Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 129-133).

Diss. Växjö : Växjö universitet, 2009.

Made available in DSpace on 2014-06-11T19:27:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-09-22Bitstream added on 2014-06-13T19:14:26Z : No. of bitstreams: 1 zaratevilchez_ca_me_ilha.pdf: 5637915 bytes, checksum: e3c2e57bc02776ffc28c0ea2eb3a7430 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os processos de soldagem são um dos principais meios de fabricação e vêm sendo cada vez mais empregado nos mais diversos ramos industriais. Um exemplo disso é aplicação em grande escala da soldagem na construção civil, sobretudo para a fabricação de perfis e estruturas metálicas. Para estruturas como pontes com grande vão livre, edifícios multiandares, estruturas off-shore, estão entre as aplicações mais modernas. Com o objetivo de racionalizar custos de processamento e de materiais empregados em junções soldadas, desenvolveu-se a técnica de soldagem de laminados planos sem chanfro em apenas um lado só. Entretanto, quando se solda este tipo de perfil estrutural com um único passe, dificilmente consegue-se penetração total. A falta de penetração origina um entalhe entre a aba e a mesa do perfil. A complexa microestrutura formada após a solidificação do cordão-de-solda e a presença do entalhe tornam esta região propicia para a nucleação e propagação de trincas, que podem originar falhas mecânicas catastróficas. Deste modo, deve-se procurar uma microestrutura que favoreça uma melhoria na tenacidade da junta soldada. Recentemente, pesquisadores têm apontado a ferrita acicular como sendo o microconstituinte mais apropriado para possibilitar ótimos níveis de tenacidade sem que com isso ocorra significativa perda de resistência mecânica. O presente projeto tem como principal objetivo estudar e compreender o efeito de ciclos térmicos na microestrutura e nas propriedades mecânicas da junta soldada do aço COS Civil 300. A investigação se deu utilizando corpos-de-prova extraídos da junta soldada submetidos a distintos ciclos térmicos. Ensaios mecânicos foram empregados com o intuito de se julgar o mérito dos ciclos térmicos empregados e, conseqüentemente, avaliar quais são os parâmetros microestruturais mais influentes nas propriedades mecânicas... / The welding processes are the main means of fabrication and have been more and more used in the most diverse industrial branch. An example of this is the application in large scale of welding in civil construction, specially for production of steel sections and metallic structures. For structures which as bridges with large span, a multi-floors building, off-shore structures are among the more modern application. By rationalizing cost of processing and employed material in welding joints, the technique was developed of welding of plane laminated without chamfer in one side only. However, when one weld this type of steel structural section in a single step, one hardly achieve total penetration. This lack of penetration causes a notch between the flap and core of steel section. The complex microstructure formed after the solidification of weld metal and the presence of notch make this region propitiated to a nucleation and a propagation of cracks, which can originate mechanical catastrophic failure. This way, one should search a microstructure that favour a improvement in toughness of weld joint. Researchers have pointed out the acicular ferrite as being the most appropriated microstructure to enable optimum levels of toughness without occuring significative loss of strength. The present project has as its main purpose study and comprehend the effect of thermal cycles in the microstructure and mechanical properties in weld joint of the steel COS Civil 300. The investigation occurred utilizing testpiece extracted from the weld joint submitted to the thermal cycles. Mechanical tests were done in order to judge the merit of thermal cycles and, consequently, to assess what microstructural parameters are more influential in the mechanical properties measure, specially in the toughness values. Through the results obtained it was noticed that the quenching condition is the one... (Complete abstract click electronic access below)

Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-10-06Bitstream added on 2014-06-13T18:31:03Z : No. of bitstreams: 1 irikura_si_me_ilha.pdf: 10628926 bytes, checksum: 6e06f10958376596936e2de7dd169f63 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Como se sabe dureza e resistência mecânica dependem da microestrutura do aço. Em aços multiestruturais é importante compreender a influência individual da estrutura do microconstituinte. O único ensaio prático que pode ser realizado individualmente no microconstituinte estrutural em aços multiestruturais é o ensaio de dureza com pequenas indentações sob cargas baixas ou ensaio de microdureza. Já que é possível obter a resistência ou a curva tensão-deformação da dureza de um aço mono estrutural, tal como ferrita, perlita, bainita ou martensita, também é possível estimar a resistência ou a curva tensão-deformação para aços multiestruturais conhecendo-se a fração volumétrica de cada constituinte estrutural individualmente presente. O trabalho tem como objetivo analisar o comportamento de microestruturas de um cordão-de-solda sob ensaio de microdureza com a tentativa de se recompor o valor de dureza Vickers (HV) obtido no ensaio de (macro) dureza, observando-se assim o comportamento individual dos constituintes. O material ensaiado foi a junta soldada por arco submerso do aço estrutural COS Civil 300. Tratamentos térmicos foram realizados para que se pudessem obter microestruturas variadas. As amostras foram analisadas metalograficamente e também por anális... / It is well known that both hardness and strength depend on the microstructure of steels. In multistructure steels, it is important to understand the influence of individual structure microconstituent. The only practical test that can be performed on the individual microstrutural constituents in multistructure steels is a hardness test with a small indentation under low load or microhardness test. If is possible to obtain strength or the stress-strain curves from the hardness of single structure steels, such as ferrite, perlite, bainite or martensite, it is may possible to estimate the strengths or stress-strain curves of multistructure steels by knowing the volume fraction of the individual structural constituents present. The purpose of the present work is analyzing the microstrutural behaviour of weld joint under microhardness test with the attempt of recomposing the Hardness Vickers (HV) value obtained on the (macro) hardness test, observing then the individual behaviour of the constituents. The material tested was the joint welded by submerge- arc welding of the structural steels COS Civil 300. Heat treatment had been carried out to obtain different microstrutures. The specimens were analyzed by metallography and quantitative analysis... (Complete abstract click electronic access below)

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Atherosclerosis is characterised by the progressive growth of a plaque, where a fibrous cap covers a lipid-rich core. Rupture of this fibrous cap can lead to thrombosis and a heart attack or stroke. This dissertation considered the role of plaque microstructure in the mechanics and rupture risk of atherosclerotic plaques. Fibre structures in human atherosclerotic plaques were characterised through scanning electron microscopy, histology, and image processing. Local primary fibre orientation and the fibre dispersion were calculated. Plaque shoulder regions, where rupture is most frequent, had higher fibre dispersion and were more misaligned with the lumen wall. Comparative FE models were made from the plaque geometries and fibre structures found by image processing: one with evenly dispersed fibres (isotropic) and one with a preferred fibre orientation (anisotropic). The isotropic and anisotropic FE models predicted significantly different stresses. Stresses were often highest in the shoulder regions. Anisotropic stresses were calculated relative to fibres: axial stresses were highest, shear stresses were intermediate, and transverse stresses were low. Since the tissue is strongest in the fibre direction (axially), axial and shear failure modes should be considered. Material tests (uniaxial tension, trouser tear, and notched specimen) were used to characterise material properties in healthy porcine arteries. Fibre structures were evaluated by histology, multiphoton microscopy, and image processing. Samples were stiffer circumferentially and toughest against radial tears. Fractures progressed between fibres, rather than by breaking them. Material properties and fracture mechanisms were explained by fibre structures. In summary, atherosclerosis altered the fibre structure of the arteries, in ways that were mechanically significant and that explained clinical observations.

