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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Efeito do tamanho do grão austenítico na cinética e na morfologia do produto da reação bainítica de um ferro fundido nodular austemperado. / Effect of austenite grain size on the morphology and kinetics of the bainitic reaction of an austempered ductile iron.

Cesar Roberto de Farias Azevedo 05 August 1991 (has links)
Investigou-se o efeito do tamanho de grão austenítico na cinética e na morfologia do produto da reação bainítica de um ferro fundido nodular austemperado (FFNA). Foram estudados 3 tamanhos de grão austeníticos, a saber: GG (grão grosseiro), GM (grao mediano); e GR (grao refinado). A condição GR foi obtida pela austenitização rápida de microestruturas martensíticas. A condição GG foi obtida por tratamento de austenitização em duas etapas, de modo a, respectivamente, provocar o crescimento de grão e manter o teor de carbono igual aos das demais condições. Na segunda etapa do tratamento da condição GG ocorreu precipitação de grafita secundária, que acelerou significativamente a taxa de reação bainítica, possibilitando estudar o efeito da.variação na quantidade de interfaces austenita/grafita e austenita/ austenita sobre a cinética e a morfologia da reação bainítica. O refino do grão austenítico acelerou a cinética de reação, aumentou a proporção de ferrita alotriomorfa de contorno de grão, refinou a microestrutura bainítica (ferrita + austenita retida) e melhorou em 14% o limite de escoamento dos FFNA. Finalmente, a predominância de ferrira alotriomorfa na condição mais fina indica que a formação de interfaces incoerentes (mecanismo difusional ao inves de reação displaciva) durante a austenitização rápida da martensita (aquecimento de 100°C/ s). / The effect of austenite grain size on the kinetics and the morphology of the bainitic reaction in an austempered ductile iron (ADI) has been investigated, Three austenite grain sizes were produced: GG (coarse grain), GH (medium grain) and GR (fine grain), The GR condition was obtained by the rapid austenitization of martensitic microstructures The secondary graphite precipitation observed in GG condition strongly accelerated the rate of bainite formation and made possible the study of the effect of austenite/graphite interface on the kinetics of this reaction, The austenite grain refinement also accelerated the bainite precipitation, increased the proportion of grain boundary alotriomorphs ferrite, refined the bainitic microstructure and improved by 14% the yield stress of ADI, The predominance of grain boundary alotriomorphs in GR was associated to the structure of austenite/austenite interface formed during the rapid austenitization of the studied ductile iron at heating rates of 100oC/s. It is suggested that the dominant mechanism of austenitization in this condition is a thermally activated one (not a displacive transformation). The different morphologies of the austenite decomposition used the Duhê\'s morphological system.
82

Influência dos elementos de liga Cu-Ni-Mo nas propriedades mecânicas e na austemperabilidade do ADI / Influence of alloys elements Cu-Ni-Mo on mechanical properties and austemperability of ADI.

