Al 7050-T7451 alloy with good combinations of strength, stress corrosion cracking resistance and toughness, is used broadly in the aerospace/aviation industry for fatigue-critical airframe structural components. However, it is also considered as a highly anisotropic alloy as the crack growth behavior along the short transverse direction is very different from the one in the long transverse direction, due to the inhomogeneous microstructure with the elongated grains distributed in the work material used in the sheet/plate applications. Further processes on these materials are needed to improve its mechanical and material properties and broaden its applications. The material with ultra-fine or nano grains exhibits improved wear and corrosion resistance, higher hardness and better fatigue life, compared to the one with coarse grains. In recent times, the development of novel processing technologies has gained great attention in the research community to enhance the properties of the materials employed in the aerospace, biomedical, precision instrument, automotive, nuclear/power industries. These novel processing technologies modify the microstructure of this alloy and improve the properties. The aim of this dissertation is to investigate the effects of cryogenic processes, including friction stir processing (FSP), machining and burnishing, on Al 7050-T7451 alloy to solve the inhomogeneity issue and improve its surface integrity. FSP is applied to modify the microstructure of Al 7050-T7451 alloy for achieving more homogeneous structure with near ultra-fine grains (UFG) which were less than 2 µm, particularly in cryogenic FSP with liquid nitrogen as the coolant. Approximately 10% increase could be observed from the hardness measurement from the samples processed by cryogenic FSP, in contrast to dry FSP. Also, the texture change from Al (200) to Al (111) could be achieved in all the samples processed by dry and cryogenic FSP. Cryogenic machining and burnishing processes were also applied to enhance the surface integrity of the manufactured components with near-UFG structure. The highest cutting temperature was reduced by up to 44.7% due to the rapid cooling effect of liquid nitrogen in cryogenic machining, compared with dry machining. Nano grains were produced in the refined layers induced by cryogenic burnishing. And, up to 35.4% hardness increase was obtained within the layer depth of 200 µm in the cryogenically-burnished surface. A numerical finite element method (FEM) model was developed for predicting the process performance in burnishing. Less than 10% difference between the experimental and predicted burnishing forces was achieved in the simulation of cryogenic burnishing, and reasonable predictions were also achieved for temperatures, severe plastic deformation (SPD) layers.

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Le développement et l'utilisation des procédés industriels à basse température ont été très importants durant ces dernières années. Le développement est surtout dû à l'accroissement de la demande en produits liquides (purs ou mélanges) sur le marché mondial. L'auteur de cette thèse propose une analyse approfondie des trois grandes familles de procédés de liquéfaction du gaz naturel utilisés en Algérie. Il commence par examiner les traitements subis par le gaz naturel avant sa liquéfaction qui consiste à le ramener à une température de -160°C et à une pression légèrement supérieure à la pression atmosphérique. Il analyse ensuite, à l'aide du logiciel ASPEN PLUS, les différentes performances des trois types de cycles et conclut en montrant que le cycle Propane-MCR est thermodynamiquement le plus avantageux.

Le développement et l'utilisation des procédés industriels à basse température ont été très importants durant ces dernières années. Le développement est surtout dû à l'accroissement de la demande en produits liquides (purs ou mélanges) sur le marché mondial. L'auteur de cette thèse propose une analyse approfondie des trois grandes familles de procédés de liquéfaction du gaz naturel utilisés en Algérie. Il commence par examiner les traitements subis par le gaz naturel avant sa liquéfaction qui consiste à le ramener à une température de -160°C et à une pression légèrement supérieure à la pression atmosphérique. Il analyse ensuite, à l'aide du logiciel ASPEN PLUS, les différentes performances des trois types de cycles et conclut en montrant que le cycle Propane-MCR est thermodynamiquement le plus avantageux.

L’isolation des cuves des méthaniers, utilisant la technologie de membrane MarkIII, est garantie par l’agencement de barrières thermiques réalisées à l’aide de blocs de mousse polyuréthane renforcée. La membrane est dimensionnée pour résister aux diverses sollicitations mécaniques et thermiques de service. De plus, dans le cadre de l’étude de scénarios de sécurité critiques, il doit être démontré que l’occurrence d’un évènement rare de type pénétration d’eau, n’engendre pas de dommages sévères des composants de la membrane.L’objet de ce travail est d’étudier le comportement de la mousse polyuréthanne renforcée par des fibres de verre en immersion afin d’aider à une meilleure compréhension des mécanismes de diffusion et de l’impact de la pénétration de l’eau sur les propriétés du matériau.La mise en place d’essais de sorption à température ambiante, suivant trois conditionnements « libre », « bloqué » et « couplé » a permis d’identifier respectivement une loi de gonflement, une loi de chargement et une loi d’endommagement.En conditionnement « libre », l’architecture cellulaire et les positionnements de fibres de verre dans les plans XY induisent un couplage hygro-mécanique anisotrope. Le gonflement de la direction Z, joue un rôle très important sur les niveaux de solubilité de l’eau.En conditionnement « bloqué », le blocage du déplacement des faces perpendiculaires à la direction Z induit une augmentation du niveau de contrainte interne en fonction de la progression du front de pénétration.En conditionnement « couplé », l’enchaînement d’un vieillissement hydrique et d’un vieillissement cryogénique engendre un endommagement, dont le degré est proportionnel au niveau de gonflement de la structure cellulaire.L’impact de ces différents conditionnements sur la durabilité des propriétés mécaniques du matériau a été évalué. / The insulation of containment membrane of liquid natural gas carrier using the MarkIII membrane system, consists of load-bearing system made of panels in glass fiber reinforced polyurethane foam. The membrane is designed to resist to mechanical and thermal service load cases. As stated by IGC code regulation, and more specifically in some critical safety scenario, it has to be demonstrated that the cargo containment system will keep its integrity and main functions when subjected to water leakage through the inner hull wall (ballast).The challenge of this study is to appreciate the behavior of the reinforced polyurethane foam in immersion, which could widen the understanding of both water diffusion mechanisms and the impact of water penetration on the properties of the material.The setting up of water sorption tests at ambient temperature, according to three conditioning "free", "blocked" and "coupled" has allowed to identify a swelling law, a loading law and a damage law.In "free" conditioning, the cellular structure and the orientation of glass fibers in XY planes induce an anisotropic hygro-mechanical coupling. The swelling of Z direction has an important impact on the water solubility levels.In "blocked" conditioning, the blocking of the displacement of the faces perpendicular to the Z direction induces an increase in the internal stress levels as a function of the progression of the penetration front. In "coupled" conditioning, the sequence of the water aging and the cryogenic aging causes several damages. The damage degree is proportional to the hygroscopic swelling level of the cellular structure.The impact of these different conditionings on the durability of the material mechanical properties has been evaluated.

