LEDs are being developed as the next generation lighting source due to their high efficiency and long life time, with a potential to save $15 billion per year in energy cost by 2020. State of the art LEDs are capable of emitting light at ~115 lm/W and have lifetime over 50,000 hours. It has already surpassed the efficiency of incandescent light sources, and is even comparable to that of fluorescent lamps. Since the total luminous flux generated by a single LED is considerably lower than other light sources, to be competitive the total light output must be increased with higher forward currents and packages of multiple LEDs. However, both of these solutions would increase the junction temperature, which degrades the performance of the LED--as the operating temperature goes up, the light intensity decreases, the lifetime is reduced, and the light color changes. The word "junction" refers to the p-n junction within the LED-chips. Critical to the temperature rise in high powered LED sources is the very large heat flux at the die level (100-500 W/cm2) which must be addressed in order to lower the operating temperature in the die. It is possible to address the spreading requirements of high powered LED die through the use of power electronic substrates for efficient heat dissipation, especially when the die are directly mounted to the power substrate in a chipon- board (COB) architecture. COB is a very attractive technology for packaging power LEDs which can lead improved price competiveness, package integration and thermal performance. In our work high power LED-chips (>1W/die) implementing COB architectures were designed and studied. Substrates for these packaging configurations include two types of power electronic substrates; insulated-metal-substrates (IMS) and direct-bonded-copper (DBC). To lower the operating temperature both the thermal impedance of the dielectric layer and the heat spreading in the copper circuit layers must be studied. In the analysis of our architectures, several lead free solders and thermal interface materials were considered. We start with the analysis of single-chip LED package and extend the result to the multi-chip arrays. The thermal resistance of the system is only a function of geometry and thermal conductivity if temperature-independent properties are used. Thus through finite element analysis (ANSYS) the effect of geometry and thermal conductivity on the thermal resistance was investigated. The drawback of finite element analysis is that many simulations must be conducted whenever the geometry or the thermal conductivity is changed. To bypass same of the computational load, a thermal resistance network was developed. We developed analytical expressions of the thermal resistance, especially focusing on the heat spreading effect at the substrate level. Finally, multi-chip LED arrays were analyzed through finite element analysis and an analytical analysis; where die-spacing is another important factor to determine the junction temperature. With this thermal analysis, critical design considerations were investigated in order to minimize device temperatures and thereby maximizing light output while also maximizing device reliability.

Aging bridges in the United States demand effective, efficient, and economical strengthening techniques to meet future traffic requirements. One such technique is to bond steel or fiber reinforced polymer (FRP) plates to the tension faces of reinforced concrete bridge beams with adhesives to strengthen them in flexure. However, beams that have been flexurally strengthened in this manner often fail prematurely, in particular by plate end peeling. The benefits of flexural strengthening by externally bonded reinforcement can only be fully realized by preventing premature failure modes so as to allow the development of composite action between the beam and the external reinforcement. With this goal in mind, several critical limit states of externally reinforced beams are examined in this thesis. Models developed by Roberts (1989) and by Colotti, Spadea, and Swamy (2004) that predict premature plate end debonding are examined in depth using data from previously conducted experimental programs that employed both steel and FRP external reinforcement. In addition, various parameters of the concrete beam, adhesive, and external reinforcement are analyzed in each model to determine the role of each parameter in failure prediction. A critical appraisal of the performance of the models using existing experimental data leads to the selection of the Roberts (1989) model. This model is used to develop recommended design guidelines for flexurally strengthening reinforced concrete bridge beams with externally bonded FRP plates and for preventing premature plate peeling.