The thesis work is performed at Norma Precision AB, a company that manufactures ammunition for hunting and competitive shooting. Two types of cases called 300 Winchester Magnum and 308 Winchester are examined on how their hardness were prior to and after the two annealing’s of the neck they experience during the manufacturing. The cases vary in hardness and an investigation will be made to draw connections to the microstructure of the cases in order to understand the variations and possibly avoid the variations in the future. The cases were selected at different days, the 300 Winchester Magnum were chosen at three different days with some properties varying and the 308 Winchester were taken at two different days. At each day twenty cases were selected, five prior to the first neck annealing, five after the first neck annealing, five after the shaping and calibrating of the cases and the final five after the second neck annealing. The selected cases were first measured by a hardness test, where they were measured at 1mm, 3mm and 6mm from the nuzzle and five times around the case at each measurement. After that, the variations were analyzed and the two most varying cases from each day and step were taken into the laboratory at Karlstad University. In the laboratory, the cases were measured by a microhardness tester. The cases were measured at even distances between them all throughout the cases to make a hardness profile. The next step was to etch the cases and examine them in an optical microscope, where the grain size was measured in micrometer and ASTM. The results from the regular hardness measurements and the microhardness tests showed similar tendencies. Variations was found in each step and each day during both hardness measurements the two types of cases behaved similarly. The grain size results showed that after annealing, the grain size increased. Although there was no clear relation between grain size and hardness since the results varied, some cases with higher hardness had a smaller grain size than a case with lower hardness. Using the grain size of the brass could work to get an idea of the hardness, but to get a sincerer perception of the material properties, more properties needs to be investigated. / Examensarbetet är utfört hos Norma Precision, ett företag som tillverkar ammunition för viltjakt och för tävlingsskytte. Två sorters hylsor vid namn 300 Winchester Magnum samt 308 Winchester undersöks hur deras hårdhet är innan respektive efter de två mynningsglödgningar hylsorna genomgår under tillverkningen. Hylsorna varierar i hårdhet och en undersökning kommer göras för att dra kopplingar till hylsornas mikrostruktur för att få en förståelse av variationerna och eventuellt kunna undvika variationer i framtiden. Hylsorna valdes ut vid olika dagar, 300 Winchester Magnum togs vid tre olika tillfällen när olika egenskaper skiljde och 308 Winchester togs vid två tillfällen. Varje dag plockades tjugo hylsor ut, fem innan första mynningsglödgningen, fem efter den första mynningsglödgningen, fem efter formning och kalibrering av hylsorna samt fem efter den andra mynningsglödgningen. På de utplockade hylsorna gjordes först hårdhetstester, då de mättes vid 1mm, 3mm och 6mm ifrån mynningen och fem mätningar runt hylsan vid varje mättillfälle. Efter det analyserades resultaten och de två hylsor som varierade mest från varje dag och varje steg togs med till labbet på Karlstads Universitet. I labbet mättes hylsorna med en mikrohårdhetsmätare. Hylsorna mättes med jämna mellanrum genom hela hylsan för att skapa en hårdhetsprofil. Nästa steg var sedan att etsa hylsorna och undersöka dem i ett ljusmikroskop, där mätningar av kornstorlek i mikrometer och ASTM gjordes. Resultaten från den vanliga hårdhetsmätningen och från mikrohårdhetsmätningen visade liknande tendenser. Det upptäckes variationer i varje steg och varje dag i båda hårdhetsmätningarna och de två sorternas hylsor betedde sig likadant. Resultaten från kornstorleksmätningarna visade att efter glödgning ökade kornstorleken. Det fanns dock inget tydligt mellan kornstorlek och hårdhet då resultaten varierade, i vissa fall hade hylsorna med högre hårdhet en mindre kornstorlek än hylsor med lägre hårdhet. Att använda mässingens kornstorlek kan fungera för att få en övergripande bild av hårdheten, men för att få en bättre förståelse av materialegenskaperna behöver fler egenskaper undersökas.

Ion Implantation of ruthenium ions into a silicon substrate followed by a high temperature anneal (known as Ion Beam Synthesis) has been used for the first time to fabricate three wafers, under the following conditions. 1. 5.67 X 1016 Ru+ cm-2, beam heated 2. 4.25 X 1016 Ru+ cm-2, heated to ~ 600°C 3. 1.27 X 1017 Ru+ cm-2, heated to ~ 600°C All wafers contained precipitates of the orthorhombic semiconducting silicide of ruthenium, Ru2Si3. No other phase was identified. The samples exhibited a complicated microstructure, with 16 different orientation variants identified, and a high degree of disorder (~ +11% strain). The first optical measurements ever carried out on this material are reported here. Absorption measurements in transmittance yielded a direct band gap, in the region of ~ 0.9eV, 0.87eV, and 0.92eV for wafers 1, 2, and 3 respectively. No discernible variation of band gap magnitude with measurement temperature was found. Upon sequential annealing, the direct band gap magnitude remained constant up to ~ 650°C after which it shifted to above that of silicon, possibly due to a change in microstructural disorder as the precipitates increase in size. This observation was confirmed by several single step anneals at various temperatures above 650°C. No photoluminescence was observed in any of the samples.

