Made available in DSpace on 2014-10-09T12:34:30Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:36Z (GMT). No. of bitstreams: 0 / As novas descobertas petrolíferas, em especial as localizadas no pré sal tem despertado uma grande preocupação na área técnica em consequência das dificuldades na sua exploração e extração. As maiores preocupações no segmento de exploração de petróleo e gás natural em águas profundas estão relacionadas, às propriedades mecânicas e a resistência à corrosão dos diversos componentes. Assim, para evitar o processo de corrosão na parte interna de uma tubulação ou componente do setor petrolífero, uma alternativa é usar um revestimento com elevada resistência à corrosão. Neste trabalho utilizou-se um aço AISI 8630 modificado, que foi revestido por soldagem GTAW (Gas Tungsten Arc Welding) ou TIG (Tungsten Inert Gas), empregando uma liga especial de níquel 625 (Inconel 625). No entanto, existe a possibilidade de formação de fases frágeis no material de base (MB) - AISI 8630, no material de adição (MA) - liga de níquel 625 ou ainda na interface entre os materiais dissimilares. Para atenuar a formação da fase martensítica oriunda do resfriamento da soldagem foram realizados diferentes ciclos térmicos de alívio de tensão (AT), mas outras fases frágeis podem surgir nas diversas juntas. Os tratamento térmicos de ATs foram realizados nas temperaturas de 620, 640, 660 e 680 C. A presença e a influência de fases frágeis foram analisadas na junta soldada, por meio de ensaios mecânicos, tais como, tração, impacto e dureza. Investigou-se a existência de fases frágeis por caracterização microestrutural por meio de microscopia ótica e microscopia eletrônica de varredura com EDS. Observou-se que nos ensaios de tração o material de base manteve sua tensão de escoamento dentro de valores estabelecidos por normas do setor, como a NACE MR0175. No entanto, no ensaio de impacto ocorreu uma perda significativa da tenacidade na temperatura de 680 C, enquanto temperaturas menores de alívio de tensão os valores míninos de impacto foram acima de 73 J. Os valores de durezas encontrados próximos da zona de ligação indicaram que houve um endurecimento, em consequência da difusão dos elementos de liga do MA para o aço baixa liga. Observações realizadas com auxílio de microscopia ótica indicaram zonas frágeis denominadas de Zonas Parcialmente Diluídas (ZPD) que reduziram a resistência ao impacto. Análise por EDS mostrou variações dos elementos de liga ao longo da interface da junta. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Additive manufacturing (AM) shows great promise for the manufacturing of next-generation engineering structures by enabling the production of engineered cellular structures, overhangs, and reducing waste. Melt-pool geometry prediction and control is critical for widespread implementation of laser powder bed processes due to speed and accuracy requirements. The process mapping approach used in previous work for different alloys and additive manufacturing processes is applied to the selective laser powder bed process for IN625 and 17-4 stainless steel alloys. The ability to predict the resulting steady state melt-pool geometry in terms of process parameters, specifically power and velocity, is explored in detail numerically and experimentally verified. A finite element model was created that simulates powder at the macro scale. This model correlates well with current experiments in showing that small amounts of powder relative to melt-pool depth have negligible effects on resulting geometry. Results indicate that the effect of powder may be negligible when comparing steady state widths of the no powder and one layer of powder cases. The work in this thesis investigates the effect of powder on the resulting steady-state melt-pool geometries for IN625 and 17-4 alloys. This analysis has been extended to the production of overhanging and cellular structures. The successful analysis will allow for better predictions and possible correction for cellular structure production issues as well as overhanging features.

