Thesis: B.S., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 1975 / Includes bibliographical references. / B.S. / B.S. Massachusetts Institute of Technology, Department of Materials Science and Engineering

The development and example applications of a new EBSD-based texture analysis system are presented. This new system uses the cross-correlation function to compare two EBSD patterns at a number of corresponding regions in each pattern to calculate the deformation gradient tensor. Bragg's Law-based simulated EBSD patterns are used as reference patterns in the cross-correlation method to enable the measurements of absolute elastic strain and lattice orientation at discrete points in a crystalline sample. The resolution limits of this new method are explored using a variety of computational and physical experiments. The simulated pattern method is estimated to be able to measure lattice orientations to within +/-0.02° and elastic strains to within +/-3.6x10-4 for small strains and +/-1x10-3 for large strains. Two example applications are demonstrated. The first demonstration is estimating the dislocation density in a 5.5% compressed Mg-based AZ91 alloy. Nye's and Kröner's formulations are used to estimate the dislocation density. Comparisons are made with traditional OIM measurements and it is found that the simulated pattern method offers an order of magnitude improvement in dislocation density estimations over OIM. The second demonstration is tetragonality measurements of HSLA 65 steel along the weld line of a friction stir welded plate. Accurate tetragonality measurements in the bainite phase of the steel can be made using information from the diagonal components of the elastic strain tensor. The measured tetragonality can be related to the concentration of interstitial carbon atoms in the iron lattice to find the carbon distribution in the sample. From these experiments, it is demonstrated that the simulated pattern method presents a new and powerful methodology for texture analysis that exhibits both ease of use and access to high resolution orientation and elastic strain data.

Purpose: The aim of this study was to compare the management approach of acute knee dislocations (AKDs) by orthopaedic surgeons from nations with different economic status. Methods: A survey sent to members of the Societe Internationale de Chirurgie Orthopedique et de Traumatologie (SICOT) compared different management strategies for acute multiligament knee injuries (aMLKIs). These were compared after categorising surgeons into developed economic nations (DEN) and emerging markets and developing nations (EMDN) based on the gross domestic product (GDP) per capita. Results: 138 orthopaedic surgeons from 47 countries participated in this study. DEN surgeons had more years of experience and were older (p <0.05). Surgeons from EMDN preferred conservative management and delayed reconstruction with autograft (p<0.05) if surgery was necessary. Surgeons from DEN favoured early, single stage arthroscopic ligament reconstruction. Significantly more EMDN surgeons preferred clinical examination (p<0.05) and duplex doppler scanning (p<0.05) compared to DEN surgeons. More surgeons from EMDN did not have access to a physiotherapist for their patients. Conclusions: Treatment of aMLKIs varied significantly based on the economic status of the country. In EMDN, aMLKIs are often treated conservatively, ligament surgery is often delayed and staged, alternative vascular assessment methods are more commonly used, and access to physiotherapy is challenging. This calls for adjusted guidelines when treating patients in areas of low resource setting.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 46-50. / by Raymond Joseph Harpin. / M.S.

Effects of dislocation emission from a mode I crack and of pinning distances on the behavior of the crack and on fracture toughness in aluminum were studied by using the Molecular Statics Technique with atomic interactions described in terms of the Embedded Atom Method. It was found that aluminum is a ductile material in which the cracks generate dislocations, blunting the cracks. The blunting and the dislocation shielding reduce the local stress intensity factor. Also, twinning, which has not been observed experimentally in Aluminum due to the high stacking fault, was obtained in the simulation. Probably, the low temperature facilitates twin formation. The applied stress intensity factor required to propagate the crack tip increases at first, and then becomes constant as the maximum distance that the first dislocation can travel away from the crack tip increases. These effects can be attributed to dislocation shielding and crack blunting. The maximum distance of the emitted dislocations from the crack tip is the equilibrium distance for the largest simulation performed (400,000 atoms) while for the smaller simulations the dislocations are hindered by the fixed boundary condition of the model. On the other hand, the total local stress intensity factor at the crack tip and the local stress intensity factor along the slip plane remain basically constant as the maximum distance of the emitted dislocations from the crack tip increases. For distances larger than , these local stress intensity factors start to increase slightly. / Master of Science

