes d'endommagement étudiés sont la corrosion et le vieillissement microstructural. La première partie de ces travaux est consacrée à l'analyse de l'influence des conditions d'exposition au milieu corrosif sur le développement de la corrosion intergranulaire et à l'identification des mécanismes de dégradation associés et de leurs cinétiques. Des conditions d'exposition originales alternant des phases d'immersion et d'émersion à différentes températures ont été explorées dans la mesure où elles semblent particulièrement représentatives des conditions d'exposition réelles. Les mécanismes proposés pour comprendre l'endommagement observé dans certaines de ces conditions d'exposition au milieu corrosif, impliquent un phénomène apparenté à de la fragilisation par l'hydrogène, phénomène qui n'est, à l'heure actuelle, pas encore reconnu pour les alliages d'aluminium de la série 2xxx. L'influence de l'hydrogène sur les propriétés physico-chimiques et mécaniques du matériau est donc étudiée dans la seconde partie de ces travaux. Enfin, l'influence d'un vieillissement microstructural sur les propriétés de l'alliage ainsi que les couplages possibles entre vieillissement microstructural et phénomènes de corrosion sont abordés dans une dernière partie. L'ensemble des résultats obtenus permet de révéler des pistes pour développer une méthode CND innovante permettant la caractérisation physique in-situ du niveau d'endommagement à l'échelle locale d'éléments de structures en alliages d'aluminium.
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Curtis, Sean Allan. "The effects of shot peening on corrosion fatigue of aluminium alloy 2024 T351 and 7150 T651." Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289664.
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Adiwijayanto, Florentinus. "Etude comparative des mécanismes de fissuration par fatigue des alliages d'aluminium 8090C T851 et 2024 T351." Poitiers, 1994. http://www.theses.fr/1994POIT2284.
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Cette etude a pour objet de comparer les mecanismes de fissuration par fatigue d'un alliage d'aluminium-lithium du type 8090c t851 et le 2024 t351, sous chargements d'amplitude constante et sous spectres representatifs des sollicitations subies par l'intrados d'une aile d'avion. Sous chargement d'amplitude constante, la resistance a la fissuration, a l'air et sous vide, du 8090c t851 est superieure ou egale a celle du 2024 t351. La difference s'amenuise lorsqu'il s'agit d'essais a l'air et a r eleve. Ce comportement est attribue a l'effet de fermeture. Sous chargement d'amplitude variable, la resistance a la fissuration sous vide de l'alliage aluminium-lithium est nettement superieure a celle de l'alliage 2024 alors que, sous air, les vitesses de fissuration sont quasi similaires pour les deux alliages. L'etude des micro-mecanismes permet d'identifier trois mecanismes principaux: 1) un mecanisme appele stade i-like, a caractere cristallographique dominant du a l'activation d'un seul systeme de glissement selon un plan 111, 2) un mecanisme associe a la propagation suivant un plan 100 par activation de glissement selon deux plans 111, 3) le mecanisme associe a l'activation de plusieurs systemes de glissement simultanes (stade ii) avec un plan moyen de fissuration 100. L'analyse quantitative des facies de rupture montre que dans le 8090c t851 le mode de rupture predominant depend des conditions de sollicitation et d'environnement, tandis que dans le 2024 t351, le mecanisme de fissuration predominant est toujours le stade ii. Cette analyse permet d'etablir des modeles de prevision de duree de vie
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Tang, Yun-chung. "Motor simulation and parameter identification in a reciprocating mechanism." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-10312009-020104/.
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Taylor, Lynn Elizabeth. "The effects of added fat on acid-base status in exercising horses." Thesis, Virginia Tech, 1991. http://hdl.handle.net/10919/45305.