Superligas à base de níquel vêm sendo extensivamente utilizadas em diversas aplicações nas indústrias devido ao excelente comportamento mecânico e anticorrosivo. No entanto, essas ligas possuem certas particularidades que levam à necessidade de desenvolvimento de técnicas de inspeção e caracterização metalúrgica, como forma de garantir a integridade estrutural dos componentes fabricados com essas ligas. Neste trabalho, a técnica de correntes parasitas foi aplicada à superligas à base de níquel com duas propostas distintas: 1) Em um primeiro momento foi realizado o estudo da evolução microestrutural da liga Inconel 718 durante o processo de envelhecimento através da combinação do ensaio por correntes parasitas, análise de difração de raios-X, análise metalográfica, medidas de dureza e tamanho de grão. As medidas foram realizadas em amostras submetidas a diferentes ciclos de tratamentos térmicos variando entre 620-1035°C. Os resultados mostraram que as diferentes microestruturas do Inconel 718 têm efeitos distintos na condutividade elétrica quando medidos através da técnica de correntes parasitas. A influência da microestrutura na condutividade pode ser mostrada sendo devido à competição de dois efeitos sobre o espalhamento de elétrons: a purificação da matriz e a morfologia, distribuição e tamanho dos precipitados. A combinação dos valores de dureza e condutividade elétrica provou ser uma forma rápida e prática de determinar o nível de envelhecimento da liga; 2) Em um segundo momento foi desenvolvido um processo de otimização de sensores através de modelagem por elementos finitos (MEF). Através de uma metodologia de otimização, os parâmetros de construção e operação de um sensor foram otimizados para inspeção de defeitos superficiais e subsuperficiais esperados em materiais cladeados com Inconel 625. O sensor com a geometria ótima foi construído e testado a fim de verificar a eficiência do processo de otimização. Uma ótima correlação entre os resultados numéricos e experimentais foi encontrada e o sensor ótimo se mostrou eficiente na inspeção de pequenos defeitos superficiais e subsuperficiais na liga Inconel 625 quando operado nas frequências apropriadas. / Nickel-based superalloys have been extensively used in various industries due to its unique mechanical and corrosion behavior. However, these alloys show particular characteristics which lead to the need for specific inspection and metallurgical characterization techniques in order to ensure the structural integrity of components manufactured from these alloys. In this work , the eddy current technique was applied to nickel-base superalloys with two aims: 1 ) Firstly, the microstructural evolution of Inconel 718 during aging processes has been studied through a combination of eddy current testing, X-ray diffraction analysis, metallography, hardness and grain size measurements. Measurements were carried out in samples subjected to different heat treatment cycles between 620-1035°C. Results show that different microstructures of Inconel 718 have a distinguishable effect on electrical conductivity when this is measured through an appropriately sensitive technique (i.e. eddy current testing). The influence of microstructure on conductivity could be shown to be due to the competition between two effects on the scattering of electrons: matrix purification and precipitate size, distribution and morphology. A combination of hardness values and electrical properties proved to be a fast and practical way of determining the stage of aging of the alloy; 2) An optimization method of eddy current sensor design was developed through finite element modeling (FEM). Through a methodology of optimization, the construction and operation parameters of the sensor were optimized for inspection of superficial and subsuperficial defect, commonly found in weld overlay Inconel 625 claddings. A prototype of this sensor with the optimum geometry was built and tested on blocks identical to those considered in the models in order to verify the efficiency of the optimization process. A very good agreement between numerical and experimental results was found. Moreover, the optimal sensor was efficient to detect small surface and subsurface defects in Inconel 625 when operated at appropriate frequencies.

The research is focused on cladding of inconel 625 using the MAG - CMT method. It was found that welding without an oscillation does not create the necessary geometry to establish additional layers. When welding with an oscillation, it was researched that the current between 150 and 200 A appears most appropriate in the synergistic mode for welding inconel 625. The resulting weld bead was made at a current of 190 A with pulse dynamics correction set to -4 and correction of arc length to +10 and welding speed of 315 mm per minute.The weld bead was not ideal mainly due to insufficient height. The improvement of results could be achieved by set oscilation with fluent change in acceleration. Because of the time options and difficulty of programming it was used only constant speed for all experiments.

No description available.

