Orientador: Marcelo dos Santos Pereira / Resumo: O ensaio de queda de peso DWTT (Drop Weigth Tear Test) é um método amplamente utilizado pela indústria de óleo e gás para determinar a capacidade de um material em impedir a propagação de uma trinca. Esse método foi desenvolvido pelo Battelle Memorial Institute, e é realizado em conformidade com a especificação API RP 5L3 "Práticas Recomendadas para a Condução de Testes de Queda de Peso". Com o desenvolvimento dos aços ARBL, o comportamento dos aços vem mostrando algumas particularidades resultantes do processamento termomecânico, e por esse motivo, podem não apresentar o mesmo comportamento à fratura que aços mais antigos, como delaminações ou inclusões não metálicas. Atualmente são propostos dois tipos de entalhe, sendo o tipo prensado, obtido pela estampagem de uma matriz na amostra, e o tipo Chevron, que deve ser usinado. A correlação entre ambos os entalhes pode ser realizada apenas para a análise da porcentagem da superfície dúctil da fratura. Outros tipos de correlação como energia absorvida para impacto, não são recomendados, uma vez que a concentração de tensão para o entalhe Chevron é muito maior, facilitando o rompimento da amostra, enquanto que o entalhe prensado demanda maior energia, uma vez que possui maior encruamento na região. No presente trabalho foram realizados os levantamentos de curvas de temperatura de transição dúctil e frágil (TTDF) do material base do tubo com dimensões de 762 mm x 38,1 mm de aço carbono com grau API X60, através da análise da porce... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The Drop Weigth Tear Test (DWTT) is a method widely used by the oil and gas industry to determine the ability of a material to prevent the propagation of a crack. This method was developed by the Battelle Memorial Institute, and is performed in accordance with API RP 5L3 "Drop-Weight Tear Tests on Line Pipe" specification. With the development of ARBL steels, the behavior of steels has shown some particularities resulting from thermomechanical processing, and for this reason, they may not present the same fracture behavior as older steels, such as delamination or nonmetallic inclusions. Currently two types of notch are proposed, being the type pressed, obtained by the stamping of a matrix in the sample, and the type Chevron, that must be machined. The correlation between both notches can be performed only for the analysis of the percentage of the ductile surface of the fracture. Other types of correlation as energy absorbed for impact are not recommended, since the stress concentration for the Chevron notch is higher, facilitating the rupture of the sample, while the notched press demands greater energy, since it has greater hardening in the region. In the present study, the ductile and brittle transition temperature (TTDF) curves of the base material of the pipe with dimensions of 762 mm x 38.1 mm of carbon steel with API grade X60 were carried out, through the analysis of the percentage of ductile fracture resulting whose results were shown to be equivalent for both notch: ... (Complete abstract click electronic access below) / Mestre

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Este trabalho comprovou a eficácia do processo de roleteamento profundo no aumento da vida em fadiga em eixos submetidos ao ensaio de fadiga sob tensão axial. Uma pesquisa bibliográfica extensa foi realizada para o entendimento do comportamento físico do fenômeno encruamento, onde esta pesquisa abrangeu a metalurgia, plasticidade e elasticidade dos materiais, processos de geração de tensão residual e ensaios destrutivos e não destrutivos para obtenção de valores reais. O corpo de prova utilizado, em relação ao corpo de prova padronizado, foi modificado para simular o efeito do entalhe como concentrador de tensões. Corpos de prova sem o tratamento mecânico de roleteamento e corpos de prova com o tratamento foram submetidas ao ensaio de fadiga de tensão axial e de difração de raios-X, a fim de comparar o ganho do processo de roleteamento profundo. Com os resultados dos ensaios de fadiga foi possível obter as curvas Wöhler, "S-N", pertinentes aos dois diferentes grupos de amostras: com e sem o tratamento de roleteamento profundo. Simulações pelo Método dos Elementos Finitos foram usadas também para tentar reproduzir os efeitos da tensão residual compressiva sobre a vida em fadiga assim como os resultados obtidos nos ensaios de fadiga e difração de raios-X. / This project has proved the effectiveness of the deep rolling process in the increasing of fatigue life on shafts submitted to axial stress fatigue test. A deep literature research has done for understanding of the physic behavior of the hardening phenomenon, where this research included metallurgy, plasticity and elasticity of materials, generation of residual stress processes and destructive and nondestructive tests to obtain the real values. The specimen used, comparing to the standard one, had been changed to simulate the notch effect as stress concentrator. Specimen with and without rolling mechanical treatment have submitted to axial stress fatigue test and X-rays diffraction test, to compare the gain of the deep rolling process. With the results of fatigue tests, became possible to obtain the Wöhler curves, "S-N", from each different groups of specimens: with and without the deep rolling treatment. Simulations by Finite Element Method have also used to try reproducing the compressive residual stress effects under the fatigue life, like the obtained results from fatigue and X-rays diffraction tests.