Aristides Rodrigues Mattar Junior 30 April 2009 (has links)
O ADI constitui-se no desenvolvimento mais recente na família dos ferros fundidos nodulares. Com o tratamento de austêmpera, consegue-se produzir uma microestrutura única, constituída de ferrita acicular e austenita estável rica em carbono, a ausferrita, proporcionando alta resistência mecânica aliada à ductilidade e tenacidade, além de boa resistência à fadiga e ao desgaste. Neste trabalho estudou-se o efeito dos elementos de liga Cu, Ni e Mo nas propriedades mecânicas e austemperabilidade do ADI. Foram produzidas barras cilíndricas de ferros fundidos nodulares nos diâmetros de Ø2, Ø3 e Ø4 ligadas com Cu, Cu-Ni, Cu-Ni- Mo respectivamente. Os corpos de prova utilizados nos ensaios de tração, impacto e microdesgaste foram retirados a meio-raio das barras. Posteriormente, cada conjunto de corpo de prova foi austenitizado a 890°C durante 2 horas, sendo em seguida submetido a uma condição de tratamento de austêmpera específica, combinando temperaturas de austêmpera de 300 e 360°C e tempos de 1, 2, 3 e 4 horas. Realizou-se análises microestruturais ópticas e por microscopia eletrônica de varredura para correlacionar propriedades mecânicas com a microestrutura. Na análise de austemperabilidade, as barras cilíndricas foram austemperadas para verificar a variação de microestrutura em função do raio da barra. Verificou-se que a temperatura de austêmpera exerce forte influência na microestrutura do ADI e consequentemente nas propriedades de tração, ductilidade, tenacidade e resistência ao desgaste. Nos tratamentos a 300°C obteve-se uma microestrutura mais refinada, com maior quantidade de ferrita acicular, responsável pela maior resistência mecânica e resistência ao desgaste; enquanto que no tratamento realizado a 360°C obteve-se uma microestrutura mais grosseira, com maior quantidade de austenita estável, responsável pela melhor ductilidade e tenacidade. Nos tempos de austêmpera analisados, não ocorreram variações significativas nas microestruturas e propriedades mecânicas. A resistência mecânica e a tenacidade decresceram com a adição de Mo, provavelmente devido à segregação deste elemento, mas a resistência ao desgaste a seco e a austemperabilidade foram mais efetivas em comparação com ligas contendo Cu e Cu-Ni. No ensaio de desgaste usando-se lubrificante, o ADI ligado com Cu-Ni austemperado a 360°C apresentou uma resistência ao desgaste um pouco inferior a de um aço 17CrNiMo6 cementado. / The ADI is the most recent development in the nodular iron family. With the austempering treatment, a unique microstructure, consisting of acicular bainite ferrite and stable austenite rich in carbon, named ausferrite is produced. This microstructure provides high mechanical strength combined with ductility, toughness and good fatigue and wear resistances. In this work, the effect of alloying elements Cu, Ni and Mo on the mechanical properties and austemperability of the ADI were studied. To conduct these studies, cylindrical bars with diameters of Ø2\", Ø3\" and Ø4\" were cast with Cu, Cu-Ni and Cu-Ni-Mo alloying, respectively. The samples were then manufactured by removing specimens from the bar midradius position. Subsequently, each set of the samples was austenitized at 890°C for 2 hours, and then subjected different conditions of austempering treatment. These treatments were developed by combining austempering temperatures of 300 and 360°C with austempering times of 1, 2, 3 and 4 hours. Microstructural analysis was carried out using optical and scanning electron microscopy to correlate mechanical properties with the microstructure. In the austemperability analysis, cylindrical bars were austempered (at 360°C for 3 hours) to correlate microstructure and radius. The experimental results showed that the austempering temperature exerts strong influence on the ADI´s microstructure and consequently on the mechanical properties. The austempering temperature of 300°C produced the best results, a refined microstructure, with a greater amount of acicular ferrite, responsible for greater strength and wear resistance. The austempering temperature of 360°C produced a coarse microstructure, with larger amount of austenite and responsible for better ductility and toughness. The austempering times used in this work did not produce significant variations in the properties and microstructures. Regarding alloying elements, the mechanical strength and toughness decreased with the addition of Mo, probably due to the segregation of this element, but the wear resistance and austemperability were more effective when compared with the alloys containing Cu and Cu-Ni. In the lubricated wear test, the ADI alloyed with Cu-Ni and austempered at 360°C presented a wear resistance only a fraction lower than a cemented 17CrNiMo6 steel.
83

Design de produto : seleção de materiais e processos com aplicação de campo magnético em núcleos de alto-falantes