Laser Powder Bed Fusion (L-PBF) is a metal additive manufacturing technique that uses a laser beam as a heat source to melt metal powder selectively. Because of the process small layer thicknesses, laser beam diameter, and powder particle size, L-PBF allows the fabrication of novel geometries and complex internal structures with enhanced properties. However, the main disadvantages of the L-PBF process are high costs and a lengthy production time. As a result, shortening the manufacturing process while maintaining comparable properties is exceptionally beneficial. Inconel 625 (IN625) is a nickel-based superalloy becoming increasingly popular in marine, petroleum, nuclear, and aerospace applications. However, the properties of IN625 parts produced by casting or forging are challenging to control due to their low thermal conductivity, high strength and work hardening rate, and high chemical complexity. Furthermore, IN625 alloy is regarded as a difficult-to-machine material. As a result, it is worthwhile to seek new technologies to manufacture complex-shaped IN625 parts with high dimensional accuracy. IN625 alloy is known for its excellent weldability and high resistance to hot cracking; thus, IN625 alloy appears to be a promising candidate for additive manufacturing. This thesis presents an experimentally focused study on optimizing L-PBF processing parameters in IN625 superalloy to increase process productivity while maintaining high material density and hardness. This study had four stages: preliminary, exploratory, modelling, and optimization. The first stage was devoted to conducting a literature review and determining the initial processing parameters. The second stage concentrated on determining the process window, for which single tracks were printed with two high levels of laser power (300, 400 W), five levels of scan speed (500, 700, 900, 1100, 1300 mm/s), and five levels of powder layer thickness (30, 60, 90, 120, 150 µm). Then, the process window was defined after investigating the top views and cross-sections of the tracks. Stage 3 involved printing 48 cubes (10 × 10 × 10 mm^3) with a laser power of 400 W, scan speeds of (700, 900, 1100, 1300 m/s), layer thicknesses of (60, 90, 120, 150 µm), and overlap percentages of (10, 30, 50%). As a result, the density of cubes was measured, and a statistical multiple regression analysis was used to predict it. Stage 4 involved estimating four sets of ideal processing parameters (based on statistical modelling of relative density) and printing 24 cubes (10 × 10 × 10 mm^3), six samples for each set. Finally, the relative density, hardness, and productivity of the samples were assessed, and a trade-off was determined. Even with the thickest powder layer of 150 µm (highest process productivity), samples with a mean relative density greater than 99% (i.e., 99.31% by Archimedes principle and 99.82% by image analysis) were printed. These findings are consistent with previously published results for L-PBF IN625 samples manufactured with smaller layer thicknesses ranging from 20 to 40 µm while maintaining comparable material hardness. The findings of this study are noteworthy because IN625 parts can be printed with higher powder layer thicknesses (less production time) while retaining similar material properties to those published with typical layer thicknesses ranging from 20 to 40 µm. Reduced production time due to optimized processing parameters can lead to significant energy and cost savings. / Thesis / Master of Applied Science (MASc)

La corrosion des échangeurs de chaleur est un problème économique et technique majeur des Unités de Valorisation Energétique de Ordures Ménagères (UVEOM). Elle est causée par l’action combinée (i) des gaz de combustion contenant notamment HCl et SO2 et (ii) des cendres riches en chlorures et sulfates alcalins, et sels de métaux lourds. Les travaux présentés dans ce mémoire s’inscrivent dans le projet ANR SCAPAC (n°11-RMNP-0016) et portent sur l’influence des paramètres expérimentaux (température, teneur en chlorures dans les cendres, présence de gaz corrosifs et présence de chlorures de métaux lourds dans les cendres) sur la tenue à la corrosion de deux alliages utilisés en milieu UVEOM : l’acier 16Mo3 et l’alliage base nickel Inconel 625. Ces travaux ont permis de mettre en évidence que la présence de phases fondues, l’augmentation de la teneur en chlorures, la présence de 10% en masse de ZnCl2 dans les mélanges de cendres et la présence de gaz corrosifs (HCl, SO2) dans l’atmosphère sont trois facteurs qui ont induit une corrosion plus importante sur les matériaux, de manière plus prononcée sur l’alliage base fer. Une autre partie du travail s’est focalisée sur l’influence des éléments d’alliage Fe, Cr et Mo. Des alliages « modèles » dont les compositions oscillent autour de la composition de l’alliage Inconel 625 commercial ont été synthétisés par fusion haute fréquence et leur tenue à la corrosion a été évaluée sous air et sous atmosphère corrosive. La bonne optimisation de l’alliage commercial a ainsi été démontrée sous air. Sous