Au cours des deux dernières décennies, l'essai d'indentation à haute température a été développé progressivement afin de satisfaire aux exigences industrielles de plus en plus importantes. Pour garantir un bon niveau de précision des mesures, il faut résoudre les problèmes notamment associés à la température élevée tels que le choix du matériau de la pointe, la stabilité thermique du système, la conception du chauffage, etc. Cette thèse s'inscrit dans la problématique du développement de la méthodologie de l'essai d'indentation à haute température pour caractériser les matériaux métalliques. Une attention particulière a été accordée à la recherche des matériaux candidats pour la pointe et à la détermination des plages de forces et de pénétrations utilisées au bon fonctionnement d'un indenteur. Les analyses éléments finis nous aident d'étudier l'influence de défauts tels que la présence d'un revêtement mince et celle d'un défaut d'alignement entre l'axe d'indentation et la surface d'échantillon. Pour trouver un bon matériau de pointe, il est nécessaire de tester la stabilité géométrique et chimique de différents matériaux candidats pouvant remplacer le diamant à haute température. La collaboration avec la société suisse Anton Paar, qui se spécialise dans la fabrication des machines de mesure pour la caractérisation mécanique d'une grande variété de matériaux, permet de développer un nouvel équipement de micro- et nano-indentation à haute température. En utilisant le nouvel dispositif, nous avons pu réaliser des essais d'indentation pour caractériser des propriétés mécaniques de différents matériaux et vérifier la stabilité thermique de cet instrument. / Over the past two decades, the high-temperature indentation experiment has been developed gradually to meet increasingly high industrial demand. ln order to guarantee a good level of accuracy of the measurements, it is necessary to solve the problems associated with high temperature, such as the choice of the indenter material, the thermal stability of the system, heating design, etc. This thesis aims to develop the methodology of the high-temperature indentation experiment to characterize metallic materials. Particular attention has been given to the search for candidate materials for the tip and to the determination of the force and penetration ranges used for the correct operation of an indenter. The finite element analysis helps us to study the influence of defects such as the presence of a thin film and that of a misalignment between the indentation axis and the sample surface. To find a better indenter material, it is necessary to test the geometric and chemical stability of different candidate materials that can replace the diamond at elevated temperature. The collaboration with the Swiss company Anton Paar, which specializes in the manufacture of measuring machines for the mechanical characterization of a wide variety of materials, enables the development of new high-temperature micro- and nano­-indentation equipment. By using the new device, we were able to carry out the indentation tests to characterize the mechanical properties of different materials and to check the thermal stability of this new instrument.

Due to changes of the thermal environment, thermal stresses are produced in structures. Two approaches based on the stochastic process theory are used to describe this phenomenon. The structure is idealized as a long hollow viscoelastic cylinder. Two sites are considered: Barrow (AK) and Yuma (AZ). First passage concepts are applied to characterize the reliability of the system. Crossings are assumed to follow either the behavior of the Poisson process or Markov process. In both cases, the distribution of the time to first passage is taken to be the exponential distribution. Because the material is viscoelastic, statistically and time varying barriers (strengths) with Normal, Log-Normal, or Neibull distributions are considered. Degradation of the barriers by aging and cumulative damage are incorporated in the analysis. / Ph. D. / incomplete_metadata

Este trabalho aborda os conceitos básicos da distribuição de temperaturas e cálculo das tensões térmicas nas estruturas de comportamento linear, utilizando o Método dos Resíduos Ponderados (variante de Galerkin). De modo a sedimentar os conceitos, foram desenvolvidos exemplos de aplicação. / This paper deals with the basic concepts of both temperature distribution and thermal stresses evaluation in structures of linear behavior, by means of the Method of Weighted Residuals (Galerkin\'s approach). Examples of application have been developed in order to sediment the concepts.

The main aim of this study is to utilize a Jk-integral based computational method in order to calculate crack tip parameters for orthotropic functionally graded materials (FGMs). The crack is subjected to mixed mode thermal loading. Mixed mode thermal fracture analysis requires the calculation of mode-I and mode-II stress intensity factors (KI ,KII ). In addition to stress intensity factors, energy release rate and T-stress are calculated by means of Jk-integral. Jk-integral is defined as a line integral over a vanishingly small curve. Since it is difficult to deal with a line integral on a vanishing curve , Jk-integral is converted to a domain independent form containing area and line integrals by the help of plane thermoelasticity constitutive relations. Steady-state temperature distribution profiles in FGMs and the components of the Jk-integral are computed by means of the finite element method. In both thermal and structural analyses, finite element models that possess graded isoparametric elements are created in the general purpose finite element analysis software ANSYS. In the formulation of Jk-integral, all required engineering material properties are assumed to possess continuous spatial variations through the functionally graded medium. The numerical results are compared to the results obtained from Displacement Correlation Technique (DCT). The domain independence of Jk-integral is also demonstrated. The results obtained in this study show the effects of crack location and material property gradation profiles on stress intensity factors, energy release rate and T-stress.