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Two groups of horses were each fed either a control diet of ground hay and concentrates (4 horses), or a Similar diet with 10% added fat after undergoing a baseline Standard Exercise Test (SET). The SET was a stepwise, incremental test to exhaustion on an equine treadmill set at a 6% slope. Resting and working heartrates and rectal temperatures were monitored, and venous blood was collected at rest, and every 3 minutes during exercise, just prior to each speed change. Blood was analyzed for pH, hemoglobin, and pCO₂, and base excess and plasma bicarbonate levels were calculated using nomogram equations. Plasma samples were analyzed for albumin at each step, and for sodium, potassium, chloride, and lactate at rest and exhaustion only. The plasma SID was calculated at rest and exhaustion by the following equation:
([Na⁺] + [K⁺]) - ([Cl⁻] + [Lactate])
The SET was performed after 16 days of interval training, and once more after another 16 days of interval training. Differences over time during exercise were found: heartrate, lactate, and potassium increased (p<.001), and hemoglobin increased (P<.01). Decreases were found in PH, pCO₂, bicarbonate concentration, base excess, and chloride (p<.001). Training effects were found in resting and working heartrates, pCO₂, bicarbonate concentration, and base excess, which all decreased during exercise with training. Hemoglobin increased during exercise with training. There were treatment * SET interactions for Strong Ion Difference, base excess, lactate concentration, pCO₂, and pH. There were no differences found between groups for any of the variables measured. Both groups showed improvements in fitness with training, and the fat group had a higher level of plasma lactate by SET 3. These results suggest that a high fat diet combined with interval training may have some effects on plasma lactate, and that training alone can affect many variables. The results also give evidence to support the evaluation of SID during exercise in horses.Master of Science
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Beal, Roger Zack. "A study comparing changes in loading conditions of an extended service life system using aluminum 2024-T351." Thesis, The University of Utah, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1569706.
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The current fiscally austere environment prevalent in the military and industry is driving extreme measures to save money. In the United States Air Force, this has driven enormous efforts to trim sustainment spending on extended life aircraft. The challenge to the aerospace engineer is to ensure flight safety in the midst of this economic pressure.
One method of cutting costs is to increase the time an aircraft is in service by delaying the point when the aircraft is taken out of service for depot maintenance. To ensure flight safety, in depth fatigue and fracture analysis needs to be accomplished to assess increasing the inspection interval.
The purpose of this study was to determine the sensitivity of Aluminum 2024-T351 alloy, a common material used in tension dominated aerospace applications, to two different loading spectra—one that is aggressive and the other that is benign. This was accomplished by conducting five different combinations of the two spectra, developing computer simulations using the AFGROW software and comparing with the measured data. The results showed that the material demonstrated significantly different behavior between the two spectra. These results provide a valuable tool for the aerospace engineer for fatigue life prediction and inspection interval evaluation.
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Billy, Fabien. "Vieillissement et propriétés résiduelles de matériaux issus du démantèlement d'avions en fin de vie." Phd thesis, ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2013. http://tel.archives-ouvertes.fr/tel-00824151.
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Cette thèse s'inscrit dans le cadre d'un vaste programme visant à établir un premier retour d'expérience sur des structures aéronautiques en fin de vie. L'objectif des travaux présentés ici est donc de caractériser le vieillissement et les propriétés résiduelles de pièces provenant d'avions après démantèlement, et donc après service. Plus précisément, deux matériaux de nature différente sont considérés : un alliage d'aluminium 2024-T351, constitutif d'une voilure d'A320 ; et un composite carbone/époxy T300/914, prélevé sur les voilures d'un Falcon X et d'un ATR.Pour les voilures composites, les travaux ont porté sur les effets de l'eau des stratifiés. L'évolution de la température de transition vitreuse en DMA a été étudiée en fonction du taux d'humidité présente dans le stratifié. Les résultats d'essais de sorption set de désorption ont été confrontés à différents modèles de diffusion. Les propriétés résiduelles ont été évaluée au travers de divers essais mécaniques. Il ressort de cette étude un très bon comportement du composite après service.Les travaux concernant la voilure métallique se focalisent sur les propriétés résiduelles en fatigue de l'alliage de voilure. Les résultats montrent qu'un durcissement structural apparaît en service, et qu'un léger abattement de la durée de vie en fatigue est observable. Cependant, le comportement à la fissuration est inchangé en comparaison avec un matériau " neuf ".Au final, ce premier retour d'expérience est positif. Il peut maintenant permettre aux avionneurs de vérifier les règles utilisées lors de la conception ou d'optimiser certains dimensionnements, mais aussi de justifier des extensions de durée de vie des avions.
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Pauze, Nathalie. "Fatigue corrosion dans le sens travers court de tôles d'aluminium 2024-T351 présentant des défauts de corrosion localisée." Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 2008. http://tel.archives-ouvertes.fr/tel-00359611.
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La gestion des flottes vieillissantes conduit à étudier les effets de la corrosion sur la tenue mécanique des structures en alliages d'aluminium, depuis les défauts de corrosion de surface jusqu'à la fissure mécaniquement active.Nous avons caractérisé la sensibilité de l'alliage 2024-T351 à la corrosion intergranulaire. Il se forme en 7h d'immersion dans NaCl 0.5 M un défaut semi-elliptique de 200 µm de profondeur. Puis la corrosion intergranulaire ralentit fortement.
