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Made available in DSpace on 2014-10-09T12:27:40Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:09Z (GMT). No. of bitstreams: 0 / Este trabalho descreve um estudo experimental dos efeitos da temperatura em um elemento de pavimento de concreto, construído em laboratório interno e instrumentado com sensores de deformação, deslocamento, força e temperatura. A estrutura foi construída em duas camadas (placa e base) assentadas sobrepostas, sem aderência, sobre um subleito artificial. Os efeitos térmicos foram gerados artificialmente seguindo padrões sazonais da natureza. Os carregamentos estáticos foram realizados por meio de uma máquina hidráulica referenciados a um eixo simples de roda simples. A estrutura foi dimensionada e construída em uma escala de tamanho reduzido, distorcida e montada sobre uma laje de reação. Sob a placa do pavimento foi construído um sistema térmico auto controlado para causar diferencial de temperatura entre o fundo e o topo da placa pela passagem de um fluido. No topo um sistema térmico com controle manual foi construído para gerar gradientes térmicos através da estrutura. Todas as ações foram registradas automaticamente por meio de um sistema de aquisição de dados. Os resultados combinam com os dados da literatura, com experimentos realizados em pistas experimentais e se correlacionam com simulações realizadas por meio de software específico. Isso implica que a metodologia usada é apropriada para ser utilizada em outras situações e experimentos. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Neste trabalho enfoca-se o efeito da variação térmica na degradação da aderência de revestimentos de argamassa. Dentre os diversos fatores que condicionam a aderência dos revestimentos de argamassa, destaca-se aqui o cenário crítico definido pela presença de macrodefeitos na interface revestimento-base e também pela intensidade com que ocorre a variação de temperatura, encontrando-se uma situação extrema quando da ocorrência do choque térmico. Assim, o objetivo desta pesquisa é avaliar, de maneira experimental, o efeito de sucessivos ciclos de choque térmico na resistência de aderência de revestimentos de argamassa, em duas situações limites de taxa de macro-defeitos no contato entre o revestimento e a base e para duas distintas argamassas. Para dar suporte ao trabalho experimental foi elaborado um modelo computacional paramétrico, utilizando modelagem com elementos finitos. Com ele foi possível obter a distribuição de temperaturas, bem como as deformações e tensões geradas no revestimento, variando-se a intensidade do contato revestimento-base e alterandose as características da argamassa de revestimento. A partir de então, definiram-se as variáveis de maior influência e a geometria dos corpos prova, bem como as condições de contorno a serem utilizadas no programa experimental. O programa experimental foi desenvolvido em duas etapas: uma etapa piloto e outra definitiva. Para sua realização foram desenvolvidos e construídos os equipamentos para execução e controle dos ensaios cíclicos de choque térmico. Finalmente, foram realizados ensaios de resistência de aderência do revestimento e avaliados os efeitos de cada uma das variáveis estudadas, empregando-se suporte estatístico. Pelos resultados pode-se comprovar que os macro-defeitos na interface revestimento-base provocam diminuição na resistência de aderência a qual é agravada quando da ocorrência de cíclicos choques térmicos, ocorrendo a situação mais crítica para os revestimentos com maior módulo de elasticidade. / The present study focus on thermal variation effects on mortar rendering bonding degradation. Among the variety of factors that condition the bonding of mortar renderings, a critic scenario can be defined by the existence of interface macro-flaws between mortar rendering and substrate, and by the thermal variation intensity in the extreme situation of thermal shock. This research aims to experimentally evaluate the effects of continuous thermal shock cycles on the bonding strength of mortar renderings in two macro-flaw rate extreme situations in the contact surface between mortar rendering and substrate for two types of mortar. A parametric model based on finite element analysis has been developed to support the experimental work, which allowed ascertaining temperature profile as well as stress and strain distribution in the mortar rendering by changing the macro-flaws rate and mortar rendering properties. As a result, one could define the variables with higher influence and test panel geometry, as well as the boundary conditions to be used in the experimental program. The experimental program has been performed first in pilot scale and then in a definite stage, which required designing and building of equipment for the execution and control of cyclic thermal shock laboratory tests. Furthermore, bond strength tests have been performed on the mortar rendering samples, and effects of variables have been analyzed by using statistical help. Results have shown that the existence of interfacial macro-flaws decreases bond strength values between mortar rendering and substrate, and this scenario worsens under thermal shock. Mortar renderings with higher Youngs modulus (E) are more affected.

Due to a relative high thermal efficiency, the gas turbine engine has wide ranging applications in various industries today. The aerospace and power generation sectors are probably the best known. One method of increasing the thermal efficiency of a gas turbine engine is to increase the turbine inlet temperature. This increase in temperature will result in an additional thermal load being placed on the turbine blades and in particular the nozzle guide vanes. The higher temperature gradients will increase the thermal stresses. In order to prevent failure of blades due to thermal stresses, it is important to accurately determine the magnitude of the stresses during the design phase of an engine. The accuracy of the thermal stresses mainly depends on two issues. The first is the determination of the heat transfer from the fluid to the blade and then secondly the prediction of the thermal stresses in the blade as a result of the thermal loading. In this study the flow and heat transfer problem is approached through the use of computational fluid dynamics (CFD). The principal focus is to predict the heat transfer and thermal stresses for steady state cases for both cooled and uncooled nozzle guide vanes through numerical modelling techniques. From the literature, two studies have been identified for which experimental data was available. These case studies can therefore be used to evaluate the accuracy of using CFD to simulate the thermal loading on the blades. One study focused only on solving heat transfer whilst the other included thermal stress modelling. The same methodology is then applied to a three-dimensional application in which flow and heat transfer was solved for a nozzle guide vane of a commercial gas turbine engine. The accuracy of results varied with the choice of turbulence model but was, generally within ten percent of experimental data. It was shown that the accurate determination of the heat transfer to the blade is the key element to accurately determine the thermal stresses. / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