Mit multiaxialen Gelegen auf Basis der Kettenwirktechnik stehen hervorragende textile Halbzeuge für die Weiterverarbeitung als Verstärkungskomponente in Faser-Kunststoff-Verbunden zur Verfügung. Die bisherige Konfiguration der für die Herstellung dieser Textilien verwendeten Nähwirkmaschinen führt verfahrensbedingt zu einem unsymmetrischen Produktaufbau mit üblicherweise nur einer Fadenlage in Gelegelängsrichtung und ebenso zu Einschränkungen bei der Anordnung des Bindefadens im Textil. Durch die Erweiterung des Nähwirkprozesses wird es möglich, Nähwirkstoffe mit einer beliebigen Abfolge der Einzellagen herzustellen, zum Beispiel in symmetrischer Anordnung. Die neuen Varianten der Lagenanordnung und der Bindungskonstruktion bilden den Ausgangspunkt für die Produktentwicklung am Beispiel zweier Anwendungen aus den Bereichen der Faser-Kunststoff-Verbunde und des textilbewehrten Betons. Hier wird deutlich, dass über die Herstellung symmetrischer Gelege hinaus der Einsatz des erweiterten Wirkprozesses die Eigenschaften der Gelege und der Endprodukte vorteilhaft beeinflussen kann. Aus den untersuchten Beispielen und grundsätzlichen Betrachtungen leitet sich ab, unter welchen maschinentechnischen Voraussetzungen der Einsatz des erweiterten Wirkprozesses sinnvoll ist. Es wird ein Konzept entwickelt, auf dessen Grundlage Nähwirkstoffe mit variabler Lagenanordnung auf Nähwirkmaschinen gefertigt werden können. / Multiaxial multi-ply fabrics made by warp knitting are excellently suited for the application in fiber reinforced composites. The usual configuration of the stitch-bonding machines, which are used to produce these fabrics, necessarily leads to composite laminates with an asymmetric layer arrangement and only one layer of yarns in the zero degree direction of the fabric. The variability of patterning with the binding yarn is also limited. By completing the stitch-bonding process with an additional work step it is possible to produce stitch-bonded fabrics without any restrictions concerning the arrangement of the individual layers in the fabric, for example with a symmetric composition. This is the basis for the development of two exemplary products in the fields of textile reinforced plastics and textile reinforced concrete. It can be shown that the application of the extended stitch-bonding process is advantageous beyond the layer arrangement, positively affecting the mechanical properties of the fabric and the composite. From these examples, conclusions are drawn regarding the configuration of future stitch-bonding machines.

Les modules de puissance ont tendance à devenir de plus en plus compacts et ceci engendre une<br />augmentation significative des densités de flux à évacuer. Un refroidissement plus performant est devenu<br />impératif. Les caloducs plats présentent un intérêt certain lorsque les applications visées intéressent le<br />domaine spatial où les critères de masse, d'encombrement et d'isolation électrique sont primordiaux.<br />L'objectif des travaux de thèse est de réaliser la conception et l'étude des mini et micro caloducs pour le<br />refroidissement de l'électronique embarquée. Dans un premier temps, des études théoriques et<br />expérimentales ont été conduites pour concevoir et réaliser de micro caloducs en silicium. La seconde<br />partie des travaux consiste l'étude de conception, de réalisation et de caractérisation des caloducs intégrés<br />dans un substrat DBC (Direct Bonded Copper). L'ensemble de ces travaux a montré tout l'apport des<br />mini et micro caloducs dans la gestion thermique des systèmes électroniques.

Les systèmes photovoltaïques à concentration, ou CPV, reposent sur le principe de la concentration des rayons du soleil sur une cellule photovoltaïque à très haut rendement. Le CPV reste jeune face au photovoltaïque (PV) classique qui accumule plus de 30 ans de retour d'expérience.La pérennisation de cette technologie CPV ne passera que par la démonstration d'une certaine maturité. Aussi, la question de la fiabilité de ces systèmes est plus que jamais d'actualité. Dans ce contexte, le Commissariat à L'Energie Atomique et aux Energies Alternatives (CEA) a répondu à la sollicitation lancée par des fabricants de modules CPV français sur la thématique de la conception et de la fiabilisation de modules CPV par une collaboration de ses différents laboratoires, dont le Laboratoire des Modules Photovoltaïques (LMPV). C'est au sein de ce laboratoire que s'effectuent les travaux de thèse. La diversité des éléments constituant un module CPV a poussé les travaux de thèse à se concentrer sur le coeur fonctionnel des modules : les assemblages CPV. Une première partie des travaux de thèse a consisté à mettre en place les bons outils de caractérisation, en partant parfois d'une feuille blanche. La mesure de caractéristique IV dans l'obscurité, la mesure de réponse spectrale, la tomographie RX ou encore l'électroluminescence sont autant de moyens de caractérisation de cellules multi-jonctions amenés par les travaux de thèse. Les efforts conduits sur l'électroluminescence auront permis l'invention d'une nouvelle technique de caractérisation des interfaces cellule/ substrat des assemblages CPV, concrétisée par le dépôt d'un brevet. Une collaboration entre le laboratoire d'accueil et l'Institut de l'Energie Solaire (IES) à Madrid a permis l'accès à la mesure de performance des assemblages CPV sous éclairement. Tous ces moyens ont rendu possible une caractérisation fine des assemblages CPV et ont permis de s'intéresser à leur robustesse-fiabilité, deuxième partie des travaux de thèse. Deux types d'assemblages CPV ont été étudiés durant les travaux de thèse. Le premier, basé sur un substrat Direct Bonded Copper (DBC) correspond à l'état de l'art et est le plus utilisé dans l'industrie CPV. Le deuxième, en rupture technologique avec l'état de l'art, repose sur un Substrat Métal Isolé (SMI), et a été intégralement développé par le CEA et ses partenaires industriels. L'étude de la robustesse de ces assemblages CPV a été faite par l'emploi de tests de vieillissement accéléré dont la nature est justifiée par le retour d'expérience et la définition des spécifications environnementales. Aucune défaillance n'a été observé sur chacun des types d'assemblage. Les assemblages SMI se comportent comme les assemblages DBC, considérés comme références. Les travaux de thèse offrent donc un premier retour d'expérience propre au laboratoire d'accueil et la mise en place d'une infrastructure complète de caractérisation d'assemblage CPV permet aujourd'hui au CEA d'être un acteur clé du CPV en France.