Nous avons étudié les mécanismes de propagation en fatigue à partir de ces défauts, en particulier la transition entre la corrosion intergranulaire et les fissures transgranulaires courtes de fatigue. A chaque étape de l'endommagement, une estimation des cinétiques, du Delta-K et la morphologie des défauts sont données. Deux mécanismes ont été distingués : un mécanisme de corrosion sous contrainte (cyclique) intergranulaire et un mécanisme de fatigue corrosion transgranulaire. Un critère de transition est proposé
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Tadepalli, Raghuram. "An empirical investigation of the relationship between purchasing professionals' perceptions of role stress and selected antecedent and consequent variables." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/74218.
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Public purchasing professionals bought approximately 500 billion dollars worth of products and services from marketers in 1979; this figure represented 20% of this country's gross national product for that year. Therefore, public purchasing professionals constitute a key segment of interest to marketers. Ascertaining the effects that 'marketer controlled' variables have on the role conflict and role ambiguity of the public purchasing professional can thus contribute to marketing management and to marketing thought.
Two of these variables are the perceived Customer Orientation of the Vendor salesperson and the Influence Strategy/s used by the salesperson. Other variables that can provide valuable information to marketers are purchasing professionals' perceptions of Uncertainty and/or Conflict regarding their organizations' performance (or reward/measurement) indexes. These three variables along with experience are hypoth- esized antecedents to role conflict and role ambiguity. The consequent variables to role conflict, role ambiguity, and experience, are the purchasing professional's perceptions of Satisfaction with the Salesperson, and Satisfaction with Organizational Policies.
Data was collected from a random sample (N=345) of the members of the National Institute of Government Purchasing. The usable response rate was 49. 92%. Data was analyzed through the use of LISREL VI. Hypotheses were tested by examining the direction of the LISREL parameters, and the statistical significance of their t-values. Support was found for ten of fourteen hypotheses.
Findings from the study can be used in training salespeople and purchasing professionals; the study also has implications for marketing strategy. The variables being researched can provide insights that can then be used in research in sales management and organizational buying behavior.Ph. D.
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Tackett, Jared Franklin. "Directing Movement and the Perception of Space." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/33437.
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An investigation on how architectural elements can direct movement and affect the way we perceive space. The idea is implemented in the design of a playground and pavilion for Elkhorn Lake, located in Jenkins, Kentucky.
Wall, column, color, roof, and floor are explored to create a variety of spatial arrangements that affect ways of perceiving and moving through the pavilion and playground.Master of Architecture
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Lacombe, Alexandra. "Influence du procédé de perçage sur l'intégrité de surface et la tenue en fatigue de pièces percées en AA2024-T351." Thesis, Toulouse 3, 2021. http://www.theses.fr/2021TOU30001.
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Dans les structures aéronautiques, les trous percés constituent des zones critiques à partir desquelles des endommagements peuvent s'initier en fatigue. En fonction des paramètres et des procédés de perçage employés, les industriels constatent des différences significatives de tenue en fatigue des structures percées. Ces travaux de thèse visent à apporter des éléments de compréhension à cette problématique industrielle, pour le cas pièces percées en AA2024-T351. Ils portent sur l'étude de configurations de perçage industrielles et se focalisent sur deux procédés de perçage : le perçage orbital qui est un procédé présentant de nombreux avantages économiques potentiels et le perçage axial qui est le procédé de perçage conventionnel. L'objectif des travaux est d'évaluer l'impact de la configuration de perçage sur la tenue en fatigue de la pièce percée, mais aussi sur l'intégrité de surface du trou percé. Cela doit permettre d'identifier les paramètres de l'intégrité de surface pilotant la tenue en fatigue et les paramètres majeurs du procédé de perçage contrôlant l'intégrité de surface. La première étape des travaux a été de mener des essais de fatigue afin d'évaluer la performance en fatigue de différentes configurations de perçage. Ceux-ci ont révélé des écarts significatifs de durée de vie en fatigue entre certaines configurations de perçage. La seconde étape a consisté à caractériser expérimentalement l'intégrité de surface des trous percés. Celle-ci a été guidée par un modèle éléments finis prédictif de la profondeur de matériau affectée en sous-surface du trou et de nouvelles méthodes d'analyse (comme la "HOCT") ont dû être envisagées pour certains aspects de