A indústria automotiva tem mostrado um crescente interesse pelas ligas de alumínio, em especial as ligas de alumínio da série 6xxx. Esta classe é amplamente empregada nas áreas de construção e de transporte, devido a sua boa resistência mecânica e excelente resistência à corrosão. No setor automobilístico sempre houve a necessidade de aprimoramento dos estudos do comportamento em fadiga, pois os componentes estruturais são submetidos a carregamentos vibratórios, esforços e tensões cíclicas e, como consequência, podem trincar e finalmente fraturar. A presença de um entalhe geralmente diminui a vida em fadiga, criando regiões de altas tensões triaxiais localizadas que restringem a deformação plástica, fragilizando o material. A resposta mecânica depende das solicitações, microestrutura, componentes da liga e propriedades do material. Neste trabalho foi realizado o estudo do comportamento em fadiga de alto ciclo e da sensibilidade ao entalhe de três ligas de alumínio da série 6xxx destinadas à fabricação de componentes de carroçarias para caminhões e ônibus: AA 6005, AA 6063 e AA 6351, todas na condição T6. As curvas S/N foram obtidas por meio de ensaios de fadiga em flexão rotativa (R = -1). Ensaios com peças entalhadas (Kt ? 3,0) permitiram determinar e comparar o fator de concentração de tensão em fadiga e a sensibilidade ao entalhe das ligas estudadas. Também foi estudada a influência da microestrutura e das partículas intermetálicas sobre as propriedades de fadiga. As superfícies das peças fraturadas foram observadas ao MEV e verificou-se que a maioria dos sítios de nucleação de trincas por fadiga ocorreram próximos a partículas de segunda fase que atuam como concentradores de tensão. / The automotive industry has shown a growing interest in aluminum alloys, particularly the AA 6xxx series. This class of alloys is widely used in construction and transportation because of their good mechanical strength, easy fabrication and excellent corrosion resistance. In the automotive sector there was always a need for improved studies of the fatigue behavior, because the structural components are subjected to vibratory loads and cyclic stresses and, as a consequence, may eventually crack and fracture. The presence of a notch generally decreases the fatigue life, creating regions of high triaxial stresses which restrain plastic deformation, weakening the material. The response depends on the mechanical solicitations, microstructure, the alloy components and the material properties. In this work it was conducted a study of the high cycle fatigue behavior and the notch sensitivity of three aluminum alloys used in components of truck and bus bodies: AA 6005, AA 6063 and AA 6351, all provided in T6 condition. The S/N curves were obtained by tests in rotating bending fatigue (R = -1). Tests with notched samples (Kt?3.0) allowed to determine and compare the fatigue concentration factor and the notch sensitivity of the studied alloys. It was also studied the influence of microstructure and the intermetallic particles on the fatigue properties. The surfaces of the fractured samples were observed via SEM and showed that most of the nucleation sites of fatigue cracking occurred near the second phase particles, which act as stress concentrators.

