Orientador: Newton de Oliveira Pinto Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-07T09:19:10Z (GMT). No. of bitstreams: 1 Carmona_TiagoGarcia_M.pdf: 1542541 bytes, checksum: 8f386834340021978bc83fc4da322af0 (MD5) Previous issue date: 2006 / Resumo: O uso de estruturas cilíndricas para armazenamento de líquidos e materiais granulares apresenta-se como uma eficiente solução, pois sob a ação da pressão interna desenvolvem-se predominantemente esforços de tração (esforços circunferenciais) nas paredes da estrutura. A obtenção dos esforços oriundos da pressão interna é apresentada de forma superficial nos primeiros capítulos do presente trabalho. A ocorrência de manifestações patológicas nestas estruturas muitas vezes está relacionada com o efeito de flexão na parede decorrente da ação de um gradiente térmico pela armazenagem de produtos a elevadas temperaturas. Para a análise deste efeito, são revisados conceitos de termodinâmica aplicados ao problema específico dos tanques. A consideração do efeito térmico é primeiramente apresentada segundo uma abordagem clássica com a seção não fissurada. Em seguida é apresentada uma formulação pouco difundida no meio técnico, onde a consideração da fissuração da seção de concreto armado modifica substancialmente o problema. É mostrado que o gradiente térmico não é capaz de produzir o estado limite último da seção, porém possui influência decisiva no controle da fissuração. Os conceitos teóricos são ilustrados pela apresentação de estudo de caso, onde após as análises decidiu-se pelo reforço com cabos externos protendidos não aderentes / Abstract: The use of cylindrical structures for storage of liquid and granular materials is an efficient solution of engineering, because under the action of the internal pressure, the wall develops preferentially tension forces (circumferential forces) in the structure walls. The first chapters of this work presents briefly how to obtain the internal forces caused by the pressure of the stored materials. Sometimes the occurrence of damages in cylindrical storage structures is related with a thermal gradient that generates bending effects in structures that store products at high temperature. For the analysis of this effect, concepts of thermodynamic are revised and applied for the case of tanks. The consideration of the thermal effect is first presented using a classic approach that takes in account a non-cracked section. After that it is present a not well known formulation, where the consideration of cracks in the reinforced concrete sections, bring great changes to the problem. It is shown that the thermal gradient is not able to produce an ultimate limit-state, but can have decisive influence in crack control. The theoretical concepts are illustrated with a case, where after the analysis, it was decided to reinforce the structure with external tendons / Mestrado / Estruturas / Mestre em Engenharia Civil

Made available in DSpace on 2014-10-09T12:25:28Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:56Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2014-11-10T11:55:57Z No. of bitstreams: 0 / Made available in DSpace on 2014-11-10T11:55:57Z (GMT). No. of bitstreams: 0 / Os moinhos de bolas são equipamentos presentes em plantas de mineração, sendo uma máquina importante no circuito de cominuição de minérios. Em função de inúmeros fatores como, por exemplo, projeto, fabricação, sobrecarga no equipamento, falta de manutenção e procedimentos de operação inadequados, são desenvolvidas descontinuidades nos componentes estruturais desse equipamento. Os componentes estruturais dos moinhos, basicamente, corpo, tampas e munhões, além do custo elevado, possuem prazos de fabricação que podem variar de dois a três anos dependendo da demanda do mercado. Portanto é cada vez mais necessário que as descontinuidades detectadas nesses componentes sejam corretamente avaliadas. Neste trabalho analisaram-se pela mecânica da fratura a criticalidade de descontinuidades, tais como trincas constatadas em um munhão de um moinho de bolas e compararam-se os valores teóricos de taxa de propagação (crescimento) dessas descontinuidades com valores reais obtidos por meio de inspeções periódicas realizadas neste componente. A nucleação das trincas foi causada por falta de lubrificação nos mancais do moinho, gerando esforços térmicos circunferenciais no munhão, em que a temperatura estimada do contato munhão e bucha atingiu a faixa de 100 °C a 150 °C. No período analisado, os resultados obtidos por meio da norma BS7910 mostraram-se mais próximos dos valores reais do que a norma ASME Seção XI, Apêndice A. O tamanho da trinca mais crítica foi aceito pelos critérios da norma BS7910 e aprovado apenas na condição de emergência da norma ASME Seção XI, Apêndice A. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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The intermetallic compound TiAl possesses a unique complex of properties that include sufficiently low material density, high values of the strength-to-ductility ratio, high elastic moduli, high oxidation resistance, low creep rate, and improved fatigue characteristics. These properties make TiAl alloys very attractive, particularly for structural applications for aerospace and aeronautic industries, where, at certain temperatures, they might be capable of replacing heavy nickel-based superalloys. However, so far applications of TiAl alloys have been limited by their poor ductility. Many of the recent studies have focused on the source of this limited ductility and on methods to improve this property. It has been found out experimentally that the strength and ductility of $gamma$-TiAl alloys can be affected by many different parameters, including alloy stoichiometry, heat treatment, deformation temperature, impurity content, grain size, and ternary element additions. In this thesis we present the results of our computer simulations of deformation and fracture in TiAl. In contrast to many previous studies our simulations include the interaction of the crack with point defects in the lattice. We use the molecular statics technique with atomic interactions described in terms of the embedded atom method. We simulate the crack propagation along (100), (001), (110) and (111) planes in TiAl. The cleavage along (100) and (001) planes shows purely brittle behavior, whereas the cleavage along (110) and (111) planes is accompanied by extensive dislocation emission. Our studies of the crack interaction with point defects reveal that vacancies and antisites near the crack tip can influence the amount of plastic deformation. Another important observation is that the antisite formation energy near the crack tip is generally lower than in the perfect lattice. This observation suggests the formation of relatively disordered zones near the crack tip at high temperatures, and leads us to a formulation of a new mechanism of a brittle-to-ductile transition in TiAl. / Ph. D.