l'intégrité de surface dû à la faible profondeur affectée. Cette campagne a montré l'influence prépondérante des aspects internes de l'intégrité de surface (écrouissage et contraintes résiduelles) sur la tenue en fatigue. Enfin, la dernière étape des travaux visait à étudier l'impact des paramètres du procédé de perçage sur l'intégrité de surface. Pour cela, un modèle éléments finis de coupe orthogonale a été développé. L'influence prépondérante de la géométrie de l'outil sur l'intégrité de surface a été montréeIn aircraft structures, drilled holes are major critical areas from where fatigue damage can be initiated. Depending on the drilling parameters and process, manufacturers observe significant different fatigue strength of the drilled structures. This thesis aims to give elements for understanding this industrial problem, for the case of AA2024-T351 drilled parts. It deals with industrial drilling configurations and focus on two drilling processes: orbital drilling which offers many potential economic advantages and axial drilling which is the conventional drilling process. The objective of the study is to assess the impact of the drilling configuration on the fatigue strength of the drilled part, but also on surface integrity of the drilled hole. This has to enable to identify the surface integrity parameters controlling the fatigue strength and the major drilling process parameters driving the surface integrity. The first step of the work was to conduct fatigue tests to assess the fatigue performance of different drilling configurations. These revealed significant differences in fatigue life between some drilling configurations. The second step was to lead an experimental characterization of the surface integrity of the drilled holes. This was orientated by a finite element model predicting the material depth affected in the hole subsurface and new analysis methods (like the "HOCT") had to be considered for some aspects of the surface integrity due to the small depth affected. This campaign showed the dominating influence of the internal aspects of the surface integrity (strain hardening and residual stress) on the fatigue strength. Finally, the last step of the work aimed to study the impact of the drilling process parameters on the surface integrity. For this purpose, a finite element model of orthogonal cutting has been developed. The dominating influence of the tool geometry on the surface integrity has been shown
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Prieto, Yespica Wolfgang José. "Etude comparative du comportement électrochimique des alliages d'aluminium 2024 T351 et 7075 T7351 en milieu neutre de sulfate de sodium." Thesis, Toulouse, INPT, 2012. http://www.theses.fr/2012INPT0054/document.
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Ce travail concerne l'étude du comportement vis-à-vis de la corrosion de deux alliage d'aluminium : l'alliage 2024 (AA 2024 T351) et l'alliage 7075 (AA7075 T7351) et de l'aluminium pur, utilisé comme référence, dans une solution de Na2SO4 0,1 M à l'aide de mesures électrochimiques (courbes de polarisation, courbes de Levich et spectroscopie d'impédance) avec des électrodes à disque tournant. Comparativement aux travaux de la littérature, des données quantitatives sur les processus anodique et cathodique qui se produisent sur les deux alliages ont été obtenues. La première partie de la thèse est consacrée à la caractérisation microstructurale des deux alliages : taille, composition chimique des précipités et fraction surfacique occupée par les différentes phases. La seconde partie présente les résultats d'impédance obtenus au potentiel de corrosion pour différents temps d'immersion et différentes vitesses de rotation. A ce potentiel, le comportement des matériaux est essentiellement contrôlé par le film passif. Les diagrammes d'impédance présentent une dispersion en fréquence, exprimée en termes de « constant phase element (CPE) ». Ce comportement a été analysé à l'aide d'un modèle physique qui permet de montrer une distribution de résistivité dans l'épaisseur des films d'oxyde. Dans la dernière partie, une attention particulière a été portée à l'analyse de la réaction cathodique à la surface des deux alliages qui est à l'origine de leur dégradation importante. La réduction de l'oxygène se produit principalement sur les particules intermétalliques. De façon surprenante, la densité de courant cathodique est nettement plus faible pour l'alliage 7075 qui présente une plus grande surface couverte par les particules. Il a été montré que pour l'alliage 2024, la réaction cathodique est contrôlée par le transport de matière par diffusion convective sur de petites électrodes alors que pour l'alliage AA 7075, la majeure partie des particules, de très petite taille, se comporte comme des microélectrodes pour lesquelles le courant est fixé par la diffusion sphérique, indépendante de la convectionThis work concerns the study of behavior the corrosion of two aluminum alloy: the alloy 2024 (AA 2024 T351) and 7075 (AA7075 T7351) and pure aluminum, used as reference, in a solution of 0.1 M Na2SO4 using electrochemical measurements (polarization curves, curves Levich and impedance spectroscopy) with rotating disk electrodes. Compared to published studies, quantitative data on the anodic and cathodic processes occurring on the two alloys were obtained. The