Modeling at the structural scale most often requires the use of beam and shell elements. This simplification reduces modeling complexity and computation requirements but sacrifices the accuracy of through-the-thickness information. Several studies have reported various design approaches for analyzing functionally graded material structures. One of these studies proposed a two-node beam element for functionally graded materials (FGMs) based on first order shear deformable (FOSD) theory. The derivation of governing equations included spatial temperature variation. However, only the constant temperature case was carried through in the element formulation. This investigation explore the effects of spatial temperature variation in the axial and through-the-thickness direction of this proposed element and present a new standard three-node beam finite element modified for structure constructed of FGMs. Also, the influence of the temperature dependency of the thermo-elastic material properties on the thermal stresses distribution was studied. In addition, variations in the layer thicknesses within multilayer beam models were studied to determine the effect on stresses and factor of safety. Finally, based on the specific factor of safety, which combines together the strength and mass of the beam, the best layer thicknesses for the beam models were established. The key contributions expected from this research are: 1. development and implementation of a three-node beam element as a finite element code into the commercial computational tool MATLAB® to analyze thermo-mechanical stresses in structures constructed of functionally graded materials; 2. a strategy to simulate different load cases in structures constructed of functionally graded materials; 3. an analysis of the influence of the FGM interlayer thickness on the factor of safety/specific gravity ratio in structures constructed of functionally graded materials under thermo-mechanical loads; 4. and an analysis/comparison of the advantages/benefits of using structures constructed of functionally graded materials with respect to those constructed with homogenous materials.

Thesis (M.S.)--State University of New York at Binghamton, Thomas J. Watson School of Engfineering and Applied Science, Department of Systems Science and Industrial Engineering, 2009. / Includes bibliographical references.

Este trabalho aborda os conceitos básicos da distribuição de temperaturas e cálculo das tensões térmicas nas estruturas de comportamento linear, utilizando o Método dos Resíduos Ponderados (variante de Galerkin). De modo a sedimentar os conceitos, foram desenvolvidos exemplos de aplicação. / This paper deals with the basic concepts of both temperature distribution and thermal stresses evaluation in structures of linear behavior, by means of the Method of Weighted Residuals (Galerkin\'s approach). Examples of application have been developed in order to sediment the concepts.

