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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Shearing on the Great Glen Fault: Kinematic and Microstructural Evidence Preserved at Different Crustal Levels

Becker, Cassandra 22 May 2023 (has links)
The NE-SW trending Great Glen Fault (GGF) is one of mainland Scotland's most significant crustal-scale faults, although our understanding of its early kinematics is in question. Previous studies generally agree that the GGF was initiated as a Silurian sinistral strike-slip fault displacing c. 425 Ma isotopically dated granitic plutons. Stewart et al. (2001) argued that dikes fed by these plutons were sinistrally sheared by the GGF while in the sub-magmatic state, suggesting continuous strike-slip motion on the GGF by 425 Ma. Strike-slip offset post-dating overlying Devonian sedimentary basins is likely only a few tens of kilometers, requiring substantial (100s of kms) Silurian-aged strike-slip movement on the GGF in most plate reconstruction models for the Caledonian mountain belt, now exposed in East Greenland, Scandinavia, and Scotland. In contrast, a recent study (Searle 2021) has argued that motion on the GGF may instead have initiated in the Upper Paleozoic and that off-set is therefore minimal, bringing current restoration models into question. Several papers report widespread field and microstructural evidence from crystalline bedrock and overlying Devonian sedimentary rocks for brittle upper-crustal shearing on the GGF. However, evidence for high-temperature crystal plastic shearing at deeper crustal levels on the GGF, potentially of Silurian to Early Devonian age, is limited. During summer 2022, suites of oriented and plastically deformed metasedimentary rock samples were collected from the NW side (Moine/Lewisian gneisses and quartzites), center (Moine quartzites), and SE side (Dalradian quartzites) of the GGF. Additional samples included plutonic rocks from locations adjacent to the GGF and the associated Strathconnon fault that were believed to have been intruded during strike-slip motion, but after regional metamorphism and deformation in the surrounding Moine rocks. Microstructures and quartz c-axis fabrics from samples on the NW side and in the center of the GGF indicate a NW side up to the SW sense of displacement about NE to E plunging slip vectors, and these results are compatible with oblique sinistral motion on the GGF below the brittle-ductile transition zone during Silurian - Early Devonian times. However, radiometric dating is needed to prove the absolute timing of this shearing. In contrast, on the SE side of the GGF, NW side up or NW side down senses of shearing are indicated at different locations. Brittle fracturing is observed in all collected samples, overprinting the earlier high-temperature (300 - 650 °C) crystal fabrics and microstructures developed below the brittle-ductile transition zone. No convincing microstructural evidence for sub-magmatic shearing during pluton emplacement was found in the samples collected. However, the local presence of high-low temperature (c. 650 - 300 °C) solid-state deformation microstructures in both quartz and feldspar grains in these 430 - 425 Ma plutons suggests that the plutons were deforming internally in response to far-field stresses generated by shearing on the adjacent GGF and Strathconnon fault during cooling to background regional temperatures. / Master of Science / The Great Glen Fault (GGF) is one of mainland Scotland's most significant large-scale faults, although our understanding of its early motion is debated. Most geologists agree that the GGF began displacing existing rocks during the Silurian (c. 444 - 419 Ma), including igneous bodies, known as plutons, of approximately the same age (c. 425 Ma). Stewart et al. (2001) argued that during shearing, dikes fed by these plutons were deformed before cooling to background temperatures, which may suggest that the GGF was continuously undergoing lateral strike-slip motion by 425 Ma and that post-Silurian offset was likely only a few tens of kilometers. Most plate reconstruction models for the Caledonian mountain belt, now exposed in East Greenland, Scandinavia, and Scotland, assume that significant lateral motion and shearing occurred on the GGF during the Silurian. However, new research has suggested that the GGF was initiated several million years later, bringing current restoration models into question. Several published papers have reported widespread evidence for upper-crustal brittle shearing of crystalline bedrock and overlying Early Devonian (c. 420 - 359 Ma) sedimentary basins within the GGF. However, evidence for lower-crustal shearing during the same time frame, resulting in plastic deformation, is limited. To address this knowledge gap, I collected suites of oriented bedrock samples and 430 - 425 Ma plutonic rocks from locations adjacent to the GGF and associated Strathconnon Fault believed to have been intruded during strike-slip motion. Samples from the NW side and center of the GGF suggest oblique left-lateral motion within the fault zone, with the rocks on the NW side of the GGF moving upward relative to the SE side, compatible with current generally accepted models for the Silurian-Early Devonian age on the GGF; however, these results must be verified with radiometric dating to constrain the absolute timing of shearing. On the SE side of the GGF, vertical offset is variable at different locations. Brittle upper-crustal shearing is observed in all samples, which overprints early high-temperature (300 - 650 °C) deformation. Early lower-crustal shearing on the GGF is recorded by these deformation indicators and was followed by uplift and fracturing within the GGF of these initially lower-crust rocks. The local presence of solid-state deformation microstructures in the plutons suggest internal deformation due to shearing on the adjacent Great Glen and Strathconnon Faults during their cooling to regional background temperatures.
52

