One of the most critical parameters in the success of a hydraulic fracturing treatment is to have sufficiently high fracture conductivity. Unbroken polymers can cause permeability impairment in the proppant pack and/or in the matrix along the fracture face. The objectives of this research project were to design and set up an experimental apparatus for dynamic fracture conductivity testing and to create a fracture conductivity test workflow standard. This entirely new dynamic fracture conductivity measurement will be used to perform extensive experiments to study fracturing fluid cleanup characteristics and investigate damage resulting from unbroken polymer gel in the proppant pack. The dynamic fracture conductivity experiment comprises two parts: pumping fracturing fluid into the cell and measuring proppant pack conductivity. I carefully designed the hydraulic fracturing laboratory to provide appropriate scaling of the field conditions experimentally. The specifications for each apparatus were carefully considered with flexibility for further studies and the capability of each apparatus was defined. I generated comprehensive experimental procedures for each experiment stage. By following the procedure, the experiment can run smoothly. Most of dry runs and experiments performed with sandstone were successful.

One of the most critical parameters in the success of a hydraulic fracturing treatment is to have sufficiently high fracture conductivity. Unbroken polymers can cause permeability impairment in the proppant pack and/or in the matrix along the fracture face. The objectives of this research project were to design and set up an experimental apparatus for dynamic fracture conductivity testing and to create a fracture conductivity test workflow standard. This entirely new dynamic fracture conductivity measurement will be used to perform extensive experiments to study fracturing fluid cleanup characteristics and investigate damage resulting from unbroken polymer gel in the proppant pack. The dynamic fracture conductivity experiment comprises two parts: pumping fracturing fluid into the cell and measuring proppant pack conductivity. I carefully designed the hydraulic fracturing laboratory to provide appropriate scaling of the field conditions experimentally. The specifications for each apparatus were carefully considered with flexibility for further studies and the capability of each apparatus was defined. I generated comprehensive experimental procedures for each experiment stage. By following the procedure, the experiment can run smoothly. Most of dry runs and experiments performed with sandstone were successful.

Distal radius fractures are the single most common type of fracture suffered among the adult population. Presently, clinical decision making regarding optimal treatment is inconclusive. The goal of this thesis was to design, develop, and biomechanically test a novel implant for the stabilization of distal radius fractures. The novel implant is intended to provide a minimally invasive, low cost alternative to locked volar plates, while still permitting an earlier return to function. The implant consists of an angled bar with a sharp cutting edge and is inserted using a minimally invasive approach through the radial styloid. Surgical instrumentation was designed to facilitate the procedure in a controlled manner. To determine whether the implant would be capable of providing an early return to function, biomechanical tests were conducted both experimentally and numerically. Biomechanical testing showed that mechanical fixation with the novel implant does not support and early return to function.

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Made available in DSpace on 2014-06-11T19:34:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-10Bitstream added on 2014-06-13T18:45:52Z : No. of bitstreams: 1 graca_mla_dr_guara.pdf: 5050152 bytes, checksum: dce8c01ce72d2ebc0e9caea4d6df5d6b (MD5) / Neste trabalho foi feita uma análise detalhada dos micromecanismos de iniciação da fratura em amostras entalhadas para cinco aços e duas ligas de alumínio. Com esse objetivo foram obtidas curvas de transição frágil-dúctil e de tenacidade à fratura em função do raio da raiz do entalhe, e realizados ensaios interrompidos antes da fratura da amostra. Análises fractográficas e micrográficas das regiões de iniciação das fraturas foram realizadas por microscopia eletrônica de varredura. A variação dos micromecanismos de iniciação em função da variação da capacidade plástica local na raiz dos entalhes, como induzida pela variação da temperatura de ensaio e pela variação do raio da raiz, foi analisada. De um modo geral, três tipos de micromecanismos de iniciação foram observados. Um frágil, em que a iniciação envolve a nucleação de uma microtrinca à frente do entalhe e sua subsequente propagação instável. Dois dúcteis, um pela ruptura por cisalhamento localizado ao longo de linhas de cisalhamento máximo formadas na raiz do entalhe, e outro pela formação de microcavidades cuja ligação entre si e a ponta do entalhe envolve um processo misto de cisalhamento localizado e de coalescência de microcavidades. Aspectos de modelos que relacionam tenacidade com a microestrutura foram discutidos com base nos micromecanismos observados. / In this study a detailed analysis of the micromechanisms of the fracture initiation in notched specimens was made, for five steels and two aluminum alloys. With that purpose brittle/ductile transition and fracture toughness x r1/2 curves were obtained, and interrupted tests before the fracture of the sample were used. Fractographic and micrographic analysis of the fracture initiation areas were accomplished by scanning electron microscopy. The variation of the initiation micromechanisms in function of the variation of the local plastic capacity in the notch root, as induced by the variation of the test temperature and by the variation of the notch root radius, was analyzed. In a general way, three types of initiation micromechanisms were observed. A brittle one, where the initiation involves the microcrack nucleation ahead of the notch and its subsequent unstable propagation. Two ductile, one by localized shear rupture along the maximum shear lines formed in the notch root, and other by microvoids nucleation whose link to each other and the notch tip involves a mixed process of localized shear and microcavoid coalescence. Aspects of relating models of fracture toughness with microstructure were discussed, based in the observed micromechanisms.