first part of the thesis is devoted to the microstructural characterization of two alloys: size, chemical composition of precipitates and surface fraction occupied by the different phases. The second part presents the results of impedance obtained at the corrosion potential for different immersion times and different speeds. At this potential, the behavior of materials is mainly controlled by the passive film. The impedance diagrams exhibit a frequency dispersion, expressed in terms of "constant stage element (CPE)." This behavior was analyzed using a physical model which allows to show a distribution of resistivity in the thickness of oxide films. In the last part, special attention was paid to the analysis of the cathodic reaction on the surface of the two alloys that is causing their degradation. The oxygen reduction occurs mainly on the intermetallic particles. Surprisingly, the cathode current density is significantly lower for the alloy 7075 which has a greater surface area covered by the particles. It was shown that for 2024 alloy, the cathodic reaction is controlled by material transport by convective diffusion of small electrodes, while for the alloy AA 7075, most of the particles, very small, behaves as microelectrodes for which the current is set by the spherical diffusion, independent of the convection
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Tang, Stanley C. "Robot positioning error analysis and correction." Thesis, This resource online, 1987. http://scholar.lib.vt.edu/theses/available/etd-04122010-083623/.
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Théberge, Francis. "Third-order parametric processes during the filamentation of ultrashort laser pulses in gases." Thesis, Université Laval, 2007. http://www.theses.ulaval.ca/2007/24401/24401.pdf.
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Tan, Jeffrey Meng-Lee. "Residual stress and fatigue crack growth life prediction in fastener holes cold-worked by uniform indentation in 2024-T351 aluminium alloy." Thesis, Open University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500610.
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This thesis concerns primarily the residual stress characterisation in fastener holes cold worked by a novel StressWave process, and the prediction of the fatigue crack growth under the influence of such residual stress. Aerospace 2024-T351 aluminium alloy plate of 6.35mm thickness containing a nominal 06.35mm hole was used. Using neutron and laboratory X-ray diffraction measurements, a large compressive residual stress was found in StressWave and split-sleeve cold-worked holes. Detailed stress mapping indicates that a StressWave hole contains a highly symmetric residual stress field with a wider compression region. Conversely, the spht-sleeve technique generates a complex asymmetric stress variation through the specimen thickness and around the hole. Independently, a comprehensive finite element study was conducted to reveal the residual stess development associated with two distinct cold-working techniques at various stages. Favourable agreement was achieved between the experiment and simulations. The deformation mechanism associated with the cold-working process is decisive to the behaviour of the residual stress field created. The symmetric crack growth behaviour observed-in StressWave specimens permits a through-thickness crack geometry to be considered. Accordingly, Green's functions for a single crack and two symmetric cracks originating from the edge of a circular hole were developed. These solutions were verified using weight function and finite element analysis and are therefore appropriate for subsequent study of fatigue crack growth. A theoretical framework was proposed to explicate the interaction of residual stress with the superimposed loading at the crack tip, which was mathematically expounded as a function of stress intensity factor and stress ratio. This analytical framework provides a reasonable correlation between the mean stress and crack closure criteria.
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Priest, Maria. "The experimental characterisation of residual stresses and fatigue crack growth in the vicinity of cold worked holes in Al 2024-T351." Thesis, University of Bristol, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387962.
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Taiyabi, Asif A. "A multi-attribute analysis of nuclear waste disposal alternatives." Master's thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-02022010-020127/.
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Terrado, Ramon. "Diversité et succession des protistes dans l'océan Arctique." Thesis, Université Laval, 2011. http://www.theses.ulaval.ca/2011/27849/27849.pdf.
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Terradas, Miguel M. "La fonction réflexive chez les mères d'enfants victimes d'abus sexuel : développement d'une échelle mesurant le fonctionnement réflexif de la mère dans un contexte d'interaction mère-enfant." Doctoral thesis, Université Laval, 2007. http://hdl.handle.net/20.500.11794/19339.
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Tang, Ruey-Er. "Computer utilization in interior design: designer attitudes, function application, and equipment usage." Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/45658.