Mozetic, Halston José January 2008 (has links)
Este trabalho tem por objetivo apresentar os resultados obtidos com o uso da técnica de campo magnético induzido durante o tratamento térmico do Ferro Fundido Nodular em desenvolvimento de núcleos de alto-falantes. Para este estudo foi escolhido como material o Ferro Fundido Nodular devido ao baixo custo de obtenção das peças e também por ser um material de fácil aquisição no mercado. Foram confeccionadas 90 amostras deste Ferro Fundido Nodular com percentuais diferenciados de Ferro, Silício e Carbono, sendo que as amostras quando foram submetidas ao tratamento térmico de recozimento também sofreram a indução magnética. Os parâmetros utilizados no tratamento térmico situaram-se na faixa de temperatura de aquecimento de 900ºC até 920ºC e uma indução magnética "B" entre 16000 e 20000 Gauss. O grande desafio deste trabalho estava no fato de que variações de composição das ligas de ferro fundido nodular, aliadas as inclusões de outros materiais não magnetizáveis, modificavam, para pior, o desempenho dos núcleos dos alto-falantes. Para obter-se, então, uma estrutura em que o fluxo magnético pudesse permear, buscou-se primeiramente selecionar a liga de ferro fundido eliminando ao máximo os materiais não magnetizáveis, e só então, estudar um processo de tratamento térmico com indução magnética que tornasse o material adequado ao uso nos núcleos de alto-falantes Para melhorar as propriedades magnéticas de forma contundente, buscou-se através do recozimento com campo induzido um alinhamento dos domínios, ou seja, uma ordenação dos "spins" dentro dos grãos do material que juntamente com a elevação de temperatura tenderam a ter um mesmo sentido, facilitando de maneira significativa a passagem do fluxo magnético, propriedade importante para o desempenho dos núcleos de alto-falantes. Foram realizados recozimentos com campo induzido observando-se o desempenho da permeabilidade magnética inicial das peças e posteriormente medidas com equipamento de saturação de campo. Esses resultados foram correlacionados com os dados obtidos pelo uso do aço SAE 1020, nas mesmas condições de uso e teste de laboratório. Foram realizados estudos metalográficos, além de análises de composição química das amostras e a relação destes fatores com as propriedades magnéticas. Também foram estudados os dados de usinabilidade das amostras do ferro fundido nodular tratadas termicamente com indução magnética e subseqüentemente comparados com o Aço SAE 1020. Do ponto de vista científico, uma das contribuições deste trabalho, está na influência da indução de campo magnético durante o tratamento térmico das amostras, pois é possível verificar um ganho significativo nas propriedades magnéticas apresentadas pelos núcleos dos alto-falantes durante os testes de desempenho. A outra está no fato de que ganhos correlacionados ao design do produto possibilitam utilizar o ferro fundido como uma alternativa economicamente viável e perfeitamente ajustável à alta performance dos alto-falantes. Como resultado deste estudo foi demonstrado à possibilidade do uso do recozimento com indução magnética, como forma de aumentar a permeabilidade de um material com alto teor de carbono, no caso específico, o ferro fundido nodular. Este trabalho permite afirmar que é possível desenvolver núcleos magnéticos de alto-falantes em ferro fundido nodular com alto desempenho e também sugerir que outras aplicações onde seja necessário aumento do desempenho magnético esta técnica possa ser aplicada. / This work aims to present the results obtained with the use of induced magnetic field during the heat treatment of Nodular Cast Iron for speaker cores. For this study development, the chosen material is the nodular cast iron due to the low trading costs and ease of purchase on the market. Ninety samples of nodular cast iron were constructed, with different iron, silicon and carbon contents. Samples, when subjected to annealing, were also subjected to magnetic induction. The final temperature on the heat treatment was in the range of 900ºC to 920ºC, and the magnetic induction was in the range of 16000 to 20000 Gauss. The challenge of this work was in the fact that compositional changes in the nodular cast iron, allied to inclusions of non-magnetizable materials, modify for worse the performance of speaker cores. To obtain a structure that the magnetic field could permeate, the cast iron alloys were selected to eliminate, at most, the presence of non-magnetizable materials, and only then consider a heat treatment process with magnetic induction to make the material suitable for use in speaker cores. To improve the magnetic properties, an alignment of dipoles of the material, through induced magnetic field during annealing was intended. Annealing with induced magnetic field was carried out, observing the performance of the initial magnetic permeability of the samples, and subsequently measured with field saturation equipment The results were correlated with the obtained data from the use of the SAE 1020 steel, with the same conditions of use and laboratory tests. Metallographic and chemical composition analyses were carried out on the samples, and the correlation of these data with the magnetic properties was estmated. Also machinability of the thermal treated with magnetic induction nodular cast iron samples were analyzed and compared with the SAE 1020 steel. From the scientific point of view, one of the contributions of this work is the influence of induced magnetic field during the heat treatment of the samples, since it was possible to verify a significant gain in the magnetic properties of the speaker cores during the performance tests. Another contribution is the fact that gains correlated with the design of the product enable the use of cast iron as an economically viable and fully adjustable material to the high performance of subwoofers. As a result of this work, the possibility of using annealing with magnetic induction was presented as a way to increase the permeability of a material with high carbon content, in this particular case, the nodular cast iron. This research allows asserting that it is possible to develop speaker magnetic cores of nodular cast iron with high performance and also suggest that this technique can be applied to other applications where it is necessary to increase their magnetic performance.
84

Taxa de inóculo na habilidade competitiva de rizóbios e eficiência na fixação do N2 em feijão-caupi ( Vigna unguiculata (L.) Walp,). / Inoculum rate in competitiveness and effective ability for nitrogen fixation of rhizobia on Cowpea (Vigna unguiculata (L.) Walp.).