Unraveling Recrystallization Mechanisms Governing Texture Development from Rare Earth Element Additions to Magnesium

Imandoust, Aidin 11 August 2017 (has links)
The origin of texture components associated with rare-earth (RE) element additions in wrought magnesium (Mg) alloys is a long-standing problem in magnesium technology. The objective of this research is to identify the mechanisms accountable for rare-earth texture during dynamic recrystallization (DRX). Towards this end, we designed binary Mg-Cerium and Mg-Gadolinium alloys along with complex alloy compositions containing zinc, yttrium and Mischmetal. Binary alloys along with pure Mg were designed to individually investigate their effects on texture evolutions, while complex compositions are designed to develop randomized texture, and be used in automotive and aerospace applications. We selected indirect extrusion to thermomechanically process our materials. Different extrusion ratios and speeds were designed to produce partially and fully recrystallized microstructures, allowing us to analyze DRX from its early stages to completion. X-ray diffraction, electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to conduct microstructure and texture analyses Our analyses revealed that rare-earth elements in zinc-containing magnesium alloys promote discontinuous dynamic recrystallization at the grain boundaries. During nucleation, the effect of rare earth elements on orientation selection was explained by the concomitant actions of multiple Taylor axes in the same grain. Isotropic grain growth was observed due to rare earth elements segregating to grain boundaries, which lead to texture randomization. The nucleation in binary Mg-RE alloys took place by continuous formation of necklace structures. Stochastic relaxation of basal and non-basal dislocations into lowangle grain boundaries produced chains of embryos with nearly random orientations. Schmid factor analysis showed a lower net activation of dislocations in RE textured grains compared to ones on the other side of the stereographic triangle. Lower dislocation densities within RE grains favored their growth by setting the boundary migration direction toward grains with higher dislocation density, thereby decreasing the system energy. We investigated the influence of RE elements on extension twinning induced hardening. RE addition enhanced tensile twinning induced hardening significantly. EBSD analysis illustrated that tensile twins cross low angle grain boundaries in Mg-RE alloys, which produced large twins and facilitated transmutation of basal to prismatic dislocations. Higher activity of pyramidal II dislocations in Mg-RE alloys resulted in higher twinning induced hardening.
53

Development and Implementation of Ice Recrystallization Inhibitors for the Preservation of Biological Material

Mangan, Sophia 17 May 2023 (has links)
Cryopreservation of biological materials has many useful applications and is currently the most effective long term storage method used across a variety of fields. The success of freezing products or biological materials, however, varies because of the process' complexity and related cryo-injuries. One of the primary issues is the ice recrystallization induced development of extracellular and intracellular ice throughout the freezing and thawing process. Ice recrystallization is a significant contributor to freezing damage, ultimately reducing post-thaw viability and function. To address this issue, the Ben laboratory has developed and synthesized a variety of classes of small molecule carbohydrate-based ice recrystallization inhibitors (IRIs). These compounds act as supplements or alternatives to current cryoprotectants, such as trehalose, DMSO, or glycerol, which do not address ice recrystallization and can be cytotoxic. This thesis focuses on the comprehensive chemical property assessment of N-Aryl-β-D-aldonamides and N-Benzyl-β-D-gluconamides, as well as optimization of biopreservation protocols for tissue products and freeze-dried proteins. Utilizing a 5-minute modified splat cooling assay, dose-response curves of five N-Benzyl-β-D-gluconamides were generated. All compounds produced ice recrystallization inhibition active IC50 values comparable to previously investigated active compounds such as, N-Octyl-β-D-gluconamide and N-4-Bromophenyl-β-D-glucopyranoside. Furthermore, validation that the dose-response curves follow a 4-parameter logistic (4PL) or 5PL sigmodal trend depending on symmetry was obtained. In addition, all tested compounds had lower cytotoxicity than N-4-Bromophenyl-β-D-glucopyranoside and higher solubility than N-Octyl-β-D-gluconamide. Overall, N-Benzyl-β-D-gluconamides proved to be a promising class of compounds with the para derivatives being the most IRI active. The second part of this work involved the examination of IRIs' ability to cryopreserve two different biological materials using different biopreservation protocols. The first being proteins and master mix (enzymes and oligonucleotides) during RT-qPCR after the freeze-drying process. The data showed that the IRIs did not interfere and were effective during both the lyophilization and qPCR processes. When compared to most effective concentration of the current industry standard, N-4-Bromophenyl-β-D-glucopyranoside increased the protein activity by ~30%, reducing the number of cycles to reach threshold value. The most significant contribution of this work was the discovery that carbohydrate-based small molecules may be working in more than one mechanism, as both cryoprotectants and lyoprotectants. In addition to proteins, the ability of IRIs to cryopreserve tissue products was investigated. Cell media supplemented with IRIs indicated that they can increase viability and reduce mortality in both cell suspension and single dermal sheets. With N-4-Methylbenzyl-β-D-gluconamide and N-Octyl-β-D-gluconamide being the most effective at reducing the damage associated with freezing and increasing recovery of the cells within the system of a simple one cell type thin tissue matrix.
54