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This research investigated the extent of computer usage in the interior design profession including attitudes toward computers, computer applications, and computer equipment usage. A questionnaire was sent to five hundred professional members of the American Society of Interior Designers across the nation.
The frequency distribution was used on 169 usable data to describe the sample background characteristics and to determine the computer equipment utilization. Means and TV test were employed to examine if a significant difference of opinion toward computers existed between designers based on experience on computers, size of organizations, and type of projects.
Findings which were statistically significant indicated that computer-experienced and non-residential interior designers had more positive attitudes toward computers. More computers had been incorporated into non-residential interior designersâ offices. Overall, interior designers from various backgrounds had the same opinion in believing that computers were not cost-effective for drafting application for most interior designers or for their own establishments at present. The most popular computer applications in this study were billing, accounting, financial management, specification, and business correspondence. Furthermore, the IBM personal computer was found to be the most used microcomputer in this study.
Master of Science
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Atlati, Samir. "Développement d'une nouvelle approche hybride pour la modélisation des échanges thermiques à l'interface outil-copeau : application à l'usinage de l'alliage d'aluminium aéronautique AA2024-T351." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0200/document.
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Ce travail de thèse a été réalisé dans le cadre d'une collaboration internationale entre l'Université de Lorraine (France) et l'Université d'Oujda (Maroc). Les travaux réalisés concernent la modélisation de l'usinage par enlèvement de matière. Deux aspects importants de l'usinage ont été abordés : le processus de la formation de copeaux et les échanges thermiques à l'interface outil-copeau. Dans la première partie de la thèse, une modélisation par élément finis (EF) du processus de la coupe a été mise en place. La segmentation des copeaux a été particulièrement analysée grâce à l'introduction d'un nouveau paramètre, le Rapport d'Intensité de Segmentation, permettant de quantifier ce phénomène. Une corrélation entre la réduction de l'effort de coupe et l'intensité de segmentation a été établie. La deuxième partie de la thèse a été consacrée à l'étude des échanges thermiques à l'interface outil-copeau, qui contribuent entre autres à l'usure de l'outil de coupe. Un des points importants de l'étude est la mise en place d'une procédure d'identification hybride (analytique/numérique) permettant d'estimer le flux thermique transmis dans l'outil de coupe et de remonter au coefficient de partage de la chaleur à l'interface outil-copeau pour chaque vitesse de coupe. Avec les valeurs identifiées du coefficient de partage de la chaleur pour chaque vitesse de coupe, une loi d'échange thermique multi-branches a été proposée et ses paramètres identifiés. Cette loi donnant l'évolution du coefficient de partage de la chaleur en fonction de la vitesse de coupe a également été définie en fonction de la vitesse relative de glissement à l'interface outil-copeau dans le but de l'implanter dans un code de calcul EF. L'interface utilisateur VUINTER du code Abaqus/Explicit a été exploitée pour implanter la loi proposée, afin d'appréhender complètement le contact d'un point de vue mécanique et thermique. Il est désormais possible d'implanter via cette interface-utilisateur n'importe quelle autre loi de contact thermomécanique (frottement, coefficient de partage de la chaleur, etc.). L'implantation via la subroutine VUINTER a été validée sur des cas tests d'abord, et puis ensuite en usinage. Les résultats obtenus pour les flux thermiques avec cette nouvelle procédure sont en très bon accord avec les mesures expérimentales pour le couple outil-matière considéré : AA2024-T351/WC-CoThis PhD. thesis is realised in the framework of an international cooperation between the University of Lorraine (France) and the University of Oujda (Morocco). The work done concerns the modelling of machining process by material removal. Two important aspects of machining have been investigated: the chip formation process and the heat exchange at the tool-chip interface. In the first part of the thesis, a FE modelling of the cutting process has been established. Chips segmentation have been particularly analysed using à new parameter (Segmentation Intensity Ratio) allowing the quantification of the phenomenon. A correlation has been established between the cutting force reduction and the chip segmentation intensity. The second part of the thesis has been devoted to the study of heat exchange at the tool-chip interface, among other phenomena that contribute to the tool wear. One important point of the study is the establishment of a hybrid identification procedure (analytical/numerical) to estimate the heat flux transmitted into the cutting tool, and identification of the heat partition coefficient at the contact interface for each cutting speed. With identified values of the heat partition coefficient obtained by varying the cutting speed, a heat exchange multi-branch law has been proposed and parameters of this law have been identified. This law corresponds firstly to the evolution of the heat partition coefficient as a function of the cutting speed. Thereafter, it was defined in term of the relative sliding velocity at the tool-chip contact interface, in order to implement it in a FE code. The user interface VUINTER of Abaqus/Explicit has been used to implement the proposed law, to fully control the mechanical and thermal contact. It is henceforth possible to implement with this user interface any thermomechanical contact (friction, heat partition coefficient, etc.). The implementation via the user subroutine VUINTER was validated first on adequate tests, then on machining. The obtained results for heat fluxes with this new procedure are in good agreement with experimental measurements for the tool-workmaterial couple considered: AA2024-T351/WC-Co
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Smith, Jarrod L. "Full-Field Measurement of the Taylor-Quinney Coefficient in Tension Tests of Ti-6Al-4V, Aluminum 2024-T351, and Inconel 718 at Various Strain Rates." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546452653747728.