ix, 44 p. : ill. (some col.) / The physical weathering of rock in cryogenic regions through a process called ice segregation is important for understanding subglacial processes, landscape evolution and cold region engineering. Ice segregation was examined by freezing water-saturated cores of Eugene Formation sandstone at temperatures between -15° and -2°C. Cores between -8° and -5°C took 30-45 minutes to crack, while cores at warmer or cooler temperatures took either more than 90 minutes or did not crack at all. Numerical modeling shows that cores break under isothermal conditions. The results of this study suggest that previous models in which temperature gradients are held responsible for driving flow towards growing cracks are incomplete. I introduce a new model of ice segregation to explain how premelted liquids from smaller pores can migrate and contribute to the growth of large cracks. This dissertation includes unpublished material. / Committee in charge: Alan Rempel, Chairperson; Joshua Roering, Member; Rebecca Dorsey, Member

DoD EO/IR applications continue to push imaging technology. Next generation advances require new material systems, novel device structures, as well as the improvement and development of read out integrated circuits. The common methodology used to assess devices and materials is to process test chip structures and focal plane arrays. Test chips have advantages over focal plane arrays; such as, variable area and stand alone devices and can be measured as a function of bias and temperature; however, focal plane arrays are the heart of the imager, but are measured through the read out integrated circuits, which can add complexity to the measurement and to the extraction of properties. Differences between a test chip and a focal plane array make it difficult to relate test chip characterization with focal plane array performance and the interaction of defects and the impact they have to the image. Therefore, it is vital to be able to characterize the detector array directly from 77 to 300 K. This thesis presents the design for a transparent cryogenic probe card based on a silicon carbide substrate. An inspection into the design for the bonding printed circuit board and its compliant structures is included. The design for the silicon carbide probe die is explored. The design and process for fabricating tungsten probe tips is discussed. Results on research efforts are presented showing the validity of the design based upon fabrication outcomes. It is recommended that future work explore additional tungsten tip fabrication methods.

The industrial demand for high strength-to-weight ratio materials is increasing due to the need for high performance components. Epoxy polymers, although often used in fiber-reinforced polymeric composites, have an inherent low toughness that further decreases with decreasing temperatures. Second-phase additives have been effective in increasing the toughness of epoxies at room temperature; however, the mechanisms at low temperatures are still not understood. In this study, the deformation mechanisms of a DGEBA epoxy modified with MX960 core-shell rubber (CSR) particles were investigated under quasi-static tensile and impact loads at room temperature (RT) and liquid nitrogen (LN2) temperature. Overall, the CSR had little effect on the tensile properties at RT and LN2 temperature. The impact strength decreased from neat to 3 wt% but increased from neat to 5 wt% at RT and LN2 temperature, with a higher impact strength at RT at all CSR loadings. The CSR particles debonded in front of the crack tip, inducing voids into the matrix. It was found that an increase in shear deformation and void growth likely accounted for the higher impact strength at 5 wt% CSR loading at RT while the thermal stress fields due to the coefficient of thermal expansion mismatch between rubber and epoxy and an increase in secondary cracking is likely responsible for the higher impact strength at 5 wt% tested at LN2 temperature. While a large toughening effect was not seen in this study, the mechanisms analyzed herein will likely be of use for further material investigations at cryogenic temperatures.

Carbon fiber composite cryogenic fuel tanks are very attractive to the aerospace industry. More information is needed on micro-cracking and how different composite formulations perform at cryogenic temperatures. In this study a cryogenic bulge test fixture was developed to rapidly screen small scale composite samples that are easily formulated in the laboratory. The design goal was to develop a simple fixture that induced thermal and mechanical strains in the same fixture. The pressure decay rate of helium gas through the composite sample after cryogenic operation gives a measure of the amount of micro-cracking induced. Uncertainty analysis techniques were employed to determine the resolution of the pressure decay determined from the bulge test.

An integrated fiber optical Raman sensor was designed for real-time, non –intrusive detection of liquid and gaseous mixtures at high pressure and high flow rates. The integrated sensor employs a high-power solid-state pumped Nd:YAG frequency doubled (532nm) laser (3W), a modified In Photonics Raman probe which has built-in Raman signal filter optics, and two high-resolution spectrometers and photomultiplier tubes (PMT) with selected bandpass filters to collect both N2 and O2 Raman signals. The detection unit was also integrated with Lab View software interfaced PMT modules for fast data acquisition.