Thesis (M.Sc.)--Memorial University of Newfoundland, 1994. / Typescript. Bibliography: leaves 95-98. Also available online.

Thesis (M. Sc.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on July 16, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Materials Engineering, Department of Chemical and Materials Engineering, University of Alberta." Includes bibliographical references.

Thesis (Ph.D.)--University of Western Australia, 2007.

Dissertation (Ph.D.)--Worcester Polytechnic Institute. / Keywords: active muscles, out-of-position, fracture mechanisms, impacts, KTH, dynamic ligament failure model. Includes bibliographical references (leaves 353-365).

Thesis (Ph. D.)--Lehigh University, 2006. / Includes bibliographical references and vita.

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Orientador: Valdir Alves Guimarães / Banca: Ana Paula Rosifini Alves Claro / Banca: Marcelino Nascimento / Banca: Carlos de Moura Neto / Banca: Wanderson Santana da Silva / Resumo: Materiais utilizados em tubulações petrolíferas são altamente suscetíveis a mudanças estruturais quando expostos em meio ambiente hostil e em baixas temperaturas. Para entender melhor o comportamento de tenacidade de fratura nos aços API 5l X70 e API 5L X80 conhecidos como aços microligados de Alta Resistência e Baixa Liga (ARBL), é proposta a avaliação da tenacidade à fratura verificando o conceito da curva mestra do método convencional da norma ASTM E1921-05. Esta metodologia usa o conceito da dependência da temperatura universal da tenacidade à fratura na região de transição dúctil para frágil, assim chamado de curva mestra. A metodologia sugere que pode ser aplicável em aços ferríticos CCC, incluindo aços martensíticos-ferríticos temperados. Neste trabalho, as amostras foram submetidas a tratamentos térmicos com o intuito de alterar a microestrutura e as propriedades mecânicas. Foram aplicados ensaios Charpy, tração, tenacidade à fratura e medições de dureza. As amostras foram testadas em várias temperaturas na região de transição para permitir a aplicação do procedimento da análise da curva mestra e a estatística de Weibull, mediante a norma ASTM E1921. Foram realizadas análises em microscópio óptico e microscópio eletrônico de varredura para avaliar as mudanças microestruturais e as superfícies de fratura, respectivamente. Os resultados dos aços API 5L X70 e API 5L X80 ensaiados mostraram uma ampla variedade de dados com características relevantes e dispersas. Com respeito ao valor de 100 MPa√m de tenacidade, o aço API X80 mostra melhor desempenho e confiabilidade do que o aço API X70. Ambos os aços mostraram fratura frágil com mecanismos de clivagem e uma microestrutura predominante de ferrita bainítica / Abstract: Materials used in oil pipelines are highly susceptible to structural changes when exposed to a hostile environment and at low temperature. For better understanding the behavior of the fracture toughness in the API 5L X70 and X80 steels, both known as high strength and low alloy (HSLA) micro-alloys steels, the fracture toughness assessment checking the master curve concept of the conventional ASTM E1921-05 standard was proposed. This methodology uses the universal dependence temperature concept of fracture toughness in brittle to ductile transition region, so-called master curve. The methodology suggests that it may be applicable in CCC ferritic steels, including hardened martensitic-ferritic steels. In this work the samples were submitted to heat treatments, in order to change their microstructures and mechanical properties. Charpy impact test, tensile test, fracture toughness and hardness measurements were applied. The samples were tested at various temperatures on the transition region to allow the master curve analysis application and the Weibull statistics by using the ASTM E1921 standard. Analysis in optical microscope and scanning electron microscope were done in order to assess the fracture surface changes and their microstructures. Both results of the API 5L X70 and 80X steels tested showed a wide range of data with relevant characteristics and scattering. According to a 100 MPa√m toughness, the API X80 steel showed better performance and reliability than the API X70 steel. Both steels showed brittle fracture with cleavage mechanisms and a ferritebainite microstructure predominant / Doutor