Surface and subsurface deformation of aluminum and aluminum alloys in dry sliding wear /

Kuo, Shun-meen January 1987 (has links)
No description available.
55

Effect of stress relaxation on the kinetics of recovery and recrystallization in hot worked ETP copper

Vazquez Brisen̄o, Lucio. January 1980 (has links)
No description available.
56

Effect of aluminum on recrystallization and precipitation of Nb HSLA steels

Wang, Ganlin. January 1986 (has links)
No description available.
57

Static recrystallization and precipitation in titanium-microalloyed steels containing different levels of manganese

Macchione, Alfred. January 1985 (has links)
No description available.
58

Effect of the joint addition of aluminum and molybdenum on the precipitation and recrystallization in HSLA steels

Anderson, Danny January 1986 (has links)
No description available.
59

Competição entre recuperação e recristalização em uma liga de alumínio contendo dispersão de precipitados. / Competition between recovery and recrystallization in a dispersion hardened aluminium alloy.

Padilha, Angelo Fernando 06 June 1977 (has links)
Através de microscopia ótica utilizando luz polarizada e de metalografia quantitativa, determinou-se a cinética de recristalização a 400 ºC de uma liga de alumínio da série 3000 contendo dispersão de precipitados, para diferentes graus de deformação produzidos por laminação. Mediram-se parâmetros, para vários tempos de recozimento, que permitiram determinar: fração volumétrica recristalizada, quantidade de interfaces por unidade de volume entre regiões recristalizadas e não recristalizadas e, entre regiões recristalizadas, assim como velocidade média de migração de interfaces. Fizeram-se também medidas de microdureza em todas as amostras. Os resultados experimentais mostraram que à medida que se diminui o grau de deformação, a quantidade de interfaces por unidade de volume responsáveis pela recristalização diminui exigindo portanto um crescimento através de distâncias maiores para a recristalização se completar, tornando a cinética de recristalização mais dependente do crescimento. Constatou-se a ocorrência de recuperação, durante a recristalização, das regiões não recristalizadas e consequente diminuição da velocidade média de migração de interfaces com o tempo de recozimento. Com a diminuição da deformação, ocorreram frações não recristalizadas residuais, as quais eram maiores para graus de deformação menores, chegando a atingir mais de 80% para 34,4% de redução em espessura. Os resultados sugerem que, para baixas deformações, a velocidade de crescimento tem um papel importante na cinética de recristalização de ligas com dispersão de precipitados. A comparação entre os resultados de metalografia quantitativa e medidas de microdureza evidenciou algumas limitações desta última técnica para estudo de recristalização. / Using polarized light optical micrsocopy and quantitative metalography, kinetics of recrystallization at 400 ºC of an aluminum alloy of 300 series were determined, for different rolling deformation. Recrystallized volume fraction, amount of interfaces per unit volume, between recrystrallized and unrecrystallized regions and between recrystallized grains, and also mean velocity of interface migration were determined. Microhardness measurements were made in all specimens. The results have shown that with decreading deformation, the amount of interfaces responsible for recrystallization, per unit volume, decreases and so the interfaces must sweep larger distances for complete recrystallization, making kinetics more dependent on growth. Recovery of the unrecrystallized regions was observed, during recrystallization, causing decrease in the average velocity of interface migration with annealing time. With decreasing deformation residual unrecrystallized volumes have been observed, after long time anneals. The fraction of residual unrecrystallized region were large than 80-% for 34,4% thickness reduction. The results suggest that, in alloys with precipitates, the growth velocity has an important role in recrystallization kinetics. Some shortcomings of hardness measurements, as a tool to study recrystallization, were shown by comparison between the quantitative metallography and hardness measurements.
60