As ligas de alumínio são aplicadas em cerca de 70% dos componentes estruturais dos aviões e o processo de fadiga e o modo de falha predominante em estruturas aeronáuticas, para a maioria das quais a presença de concentradores de tensão e inevitável. O comportamento em fadiga e as propriedades mecânicas das ligas de alumínio endurecíveis por precipitação são fortemente influenciadas por parâmetros como tamanho, espaçamento e densidade dos precipitados endurecedores. Neste contexto, pesquisas anteriores tem mostrado que o envelhecimento interrompido (T6I4) pode proporcionar melhores combinações de propriedades mecânicas para estas ligas. O presente trabalho tem como objetivo o estudo das propriedades mecânicas e do comportamento em fadiga de alto ciclo das ligas de alumínio AA6351 e AA7050 nas condições de tratamento térmico convencionais (T6 e T7451, respectivamente) e na condição T6I4, bem como da influência das características microestruturais e do tratamento térmico sobre estas propriedades. Dentro deste contexto, analises de Microscopia Eletrônica de Transmissão (MET) da liga AA6351 mostraram que a condição T6I4 resultou em uma maior densidade de precipitados endurecedores com tamanho heterogêneo, quando comparada com a condição T6. Para esta liga, a condição T6I4 também resultou em menores valores de tensão limite de escoamento, resistência a tração, resistência a fadiga e sensibilidade ao entalhe, com maior ductilidade e tenacidade. Para a liga AA7050, as análises de MET mostraram que a condição T6I4 resulta em uma maior densidade de precipitados endurecedores com menor tamanho, promovendo um melhor impedimento ao movimento de discordâncias durante a deformação por fadiga, quando comparada com a condição T7451. Esta alteração microestrutural proporcionou a condição T6I4 valores de resistência ao escoamento e resistência a tração similares a condição T7451, com maior ductilidade e tenacidade. A resistência a fadiga da condição T6I4 foi similar a condição T7451, entretanto o envelhecimento interrompido resultou em um melhor comportamento em sensibilidade ao entalhe. / Aluminum alloys are applied in approximately 70% of the aircraft structural components and the fatigue process is the dominant failure mode in aeronautical structures, for the most of which, the presence of stress concentrators is unavoidable. The fatigue behavior and the mechanical properties of the age hardenable aluminum alloys are strongly influenced by parameters including the size, spacing and density of strengthening precipitates. Within this context, previous researches have shown that the interrupted ageing (T6I4) could provide an improved combination of mechanical properties for these alloys. This work aims to study the mechanical properties and the high cycle fatigue behavior of AA6351 and AA7050 aluminum alloys in the conventional heat treatment conditions (T6 and T7451, respectively) and in the T6I4 condition, as well as the influence of the microstructural characteristics and of the heat treatment on these properties. Within this context, Transmission Electron Microscopy (TEM) analyzes of the AA6351 alloy showed that T6I4 condition resulted in higher density of hardening precipitates with heterogeneous size compared to T6 condition. For this alloy, the T6I4 condition resulted in lower values of yield stress, ultimate tensile strength, fatigue strength and notch sensitivity, with higher ductility and toughness. For the AA7050 alloy, TEM analyses showed that T6I4 condition presented a higher density of strengthening precipitates with smaller size promoting an improved dislocation pinning effect during the fatigue deformation compared to T7451 condition. This microstructural change provided to T6I4 condition yield stress and ultimate tensile strength similar to T7451, with higher ductility and toughness. The fatigue strength of T6I4 condition was also similar to T7451, however the interrupted ageing provided a better notch sensitivity behavior.

Le laboratoire d’Embryologie Moléculaire étudie les mécanismes moléculaires contrôlant le développement embryonnaire et utilise comme système expérimental l’embryon de xénope. En collaboration le laboratoire du Dr Daniel Christophe, nous avons abordé l’étude du gène XHRT1 chez le xénope. Ce gène est l’orthologue du gène HRT-1/Hey1/Hesr-1/HERP2/CHF2 de souris. Celui-ci, avec deux autres protéines apparentées (HRT2 et HRT3) forme une sous-famille de facteurs de transcription de type bHLH-O qui se différencient des autres facteurs bHLH-O par l’absence d’un motif carboxy-terminal de séquence « WRPW » et par la présence d’un nouveau motif carboxy-terminal conservé de séquence « TEI/VGAF ». Le rôle de ces facteurs HRT dans le développement est encore actuellement mal connu. <p>Dans un premier temps, nous avons déterminé le profil d’expression de XHRT1 au cours de l’embryogenèse. Nous avons observé que ce gène est fortement exprimé au stade neurula dans le plancher du tube neural, et que plus tardivement celui-ci est exprimé dans différentes régions du système nerveux, dans les somites et le dans le pronéphros. Comme attendu pour un membre de la famille des facteurs bHLH-O, nous avons également observé que l’expression précoce de HRT1 au niveau du plancher du tube neural est bien régulée par la voie de signalisation Notch.<p>Dans un deuxième temps, nous nous sommes intéressés au rôle et au mode d’action du facteur XHRT1 dans le développement du plancher du tube neural. Nous avons pu montrer que XHRT1 agit comme répresseur transcriptionnel et que cette répression nécessite la présence du domaine bHLH et de séquences en aval de celui-ci. Nous avons montré en embryon que la surexpression précoce de XHRT1 induit un blocage de l’expression des marqueurs du mésoderme et une augmentation de marqueur du plancher du tube neural, ce qui est en accord avec le modèle selon lequel la voie de signalisation Notch interviendrait dans le choix de la destinée des cellules de la région médiane en inhibant la différenciation des cellules en notocorde et en favorisant leur différenciation en cellules du plancher du tube neural. XHRT1 n’étant cependant activé qu’à partir du stade neurula, nous avons conclu que les effets observés n’étaient probablement pas dus à XHRT1 mais à un autre facteur bHLH-O apparenté exprimé plus précocement dans les cellules de la ligne mediane de l’embryon. Afin d’éviter ces effets non spécifiques précoces, nous avons utilisé un vecteur d’expression de XHRT1 permettant un contrôle temporel de l’activité de la protéine. Nous avons ainsi montré que l’activation de XHRT1 au stade neurula dans l’ectoderme inhibe la différenciation des cellules précurseurs neurales en neurones et qu’il pourrait ainsi jouer un rôle important dans le développement du plancher du tube neural. Nos résultats ont montré également que XHRT1 est capable d’homo- et hétérodimériser in vivo avec les facteurs Xhairy1 et Xhairy2b coexprimés avec XHRT1 dans le plancher du tube neural. Enfin, nous avons montré que les propriétés de dimérisation de XHRT1 sont dépendantes non seulement du domaine bHLH, mais aussi du domaine Orange et des séquences situées en aval, séquences jouant un rôle important dans le choix du partenaire.<p>Des travaux récents ayant montré que la voie de signalisation Notch joue un rôle important dans le développement du rein, nous avons voulu déterminer l’importance de XHRT1 dans le développement du pronéphros. Nos résultats ont montré que XHRT1 ainsi que d’autres facteurs bHLH-O sont exprimés de manière dynamique, d’abord dans le glomus puis dans la partie dorso-antérieure de l’ébauche du pronéphros à l’origine des tubules proximaux, et que leur expression est régulée positivement par Notch. La surexpression de XHRT1 à la fin de la neurulation inhibe la formation du canal et du tubule distal, tandis que l’inhibition de la traduction de la protéine entraîne une réduction de l’expression de marqueurs spécifiques des tubules proximaux et du glomus. Ces résultats démontrent que XHRT1 joue un rôle important comme médiateur de la voie de signalisation Notch dans le pronéphros. / Doctorat en sciences, Spécialisation biologie moléculaire / info:eu-repo/semantics/nonPublished

