The architectural practice has long held several ideas about how a building should present itself relative to its structure. With modern building technologies and building codes, the structure of a building and the facade can often be very different. Modernist architects theoretically felt very strongly about the importance of material honesty in a buildings, as the 20th Century moved on, many architects moved towards buildings that used materials to create forms and atmospheres that were less dependent on the structural materials and forms of these buildings. The following thesis explores these ideas about material and structure through three separate examples of buildings with a similar size, site, and program. The project is a theme and variation, with the theme being the building type, and the variation being the philosophy of the relation between structure and material. Researching drawings in Edward R. Ford's book The Details of Modern Architecture, along with specific details of Peter Zumthor's Therme Vals help to inform my personal thought process when it comes to detailing the buildings I have designed. The designs propose three small chapels on a Catholic college campus in Northeast Washington, DC. / Master of Architecture

The Master thesis is focused on the influence of procedural parameters on the properties of heterogeneous weld in laser welding. The literature review section offers an overview of the industrial application of the laser welding technology as well as it explains the issue of heterogeneous weld creation. The experimental part of the thesis aims to describe how six carbon steel samples have been welded together with ferritic stainless steel by usage of several different beam oscillation configurations. Tested samples have been used to create trial ensembles that were subjected for a tension testing, Vickers hardness testing, metallographic testing and corrosive resistant testing. As a result of the experiment, there is a suggestion of the study that could be used for an industrial using of a combination of these materials.

A detecção nos meios interestelar e circunstelar de espécies diatômicas contendo silício como SiC, SiN, SiO e SiS, assim como espécies contendo fósforo, sugere que a molécula SiP seja também uma forte candidata a ser observada nesses meios devido à abundância relativa de seus átomos componentes. A importância tecnológica do silício é também motivadora para a caracterização estrutural e espectroscópica de seus derivados. Neste particular, complementando estudos anteriores de espécies contendo átomos de silício em nosso grupo, este trabalho está voltado para uma descrição teórica detalhada de cerca de duas dúzias de estados eletrônicos dupletos e quartetos da espécie SiP que se correlacionam com os quatro primeiros canais de dissociação. Essa descrição compreende a construção de curvas de energia potencial, da função momento de dipolo e da função momento de transição. Os estados ligados são também caracterizados por suas constantes espectroscópicas e as possíveis transições vibrônicas expressas em termos de probabilidades de transições radiativas calculadas pelo coeficiente Av\'v\" de Einstein; tempos de vida radiativa complementam esses cálculos. Na descrição dos estados eletrônicos e de suas propriedades usamos a metodologia interação de configurações com referências múltiplas, onde a função de onda foi gerada como excitações simples e duplas a partir de um conjunto de funções de configurações de referência determinado por um cálculo prévio do tipo campo auto-consistente multi-configuracional com espaço ativo completo. Funções atômicas do tipo aug-cc-pVQZ foram usadas na construção dos orbitais moleculares. Dentre todos os estados caracterizados, destacamos a descoberta de um estado 2π abaixo do estado anteriormente rotulado de B 2Σ+, o que nos levou a uma nova renomeação da ordem energética. Esse novo estado oferece uma possibilidade realista de se acessar estados vibracionais mais altos dos estado X 2π e A 2Σ+ e com isso obter uma descrição experimental melhorada desses dois estados. Além do conjunto de estados dupletos possíveis descritos, salientamos também as possibilidades aqui apontadas e quantificadas de se detectar experimentalmente transições eletrônicas entre os estados quartetos. No seu todo a descrição detalhada e rigorosa de cerca de duas dúzias de estados eletrônicos fornece um conjunto de dados energéticos e espectroscópicos que certamente contribuirá para um melhor entendimento de sistemas diatômicos contendo silício e fósforo. / The detection in interstellar and circumstellar spaces of diatomic species containing silicon like SiC, SiN, SiO, and SiS, as well as species containing phosphorous suggests that the molecule SiP be also a strong candidate is observed in these regions due to the relative abundance of its constituting atoms. The technological importance of silicon is also a motivation for the structural and spectroscopic