Orientador: Dayse Iara dos Santos / Banca: Adilson Jesus Aparecido de Oliveira / Banca: Paulo Noronha Lisboa Filho / Resumo: O intermetálico diboreto de magnésio passou a ser um material intensamente estudado a partir de 2001, quando nele encontrou-se a propriedade de supercondição de corrente elétrica. Embora sua transição seja em temperatura relativamente baixa, próximo de 40 K, é grande o interesse comercial neste material devido à provável simplicidade da cinética de reação e à maneira direta e barata de processamento. Partindo de pós precursores ultrafinos de boa qualidade a formação da fase Mg'B IND. 2' parece ocorrer em apenas alguns minutos em temperatura relativamente baixa (650ºC). Sob este ponto de vista, este material é considerado bastante atrativo comercialmente, quando comparado aos supercondutores cerâmicos cujo processamento é muito mais complexo. Entretanto, suas propriedades supercondutoras, assim como nas cerâmicas, dependem da sua microestrutura e, portanto da cinética de formação da fase supercondutora. Além disso, com o objetivo de ampliar a densidade de corrente elétrica sob campos magnéticos cada vez mais altos, tem-se utilizado artifícios tais como a adição de diversos compostos geradores de centros de aprisionamento de fluxo magnético. Entre eles figuram o SiC e o silicone, formados por elementos que podem substituir um dos átomos do composto supercondutor, ou que apenas geram defeitos intersticiais. Neste trabalho, investigou-se a influência das adições de alguns compostos de carbono na formação da fase Mg'B IND. 2', assim como a determinação de alguns aspectos das microestruturas obtidas. Estudou-se também as mudanças na cinética de formação da fase devido à diferente granulação do precursor de magnésio. Os dados obtidos por DRX, ATD/TG, BET e técnicas de medidas magnéticas indicaram que um novo composto testado (gasolina azul) poderá apresentar características vantajosas com relação a outras adições mais conhecidas. / Abstract: The intermetallic magnesium diboride has become the object of many studies since was found to be a superconducting material, at 2001. Although it shows relatively low critical temperature, it presents very interesting points, like the simplicity of the formation of a binary compound and non expensive precursors powders. Starting from ultrafine quality precursor powders the formation of Mg'B IND. 2' phase seems to occur in a few minutes at low temperature (650ºC), what is considered commercially quite attractive when compared to complicated ceramic superconductors. Nevertheless, its superconducting properties, as well as the ceramics, depend on its microsstructure and, consequently on the kinetics of formation of the superconducting phase. Besides that, with the aim of enlarging the critical current density under higher magnetic fields, the addition of several compounds has been used in order to generate pinning centers. Silicon carbide and silicon oil are cited among the most used additions, which act like substitutional or interstitial impurities and defects generators. In this work, the influence of the addition of a few carbon compounds on the Mg'B IND. 2' phase formation was investigated, as well as the determination of a few structural parameters of the obtained materials. It was also studied the changes in the phase formation kinetics due to different magnesium precursor granulation. The XRD, DTA/TGA and magnetic measurements results indicated that the addition of a new compound (petrol) may present advantages to the additions already found in literature. / Mestre

O refratário dolomítico é amplamente utilizado como revestimento de trabalho para panelas no processo de Aciaria, por sua excelente refratariedade em condições de serviço, principalmente em usinas que produzem aços acalmados ao silício. O emprego deste refratário é em virtude de uma formação natural de uma capa protetora, a qual potencializa a vida do refratário, acarretando em um aumento da vida útil do equipamento. O trabalho baseia-se em um estudo comparativo entre dois tijolos dolomíticos nomeados aqui como tijolos A e B. Os testes em escala industrial foram dados pela montagem de seis revestimentos, de cada tijolo, colocados sob as mesmas condições, monitorando-se a temperatura e o grau de oxidação do banho metálico. Ao final da campanha da panela se realizou alguns testes POST MORTEM, onde se destaca as medidas dos residuais. Além disso, para completar este estudo comparativo, separaram-se tijolos novos de cada marca, os quais foram submetidos às análises microestruturais via MEV, análises termogravimétricas, análises químicas por EDS e DRX, entre outros ensaios. Os resultados mostraram que o tijolo A teve um desempenho 20% superior ao tijolo B. O tijolo A tem maior pureza, microestrutura com agregados arredondados, com maior homogeneidade, uma ótima distribuição entre partículas finas e médias, favorecendo o empacotamento o que justifica sua maior tenacidade à fratura e resistência à corrosão. Também foi evidenciada de forma clara a presença de carbono grafite no tijolo A, conferindo-lhe uma maior resistência ao choque térmico e à corrosão. / The refractory dolomite is widely used as coating for ladles work in steelmaking process for its excellent refractoriness in terms of service. The use of this refractory is due to a natural formation of a protective layer, which enhances the life of the refractory, resulting in increased equipment life. This work is based on a comparative study between two bricks dolomite named here as A and B. Tests were given on an industrial scale by assembling six coatings of each brick placed in the same conditions by monitoring the temperature and the degree of oxidation of the metal bath. At the end of the campaign applied some tests POST MORTEM, how measurements of residual stresses. Moreover, to complete this comparative study, separated from each brand new bricks, which were subjected to microstructural analyzes via MEV, thermogravimetric analysis, chemical analysis by EDS and XRD, among other tests. The results showed that the performance of brick A was 20% higher than brick B. The Brick A has a higher purity, microstructure with rounded aggregates with greater homogeneity, optimal distribution between fine and medium particles, favoring the packaging which justifies a higher fracture toughness and corrosion resistance. It was also clearly evidenced the presence of graphitic carbon in the brick A, giving it a higher resistance to thermal shock and corrosion.