L’amélioration de la figure de mérite ZT des matériaux thermoélectriques (TE) est actuellement entreprise via des procédés de métallurgie, tels que la nanostructuration et l’introduction contrôlée de dislocations. De tels niveaux de complexité de microstructure soulèvent la problématique du comportement mécanique associé. En effet, malgré les valeurs de dureté et module d’élasticité connues pour la plupart des matériaux TE, rares sont les données sur les mécanismes de déformation. Portant sur le Half-Heusler Hf0.44Zr0.44Ti0.12CoSb0.8Sn0.2 de type p, notre étude multi-échelle propose de caractériser les mécanismes de déformation de cet alliage. Les expérimentations menées aux échelles macroscopique, mésoscopique, et microscopique sont pensées pour déclencher puis examiner les mécanismes de plasticité. Les tests en compression sur échantillons massifs dans un environnement de pression de confinement et température ont aboutis à une rupture exclusivement fragile. Les mécanismes de rupture sont identifiés comme associés une propagation de fissure intra- et inter granulaire, dépendant de la taille de grain rencontrée par le front de fissure. La méthode « indentation toughness » à l’échelle mésoscopique permet l’insertion de fissures, où les analyses MET en front de fissure confirment une abscence d’activité de dislocations, également confirmé par 3D-EBSD. À l’échelle microscopique, les données de compression de micro-pilliers ainsi que les observations de faciès de fracture sont comparable avec les échantillons massifs. Ces résultats peuvent être utilisés comme guide pour produire des matériaux TE plus résistants à la fissuration. / Increasing the figure of merit ZT of thermoelectric (TE) alloys is a challenge that is currently attempted through various metallurgy methods, including nanostructuring and dislocation engineering. Microstructures with such level of complexity raises questions about the mechanical reliability of these new materials. Indeed, despite the values of hardness and elastic modulus known for the clear majority of TE materials, the data on deformation mechanisms are still rare. Focusing on the nanostructured p-type half-Heusler Hf0.44Zr0.44Ti0.12CoSb0.8Sn0.2, our multi-scale study aims to analyze the deformation mechanisms. Experiments conducted at macro-, meso- and micro-scale are designed to trigger and assess plasticity mechanisms. Compression testing on bulk samples subject to a confining pressure environment and temperature leads to an exclusive brittle failure. The mixed-mode failure mechanisms involve switching between intra- and inter-granular crack propagation, depending on the grain size met by the crack tip. Indentation toughness at meso-scale generates cracks, while TEM analysis of the crack tip area confirms no dislocation activity and 3D-EBSD technique confirms the mixed crack propagation behavior. At micro-scale, micro-pillar compression stress-strain curves and failure mechanisms are comparable with bulk samples testing analysis. These results can be used to provide design guidelines for more crack-resistant TE alloys.

La déformation visco-plastique de la glace est fortement anisotrope, le plan de glissement préferé étant la plan de base. Le fait que dans un polycristal chaque grain possède sa propre direction de déformation produit des incompatibilités et un champ de contrainte complexe. La déformation à été étudiée expérimentellement en mésurant la dis- tortion des plans cristallins de mono- et polycristaux de glace artificielle. Les expériences ont été réalisées à l'aide d'un faisceau synchrotron. Une nouvelle procédure éxperimental, basée sur les méthodes de l'imagerie en diffraction de Bragg, comme lumière blanche, im- agerie sur la courbe de diffraction et topographie laminaire et ponctuelle, a été dévéloppée. Les désorientations angulaires, les largeurs à mi-hauteur et les intensités intégrées ont été mésurées dans les trois dimensions spatiales de l'échantillon et avec une résolution de 50× 50 × 50µm3. Les algorithmes d'analyse de données ont été écrits pour extraire des données des résultats quantitatifs, et pour calculer les neuf composantes du tenseur de courbure ainsi que la distortion entière des plans cristallins. Les résultats ont permis d'observer les premières étappes de la déformation de la glace. Par example la polygonisation d'un grain à été observée.