No description available.

<p> The role of plastic deformation in the initiation and propagation of cracks in Cu-17Al alloy embrittled by liquid mercury has been studied. It is proposed that extensive plastic deformation and work hardening must occur at the crack-tip during propagation in order to raise the local flow stress to a critical level at which the maximum normal stress is equal to the cohesive strength. A crack initiation mechanism is proposed involving grain boundary diffusion enhanced by the stress concentration at the head of dislocation pile-ups at the grain boundary. Micro-cracks are formed at the weakened grain boundary and a period of stable crack growth made over a period of increasing applied stress may be necessary before the crack is long enough to become unstable.</p> / Thesis / Master of Science (MSc)

The ability of a filter to stop erosion through cracks in the core of a embankment dam requires that the filter be graded so that it will restrain movement of particles from the core, and that the filter be truly cohesionless, so that it will not crack even when subjected to the same types of deformations that cause cracks in the core. To achieve resistance to cracking, most current filter criteria require that the filter should contain no more than 5% of material finer than the #200 sieve, and that this fine material should be non-plastic. This research study was conducted to investigate whether there specifications do, in fact, result in filters that can be relied upon to slump, fill cracks, and prevent interval erosion in embankment dams. The research study involved filter erosion tests using a 4-inch diameter device and a 12-inch square device, and "sand castle" tests to investigate the tendency for candidate filters to slump when immersed in water. These tests showed that conventional filter criteria &#61485; no more than 5% fines, and fines that are non-plastic, are conservative. The research study showed that even filters with 5% of highly plastic fines are able to slump, fill cracks, and prevent erosion. / Ph. D.

Effects of dislocation emission from a mode I crack and of pinning distances on the behavior of the crack and on fracture toughness in aluminum were studied by using the Molecular Statics Technique with atomic interactions described in terms of the Embedded Atom Method. It was found that aluminum is a ductile material in which the cracks generate dislocations, blunting the cracks. The blunting and the dislocation shielding reduce the local stress intensity factor. Also, twinning, which has not been observed experimentally in Aluminum due to the high stacking fault, was obtained in the simulation. Probably, the low temperature facilitates twin formation. The applied stress intensity factor required to propagate the crack tip increases at first, and then becomes constant as the maximum distance that the first dislocation can travel away from the crack tip increases. These effects can be attributed to dislocation shielding and crack blunting. The maximum distance of the emitted dislocations from the crack tip is the equilibrium distance for the largest simulation performed (400,000 atoms) while for the smaller simulations the dislocations are hindered by the fixed boundary condition of the model. On the other hand, the total local stress intensity factor at the crack tip and the local stress intensity factor along the slip plane remain basically constant as the maximum distance of the emitted dislocations from the crack tip increases. For distances larger than , these local stress intensity factors start to increase slightly. / Master of Science

Steel corrosion is one of the major distress mechanisms that causes the deterioration of reinforced concrete structures around the world. It is an electrochemical reaction between the reinforcing steel and the surrounding concrete that produces a mass loss of the metal. Through the process of corrosion in reinforced concrete, iron ions get oxidized to form corrosion products (CP). Although multiple experiments and studies have been developed to understand the rheological behavior of corrosion products, this topic stays inconclusive. This work aims to characterize corrosion products at micro-scale in order to trace the progress of the formation of rust, to determine its nature and to analyse its rheological behavior in reinforced concrete. An experimental procedure to produce CP in the laboratory is also presented in this research. In addition, material characterization methods have been used to identify the iron oxide phases present in CP, determine their viscosity and rheological behavior and to study how CP flows in a porous media. In order to identify the different stages in the corrosion process, the CP was analysed at 2, 4, 6 and 8 weeks. The experiments identified four phases of iron oxide for each period. Furthermore, it was found that CP behaves as a shear-thinning slurry and as a result, its viscosity decreases with the applied shear rate. In addition, the damage caused by CP on concrete depends on the w/c ratio of the concrete mix and the exposure time to a corroding environment. The rebar mass loss results show that CP is formed in layers around the rebar, and the flow of each CP layer can differ.