SILVA, Maria de Fátima da 28 February 2011 (has links)
Submitted by (lucia.rodrigues@ufrpe.br) on 2016-08-10T13:22:32Z No. of bitstreams: 1 Maria de Fatima da Silva.pdf: 619107 bytes, checksum: 566cd7dafe2052de47a3a66eb87eda27 (MD5) / Made available in DSpace on 2016-08-10T13:22:32Z (GMT). No. of bitstreams: 1 Maria de Fatima da Silva.pdf: 619107 bytes, checksum: 566cd7dafe2052de47a3a66eb87eda27 (MD5) Previous issue date: 2011-02-28 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Cowpea (Vigna unguiculata (L.) Walp) in Brazil is grown in the most different climatic conditions. By the adaptability to tropical conditions and recognized as a culture of high socioeconomic value, this legume has an important role for the capitalization of small farmers in the Northeast region. Cowpea may obtain adequate quantities of N by the process of biological nitrogen fixation (FBN) when associated with specific and effective bacteria. However, in Brazil the practice of inoculation is not widely processed due to the low agricultural technology and inconsistent responses using the seed inoculation process. The main goal of this study was to evaluate the effect of different rates of inoculum on effectivity and competitiveness of Bradyrhizobium (strain BR 3267) on cowpea grown in greenhouse conditions. The first experiment was carried out with five different concentration of strain BR 3267 (rhizobia cells/mL of inoculant), N mineral fertilizer treatment without inoculation, and a control without inoculation and N mineral fertilizer. The second experiment conducted in Leonard jars with inoculant produced with BR 3267 strain, 15 native rhizobia (isolated from the used soil), and a control treatment without inoculation and no N mineral fertilizer applied. The application of the low recommended rate increased number and dry biomass of nodules, shoot dry biomass and shoot N total uptake. In the Leonard jars experiment the rhizobia strain BR 3267 was more effective on nitrogen fixation and showed greater competitiveness compared to the native rhizobia isolates. The BRS Pujante cultivar was benefit by the FBN process when inoculated with strain BR 3267 proportional to the inoculum rate. / O feijão - caupi (Vigna unguiculata (L.) Walp.) é cultivado, no Brasil, nas mais diferentes condições edafoclimáticas. Devido a sua boa adaptabilidade às condições tropicais e por ser uma cultura de alto valor sócio-econômico, tem um papel importante para a capitalização de pequenos agricultores na região Nordeste. Por ser uma leguminosa, o feijão-caupi pode adquirir N em quantidades adequadas para suprir suas necessidades através do processo de fixação biológica do nitrogênio (FBN) quando associado com bactérias específicas e efetivas. Entretanto a prática da inoculação não é muito utilizada devido ao baixo aporte tecnológico nas aéreas de cultivo e respostas inconsistentes com os inoculantes utilizados. O objetivo do presente estudo foi de avaliar o efeito da aplicação de diferentes taxas de inóculo, habilidade competitiva e eficiência para a FBN da estirpe de Bradyrhizobium sp. BR 3267 na cultura do feijão-caupi em casa de vegetação. No primeiro experimento, conduzido em vasos com solo foram usados sete tratamentos, compreendendo cinco concentrações de células da estirpe BR 3267 (células/mL de inoculante), um tratamento sem inoculação e com adição de fertilizante nitrogenado, e um controle sem inoculação e sem adição de fertilizante nitrogenado. O segundo experimento constituiu de 17 tratamentos, compostos por 15 estirpes nativas, a estirpe BR 3267 e um tratamento sem inoculação e sem adição de nitrogênio, em vasos de Leonard com substrato estéril. A aplicação da dose mínima recomendada incrementou número e biomassa seca dos nódulos, biomassa seca da parte aérea e o acúmulo de nitrogênio na parte aérea. Em substrato estéril a população rizobiana nativa não foi mais eficiente quando comparada à estirpe BR 3267. A estirpe BR 3267 foi mais competitiva e eficiência em relação à população rizobiana nativa. A cultivar BRS Pujante foi mais beneficiada pela FBN quando inoculada com a estirpe BR 3267, proporcionalmente à taxa de inóculo.
85

Etude de l'endommagement lors du démasselotage à chaud de bielles en fonte GS ADI moulées forgées. / Study of damage during the hot-cutting of molded and forged austempered ductile iron automotive connecting rods.