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Recent advances in the use of thermal proxies provide a window into how faults slip during earthquakes. Faults have a similar large-scale structure with a fault core, where earthquakes nucleate, and a surrounding damage zone, but complexities in fault zone architecture and rheology influence earthquake propagation. For example, changes in thickness of slipping layers in the fault core, compositional heterogeneity, and fault surface topography can influence fault strength and either facilitate or arrest a rupture. A further barrier to our understanding of earthquake behavior is in constraining the frictional energy that goes into the earthquake energy budget. Earthquakes can propagate when the energy available at the rupture tip is greater or equal to the energy being expended through radiation of seismic waves, permanent deformation within the process zone, and heat through friction. By quantifying the total energy involved in coseismic slip we can gain a more complete picture of the energy required for rupture propagation and how this may vary across faults. Although fracture and radiated energy can be constrained seismologically, thermal energy requires quantification by other means, and up until recently only few estimates existed for frictional energy. In this thesis I utilize biomarker thermal maturity to quantify temperature rise across multiple faults and explore what this can tell us about earthquake behavior. In chapters two through four, I focus on three large faults of varying structural and rheological complexity. Beginning with the Muddy Mountain thrust of southeast Nevada in Chapter two, I identify thermal evidence of coseismic slip in principal slip zones (PSZs) along this exhumed fault. I show that considerable heterogeneity in the thickness of slipping layers occurs a long a fault and that this has a large effect on coseismic temperature rise and hence fault strength, due to the effect of high temperature dynamic weakening mechanisms. In Chapter three, I move on to the creeping central deforming zone of the San Andreas fault, and show that it has experienced many large earthquakes that are clustered in a 4 m-wide zone adjacent to an actively creeping region. This work shows that the central San Andreas fault and other creeping faults can host seismic slip and should be included in seismic hazard analyses. Furthermore, I demonstrate the potential of K/Ar dating as a tool to constrain the age of earthquakes and find that these central San Andreas fault events are as young as ~3.3 Ma. In Chapter four, I focus on the Hikurangi Subduction zone, which has hosted large earthquakes and regular slow slip events in the past. Here, using drill core collected through the Pāpaku fault, a splay fault of the Hikurangi megathrust, I find evidence of temperature rise in the fault zone and deep hanging wall. Coupled forward models of heat generation and biomarker reaction kinetics estimate that displacement during these earthquakes was likely 11-15 m. These and other splay faults along the margin may pose considerable seismic and tsunami hazard to near-shore communities in the North Island of New Zealand. In Chapter five I explore what we have learned about fault behavior from biomarkers and other thermal proxies. I include measurements from five new faults and compile observations and measurements from past studies to explore how coseismic slip is localized across fault zones and put together a database of frictional energy estimates. Coseismic slip can broadly be described by two different scales of earthquake localization and that this is a function of total displacement, and to a lesser extent, material contrast across the fault. I see that frictional energy is relatively similar across faults of different displacement, depth, and maturity, and conclude that frictional energy is limited by the onset of dynamic weakening. Finally, I put together constraints on the energies involved in the budget to produce the first complete view of the earthquake energy budget and provide estimates of the total energy required for earthquake rupture across different faults.

Functionally graded materials (FGMs) are advanced materials and their main characteristic is microstructure and composition variation over the volume of the specimen. This variation of the composition results in changing of material properties in the component. In FGMs usually there are two different types of powder materials such as metal and ceramic powders which are mixed to build up the graded region. These grade layers are placed between the metal and ceramic layers and by this approach a smooth and gradual transient from metal to ceramic can be achieved.Sintering is the main technique to manufacture these types of materials. During the sintering process, cooling of the specimen from sintering temperature to room temperature results in generation of thermal residual stresses within the material. These thermal stresses may cause crack propagation and failure of the material.Distribution analysis of these thermally induced stresses within the material has been carried out in this thesis work. Finite element package ABAQUS has been used in order to simulate the distribution of the thermal residual stresses in the materials. In order to achieve the optimal design for different geometries the parametric study also has been performed. For example influence of number of layers, mixing ratio and porosity has been investigated.Based on the finite element results for cylindrical and cuboid models, non-linear composition variation for both geometries has no improving effect in terms of induced thermal residual stresses. Porous material shows less thermal stress than non-porous material. As the amount of porosity for individual layer was considered in simulation process, this approach resulted in decreasing of thermal stresses within the material. Moreover, non-uniform thickness of graded layers was not beneficial for stress reduction. This variation of thickness results in increasing of thermal residual stresses within the material.

As electronic packages and their thermal solutions become more complex the reliability margins in the thermal solutions diminish and become less tolerant to errors in reliability predictions. The current method of thermally stress testing thermal solutions can be over or under predicting end of life thermal performance. Benefits of accurate testing and modeling are improved silicon yield in manufacturing, improved performance, lower cost thermal solutions, and shortened test times. The current method of thermally stress testing is to place the entire unit in an elevated isothermal temperature and periodically measure thermal performance. Isothermally aging is not an accurate representation of how the unit will be used by the customer and does not capture the thermal gradients and mechanical stresses due to different coefficients of thermal expansion of the materials used in the thermal solution. A new testing system, CITRAM which is an acronym for Constant Interface Temperature Reliability Method, has been developed that uses an electronic test board. The approach captures the thermal and mechanical stresses accurately and improves test time by 20-30% as a result of automation. Through this study a difference in the two methods has been identified and the new CITRAM method should be adopted as current practice.