Le séchage d’une suspension colloïdale produit une couche solide plus ou moins poreuse. Ce processus intervient dans de nombreuses applications, telles que le procédé sol-gel ou la fabrication de laques et de peintures. Durant le séchage, l’évaporation du solvant entraîne la rétraction du matériau ; des contraintes importantes peuvent alors apparaître dans les couches colloïdales, les rendant susceptibles de se fracturer. Il est ainsi crucial de comprendre l’influence de paramètres de contrôle tels que la vitesse de séchage, l’épaisseur de la couche ou la taille de particule sur les propriétés mécaniques et de structure du matériau final. Dans cette thèse, nous avons utilisé des suspensions de Ludox (silice colloïdale) comme système modèle afin d’étudier l’effet de la vitesse de séchage sur les propriétés du matériau solide obtenu. Dans une première partie, nous avons mis en œuvre des mesures de porosité, ainsi que de microscopie à force atomique et de diffraction de rayons X, afin de caractériser l’effet de la vitesse de séchage sur les propriétés de structure des couches sèches. Nous avons mis en évidence l’importance de la polydispersité des suspensions initiales, ainsi que des phénomènes d’agrégation de particules, sur la structure et la compacité du matériau obtenu. Dans une deuxième partie, des mesures de constantes élastiques par propagation d’ultrasons nous ont permis de déterminer l’élasticité tensorielle (i.e. le module de compressibilité et celui de cisaillement) des couches colloïdales. Ces modules élastiques dépendent de la porosité du matériau ainsi que de la taille des particules de silice. Les données expérimentales ont été comparées aux prédictions de deux schémas d’homogénéisation (Mori-Tanaka et auto-cohérent), ainsi qu’au modèle de Kendall pour le module d’Young, qui prend en considération une énergie d’adhésion entre les particules. Enfin, nous avons déterminé la résistance à la fracture des couches colloïdales à l’aide de tests d’indentation Vickers. Cette résistance à la fracture, mesurée à la fin du séchage, est mise en relation avec la vitesse d’évaporation, la porosité du matériau, ainsi que la densité de fractures observées pendant le processus d’évaporation du solvant. / Drying a colloidal suspension results in the formation of a more or less porous solid layer. This procedure is central to many applications such as sol-gel processes, the design of paints and lacquers... As the solvent evaporation induces shrinkage of the material, large stresses can develop in these layers, making them prone to fracture. A crucial challenge is thus to understand the role of the control parameters, such as drying rate, film thickness and particle size, on the structural and mechanical properties of the final layer. In this thesis work, Ludox (colloidal silica) was used as a model system to study the effect of the drying rate on the structural and mechanical properties of the resultant solid. The effect of the drying rate on the structural properties of the dry layers was studied using porosity measurements as well as atomic force microscopy and small-angle X-ray scattering. We could evidence the importance of initial suspension dispersity and particle aggregation on the structure of the dry layers. Using ultrasound measurements, we determined the tensorial elasticity (bulk and shear moduli) of the dry layers. The elastic moduli can be related to the material porosity and the particle size. Thus, the experimental data was used to test several homogeneization schemes (Mori-Tanaka and self-consistent) as well as Kendall's model for the Young’s modulus, which considers the effect of adhesive forces between particles. Finally, hardness and fracture toughness of the materials were inferred from Vickers indentation tests. The fracture properties of the layers in their dry, final state were related to their packing fraction, the evaporation rate, and the density of the cracks formed during the desiccation process.

A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Medicine Johannesburg, 2019 / Hand infection is the most common condition seen at Chris Hani Baragwanath Academic Hospital Orthopaedic casualty. In 2017, 31% of orthopaedic admissions at our institution were patients with hand sepsis. Failure to adequately treat these infections results in severe loss of hand function and disability, and this leads to a significant socioeconomic impact in our population. The infected patients are usually started on empiric antibiotics (amoxicillinclavunate (Augmentin)) on admission, and prior to surgical drainage. The purpose of this study was to identify the microbiology profile of hand infections and their antibiotic sensitivity at our institution. The laboratory results of antimicrobial sensitivity were compared with the antibiotics started empirically. The impact of associated co-morbidities on the microbiology profile was also assessed. The results showed that Staphylococcus aureus (S. aureus) is the most common cultured organism. Most organisms were sensitive to cloxacillin. The culture results in HIV infected patients did not differ to those in the uninfected population. Acquired Methicillin-Resistant S. Aureus remains low in our population setting. / E.K. 2019