characterization of its derivatives. In this particular, complementing previous studies in our group of species containing silicon atoms, this work is focused on a detailed description of about two dozen doublet and quartet electronic states of the SiP species correlating with the first four dissociation channels. This description comprises the construction of potential energy curves, and dipole and transition moment functions. The bound states are also characterized by their spectroscopic constants and the possible vibronic transitions expressed in terms of the radiative transition probabilities calculated as Einstein Av\'v\'\' coefficients; radiative lifetimes also complement these calculations. In the description of the electronic states and of their properties we used the multi-reference configuration interaction method, with the wavefunction generated as all single and doubles excitations from a set of reference configuration state functions determined from a previous complete active space multiconfigurational selfconsistent field calculation. Atomic functions of the type aug-cc-pVQZ were used in the construction of the molecular orbitais. Of all the electronic states c haracterized, we call the attention to the discovery of a 2π state below a state previously know as B 2Σ+, a fact that led us to a new labelling of the energetic order. This new state offers a realistic possibility of accessing higher vibrational states of the states X 2π and A 2Σ+, thus providing the possibility of obtaining an improved experimental description of these two states. Besides the set of possible states described, we also note the possibilities here pointed out and quantitatively characterized of experimentally detecting electronic transitions between quartet states. On the whole, the detailed and rigorous description of about two dozen electronic states provides a set of energetic and spectroscopic data that certainly will contribute to a better understanding of diatomic systems containing sillicon and phosphorus.

A detecção nos meios interestelar e circunstelar de espécies diatômicas contendo silício como SiC, SiN, SiO e SiS, assim como espécies contendo fósforo, sugere que a molécula SiP seja também uma forte candidata a ser observada nesses meios devido à abundância relativa de seus átomos componentes. A importância tecnológica do silício é também motivadora para a caracterização estrutural e espectroscópica de seus derivados. Neste particular, complementando estudos anteriores de espécies contendo átomos de silício em nosso grupo, este trabalho está voltado para uma descrição teórica detalhada de cerca de duas dúzias de estados eletrônicos dupletos e quartetos da espécie SiP que se correlacionam com os quatro primeiros canais de dissociação. Essa descrição compreende a construção de curvas de energia potencial, da função momento de dipolo e da função momento de transição. Os estados ligados são também caracterizados por suas constantes espectroscópicas e as possíveis transições vibrônicas expressas em termos de probabilidades de transições radiativas calculadas pelo coeficiente Av\'v\" de Einstein; tempos de vida radiativa complementam esses cálculos. Na descrição dos estados eletrônicos e de suas propriedades usamos a metodologia interação de configurações com referências múltiplas, onde a função de onda foi gerada como excitações simples e duplas a partir de um conjunto de funções de configurações de referência determinado por um cálculo prévio do tipo campo auto-consistente multi-configuracional com espaço ativo completo. Funções atômicas do tipo aug-cc-pVQZ foram usadas na construção dos orbitais moleculares. Dentre todos os estados caracterizados, destacamos a descoberta de um estado 2π abaixo do estado anteriormente rotulado de B 2Σ+, o que nos levou a uma nova renomeação da ordem energética. Esse novo estado oferece uma possibilidade realista de se acessar estados vibracionais mais altos dos estado X 2π e A 2Σ+ e com isso obter uma descrição experimental melhorada desses dois estados. Além do conjunto de estados dupletos possíveis descritos, salientamos também as possibilidades aqui apontadas e quantificadas de se detectar experimentalmente transições eletrônicas entre os estados quartetos. No seu todo a descrição detalhada e rigorosa de cerca de duas dúzias de estados eletrônicos fornece um conjunto de dados energéticos e espectroscópicos que certamente contribuirá para um melhor entendimento de sistemas diatômicos contendo silício e fósforo. / The detection in interstellar and circumstellar spaces of diatomic species containing silicon like SiC, SiN, SiO, and SiS, as well as species containing phosphorous suggests that the molecule SiP be also a strong candidate is observed in these regions due to the relative abundance of its constituting atoms. The technological importance of silicon is also a motivation for the structural and spectroscopic characterization of its derivatives. In this