Martinez, Thomas 19 December 2016 (has links)
Les travaux de cette thèse ont été initiés par la volonté industrielle de lever le verrou technologique du démasselotage à chaud de bielles en fonte GS. Ces bielles sont obtenues par un procédé de fabrication hybride innovant mêlant forgeage et fonderie en moule métallique. Ce procédé exige que le démasselotage soit effectué dans la « chaude de coulée » lorsque la fonte GS est en phase austénitique. La découpe de la fonte dans ces conditions de température fait apparaître des défauts majeurs sur les surfaces découpées préjudiciables à la suite du process. Pour pouvoir répondre à cette problématique, une étude est menée sur la caractérisation du comportement et de l’endommagement de la fonte GS dans les conditions de température du process. Une attention particulière est portée sur l’influence de la microstructure nodulaire sur les mécanismes de la rupture. Afin de se doter d’outils de simulation pour mettre au point le processus de démasselotage à chaud, les paramètres du modèle de comportement et d’endommagement de Gurson-Tvergaard-Needleman appliqués à la fonte GS sont identifiés par méthode inverse. Enfin, un plan d’expérience est déployé sur un démonstrateur de découpe instrumenté afin d’obtenir la configuration optimale des paramètres process pour une découpe sans défaut. Cette dernière étude met en avant la présence d’une transition d’un mode de rupture ductile à fragile lors de l’apparition des défauts de démasselotage. / This work was initiated by the technological problematic of hot trimming of nodular cast iron connecting rods. These connecting rods are obtained by an innovative hybrid process that combines forging and metal mold casting. This process requires the trimming to be conducted at high temperatures in the is the austenitic phase of the cast iron. Hot trimming of cast iron brings up major defects on the cut surfaces which are detrimental to the continuing process. To address this problem, a study is conducted on the characterization of the mechanical behavior of nodular cast iron in the process temperature conditions. A particular attention is paid to the influence of the nodular microstructure on the failure mechanisms. To develop simulation tools for nodular cast iron hot trimming, the parameters of Gurson-Tvergaard-Needleman model are identified by inverse method for our material. Finally, a design of experiment is deployed using an instrumented demonstrator to obtain the optimum parameters configuration for a maximized cut surface quality. This latest study highlights the presence of a transition from ductile to brittle mode of failure leading to the hot trimming defects.
86

Caracterização e proposição de métodos estimativos das propriedades monotônicas e cíclicas dos ferros fundidos nodulares / Characterization and estimative models of monotonic and cyclic properties of ductile iron

Elton Franco de Magalhães 09 March 2012 (has links)
Para o correto dimensionamento da maioria dos componentes estruturais é necessário informações sobre a resposta do material quando submetido à fadiga de alto e baixo ciclo, bem como conhecer as propriedades monotônicas (não-cíclicas) e cíclicas dos materiais. Na literatura são encontradas amplas divulgações de dados sobre diversos materiais de engenharia (Ex. SAE J1099 Technical Report on Fatigue Properties). Porém, quando se trata de ferro fundido nodular estas informações são limitadas, sendo assim, visa-se neste trabalho caracterizar as propriedades monotônicas e cíclicas destes materiais em complemento aos trabalhos já publicados na literatura e propor métodos para a estimativa destas propriedades a partir da dureza. Faz-se necessário a proposição de métodos estimativos das propriedades mecânicas destes materiais baseados na dureza devido às suas grandes variações que são inerentes ao processo de fundição. Em um mesmo componente podem existir diferentes classes de ferro fundido, que apesar de possuir a mesma composição química, podem apresentar variações nas propriedades mecânicas devido à formação de diferentes estruturas metalúrgicas que são sensíveis às taxas de resfriamento do material que variam de acordo com as características geométricas da peça que está sendo fundida, principalmente a variação da espessura. Neste estudo a determinação das relações entre as propriedades monotônicas e cíclicas dos ferros fundidos nodulares foram obtidas a partir do tratamento dos dados publicados na literatura levando-se em consideração o índice de qualidade. Foi proposto um modelo contínuo com relação à dureza para a estimativa das propriedades monotônicas, do coeficiente de resistência cíclico e do expoente de encruamento cíclico e para a estimativa das propriedades cíclicas que experimentalmente demonstraram não ter correlação com a dureza foi proposto uma forma discreta, que consistiu na recomendação de valores típicos definidas por faixas de dureza. / For the correct design of the most part of structural components is necessary to have information about the material response under both high cycle and low cycle fatigue, as well as the knowledge of monotonic and cyclic materials properties. In literature a major publication of several engineering material data can be found (e.g, SAE J1099 - Technical Report on Fatigue Properties), but regarding to ductile iron this information is quite limited. Therefore, this work aims to characterize the monotonic and cyclic properties of this material in complementing to the available data in the literature and also make a proposition of methods to estimate this properties from hardness. The mechanical properties estimation model from hardness is relevant to take into account the inherent variations of casting process, which for the same chemical composition can be found different grades in a same part. This fact occurs due to the formation of different metallurgical structures that is influenced by cooling ratio which changes accordingly to geometrical characteristic of the part, especially the thickness variation. In this study the determination of the relation between monotonic and cyclic properties from hardness has been determined from literature data processing taking into account the Quality Index. For monotonic properties, the cyclic strength coefficient and the cyclic strain hardening exponent estimation has been proposed a continuous method based on hardness and for the cyclic properties that experimentally showed to remain independent of hardness has been recommended one set of properties for specific hardness ranges.
87