This work deals with the influence of atmospheric corrosion on high-cycle fatigue properties of a weathering steel ATMOFIX B. New experimental data on fatigue strength of a steel exposed for 20 years to an atmospheric corrosion were compared to those characterizing the base material. Reduction of the fatigue lifetime of the exposed material compared with the base material was predicted on the basic of fractographic examination of fracture surfaces and the influence of surface notches on fatigue strength. The predicted results agree well with the experimental results.

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Osteoarthritis (OA) is the leading cause of disability in North American and has major economic consequences for society. People with knee OA experience the worst quality of life, among musculoskeletal conditions, with function and mobility being influenced by symptoms such as pain and stiffness. However, the impact of OA symptoms varies due to intrinsic and extrinsic factors, leading many researchers to employ biopsychosocial and other population health frameworks to study the disease. These population health approaches have not been adopted when studying knee OA outcomes in bioarchaeology, where a limited biological lens prevails due to the sole reliance on skeletal remains. The purpose of this research was to explore methods for identifying the impairment potential of knee OA in archaeological populations using a clinical sample and population health approaches. Clinical studies have the advantage of assessing not only the biological implications of knee OA but also the functional outcomes. By creating a knee OA grading system applicable for both MRI and dry bone femora samples (Clinical Archaeological Osteoarthritis Score) a link between clinical and archaeological populations was proposed. Using this link to infer functional deficits onto archaeological populations using population health frameworks, a theoretical analysis was performed with two populations; the 17th century Huron and the 19th century Inuit from the Igloolik region of Nunavut. The results demonstrated the increased impairment potential of knee OA in the Inuit population versus the Huron population, produced by contrasting factors captured by the determinants of health, including social and physical environments.

3D woven composites, due to the presence of through-thickness fibre bridging, have the potential to improve damage tolerance and at the same time to reduce the manufacturing costs. However, the ability to withstand damage depends on weave architecture as well as the geometry of individual tows. A substantial amount of research has been performed to understand in-plane properties as well as the performance of 3D woven composites exposed to impact loads, but there is limited research on the damage tolerance and notch sensitivity of 3D weaves and no work is reported on the damage tolerance of 3D weaves with a weft binding pattern. In view of the recent interest in 3D woven composites, the influence of weft binder on the tensile, open hole tensile, impact resistance and subsequent residual compressive strength properties and failure mechanisms of 3D woven composites was investigated against equivalent UD cross-ply laminate. Four different 3D woven architectures; layer-to-layer, angle interlocked, twill angle interlock and modified angle interlock structures were produced under identical weaving conditions. All the above mentioned tests were performed in both the warp and weft directions on 3D woven and UD cross-ply laminates. Stress concentration and yarn waviness due to through-thickness reinforcement led to lower mechanical properties compared with the UD cross-ply laminate. However, improved in-plane and damage tolerance properties of 3D woven composites under tensile loads were achieved by modifying the weave architecture. The influence of the weave architecture and binder yarn orientation on the notch insensitivity and damage tolerance of 3D woven composites was less significant for compressive loads. Despite the lower undamaged compression strength of 3D woven structures, their residual compressive strength was found to be superior to their equivalent UD cross-ply laminates. The lower rate of strength reduction in the 3D woven fabrics laminates was attributed to a crack bridging mechanism, effectively inhibiting delamination propagation.