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Resumo: Revestimento de estruturas aeronaúticas são, em sua maioria, unidos por meio de juntas rebitadas. Para o dimensionamento dessas juntas deverão ser consideradas não somente a resistência das mesmas diante de condições limites de carregamento estático, mas também sua resistência a fadiga quando sujeitas a carregamento cíclico e sua resistência residual no eventual surgimento de trincas. Nesta dissertação são estudadas duas juntas: sobreposta e de topo simples. A modelagem das juntas é feita no software de elementos finitos ANSYS. O objetivo das simulações é reproduzir, de maneira satisfatória, o comportamento das mesmas quando submetida a esforços de tração monotônica. Há uma grande preocupação com simulação do comportamento dos rebites durante o tracionamento das juntas. Comparando os reultados das análises e os resultados dos ensaios (extensômetros e fotoelasticidade). é então proposta uma nova modelagem para os rebites. Por fim, é estudada a excentricidade que as juntas sobreposta e de topo simples apresentam, através da análise teórica do comportamento da tensão do momento secundário e do fator de momento não linear. / Abstract: Aerospace structure surface are mostly, united with rivet joint. These joint specifications must include the limit resistance within static charging conditions as well the limit resistance for fatigue within cyclic charging and residual resistance in eventual crack show up. In this paper two type ofjoint were studied; overlap and top. The modelings were done in ANSYS, infinity element software. The Main objective in these simulations is to reproduce, in a satisfactory manner, the behavior of these joint when subject to monotonic traction stress. There is a major concern about the rivet behavior simulation during joint traction experiments. Comparing the analyses and the results of these essay (strain gages and photoelasticity) a new rivet modeling is proposal. In thes paper, it is also studied the overlap joint and top joint eccentricity behavior thru a theoretical secondary moment tension behavior analysis and also the non-linear moment factor. / Orientador: Fernando de Azevedo Silva / Coorientador: Carlos Eduardo Chaves / Banca: Luis Rogerio de Oliveira Hein / Banca: Marcio Tadeu de Almeida / Mestre

Exposure of concrete structures to high temperatures leads to significant losses in mechanical and physical properties of concrete and steel reinforcement as well as the bond characteristics between them. Degradation of bond properties in fire may significantly influence the load capacity of concrete structures. Therefore the bond behaviours need to be considered for the structural fire engineering design of reinforced concrete structures. At present, the information about the material degradations of concrete and reinforcing steel bars at elevated temperatures are generally available. However, the research on the response of the bond characteristic between concrete and reinforcing steel bar at elevated temperatures is still limited. Due to the lack of robust models for considering the influence of the bond characteristics between the concrete and steel bar at elevated temperatures, the majority of the numerical models developed for predicting the behaviour of reinforced concrete structures in fire was based on the full bond interaction. Hence, the main purpose of this research is to develop robust numerical models for predicting the bond-slip between concrete and the reinforcement under fire conditions. Therefore, the bond-slip between the concrete and reinforcement for conventional and prestress concrete structures at both ambient and elevated temperatures has been investigated in this research. Two models have been developed in this study: the first model is to simulate the behaviour of bond-slip of deformed steel bars in normal concrete at room temperature and under fire conditions. The model is established based on a partly cracked thick-wall cylinder theory and the smeared cracking approach is adopted to consider the softening behaviour of concrete in tension. The model is able to consider a number of parameters: such as different concrete properties and covers, different steel bar diameters and geometries. The proposed model has been incorporated into the Vulcan program for 3D analysis of reinforced concrete structures in fire. The second robust model has been developed to predict the bond stress-slip relationship between the strand and concrete of prestressed concrete structural members. In this model, two bond-slip curves have been proposed to represent the bond-slip characteristics for the three-wire and seven-wire strands. This model considers the variation of concrete properties, strands’ geometries and the type of strand surface (smooth or indented). The degradation of materials and bond characteristic at elevated temperatures are also included in the model. The proposed models have been validated against previous experimental results at both ambient and elevated temperatures and good agreements have been achieved. A comprehensive parametric study has been carried out in this research to examine the influence of bond-slip model on the structural behaviours of normal reinforced concrete structures. The study investigated the most important factors that can affect the bond characteristics between concrete and steel reinforcement at elevated temperatures. These factors are: the concrete cover, spalling of concrete, concrete compressive and tensile strengths.

abstract: The present understanding of the formation and evolution of the earliest bodies in the Solar System is based in large part on geochemical and isotopic evidences contained within meteorites. The differentiated meteorites (meteorites originating from bodies that have experienced partial to complete melting) are particularly useful for deciphering magmatic processes occurring in the early Solar System. A rare group of differentiated meteorites, the angrites, are uniquely suited for such work. The angrites have ancient crystallization ages, lack secondary processing, and have been minimally affected by shock metamorphism, thus allowing them to retain their initial geochemical and isotopic characteristics at the time of formation. The scarcity of angrite samples made it difficult to conduct comprehensive investigations into the formation history of this unique meteorite group. However, a dramatic increase in the number of angrites recovered in recent years presents the opportunity to expand our understanding of their petrogenesis, as well as further refine our knowledge of the initial isotopic abundances in the early Solar System as recorded by their isotopic systematics. Using a combination of geochemical tools (radiogenic isotope chronometers and trace element chemistry), I have investigated the petrogenetic history of a group of four angrites that sample a range of formation conditions (cooling histories) and crystallization ages. Through isotope ratio measurements, I have examined a comprehensive set of long- and short-lived radiogenic isotope systems (26Al-26Mg, 87Rb-87Sr, 146Sm-142Nd, 147Sm-143Nd, and 176Lu-176Hf) within these four angrites. The results of these measurements provide information regarding crystallization ages, as well as revised estimates for the initial isotopic abundances of several key elements in the early Solar System. The determination of trace element concentrations in individual mineral phases, as well as bulk rock samples, provides important constraints on magmatic processes occurring on the angrite parent body. The measured trace element abundances are used to estimate the composition of the parent melts of individual angrites, examine crystallization conditions, and investigate possible geochemical affinities between various angrites. The new geochemical and isotopic measurements presented here significantly expand our understanding of the geochemical conditions found on the angrite parent body and the environment in which these meteorites formed. / Dissertation/Thesis / Ph.D. Geological Sciences 2012

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