Thermal shock resistance is a key property of refractory materials. Its determination and prediction is essential for the design of structural refractories as well as lining materials. Young’s modulus of elasticity (E) is a crucial parameter for the calculation of thermal shock resistance. For all investigated carbon-bonded alumina composition a significant increase of E was observed. This increase was attributed to a mismatch of the coefficient of thermal expansion of the composite constituents. Besides others, the graphite content as well as the maximum alumina particle size were identified as crucial factors influencing E(T). Furthermore, the influence of the porosity on E was shown and existing models were fitted to the experimental data for future predictions of E. Finally a metal melt filter structure was investigated to investigate the relationship between its strut Young’s modulus and the structures’ E at high temperatures. Further research should address the filter topic since it was uncertain how to find the normal modes of those structures.

In this Thesis, the problems of the Free Flexural (or Bending) Vibrations of Composite, Orthotropic Plates and/or Panels with Various Bonded Joints are formulated and investigated in detail. The composite bonded plate system is composed of Plate Adherends adhesively bonded by relatively very thin adhesive layers. The general problem is considered in terms of the three Main PROBLEMS, namely Main PROBLEM I, Main PROBLEM II and Main PROBLEM III. The theoretical formulation of the Main PROBLEMS is based on Mindlin Plate Theory which is a First Order Shear Deformation Plate Theory (FSDPT). Thus, the transverse shear deformations, the transverse and the rotary moments of inertia of the plates are included in the formulation. Very thin, elastic deformable adhesive layers are considered as continua with transverse normal and shear stresses. The damping effects in the plates and the adhesive layers are neglected. The entire composite bonded joint assembly is assumed to be simple supported along the two opposite edges, so that the Classical Levy&amp / #8217 / s Solutions can be applied in this direction. The dynamic equations of the Bonded Joint System which combines together the Mindlin Plate dynamic equations with the adhesive layer equations are reduced to a system of First Order Ordinary Differential Equations in the state vector form. This special form of the Governing System of the First Order Ordinary Differential Equations are numerically integrated by means of the Modified Transfer Matrix Method which is a combination of the Classical Levy&amp / #8217 / s Method, the Transfer Matrix Method and the Integrating Matrix Method (with Interpolation Polynomials and/or Chebyshev Polynomials). The Main PROBLEMS are investigated and presented in terms of the mode shapes and the corresponding natural frequencies for various sets of boundary conditions. The significant effects of the hard and the soft adhesive layer elastic constants on the mode shapes and on the natural frequencies are demonstrated. Some important parametric studies such as the influences of the Joint Length Ratio, the Joint Position Ratio, the Bending Stiffness Ratio, etc. on the natural frequencies are computed and plotted for the hard and soft adhesive cases for several support conditions.