Submitted by Irene Nascimento (irene.kessia@ufpe.br) on 2016-06-20T17:29:06Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação_ElderSilva.pdf: 10947725 bytes, checksum: de00b6e9f2c93bb210ce6ec7e6d47497 (MD5) / Made available in DSpace on 2016-06-20T17:29:06Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação_ElderSilva.pdf: 10947725 bytes, checksum: de00b6e9f2c93bb210ce6ec7e6d47497 (MD5) Previous issue date: 2016-02-29 / Capes / O transporte de petróleo e seus derivados é uma atividade que requer muito cuidado, não somente pelo custo elevado dos produtos, mas também pelo seu potencial de causar graves acidentes. Um dos modos de transporte mais utilizados e seguros para esse tipo de operação são os dutos metálicos, tanto para prospecção quanto para o transporte. Inspeções periódicas em dutovias são fundamentais para detecção de danos físicos e avaliação da corrosão. A corrosão por sua vez, se trata de um processo natural que pode ser controlado e retardado, mas não eliminado. Portanto a inspeção das linhas é fundamental para obter dados sobre os defeitos de corrosão e assim avaliar a resistência dos dutos corroídos, visando uma operação segura das linhas. Para realizar as avaliações de integridade estrutural de dutos, vários métodos podem ser empregados. Os Métodos Analíticos Semi-Empíricos, que embora geralmente fornecem resultados muito conservativos implicando em parada prematura das linhas com defeitos de corrosão, ainda são largamente utilizados pois geram resultados seguros com razoável rapidez. Os Métodos Numéricos, particularmente o Método dos Elementos Finitos (MEF), têm gerado resultados com excelente acurácia em relação aos ensaios experimentais, mas não são tão empregados devido à complexidade de uso, que implica em uma análise demorada e necessidade de profissionais especializados para sua utilização. Na literatura são encontrados vários trabalhos sobre a avaliação da integridade de dutos corroídos com carregamento exclusivo de pressão interna. Em contrapartida, foram desenvolvidos poucos estudos acerca da avaliação de resistência de dutos sob carregamento combinado de pressão interna com outros tipos de carregamento. Com as recentes demandas de produção e exploração onde os dutos podem transportar fluídos de alta temperatura sob pressão, torna-se cada vez mais necessário levar em conta os fenômenos termomecânicos acoplados. Esse trabalho se propõe a estudar dutos com defeitos de corrosão interagentes sob carregamento combinado de pressão interna e cargas térmicas através do MEF para mostrar a importância da consideração das cargas térmicas para avaliar a integridade de dutos corroídos. Ao fim das análises, foi constatado que as cargas térmicas podem reduzir significativamente a pressão de falha de dutos corroídos, com perdas percentuais até 8,86%, quando é aplicado uma temperatura relativa de 100°C. Por fim mostrouse que a consideração das cargas térmicas influencia significativamente a integridade estrutural de dutos corroídos, principalmente para dutos com defeitos de corrosão com comprimento total longo e/ou profundos. / The transport of oil and its derivatives is an activity that requires special attention, not only due to the high costs of the goods, but also for its potential to cause serious accidents. One of the safest modes to realize exploration and transport operations is the use of metallic pipes. Periodic inspections of pipes are critical to detect injury and to evaluate the action of corrosion. Corrosion is a natural process that can be controlled and delayed but not completely avoided. Proper inspection and monitoring of the lines are critical to obtain data of the corrosion defects and assess the structural resistance of corroded pipes, thus allowing safe operation of the lines. To assess the structural integrity of pipes, various methods can be employed. The Semi- Empirical Analytical Methods, which usually provide very conservative results resulting in premature shutdown of the lines with corrosion defects, are still widely used as they generate quickly reliable results. The numerical methods, particularly the Finite Element Method (FEM), have generated results with excellent accuracy compared to experimental tests, but are not very employed yet due to the complexity of use, which involves time-consuming analysis and specialized professionals. On one hand, several papers about the evaluation of the integrity of corroded pipes with internal pressure loading can be found in the literature. On the other hand, few studies have been developed about the integrity of pipes submitted to combined loading, such as internal pressure with other types of loads. With the recent demands of production and exploration, where pipes can transport high temperature fluids under pressure, it becomes increasingly necessary to take into account the coupled thermo-mechanical phenomena. This work aims to study the integrity of pipes with interacting corrosion defects under combined load composed by internal pressure and thermal loads. The MEF is used to perform the numerical analysis and to show the importance of considering the thermal loads to evaluate the integrity of corroded pipes. It was highlighted that the thermal loads can significantly reduce the failure of corroded pipe pressure, by percentage losses up to 8.86% when considering a relative temperature of 100°C. Finally it was shown that the consideration of the thermal loads in the models significantly influences the structural integrity of corroded pipes, particularly for those with long total length and/or deep corrosion defects.

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Civil and Environmental Engineering; and the Woods Hole Oceanographic Institution), 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references. / Under global climate change, our oceans are warming at an unprecedented rate. Increased temperatures represent a severe source of stress for many marine organisms. This thesis aims to understand how corals and anemones respond to changing temperatures across different timescales and investigates mechanisms that can facilitate persistence in light of environmental change, from selection and adaptation across generations to phenotypic plasticity within a single individual's lifespan. In this context, I explore three case studies of thermal stress in corals and anemones. I begin with massive Porites lobata corals from the central Pacific. Here, reefs that are most affected by El Niflo, such as Jarvis and the northeast Phoenix Islands maintain genetic diversity indicating recruitment from nearby reefs may occur. Yet, they show significant genetic differentiation (FsT) from farther areas, suggesting this dispersal may be limited. / Thermal variability in this region may also favor plasticity over adaptation, as we do not find differences in bleaching histories among genetic groups. Next, I investigate genetic connectivity and adaptation to chronically elevated temperatures across a natural temperature gradient within the Palauan archipelago. Combining genetic data and historical growth measurements from coral cores, I find that Palau's warmest reefs harbor unique genetic subpopulations of Porites lobata and find evidence for a genetic basis of their higher thermal tolerance. Lastly, I explore if parents can modulate parental effects to increase the thermal tolerance of their offspring over short time scales, using the estuarine anemone Nematostella vectensis. Indeed, I find parents exposed to increased temperatures quickly produce more thermally tolerant larvae. In fact, offspring from these Massachusetts parents show thermal thresholds that are indistinguishable from more southern populations. / This thesis highlights the ability and potential of corals and anemones to persist under variable conditions over different timescales. Nevertheless, a compelling effort to reduce rates of warming worldwide will be imperative to the survival and integrity of key marine ecosystems such as coral reefs. / Funding for this research came from the National Science Foundation (Awards OCE- 1537338, OCE-1605365, OCE-1220529, and OCE-1031971), the Link Foundation, Bermuda Institute of Ocean Sciences Grants-in-Aid, the Tiffany & Co. Foundation, the Nature Conservancy, the Dalio Foundation, Inc., through the Dalio Explore Fund, and Ray Dalio through the WHOI Access to the Sea Fund, all to Anne Cohen; and a Gordon and Betty Moore Foundation grant (#4033) to Ann Tarrant / by Hanny Elizabeth Rivera. / Ph. D. / Ph.D. Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Civil and Environmental Engineering; and the Woods Hole Oceanographic Institution)