Cinética de amolecimento da liga de alumí­nio AA 7075 durante recozimento após laminação a frio. / Softening behavior during annealing of col-rolled aluminium alloy 7075.

Souza, Saul Hissaci de 06 February 2018 (has links)
O presente trabalho apresenta um estudo sobre o amolecimento após laminação e recozimento da AA 7075, uma liga de alumínio endurecível por precipitação . As amostras recebidas no estado T6 foram caracterizadas com auxílio das técnicas de microscopia óptica de luz polarizada, microscopia eletrônica de varredura, espectroscopia de raios X por dispersão de energia, difração de raios X, condutividade elétrica e dureza Vickers . As amostras foram então separadas em dois grupos. O primeiro sofreu um tratamento térmico de solubilização (485°C por 5 horas) enquanto o segundo foi submetido a um tratamento de superenvelhecimento (300°C por 5 horas) e, em seguida, ambos os grupos de amostras tratadas foram novamente caracterizadas pelas técnicas descritas anteriormente (exceto microscopia óptica) e laminadas a frio. Durante a etapa de laminação, constatou-se a dificuldade em causar deformação plástica na amostra solubilizada. Optou-se em conduzir o estudo com as amostras superenvelhecidas, que foram laminadas com reduções de 45%, 75% e 90% em espessura. A seguir, estas foram submetidas a tratamentos isotérmicos e isócronos com o objetivo de estudar a cinética de amolecimento das amostras deformadas a frio. As amostras superenvelhecidas e deformadas em 45% em redução de espessura, apresentaram somente indícios de início de recristalização (nas amostras tratadas a partir de 250°C por 1 hora) via EBSD, sendo que a maior parte do amolecimento pode ser explicada pelo mecanismo de recuperação. Além disso, a cinética de amolecimento das amostras recozidas nesse grupo apresentaram boa concordância com a lei logarítmica proposta por Kulhmann (1948) e (coincidentemente) também com o consolidado modelo JMAK. As amostras superenvelhecidas e deformadas em 75% e 90% apresentaram comportamento similar (isso é, principalmente recuperação) para recozimentos realizados em temperaturas de até 350°C por uma hora. Recozimentos realizados a 400°C promoveram a recristalização total das amostras desse grupo para tempos inferiores a 15 minutos. Dessa forma, não foi possível estudar a cinética de recristalização para esse segundo grupo de amostras. / This work presents a study about the softening after cold rolling and annealing of aluminium alloy AA 7075. Firstly, polarized light optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, electrical conductivity and Vickers hardness have been used at the starting material (T6). The samples were then separated in two groups. The former underwent a solubilization heat treatment (485°C for 5 hours) whilst the latter underwent an overaging treatment to grow up the existing precipitates (300°C for 5 hours). Both groups of treated samples were again characterized by the techniques described above (except optical microscopy). In the rolling stage, the difficulty in straining the solubilized sample and the relative ease for doing so to the overaged sample was verified. It was therefore decided to conduct the study with the samples of the second group, which were 45%, 75% and 90% rolled in thickness reduction. Then, they underwent isothermal and isochronous treatments in order to study its softening kinetics by Vickers hardness measurements, polarized light optic microscopy and EBSD. The overaged and rolled samples (45% in thickness reduction) didn\'t present evidences of recrystallization except by very few grains found via EBSD (in samples treated from 250 ° C for 1 hour). So, most of the observed softening can be explained by recovery. In addition, the softening kinetics of the annealed samples in this group showed good agreement with the logarithmic law proposed by Kulhmann (1948) and (coincidentally) also with the consolidated JMAK model. The overaged samples that underwent thickness reduction of 75% and 90% showed a similar behavior (that is, mainly recovery) for annealing at temperatures up to 350 ° C. Annealing at 400 ° C promoted total recrystallization of the samples from this group (75% and 90% in thickness reduction) in less than 15 minutes. Thus, it was not possible to study the kinetics of recrystallization for this second group of samples.

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