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Assim como em outras áreas do conhecimento a construção civil vem evoluindo ao longo dos anos. Grandes investimentos e elevadas taxas de demandas por novos projetos requerem uma maior velocidade na consolidação de obras. Neste cenário, ficam precários os estudos e pesquisas que avaliam a capacidade de novas tecnologias. Na área do concreto e estruturas de concreto armado, depara-se a associação de técnicas consolidadas à métodos inovadores. A utilização de polímeros como material de construção, como é o caso dos aditivos para concreto, dos tubos e conexões, das esquadrias e como adesivos, utilizados em ligações de aduelas de pontes, associados a fibras de vidro ou carbono para reforços estruturais e para fixação de armaduras ou conectores no caso de reparação de estruturas, oferecendo uma solidarização eficiente entre elementos estruturais. O presente trabalho visa avaliar uma pequena parcela de aplicação de materiais poliméricos, principalmente quanto a sua característica de aderência e colagem de barras de aço ao concreto. O desenvolvimento do estudo ocorreu sobre uma perspectiva de ensaios laboratoriais de arrancamento de barras coladas com resina epóxi em blocos de concreto, sendo estes resultados comparados com barras de aço concretadas em blocos de concreto. Desse modo o principal fator de comparação seria a tensão de aderência desenvolvida na área de contato da barra com o substrato. Alguns parâmetros foram inseridos para uma abordagem de maior amplitude, tais como variação do diâmetro da barra (&#966; = 10,0mm; &#966; = 12,5mm e &#966; = 16,0mm), do comprimento de ancoragem (múltiplos do diâmetro, sendo 5&#966; e 7,5&#966;) e da espessura da resina (1mm, 2mm e 3mm). De forma complementar procedeu-se ao ensaio de vigas bi-apoiadas submetidas à flexão visando representar o comportamento de uma recuperação/reforço estrutural aplicado em escala. Para avaliar o comportamento destas vigas, foram ensaiados dois espécimes, uma viga padrão concretada de uma única vez e outra submetida a um reparo estrutural, onde possuía a armadura inferior inserida posteriormente à concretagem inicial, colada com resina epóxi nas extremidades da viga. / Just like others fields of knowledge, the civil construction is evolving. Hughes investments and the need for new projects improve the speed and the technology usually applied for basic infrastructures development. These scenarios achieve issues as the miss understanding of the behavior of this technological advances in long terms, caused by the few studies and researches about these subjects. At the concrete structures field, an extremely self consolidate knowledge whose have been replaced for new methods, as the case of the polymeric materials. This kind of material have large scale of applications at construction and projects of structural elements, used as a bond interface for different elements and offering a significant monolithically performance between structural pieces. The current study pretends analyze the behavior of bonded steel bars at the concrete using epoxy resin. The development of the study occur by lab tests where a steel bar is pulled out of a concrete block, named Pull-out-test. This one was adapted for a bond whit epoxy resin, were the results was compared whit the regular ones (concrete bonded bars), in this method the phenomenon of the stress occurred at the bar surface in contact whit the concrete or the resin evaluate. Some parameters were included for a better understanding of the bond behavior, such as: Steel bar diameter (10mm, 12,5mm and 16mm); Length of anchorage (5&#966; and 7,5&#966;), and Resin thickness (1mm, 2mm and 3mm). For the same purpose, was molded a concrete beam to represent the bonded situation at a real condition, these beam had two different configuration, one of those were a regular reinforcement beam, and the other one were a recuperated reinforcement beam, whit yours inferior steel bar added post concrete solidification, simulating a intervention at a problematic beam, in this case the steel bars were bonded whit epoxy resin at the edges of the beam.