atmosphère gaz corrosifs, une teneur en chrome supérieure à 22% massique s’est montrée indispensable à la bonne tenue de l’alliage / Corrosion of heat exchangers is an economic and technical issue in Waste-to-energy plants. It is caused by the combined action of (i) flue gas containing HCl and SO2 and (ii) chlorides and alkali sulfates rich ash. This work is part of the ANR project SCAPAC (supported by the ANR-11-RMNP 0016) and focused on the influence of experimental parameters on the corrosion behavior of two commercial alloys used in Waste-to-Energy plants: the 16Mo3 steel and the nickel-based alloy Inconel 625. This study allowed to highlight that the presence of molten phase, the increase in the chloride content, the presence of 10% by weight of ZnCl2 in the ash mixtures and the presence of corrosive gases (HCl, SO2) in the atmosphere are three factors that have induced an higher corrosion of materials, more pronounced on the iron alloy base. Another part of the work has been focused on the influence of alloying elements Fe, Cr and Mo. Thus, model alloys with compositions oscillating around the composition of Inconel 625 commercial alloy were synthesized by high frequency induction and their corrosion resistance was evaluated in air and in corrosive atmosphere. Good optimization of the commercial alloy has been demonstrated in air. In corrosive atmosphere, a minimum chromium content was required to obtain a good corrosion resistance

Das Ohde-Kolloquium 2018 mit der traditionellen Überschrift — Aktuelle Themen in der Geotechnik – wird wieder in Zusammenarbeit mit der Bundesanstalt für Wasserbau an der Technischen Universität Dresden veranstaltet. Damit werden die beiden Wirkungsstätten von Professor Johann Ohde gewürdigt, mit denen er seine Lehr- und Forschungstätigkeit verknüpft hat. Die Beiträge des diesjährigen Kolloquiums können grob in drei Themengruppen unterteilt werden: • Bodenverhalten • Feld- und Modellversuche • Numerik und Anwendungen Die meisten Themen sind eng mit der Komplexität des Bodenverhaltens verbunden. In Abhängigkeit ihres Zustandes und einer aufgebrachten Belastung können Böden verschiedene Zustandsformen – gasförmig, flüssig und fest. Insbesondere der Übergang vom Feststoff zur Flüssigkeit (Bodenverflüssigung, hydraulischer Grundbruch, usw.) ist mit einem hohen Schadenspotenzial für Bauwerke und Menschen verbunden. Modellversuche im Labor und Monitoring im Feld sind für das Verständnis und die rechtzeitige Erkennung der Gefahrenzustände unumgänglich. Inwieweit die jetzigen Prognosen ausgereift sind, zeigen die numerischen Berechnungen für ausgewählte Anwendungen.:Bewertung von Scherversuchen aus Vergleichsuntersuchungen an feinkornigem Boden -- Erik Schwiteilo, Ivo Herle Experimentelle Untersuchungen zur Rissinitiation hydraulisch belasteter feinkörniger Böden -- Helen Günther Verdichtung und Zustandsbeschreibung gemischtkörniger Böden -- Carsten Lauer, Jens Engel Zur Strukturentwicklung granularer Materialien in Scherversuchen -- Max Wiebicke, Edward Andò, Gioacchino Viggiani, Ivo Herle Ein erweitertes Bounding Surface Modell für die Anwendung auf allgemeine Spannungspfade im Sand -- Katharina Bergholz Anwendung der Dimensionsanalyse zur Untersuchung des Erosionsdurchbruches in feinkornigen Boden -- Johannes Welsch, Ivo Herle Laborversuche und Berechnungen zur Ermittlung der wirksamen Wandschubspannungen im Hole-Erosion-Test zur Bestimmung der Erosionsparameter bindiger Böden -- Manuel Hark Beurteilung der Verflüssigungsneigung grobkörniger Böden -- Bozana Bacic Untersuchungen zur Gebrauchstauglichkeit der Gründungen von Offshore-Windenergieanlagen -- Torsten Wichtmann 1g Modellversuche mit granularen Säulen in organischen Böden -- Marcel Ney, Frank Rackwitz Bodenverdichtung - Experimentelle und numerische Untersuchungen -- Holger Pankrath Herausforderungen für die Spezialtiefbau-Forschung -- Wolfgang Wehr Zur Prognose von Ersatzfedersteifigkeiten von Tiefgründungssystemen am Beispiel der Itztalbrücke -- Thomas Meier Dynamische numerische Berechnungen zur Bewertung der Standsicherheit von Erddämmen unter Erdbebeneinwirkung -- Jamal Hleibieh, Ivo Herle CFD Simulation von Fluidstromung in Gesteinskluften mit OpenFOAM -- Maxim Finenko, Heinz Konietzky

Gegenstand dieser Dissertation ist die Etablierung des Elastizitätsmoduls als Parameter, der qualitative Aussagen über den Schädigungszustand des Baustoffs Straßenbeton ermöglicht. Zu diesem Zweck erfolgte eine systematische Ermüdung von labormaßstäblichen Betonprobekörpern bei zeitgleicher Messung des Elastizitätsmoduls mit Hilfe von unterschiedlichen Verfahren. Im ersten Schritt wurde ein Versuchsprogramm entwickelt, mit dem Probekörper mittels des Spaltzug-Schwellversuchs gezielt in einen definierten Ermüdungszustand versetzt werden können. Hierfür wurde der Parameter des Grenz-Elastizitätsmoduls definiert, welcher, wenn er unterschritten wird, zum Pausieren des Versuchs führt. In diesen systematisch eingehaltenen Lastpausen erfolgten begleitende Untersuchungen der Ultraschalllaufzeit und der Eigenfrequenz zur Bestimmung des