Residual stresses generated during the casting and heat treatment of a low alloy steel, BW2 have been studied using ta theta ring so that temperature differentials could be varied using different tie bar sizes. Residual stresses have been measured using centre hole drilling and tie bar sectioning techniques. Centre hole drilling was shown to be sensitive to surface preparation methods. Stresses induced by drilling were accounted for in measured stresses and drilling stresses were found to be greater in cast than annealed samples. Cast theta rings have been shown to have compressive residual stresses, becoming less compressive or tensile as the tie bar width was reduced. Tie bar sectioning producedexpansion which increased with increasing tie bar width, although there was no direct correlation between tie bar stress and width. Results from both techniques have been explained using factors contributing to residual stress formation. The S-shaped runner contained residual stresses and its removal altered residual stress levels. Heat treatments have been found to produce different amounts of stress relief according to the geometry and thermal cycle imposed. In a uniform section theta.ring normalising and tempering relieved stresses in the tie bar but not in the outer ring, and the tie bar contained no stresses after sectioning. For the non-uniform section theta ring annealing made stresses more compressive whilst normalising and tempering generated stresses due to differential cooling, and the tie bar contained compressive stresses after sectioning. Maximum Von Mises equivalent in the cast theta ring was shown to be 25% of the yield strength and reduced further after heat treatment. A computational model based on finite difference has been used to simulate solidification of a tie bar across the width. Temperature gradients computed along this bar axis were shown to be small and are believed not to significantly contribute to residual stresses.

This project originated from the desire to provide the sintered preform designers in forging industries with useful information on the effects of certain process variables on the forged product and to formulate these effects into comprehensive relationships of the basic rheological characteristics of the material. A further aim was to establish a technique to theoretically demonstrate the applicability of these relationships,by analysing simple forging of sintered billets. A literature survey covering three main areas in general is presented highlighting the effects of various process variables on the mechanical properties, the deformation characteristics of various sintered materials, and the attempts to establish a yield criterion for porous materials on the basis of experimental results and theoretical analysis. The experimental programme involved the design, construction and machining, where appropriate, of a double cone powder mixer, a sintering unit, and three die compaction sets, compacts of atomised iron powder, mixed with 0.25% flake graphite were made of various heights, diameters anddensities and sintered at various sintering conditions. Further work included preparation of testpieces for compression, tension, impact, hardness, chemical analysis and metallographic tests and making of forging dies for upsetting, upset-extrusion, capped ends upsetting, triangular cavity and multi-cavity closed die forging. The programme of work involved the study of 1. The effects of sintering time and temperature on the mechanical properties of sintered iron, on the deformation characteristics and on the properties of the upset specimens. 2. The effects of aspect ratio on the deformation characteristics of sintered billets. 3. The behaviour of the material through testing specimens of various cross-sections(circular, square rectangular, triangular and semi-circular) and by changing die geometry in order to simulate effects inactual closed die forging. 4. Closed die forging simulating the production of two and four gear teeth of various widths. 5. The existing yield criteria in an attempt to improve their applicability in respect of sintered iron. 6. A finite-difference numerical technique in order to simulate the upsetting process of a variable density material. Comparison of the predicted results with those observed experimentally showed good agreement.

Fretting fatigue occurs when components are in contact and subjected to cyclic loads or vibrations. The following research programme investigates the fretting fatigue phenomenon using a specific flat contact geometry encompassing sharp comers. The pressure distribution at the contact interface is fundamentally important in the understanding of fretting fatigue problems. In the case of sharp comer contacts, the analysis of the pressure distribution results in an infinite gradient occurring at the edges of the contact. The infinite gradients generate deformation singularities and closed form solutions are not available for this contact geometry. The specific contact pressure generates friction forces, which affect the nucleation and growth of dominant fretting cracks by influencing the stress distributions in the region of the contact. The current research programme presents a method of analysing flat contacts containing sharp comers. The method includes the development of a finite element solution capable of accurately predicting the friction force behaviour observed in fretting fatigue. The subsequent numerically determined stress distributions in the contact region are then used to generate a multiaxial stress concentration factor, which provide the basis for a fretting fatigue life prediction method. Furthermore, the research programme investigates the phenomenological effects observed during fretting fatigue. The study investigates friction behaviour and its effects on the initiation of fretting cracks and fretting fatigue lives.