The structural integrity of a welded structure depends mainly on the performance of the welded joints. Due to the welding process, the mechanical properties of the structure change and different regions are created in the weldment. The mechanical properties of welded joints change significantly around the heat affected zone (HAZ). So to predict stress distribution around the weld, these changes should be considered in the finite element model (FEM) of the welded structure. In this research, the changes of mechanical properties around the welded joint were experimentally tested and used to develop a FEM model of a welded joint which can predict the stress behavior around the weld. First, an experimental analysis was carried out on an ASTM standard arc welded joint of stainless steel specimen to observe the microstructural change in the HAZ. This enables to find out the HAZ width using an optical microscope. Moreover, a tensile testing was performed to investigate the change of Young’s modulus of the HAZ compared to the base metal (BM). Another experimental analysis was also performed on a real arc welded structure of the same material to observe its’ strain distribution around the HAZ. The HAZ width and Young’s modulus obtained from the experimental testing were then applied to generate the FEM model of an ASTM standard arc welded joint as well as a real arc welded structure of stainless steel. The finite element analysis (FEA) results of stress distribution around the weld joint in both cases show a good agreement with the experimental results. Therefore, the developed material property based FEM model can predict the stress behavior of similar type of structures with the same welding process on the same material studied in this research. / February 2017

La tesis propone un nuevo conformador de haz para la recepción de señales con modulación de saltos frecuenciales "frequency hopping" (FH) basado en el conocimiento de la secuencia de frecuencias utilizada en la modulación denominándose por ello conformador de haz de referencia por código "code reference beamformer" (CRB). Este conformador se divide en dos etapas, cada una de ellas implementa uno de los factores del vector de enfoque óptimo; es decir, la primera etapa es igual a la inversa de la matriz de covarianza de ruido más interferencias y la segunda es igual al vector de dirección de la señal deseada. La obtención de estas etapas es posible gracias a la predicción del escenario que se tendrá durante el salto siguiente, la cual puede realizarse simultáneamente a la recepción gracias al conocimiento de la secuencia frecuencial. El sistema receptor se compone de dos procesadores: el procesador anticipado que se dedica a la estimación de la matriz de covarianza de ruido más interferencias presentes en la banda frecuencial del siguiente salto y el procesador directo que es el encargado de la conformación de haz. Finalmente se propone la extensión de crb a un conformador de haz autocalibrado de aplicación general que no requiere referencia alguna, ni temporal ni espacial.

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Trata sobre la teoría de haces y esquemas. El objetivo principal es desarrollar detalladamente un teorema de J.-P. Serre (en el libro de Hartshorne [6], aparece como ejercicio (5.9) del capítulo II) que establece la correspondencia entre haces coherentes sobre esquemas proyectivos y módulos graduados de tipo casi infinito. Además, usando métodos cohomológicos, da una generalización de este teorema de Serre. Asimismo se redacta la solución de otros ejercicios de [6] que son necesarios para la solución del ejercicio principal, los cuales son presentadas por medio de proposiciones y teoremas. / Tesis

El biotipo periodontal es considerado un factor significativo relacionado con el éxito en el resultado de los tratamientos odontológicos. El objetivo de este estudio es determinar la una posible relación entre el grosor gingival con respecto al grosor de la tabla ósea subyacente en los dientes incisivos y caninos maxilares y mandibulares. Material y Métodos Una muestra de 180 dientes anteriores (incisivos y caninos, 90 mandibulares y 90 maxilares) procedentes de 15 pacientes fueron incluidos en la muestra. El grosor gingival (GG) se midió usando la técnica de sondaje transgingival en tres posiciones: 1 mm apical al margen gingival (GGC), 1 mm coronal a la línea mucogingival (GGA), y un punto medio entre las dos posiciones anteriores (GGM). El espesor de la tabla ósea vestibular (GO) se midió haciendo uso de la tomografía computarizada en haz de cono(CBCT). Las mediciones fueron registradas en tres posiciones: 4mm apical a la unión amelo-cementaria (GOC), a nivel apical del diente (GOA), y un punto medio entre los dos anteriores (GOM). Además, el ancho inciso-apical de encía queratinizada (AEQ) y la profundidad de sondaje (PS) fueron registrados. Las mediciones clínicas y CBCT se compararon y se correlacionaron. Resultados. No se observó una relación estadísticamente significativa entre los valores de GG y el GO en cualquiera de las tres posiciones estudiadas. La media de GG a nivel crestal, medio y apical de los dientes superiores fue 1.01mm (± 0.58mm), 1.06mm (± 0.48mm) y 0.83mm (± 0,47 mm), respectivamente, y la media de GO correspondiente 1.24mm (± 0,90 mm ), 0.81mm (± 0,33 mm) y 2.78mm (± 1.62mm), respectivamente. Se observó una relación estadísticamente significativa entre el AEQ y el GOC (R = 0,007, P <0,05) . De igual manera se observó una relación similar entre la PS y el AEQ en los incisivos centrales superiores.(P = 0,01). Conclusiones: De acuerdo con nuestros resultados, el grosor del tejido gingival vestibular no está relacionado al grosor de la tabla ósea subyacente. Sin embargo, el AEQ parece correlacionarse con el grosor de la tabla ósea en el punto crestal. Estos resultados confirman la importancia de una adecuada evaluación del biotipo antes de establecer un plan de tratamiento