Elastizitätsmoduls der Probekörper während des Ermüdungsvorganges. Es zeigt sich zwischen den Ergebnissen aller untersuchten Verfahren eine sehr gute Synchronität hinsichtlich des qualitativen ermüdungsbedingten Verlaufs des Elastizitätsmoduls. Die vier angewandten Verfahren, die sich voneinander unabhängiger physikalischer Phänomene bedienen, ermöglichen neben einer qualitativen Aussage über die Schädigung des Materials die Bestimmung von Absolutwerten des Elastizitätsmoduls. Je nach verwendetem Verfahren weichen die absoluten Elastizitätsmoduln leicht voneinander ab. Der Elastizitätsmodul bestätigt sich als geeigneter Parameter zur Beschreibung der Degradation des Baustoffs Straßenbeton im Zuge des Ermüdungsprozesses. Im zweiten Schritt wurden der Einfluss längerer Lastpausen sowie die Verminderung der Betonfestigkeit im Zuge der Materialermüdung tiefergehend untersucht. Es wurde festgestellt, dass längere Lastpausen in der zyklischen Belastung einen signifikanten Einfluss auf den ermüdungsbedingten Verlauf des Elastizitätsmoduls haben können. Weiterhin legen die Untersuchungen nahe, dass es im Zuge einer starken Ermüdung zu einer zum Teil signifikanten Verminderung der Festigkeit kommt. Als Resultat der Untersuchungen konnten sowohl ein Verfahren zur Bestimmung charakteristischer Verläufe für die Verminderung des Elastizitätsmoduls als auch ein Verfahren zur Abschätzung der materialspezifischen Verminderung der Festigkeit im Zuge der Ermüdung entwickelt werden. Diese Verfahren könnten zukünftig den Regelwerken der RSO Beton und der RDO Beton zugeführt werden, um die ermüdungsbedingte zeitliche Entwicklung des Elastizitätsmoduls und der Festigkeit in den durch die Regelwerke festgeschriebenen Prognose- und Dimensionierungsprozessen zu berücksichtigen. Durch die Einbeziehung zeitlich veränderlicher Werte im Prognoseverfahren, welches als Grundlage für die RSO Beton dienen soll, wird in dieser Dissertation exemplarisch gezeigt, dass die Berücksichtigung der Auswirkungen der Betonermüdung auf diese für die Prognose und die Dimensionierung von Betonfahrbahnbefestigungen sehr relevanten Parameter zur signifikanten Erhöhung der Ausfallrate gegenüber der Verwendung konstanter Werte führen kann. / The subject of this doctoral dissertation is the establishment of the elastic modulus as a parameter that enables qualitative statements about the state of damage of the concrete pavement building material. For this purpose, a systematic fatigue of laboratory-scale concrete specimens was carried out with simultaneous measurement of the elastic modulus by means of different methods. In the first step, a test program was developed for the targeted and systematic fatigue of concrete specimens by means of the cyclic indirect tensile test. For this purpose, a limit value for the elastic modulus was defined. When the elastic modulus fell below the limit, the test was paused to perform accompanying investigations of the ultrasonic transit time and the natural frequency in order to determine the change of the elastic modulus of the specimens during the fatigue process. There is a very good synchronicity between the results of all investigated methods for the qualitative determination of the elastic modulus. The four methods applied, which make use of physical phenomena that are independent of each other, allow, in addition to a qualitative statement about the damage to the material, the determination of absolute values of the elastic modulus. Although there are slight differences between the methods for the determination of the elastic modulus, it is confirmed as a suitable parameter for describing the degradation of the concrete pavement building material in the course of the fatigue process. In the second step, the influence of longer loading pauses and the reduction of concrete strength due to material fatigue were investigated in more detail. It was found that longer loading pauses during cyclic loading can have a significant influence on the fatigue-related course of the elastic modulus. Furthermore, the investigations suggest that in the course of severe fatigue there is a sometimes significant reduction in strength. As a result of the investigations, both a method for determining characteristic curves for the reduction of the elastic modulus and a method for estimating the material-specific reduction of strength in the course of fatigue could be developed. In the future, these methods could be implemented into the RSO Beton and RDO Beton regulations in order to take into account the fatigue-related temporal development of the elastic modulus and the strength in the forecasting and dimensioning processes specified by the regulations. By including time-varying values in the forecasting procedure, which is to serve as the basis for the RSO Beton, this doctoral dissertation exemplifies that the consideration of the effects of concrete fatigue on these very relevant parameters for the forecasting and dimensioning of concrete pavements, can lead to the significant increase of the failure rate compared to the use of constant values.

