Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 76-79).

Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 215-224).

Th. 3e cycle--Océanogr. biol.--Brest, 1977. N°: 73.

L’objectif principal de ce travail est la compréhension des mécanismes qui gouvernent la fissuration assistée par l’hydrogène dans les métaux, en s’appuyant sur l’analyse expérimentale de la propagation des fissures en atmosphère hydrogénant et de l’interaction entre hydrogène et défauts cristallins, et sur le développement d’un modèle de zone cohésive influencé par l’hydrogène.Des essais de propagation de fissure de fatigue ont été réalisés sous haute pression d'hydrogène gazeux sur le fer de pureté commerciale Armco. Les résultats montrent une forte influence de la pression, de la fréquence et de la valeur de ΔK sur la modification des modes de rupture, et, par conséquent, sur les vitesses de propagation. Afin d’identifier les paramètres physiques pertinents qui gouvernent les modes de rupture, une étude sur l’interaction entre hydrogène et défauts cristallins développés lors d’une sollicitation cyclique a été réalisée. Nous avons observé une augmentation de l’absorption totale d’hydrogène avec la déformation plastique cumulée, qui peut être attribuée à l’augmentation du piégeage de l'hydrogène par les dislocations générées au cours de la déformation. Ces données seront ensuite introduites dans un modèle pour reproduire la modification de la diffusion de l’hydrogène en pointe de fissure, et son effet sur la plasticité.Par ailleurs, des mesures de la déformation plastique hors plan en pointe de fissure en présence d’hydrogène ont permis de proposer une amélioration d’un modèle de zone cohésive en introduisant un effet de l’hydrogène sur le comportement plastique des éléments de volume. De plus, l'étude des composantes de la loi de diffusion de Krom a montré l'importance du gradient de contrainte hydrostatique sur la diffusion et l'accumulation de l'hydrogène en pointe de fissure. Le modèle prédit une forte dépendance de la propagation de fissures vis-à-vis de la diffusion de l’hydrogène en pointe de fissure, et est capable de simuler la propagation de fissure sous chargement statique, validant ainsi la superposition d’une composante de fissuration cyclique et d’une contribution statique (due à la présence d’hydrogène), et expliquant la transition des vitesses de propagation observée expérimentalement. / The main purpose of this work is to understand the mechanisms that govern hydrogen assisted cracking in metals, based on the experimental analysis of crack propagation data under gaseous hydrogen and the interaction between hydrogen and lattice defects on the one hand, and on the development of a cohesive zone model influenced by hydrogen on the other hand.Fatigue crack propagation tests were performed under high pressure of gaseous hydrogen on the Armco iron. The results show a strong influence of the pressure, the frequency and the ΔK value, on the modification of the failure modes and on the fatigue crack growth rates. In order to identify the physical parameters that govern the changing of the failure modes, a study on the interaction between hydrogen and the crystallographic defects developed during a cyclic loading was performed. We observe an increase in the total absorption of hydrogen with the cumulated plastic deformation, which can be attributed to the increase in the hydrogen trapping by the dislocations generated during the cyclic deformation. These data have to be introduced into a numerical model to reproduce the modification of the hydrogen diffusion at the crack tip, and its effect on plasticity.Moreover, measurements of the out-of-plane plastic deformation at the crack tip in presence of hydrogen have conducted to an improvement of the cohesive zone model by introducing an effect of hydrogen on the plastic behavior of the volume elements. In addition, the study of Krom diffusion law components has shown the importance of the hydrostatic stress gradient on the diffusion and accumulation of hydrogen at the crack tip. The model predicts a strong dependence of the crack propagation with respect to the hydrogen diffusion at the crack tip, and it is able to simulate the propagation under static load, thus validating the cyclic cracking and static cracking superposition, and explaining the transient regime in fatigue crack growth rates experimentally observed.

<p> Geophysical studies of the northwest trending Sudbury olivine diabase dikes, to the south of Coniston, Ontario establish a deformation zone, within the Southern province up to 10 km from the Grenville Front. Paleomagnetics reveal two directional groups within the dikes; those with a NRM direction of 300°/32° representing the primary magnetization of the dikes and those dikes with a Grenville overprint direction of 116°/56°. The deviation in direction of the two groups, in relation to previous studies (Palmer et al., 1977) is interpreted to be due to fault block movement. Aeromagnetics reveal extensive ductile and brittle deformation in the dikes as they approach the front. The general orientation of deformation is to the northeast. </p> / Thesis / Bachelor of Science (BSc)

This work describes methods for making dynamic observations of the effects of electron beam heating, in a range of applications to semiconductors. The studies were based on the use of the time resolved reflectivity (TRR) method, in which the reflectivity of the specimens surface is measured during the heating cycle. The best experimental conditions for this technique have been identified and several applications are described in detail. Studies were made of epitaxial regrowth of amorphous layers created by ion implantation into silicon. The TRR method was applied using red and infra-red wavelengths, to characterize the regrowth kinetics, paying special attention to the influence of electrically active dopants. The results demonstrate that doping has a large effect on the regrowth process, for reasons which are related to both electrical and structural factors. The use of isothermal electron beam heating for annealing silicon-on-sapphire (SOS) specimens was investigated. In these studies, the TRR technique was applied to measurement of the temperature of the specimens and to observation of epitaxial recrystallization of amorphous layers created by self-implantation. In SOS films the amorphous layers could be at the surface or buried beneath a thin single crystal layer, and these cases resulted in different regrowth behaviour. TRR methods using green and red probe wavelengths proved to be sensitive to the type of crystallization, as well as the rate at which it occurs. They should also help to identify the best conditions for improvement of the crystal quality of SOS films. TRR was also used to examine heating of silicon-on-insulator materials by swept line electron beams. Temperature distributions were evaluated by measuring the reflectivity of a small area as the electron beam passed through it and the effects of various changes in the heating conditions were explored. Studies were made of zone melting recrystallization by observing the abrupt reflectivity changes which occur when silicon melts or freezes. In future work, TRR techniques could be developed to allow detailed investigation of the recrystallization process in structures intended for seeded recrystallization.

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