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Assim como em outras áreas do conhecimento a construção civil vem evoluindo ao longo dos anos. Grandes investimentos e elevadas taxas de demandas por novos projetos requerem uma maior velocidade na consolidação de obras. Neste cenário, ficam precários os estudos e pesquisas que avaliam a capacidade de novas tecnologias. Na área do concreto e estruturas de concreto armado, depara-se a associação de técnicas consolidadas à métodos inovadores. A utilização de polímeros como material de construção, como é o caso dos aditivos para concreto, dos tubos e conexões, das esquadrias e como adesivos, utilizados em ligações de aduelas de pontes, associados a fibras de vidro ou carbono para reforços estruturais e para fixação de armaduras ou conectores no caso de reparação de estruturas, oferecendo uma solidarização eficiente entre elementos estruturais. O presente trabalho visa avaliar uma pequena parcela de aplicação de materiais poliméricos, principalmente quanto a sua característica de aderência e colagem de barras de aço ao concreto. O desenvolvimento do estudo ocorreu sobre uma perspectiva de ensaios laboratoriais de arrancamento de barras coladas com resina epóxi em blocos de concreto, sendo estes resultados comparados com barras de aço concretadas em blocos de concreto. Desse modo o principal fator de comparação seria a tensão de aderência desenvolvida na área de contato da barra com o substrato. Alguns parâmetros foram inseridos para uma abordagem de maior amplitude, tais como variação do diâmetro da barra (&#966; = 10,0mm; &#966; = 12,5mm e &#966; = 16,0mm), do comprimento de ancoragem (múltiplos do diâmetro, sendo 5&#966; e 7,5&#966;) e da espessura da resina (1mm, 2mm e 3mm). De forma complementar procedeu-se ao ensaio de vigas bi-apoiadas submetidas à flexão visando representar o comportamento de uma recuperação/reforço estrutural aplicado em escala. Para avaliar o comportamento destas vigas, foram ensaiados dois espécimes, uma viga padrão concretada de uma única vez e outra submetida a um reparo estrutural, onde possuía a armadura inferior inserida posteriormente à concretagem inicial, colada com resina epóxi nas extremidades da viga. / Just like others fields of knowledge, the civil construction is evolving. Hughes investments and the need for new projects improve the speed and the technology usually applied for basic infrastructures development. These scenarios achieve issues as the miss understanding of the behavior of this technological advances in long terms, caused by the few studies and researches about these subjects. At the concrete structures field, an extremely self consolidate knowledge whose have been replaced for new methods, as the case of the polymeric materials. This kind of material have large scale of applications at construction and projects of structural elements, used as a bond interface for different elements and offering a significant monolithically performance between structural pieces. The current study pretends analyze the behavior of bonded steel bars at the concrete using epoxy resin. The development of the study occur by lab tests where a steel bar is pulled out of a concrete block, named Pull-out-test. This one was adapted for a bond whit epoxy resin, were the results was compared whit the regular ones (concrete bonded bars), in this method the phenomenon of the stress occurred at the bar surface in contact whit the concrete or the resin evaluate. Some parameters were included for a better understanding of the bond behavior, such as: Steel bar diameter (10mm, 12,5mm and 16mm); Length of anchorage (5&#966; and 7,5&#966;), and Resin thickness (1mm, 2mm and 3mm). For the same purpose, was molded a concrete beam to represent the bonded situation at a real condition, these beam had two different configuration, one of those were a regular reinforcement beam, and the other one were a recuperated reinforcement beam, whit yours inferior steel bar added post concrete solidification, simulating a intervention at a problematic beam, in this case the steel bars were bonded whit epoxy resin at the edges of the beam.

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / Juntas coladas têm se mostrado como a principal alternativa de união entre componentes fabricados em materiais distintos ou não, tendo como vantagem principal a ausência de aporte de calor e melhor distribuição de tensões. A literatura mostra que estudos anteriores foram realizados com o objetivo de caracterizar diversas propriedades associados às juntas, porém, pouco ainda se conhece sobre o comportamento dessas uniões relacionado à fluência. Os ensaios de fluência têm como principal desvantagem a baixa produtividade de resultados visto que, na maioria dos casos, os equipamentos aptos a realizarem este tipo de teste ensaiam apenas um corpo de prova por vez. Neste caso, o tratamento estatístico é baseado em uma pequena quantidade de resultados, reduzindo a confiabilidade na predição do comportamento em fluência. O Laboratório de Adesão e Aderência (LAA/UERJ/IPRJ) desenvolveu o equipamento pneumático de fluência (EPF) capaz de realizar dez ensaios simultâneos com parâmetros distintos. Este trabalho investiga o comportamento de juntas de cisalhamento simples (SLJ) compostas por substratos metálicos colados com adesivo epóxi e poliuretano. As juntas foram fabricadas em conformidade a norma ASTM D 1002, seguindo procedimento de preparo RT-003/08 TMC/CENPES/PETROBRAS. Os resultados mostram que, para projetos onde esteja prevista utilização das juntas durante longos períodos de tempo sob carregamento, conhecer apenas suas tensões médias de ruptura não é o suficiente para garantir a segurança do empreendimento. É proposto um modelo inicial do comportamento sob fluência de juntas coladas. / Bonded joints have been used as the main alternative to join components made of different materials, especially because high temperatures, like in welding process, are not required and because tensions are better distributed. Literature shows that although prior studies focused on the evolution of several mechanical properties related to joints, little is known about the creep behavior of bonded joints. Creep testings main disadvantage is the low productivity of results, since that, in most cases, testing machines capable of performing these tests only test one joint at a time. In this case, statistical treatment is made based on a small amount of results, reducing the reliability of the predictions. Thus, the Laboratory of Adhesion and Adherence (LAA/UERJ/IPRJ) developed a pneumatic creep equipment (PCE), capable of testing ten specimens simultaneously, under distinct scenario. This work looks into the behavior of single-lap joints (SLJ) made of metallic substrate and bonded with epoxy and polyurethane adhesives. The joints were produced according to ASTM D 1002 standard, following the RT-003/08 TMC/CENPES/PETROBRAS repair procedure. Results show that, for long term applications, knowing the average tensile strength of the joints isnt enough to guarantee project safety. An initial model for the creep behavior of bonded joints is proposed.