IN-738 LC, a precipitation hardened nickel based superalloy, containing substantial amounts of Al + Ti contents, is very difficult to weld due to its high susceptibility to HAZ cracking, during welding via conventional fusion welding techniques and subsequent PWHT. The cracking is mainly intergranular in nature and associated with liquation of secondary solidification products (such as MC carbides,  -  eutectic phases), and solid state reaction products ( precipitate particles) that are present along the grain boundaries in the pre-weld material. The current research was to find effective ways to improve weldability of IN-738 LC. Laser welds were produced autogenously on conventionally solidified (CS) and directionally solidified (DS) polycrystalline, and single crystal (SC) IN-738 LC subjected to two preweld heat treatments. Weldability was assessed by measuring the total crack lengths in HAZ. The influence of grain boundaries and heat treatment on extent of cracking in IN-738 LC was studied.

The controlled, _ne-grained microstructure of thermomechanically processed Nb microalloyed linepipe steels is destroyed in the vicinity of welds used in fabricating pipelines. There are conflicting views on the influence of niobium in the `heat-affected zone', particularly in the region closest to the weld fusion line which is most dramatically impacted by the thermal cycling that occurs during welding. Consequently, there is a need to fully characterise the influence of niobium on the evolution of structures and properties in this zone. The aim of the work presented in this thesis was to quantify and characterise precipitates of niobium and dissolved niobium across sub-zones of the weld heat-affected zone, in order to develop a better understanding of the effects of niobium across the region. In order to achieve this, heat treatments were undertaken for the first time to simulate each sub-zone of the heat affected zone such that unique states of dissolved niobium and precipitated niobium was developed. A novel technique as designed and applied for the first time to measure and quantify the precipitate sizes and size distributions in bulk samples of Nb micro-alloyed steels. In addition, measurements of the dissolved niobium across the heat-affected zone were completed in order to ensure that the discrete effects of all states of niobium were subjected to analysis. Weld simulations of the coarse-grained heat-affected zone, the region closest to the weld fusion line, were conducted and assessed against the measured states of niobium. This was followed by the manufacture of commercial welds in order to assess the variation of structures and properties across the heat-affected zone for different plate conditions generated by heat treatment prior to welding. This work established that that a wide range of niobium carbide precipitate sizes were crucial in assuring the excellent mechanical properties in the line-pipe steel, coarser precipitates were found to control the austenite grain size that evolved in the coarse-grain heat affected zone, while fine precipitates dissolved in the thermal cycles close to the weld fusion line, and produced finer microstructures.

Este trabalho teve como objetivo observar o resultado da variação dos parâmetros do processo FHPP (Friction Hydro Pillar Processing), dando-se atenção aos efeitos destes na microestrutura e na qualidade do reparo. O estudo foi realizado através de investigações metalográficas nos reparos obtidos, bem como análises via perfis de microdureza Vickers. Foram utilizadas diferentes forças axiais, que levaram a obtenção de reparos isentos de defeitos no seu preenchimento. Observou-se que o utilizando forças axiais maiores contribuíram para obter microestrutura mais refinada e homogênea, com formação predominante de martensita, menor tempo de processamento, menor quantidade de constituinte Martensita-Austenita e uma Zona Termicamente Afetada (ZTA) de menor tamanho. / This study aimed to observe the result of the variation of the Friction Hydro Pillar Processing parameters, giving attention to the microestructural effects and quality of repair. The study was carried out by metallographic investigations in repairs obtained and Vickers microhardness profiles. Were used different axial forces, which led to obtain no defects in repairs. It was observed that using higher axial forces helped to get more refined and homogeneous microstructure with predominant formation of martensite, lower processing time, less amount of Martensite-Austenite constituent and lower Heat Afecfted Zone (HAZ) size.

Este trabalho teve como objetivo observar o resultado da variação dos parâmetros do processo FHPP (Friction Hydro Pillar Processing), dando-se atenção aos efeitos destes na microestrutura e na qualidade do reparo. O estudo foi realizado através de investigações metalográficas nos reparos obtidos, bem como análises via perfis de microdureza Vickers. Foram utilizadas diferentes forças axiais, que levaram a obtenção de reparos isentos de defeitos no seu preenchimento. Observou-se que o utilizando forças axiais maiores contribuíram para obter microestrutura mais refinada e homogênea, com formação predominante de martensita, menor tempo de processamento, menor quantidade de constituinte Martensita-Austenita e uma Zona Termicamente Afetada (ZTA) de menor tamanho. / This study aimed to observe the result of the variation of the Friction Hydro Pillar Processing parameters, giving attention to the microestructural effects and quality of repair. The study was carried out by metallographic investigations in repairs obtained and Vickers microhardness profiles. Were used different axial forces, which led to obtain no defects in repairs. It was observed that using higher axial forces helped to get more refined and homogeneous microstructure with predominant formation of martensite, lower processing time, less amount of Martensite-Austenite constituent and lower Heat Afecfted Zone (HAZ) size.