Assembling original documents, historical material, completed or unrealized projects and the evolution of governmental and professional structures, this dissertation explores the development and construction of urban expressways in American cities, from their conception at the dawn of the 20th-century, to the end of the 1960’s. Beyond the force of its physical imprint, and its impact on the operative restructuring of the city, the arrival of the urban expressway led to profound doubts about the value and the meaning of the urban, about the legitimacy or professional relevance of urbanism—the discipline that ostensibly had the expertise to deal with the city—and an institutional and political structure supported by what were in theory democratic ideals, but which were, in many cases, closely tied to private interests. Much has been written about the reasons behind the construction of the system of expressways and the need for great technical ability in order to complete this system. More still has been written about the consequences of this system, frequently linked to a string of negative adjectives when discussing their impact on the urban fabric. And not a few have written about the intricate political web behind this infrastructure. Nevertheless, relatively little has been written about urban expressways and the invisible network of questions, episodes, causes and consequences that shaped the decisions that would later be translated into a radical change of the American city.Theory versus method, disciplinary impotence versus professional competence, institutional orphanhood versus executive institutionalization would be, both successively and simultaneously, battlegrounds for a debate unleashed through a series of specific outgrowths of what is, or what may perhaps once have been, a mere piece of infrastructure.This dissertation will explore these questions, understanding the urban expressway in the American city to be only the tip of the iceberg of a profound change in the history of what we still refer to, generically, as the urban / Conjugando archivos originales, material histórico, proyectos ejecutados o nunca realizados y la evolución de estructuras profesionales y gubernamentales, esta tesis explora las autopistas urbanas en las ciudades de Estados Unidos desde su germen a comienzos de la primera mitad de siglo XX hasta finales de la década del ‘60. El advenimiento de las autopistas urbanas produjo, más allá de su impresión física y su impacto en la reestructuración operativa de las ciudades, profundos cuestionamientos sobre el valor y significado de lo urbano, la legitimidad o relevancia profesional sobre la disciplina que pretendía ser su especialista, el urbanismo, y una estructura institucional y política siempre sostenida sobre supuestos ideales democráticos pero perversamente atado a intereses privados. Mucho se ha sido escrito sobre las razones para la construcción del sistema de autopistas como infraestructuras y el desarrollo de una rigurosa pericia técnica para su ejecución, más aún sobre sus consecuencias, casi siempre adjetivadas como nefastas, en los entornos urbanos, y no pocos han escrito sobre la intrincada red política detrás de ellas. Sin embargo, poco se ha escrito sobre las autopistas urbanas en forma específica y la invisible trama de cuestiones, episodios, causas y consecuencias que dieron forma a decisiones que se traducirían luego en el más drástico cambio de la ciudad en Estados Unidos.Teoría versus método, impotencia disciplinar versus competencia profesional, orfandad institucional versus institucionalización ejecutiva serán por turnos, y simultáneamente, campos de batalla para un debate desencadenado a través de unas ramificaciones específicas de lo que en apariencia es, o era si alguna vez lo fue, simplemente una pieza de infraestructura.Esta tesis indagará en estas cuestiones, entendiendo las autopistas urbanas en las ciudades de Estados Unidos sólo como la punta del iceberg de un cambio rotundo en el curso de la historia, de la que aún genéricamente llamamos, urbana.