particular, complementing previous studies in our group of species containing silicon atoms, this work is focused on a detailed description of about two dozen doublet and quartet electronic states of the SiP species correlating with the first four dissociation channels. This description comprises the construction of potential energy curves, and dipole and transition moment functions. The bound states are also characterized by their spectroscopic constants and the possible vibronic transitions expressed in terms of the radiative transition probabilities calculated as Einstein Av\'v\'\' coefficients; radiative lifetimes also complement these calculations. In the description of the electronic states and of their properties we used the multi-reference configuration interaction method, with the wavefunction generated as all single and doubles excitations from a set of reference configuration state functions determined from a previous complete active space multiconfigurational selfconsistent field calculation. Atomic functions of the type aug-cc-pVQZ were used in the construction of the molecular orbitais. Of all the electronic states c haracterized, we call the attention to the discovery of a 2π state below a state previously know as B 2Σ+, a fact that led us to a new labelling of the energetic order. This new state offers a realistic possibility of accessing higher vibrational states of the states X 2π and A 2Σ+, thus providing the possibility of obtaining an improved experimental description of these two states. Besides the set of possible states described, we also note the possibilities here pointed out and quantitatively characterized of experimentally detecting electronic transitions between quartet states. On the whole, the detailed and rigorous description of about two dozen electronic states provides a set of energetic and spectroscopic data that certainly will contribute to a better understanding of diatomic systems containing sillicon and phosphorus.

L’hydrogène liquide est un ergol utilisé en complément de l’oxygène liquide pour la propulsion de nombreux lanceurs en particulier ceux de la famille Ariane. Cependant, sa dangerosité interdit la réalisation d’essais, en particulier vibratoires, sur des réservoirs remplis. Cette thèse explore une piste d’étude permettant de réaliser ces essais vibratoires sur le réservoir rempli d’un matériau de substitution : un ensemble de billes pré-contraintes. L’objectif est d’obtenir un comportement modal similaire en termes de modes et de fréquences propres à celui du réservoir rempli d’hydrogène liquide pour l’étude des premiers modes. Pour répondre à cet objectif, cette étude est développée en deux parties. Dans la première partie, une approche analytique basée sur une méthode par équivalences fréquentielles est détaillée. Après avoir présenté les grandes lignes de la méthodologie utilisée et l’ensemble des modèles développés, la méthodologie est appliquée au cas étudié expérimentalement de manière à mettre en évidence l’influence des différents paramètres et de proposer une première méthode pour choisir un jeu de billes adapté. La seconde partie, traite principalement des aspects expérimentaux et numériques. Après avoir détaillé la caractérisation des billes utilisées, le montage expérimental conçu et réalisé pour effectuer des essais vibratoires sur un réservoir rempli de billes pré-contraintes est présenté. Les différents résultats obtenus avec ce montage sont étudiés au regard de l’approche analytique, mais aussi de modèles numériques utilisant des éléments-discrets et des éléments-finis. / Liquid hydrogen is a propellant alternatively used with liquid oxygen for the propulsion of many launchers, especially those of the Ariane family. However, its dangerousness prohibits vibration tests on filled tank. The aim of this PHD is to explore the possibility to carry out such vibration tests by filling these tanks with a substitute material : a set of pre-stressed balls. As further argued and developed in the report, the objective is to obtain a modal behavior similar in term of mode shapes and natural frequencies to those of the tank filled with liquid hydrogen for the first modes. In the first part, an analytical approach based on a method using frequency equivalences is detailed. After presenting the outlines of the methodology used and all the models developed, the methodology is applied to the experimentally studied case in order to highlight the influence of the different parameters as well as then to propose a first method to choose a set of well adapted balls. The second part deals mainly with experimental and numerical aspects. Firstly, the balls used in the thesis are characterized. Then, the experimental set-up designed and realized to carry out vibration tests on a tank filled with pre-stressed balls is presented. The different results obtained are compared with both analytical results and numerical based on discrete-elements and finite-elements results.