Vliv cementových forem na strukturu odlitků z litiny LKG / Influence of cement moulds on the structure of nodular iron castings

Stachovec, Ivo January 2009 (has links)
The object of the diploma thesis was to solve and to describe the influence of cement sands moulds on the structure of castings with cast iron LKG. The work was intent on watching the tendency of cement sands to the metal penetration of castings, rising of the compounds on the metal mould interface and liquid metal and accompanies elements on the shape of the graphite in the surface of casting. The study of this processes has a big theoretical and a practical meaning, for prevent and prediction of rising of the defects that are attached with unsuitable choice of sand.
88

PROGRESIVNÍ VÝROBNÍ POSTUPY A MODELOVÁNÍ STRUKTUR A VLASTNOSTÍ LITIN S KULIČKOVÝM GRAFITEM / PROGRESSIVE PRODUCTION PROCESSES AND SIMULATION OF STRUCTURES AND PROPERTIES OF SPHEROIDAL GRAPHITE CAST IRON

Musilová, Iveta January 2010 (has links)
The thesis is concerned with relationships between progressive technological processes of spheroidal graphite cast iron’s production and their structural properties. The aim of the work is to explain causal relationship between parameters of the proposed manufacturing technology of the iron type given (involving selected variants of modification and inoculation of melt and the parameters of melt crystallization, solidification and cooling down in a mould), their structure and even chemical heterogeneity of elements in this structure. For close specification of presented relationships three-dimensional model of spheroidal graphite growth was used, which was developed at the Brno University of Technology, Faculty of Mechanical Engineering. Its usability in praxis has been verified on the basisis of the application of this model on experimentally acquired data. The U GRAFIT 20 model of the authors Stránský and Million counting segregation in the frame of eutectic cell has not still been used for prediction of segregation in real condition in greater extent. On the basis of the above mentioned model microsegregation within “on average” of the cell has been discovered during experimental melts. Microsegregation has been described by segregation and heterogeneity indexes. Calculated values of segregation and heterogeneity indexes have been compared with experimentally verified values. On the basis of comparison of calculated and measured values the possibility of further usage of the mentioned model in praxis has been explored.
89

Nuclear Waste Canister : Evaluating the mechanical properties of cassette steel after casting