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List, Gautier. "Etude des mécanismes d'endommagement des outils carbure WC-Co par la caractérisation de l'interface Outil-Copeau: application à l'usinage à sec de l'alliage d'aluminium aéronautique AA2024 T351." Phd thesis, Paris, ENSAM, 2004. http://pastel.archives-ouvertes.fr/pastel-00001178.
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L'étude proposée traite de la compréhension des mécanismes d'endommagement des outils carbure dans le cas de l'usinage à sec d'un alliage d'aluminium aéronautique (AA2024 T351). Elle a pour but de déterminer les différents paramètres tribologiques de l'interface outil-copeau (frottement, température, pression) et de les confronter aux différents modes d'usure. Une modélisation du contact entre le copeau et l'outil basée sur les propriétés viscoplastiques de l'écoulement du matériau est d'abord proposée. Elle permet d'établir les relations qui existent entre la géométrie du copeau (angle de cisaillement), les contraintes appliquées sur l'outil, le coefficient de frottement et la vitesse de glissement du copeau au voisinage de la pointe de l'outil. Le modèle analytique est alors employé pour déterminer la nature du contact (collant, glissant) et calculer la vitesse de glissement. Pour déterminer la température et la pression de contact, un dispositif d'étude basé sur l'observation expérimentale de la formation du copeau (caméra vidéo rapide, mesure des efforts, calcul de flux thermique) et la simulation numérique par la méthode des éléments finis est ensuite mis en place. La caractérisation physico-chimique réalisée à l'aide de techniques complémentaires d'analyse de surface (MEB, EDS, AES, profilométrie optique) a permis d'identifier clairement les différents types d'endommagement. Ils se traduisent par la formation d'arêtes rapportées et de couches adhérentes (couches de transfert formées par extrusion de précipités) ainsi que par la fragilisation de l'outil provoqué par la diffusion de certaines espèces chimiques du copeau vers l'outil. Grâce à la démarche proposée, il est possible de relier ces différents modes d'endommagement aux conditions de contact existant à l'interface outil-copeau.
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Tang, Guanghua. "High temperature thin film superconductors and microstrip spiral delay lines." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-01242009-063221/.
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Thadal, Philippe. "Impact des interactions sociales sur les transferts des migrants : cas du district thaïlandais de Nang Rong." Thesis, Université Laval, 2009. http://www.theses.ulaval.ca/2009/26219/26219.pdf.
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Judas, Jakub. "Extrémně nízkocyklová únavová životnost slitin neželezných kovů." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400859.
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This thesis is focused on fatigue behaviour of aluminium alloy 2024-T351 in low cycle and extremely low cycle fatigue regime. Test specimens were firstly subjected to quasi-static tensile and compression tests to establish basic mechanical properties of the experimental material. Fatigue tests were conducted in strain-control mode, when cyclic plastic response and S-N curves were determined. All of the experiments were conducted at room temperature. Shapes of mechanical hysteresis loops are dependent on the strain amplitude and clearly exhibit cyclic plasticity of the alloy. Cyclic deformation curve was fitted by power regression function and subsequently compared with the tensile test. Experimental data of the S-N curves were fitted by Manson-Coffin and Wöhler-Basquin law. The discrepancy of the fatigue data was observed in the extremely low cycle fatigue regime. Based on this phenomenon, new regression function was used to overcome shortening of fatigue life in the extremely low cycle regime.
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Taylor, Beatrice Dietering. "A study of high school biology students engaged in a Science-Technology-Society (STS) landfill restoration project." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/37429.
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