A large number of advanced structural materials are based on metallic materials where alloying additions play a key role in imparting the required properties. Most of the commercially important aluminium alloys are classified by the nature of the alloying additions. Among them the 2219, 2618, 5086, and 7075 are important class of lightweight alloys that plays critical role in modern engineering application. However, despite having a series of commercially useful aluminum alloys for commercial applications the increasing need of improved performance requires newer development in particular for applications that require high strength at elevated temperatures and performance at extreme environments. Precipitations of the intermetallic compounds containing copper during thermal treatments play a very important role in developing high strength aluminium alloys. Although,these precipitates are stable at fairly high temperatures, the rapid coarsening of these second phase precipitates (e.g. Al2Cu), leads to loss of strength at elevated temperature. Several approaches are explored to overcome this problem. One of them is to utilize non-equilibrium solidification route, which can increase solid solubility and hence increasing the precipitate density. Nonequilibrium processing can also alter the selection pathway of the competitive phases and evolution of the microstructure. Recently, non–equilibrium solidification by suction casting technique is becoming increasingly popular for casting of metallic materials of any shape. In this technique solidification is effected by sucking the molten alloy into water cooled copper mold using a suction force resulting from the differences between the melting chamber in Argon gas pressure and casting chamber under vacuum. The present thesis aims to develop a set of newer alloys with small amount of alloying additions primarily based on nickel that can retain reasonable strength at high temperature by utilizing the non-equilibrium solidification route. In addition to Ni (≤ 0.10at.%), the thesis present results of the effect of minor addition of Sc and Zr as ternary and quaternary additions. Following a short review in chapter 2, Chapter 3 presents the experimental techniques adopted for both preparation of alloys and their characterization. Chapter 4 deals with the results of alloying of aluminum with minor amount of nickel. The Ni in the range of 0.05-0.20at% was used to develop a high temperature template, containing a set of hardening intermetallic compounds to increase the strength of the host matrix. The microstructural investigations of the suction cast alloys reveal a characteristic feathery microstructure. At higher magnification the microstructure reveals the presence of fine dispersions of a second phase. Both x-ray and transmission electron microscopy confirms the phase in the dispersions to be primarily crystalline Al9Ni2 phase having a monoclinic crystal structure. This phase does not exist in equilibrium phase diagram. Only at higher concentration one can observe equilibrium Al3Ni (Orthorhombic) particles. The size of the particle ranges from 50-200nm. Beyond~0.5at%Ni, the microstructure changes to normal cellular type solidification morphology with interdendritic space decorated by the eutectic network of Al-Al3Ni having a rod eutectic morphology. A careful observation of alloys with small amount of Ni reveals that the feathery structure is associated with the thin cells, which have grown by continuously splitting the tip yielding a fractal like dendritic morphology. The dispersoids form at the intercellular regions. We have presented clear evidence of their origin from the interdendritic liquid, which most likely underwent Rayleigh instability. The random distribution reflects the nature of the dendritic growth. We have argued that these inter-dendritic liquid droplets, which are enriched with Ni, get undercooled. The metastable Al9Ni2 phase nucleates and grows in this liquid. In order to confirm this scenario, we have carried out a phase field simulation for dendritic growth of aluminium solid solution in the alloy melt both under the condition of constraint growth and free growth. The observed distribution of the dispersoid is well reflected in the phase field simulation. The chapter also report the response of effect of direct ageing of suction cast alloy as one expect an extension solid solubility of Ni in Al. A small increase in hardness could be observed during ageing treatment. In order to determine the thermal stability of the intermetallic particles, the samples of the suction cast alloys were exposed at 200°C for 200h and 500°C for 100h respectively. No change in the microstructure could be observed excepting a slight coarsening indicating the dispersed particles are thermally stable. After exposure at two different temperatures the maximum retained hardness was measured to be 350MPa. We have also attempted to correlate the hardness with coarsening behavior of particles. The feathery morphology of the cast structures