Fager, Fredrick, Chanouian, Serg January 2017 (has links)
Företaget Svensk Kärnbränslehantering AB (SKB) håller på att utveckla en slutförvaringskapsel som kommer innehålla avfall från den svenska kärnkraften. Det är dock fortfarande en process under utveckling och därför undersöks olika typer av metoder och kapselmaterial för att kunna tillverka en hållbar och säker kapsel. Kapseln består av ett hölje av kopparrör med svetsad botten och lock och en insats med stållock. Insatsen är en cylindrisk konstruktion  av segjärn och innehåller en svetsad stålkassett för att skapa utrymmen till det använda kärnbränslet. Insatsen innehåller bland annat stålrör som under tillverkning får utstå en gjutprocess med segjärn och erhåller efter det icke homogena egenskaper. Målet med undersökningen är hur stor påverkan gjutningen har på stålets kemiska sammansättning samt mikrostrukturer. Det som orsakar de inhomogena egenskaperna är främst värmebehandlingen som driver diffusionen av kol från gjutjärnet till stålet, som då ger ett hårdare men sprödare material. Med hjälp av experiment och simuleringar upptäcks hur mycket kol som diffunderar in i stålet samt ändringar i den kemiska sammansättningen i de påverkade zonerna. Identifiering av fasomvandlingar, diffusion och ändringar i mikrostrukturer är stora faktorer som i sin tur ändrar de mekaniska egenskaperna i stålet. / The Swedish Nuclear Fuel and Waste Management Company (SKB) have developed a final storage canister that will contain waste from the Swedish nuclear power plants. However, it is still in a development phase and therefore different types of methods and canister materials are investigated to produce the most durable and safe canister. The canister is made of a copper tube with a welded bottom and lid with an insert. The insert is a cylindrical construction of nodular cast iron that contains a welded steel cassette, to make space for the spent fuel, and a steel lid. The steel tubes showed inhomogeneous properties after being exposed to a casting around them. The aim of this investigation is to clarify the impact of casting on the chemical composition of the steel as well as the microstructure. The cause to the inhomogeneous properties were the diffusion of carbon from the cast iron to the steel, which then produced a harder and more brittle material. Experiments and simulations were used to see the carbon diffusion into the steel as well as what happens with the chemical composition in the affected zones. Identification of phase changes, diffusion and microstructures contributed to changes of mechanical properties in the steel.
90

Isotopic Investigations of Carbon Cycling And Microbially Influenced Carbonate Precipitation In Freshwater Microbialites And Carbonate-Rich Microbial Mats / Microbial Carbon Cycling and Isotope Biosignatures

Brady, Allyson Lee January 2009 (has links)
<p>Modern microbialites and microbial mats are the focus of ongoing research as they provide an opportunity to understand microbial-mineral interactions during carbonate precipitation and the generation of biosignatures that can inform our interpretation of the geological record. This study determined the natural abundance isotopic compositions ([13]C, [14]C) of the primary carbon pools and microbial communities associated with modern freshwater microbialites located in Pavilion Lake and in carbonate rich microbial mats on the nearby Cariboo Plateau in British Columbia, Canada. </p> <p> Natural abundance [14]C analysis of carbon pools associated with the Pavilion Lake microbialites demonstrated that structures were actively growing and that groundwater carbon inputs to the lake and microbialites were minimal. Rather, ambient dissolved inorganic carbon (DIC) was the primary carbon source for both microbial communities and recent carbonate. </p> <p> Isotopic enrichment of calcium carbonate within microbial communities associated with the microbialites was identified as a biosignature of microbial photosynthetic influence driving precipitation. Elevated oxygen concentrations and pH within the microenvironment of small, sporadic nodular microbial surface communities was concurrent with in situ precipitation of carbonate with δ[13]C values higher than predicted abiotic values and δ[13]C of bulk organic matter and phospholipid fatty acids (PLFA) that were consistent with a photosynthetically dominated community. Elevated carbonate δ[13]C values were also noted in the thin surface microbial mat recovered from shallow (11m) microbialites. These samples showed increased biomass during summer sampling periods as compared to deeper samples, consistent with expected high rates of photosynthetic activity due to higher light levels and temperature at these depths. These results contrast other recent studies of modern microbialite systems that identified biosignatures of heterotrophic influences on precipitation of carbonates. PLFA profiles demonstrated that the surface microbial mat community consisting of both photosynthetic and heterotrophic microbes was stable over seasonal and spatial changes in light and temperature. However, changes in microbial biomass with depth and season indicated that microbial activity and growth plays an important role in the development of isotopic biosignatures. </p> <p> Biosignatures of high levels of photosynthetic activity were also observed in carbonate, rich microbial mats that exhibited undersaturated p CO2 concentrations during the summer and DIC δ[13]C values enriched above values predicted for isotopic equilibrium with atmospheric CO2. Seasonal and annual shifts in the balance of heterotrophy and autotrophy in the lakes and microenvironment of the mat accounted for observed variations in DIC and associated carbonate δ[13]C values. In contrast to other organic rich microbial mats, bulk organic δ[13]C values were not enriched and the systems did not show evidence of CO2 limitation. Rather, these results indicated that low bulk organic δ[13]C values and large isotopic discriminations can exist under conditions of high DIC concentrations and carbonate content that provide a non limiting carbon source to replenish photosynthetic drawdown. </p> / Thesis / Doctor of Philosophy (PhD)

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