L’objectif fondamental de cette étude est de montrer la faisabilité de l’élaboration des couches épaisses de zircone non dopée, en contrôlant la microstructure et l’état mécanique, par MOCVD et par Sol-Gel. Dans un premier temps, nous avons essayé d’optimiser les conditions de dépôt de MOCVD, en faisant varier ou en jouant sur les différents paramètres du procédé, conduisant à l’obtention des couches de ZrO2 micrométriques et denses. La stabilité de la phase quadratique de la zircone est conditionnée par la pression partielle en oxygène, la température du substrat ainsi que l’épaisseur du dépôt. La texture cristallographique de type {100} est obtenue pour les dépôts réalisés à une température de substrat T ≤ 850°C et pour de faibles pressions totales. Concernant l’état mécanique des couches de zircone, l’augmentation de l’épaisseur de la couche peut relaxer les contraintes résiduelles de tension au sein du dépôt. Ce phénomène s’accentue au-delà d’une épaisseur critique suite à la création des espacements entre les colonnes de croissance de la couche. Parallèllement, nous avons montré que la qualité des dépôts Sol-Gel est maitrisée par le choix du substrat, l’utilisation de « sols » vieillis, la multiplication du nombre de couches « spin-coating », le mode de dépôt ainsi que la température de recuit. Certaines propriétés caractéristiques du dépôt telles que la cristallisation, la composition de phase et l’adhérence sont aisément contrôlées respectivement par l’âge du sol, la température de recuit et le coefficient de dilatation thermique associé au substrat utilisé. La microstructure (changement de phases, taille des cristallites, texture cristallographique) et les contraintes internes (thermiques et intrinsèques) ont été caractérisées. Le Sol-Gel présente l’avantage de proposer des couches de zircone très peu contraintes par rapport aux films obtenus par le procédé MOCVD. Quel que soit le procédé de dépôt, MOCVD et/ou Sol-Gel, l’élaboration des films de ZrO2 orientés demeure fonction de la température du traitement. La tentative d’élaborer des multicouches de zircone par un couplage MOCVD/Sol-Gel montre la possibilité de sélectionner des paramètres de dépôt propices à la fabrication d’un film présentant un état microstructural et mécanique contrôlé et voulu. / The fundamental purpose of this study is to demonstrate the feasibility to obtain an undoped zirconia thick film, by controlling the microstructure and mechanical state, using MOCVD and Sol-Gel technique. Firstly, we try to optimize the MOCVD deposition conditions, by varying the different process parameters, leading to the production of ZrO2 micrometric and dense films. The stability of the tetragonal zirconia phase depends on the oxygen partial pressure, the substrate temperature and the film thickness. The crystallographic texture of {100} type is obtained for the deposits obtained under a substrate temperature T ≤ 850°C and a low total pressure. Concerning mechanical state of the zirconia films, the thickness increasing can relax the tensile residual stress within the deposit. This phenomenon accents beyond a critical thickness due to the creation of columns spaces during film growth. In the second part, we show that the quality of the Sol-Gel deposition is controlled by substrate origin, use of aged sol, increase of “spin-coating” layers number, deposition mode and annealing temperature. Some deposit characteristics such as crystallization, phase composition and film adhesion are easily controlled by sol aging, annealing temperature and thermal expansion coefficient associated to the used substrate, respectively. The microstructure (phase change, crystalline size, crystallographic texture) and the internal stresses (thermal and residual) were characterized. The Sol-Gel technique has the advantage of providing zirconia films with low stress level compared to the films obtained by MOCVD. Regardless of the deposition process, MOCVD and / or Sol-Gel, the development of ZrO2 oriented films is in function of the treatment temperature. The attempt to get multilayer zirconia by coupling MOCVD/Sol-Gel methods shows the possibility to choose the deposition parameters in order to produce films with controlled and wanted microstructure and mechanical state.