and fine dispersion of the intermetallic phase is expected to improve the tensile strength of the alloy. The tensile yield strength of cast alloys was determined to be 150MPa ± 20 for Al- 0.09at%Ni alloy. We have tried to estimate the expected strength of the alloy from quantitative microstructural parameters using possible hardening mechanism. The estimates are in good agreement to the observed values. The chapter 5 reports attempts to develop thermally stable precipitation strengthened aluminum alloys by retaining the dispersion template developed earlier alloyed with Ni. Then, the binary alloys were added with extremely low diffusivity element Zr. The element Zr is traditionally added in the aluminium alloys as grain refiner and as a powerful agent for inhibiting recrystallization especially for high strength aluminium alloys. However, in this work we have alloyed Zr for imparting precipitation hardening. An amount of 0.15at%Zr was added to the suction cast alloys of Al-0.05, 0.09 and 0.20at%Ni. The first two alloys exhibit the formation of metastable phase Al9Ni2 during solidification stage. Increase the concentration of the alloy to Al-0.20at% Ni with 0.15at%Zr additions exhibits combination of both stable Al3Ni and Al9Ni2 metastable phases. Microstructures of these alloys show columnar cells of ~200μm with dispersions of spherical nodules of Al9Ni2 and Al3Ni with varying size ranges from 200-500nm. Particle size distribution of Zr containing aluminium alloys with 0.05at% Ni is 595nm ± 20 while the alloy having the 0.09 at% Ni has the optimum size of 290nm. Further increase of Zr composition above 0.20at % led to columnar to equiaxed transition. The as cast alloys containing Zr does not show the improvement with limited yield strength of the order of 150MPa. The equivalent hardness of the samples has been measured to be about 370-420MPa. Heat-treated alloys however show the presence of Al3Zr (L12) precipitates with ~20nm size that are coherent with the matrix. Binary suction cast Al-0.15at%Zr alloy after ageing exhibits tensile yield strength of ~200MPa. With ternary aluminium alloy with minor additions Ni and Zr, The strength increases to ~300MPa. Additionally, the alloy continue retain a maximum hardness of 870-920MPa even after long hours of aging. The Zr containing alloys were proved to be stable. When the tests were carried out on a nominally alloyed sample of Al-0.09at%Ni-0.15at%Zr peak aged and exposed to 250°C for 200h, the yield strength under compression tests was found to be 280MPa. The chapter 6 of the thesis discusses the role of Sc with the ternary Al-alloys with Ni and Zr. Addition of small quantities 0.1 and 0.2at%Sc substantially reduces the inter-particle distance of precipitates by increasing volume fraction and number of nano-sized particles. It has been observed and presented in this thesis that the Sc addition provides the highest incremental strengthening per atom percent of any alloying element. Chill-suction cast samples show equiaxed cells in the samples with dispersions of particles inside and some segregated particles at the cell boundaries. To achieve a further increase in the number density of precipitates we processed the suction cast alloys with additional heat treatment at 375 and 450°C. All the suction cast alloys with varying Ni content and keeping the Sc and Zr constant at 0.10 and 0.15at% respectively exhibit formation of Al9Ni2 phase. The alloy Al-0.20at%Ni-0.10at%Sc-0.15at%Zr also contain stable phase of Al3Ni with an eutectic morphology. The DSC experiments in the dynamic mode with heating rate of 10°C min-1 exhibit two distinct exothermic peaks due to precipitates from solution at 375 and 450°C. The TEM analysis using STEMEDX has further confirmed the existence of nano-sized particles 30-50 nm of both phases of Al3Sc and Al3 (Sc, Zr). The tensile yield strength of the as cast alloy show 200MPa while after precipitation treatment, we observe improved yield strength 350-450MPa. Thermal stability of the alloys were tested after peak aged condition and exposed to 200°C for 250h. The results show that the yield strength is unaffected implying the coarsening resistance of the precipitate particles. Overall the thesis establishes that with minimum alloying additions, it is possible to design alloys that are expected to perform for high temperature applications by the formation of set of dispersions of Al9Ni2 (monoclinic) and precipitates of ordered cubic phases of (L12) structure of Al3Zr, Al3Sc and Al3 (Sc, Zr) with required number density of particles.

The goal of this thesis is to describe the possibility of using a microscope for documentation defects and innovation of electrical machines. I used an electron microscope to document carbon brushes and nanomaterials for possible upgrade of the sliding contact. Use microscopes gives us detailed information about the structure of materials, at the largest stress of the electrical machine. Based on the collected data can be further analyzed and innovation of the carbon brush.