This thesis discusses the effect of cryogenic temperatures on composite materials. The work includes estimating the shear strength of carbon/epoxy and glass/polyester composites at low temperatures and finding the rate of generation of microcracks in composites at cryogenic temperatures by acoustic emission technique. Microcracks increase the permeability of composites. So to study the permeability growth with microcracks, equipment is also designed to measure the permeability of composite to low temperature fluids. With short beam shear testing it was observed that the shear strength of composites increases with decreasing temperatures. Also carbon/epoxy composites were found to be much stronger than glass/polyester composites. Cryogenic temperatures improve the strength of composites but also generate microcracks in the structure due to the thermal expansion mismatch between the matrix and fiber. With acoustic emission testing from room to –150ºC, it was found that the rate of generation of microcracks increases with reducing temperatures. The work is extended to design a permeability equipment.

<p> The effects of small additions of Fe2O3, GeO2, Ta2O5, V2O5, TiO2, and SiO2 on the microstructure and fracture toughness of magnesia enriched doloma were investigated. Effects of up to 5% additive oxides on grain growth and sintering in MgO and CaO were determined in preliminary tests. One percent additions were made to 40%, 60% and 80% MgO dolomas and the fracture toughness at temperatures up to 1500°C determined using the single edge notched beam specimen. Fracture surfaces were studied on the scanning electron microscope to determine fracture mode. Silica and Ta2O5 doped material showed high toughness at 1500°C possibly due to microcracks, while TiO2 resulted in formation of a viscous grain boundary film producing high toughness at 1300°C followed by a rapid decline by 1500°C. In undoped samples increases in MgO resulted in the appearance of a toughness peak near 1300°C. This was attributed to grain boundary segregation of impurities.</p> / Thesis / Master of Engineering (MEngr)

The failure of brittle rocks around deep underground excavations due to the high induced stress is controlled by the crack accumulation in the rock. The study shows that the damage initiation strength, CI, corresponds to the long-term strength, and the short-term strength of the brittle rocks in-situ is the crack interaction strength, CD. Therefore the damage thresholds that are being used for the calibration and validation of numerical models are important parameters in the design of underground structures. The accurate detection of the damage thresholds is important as they define the in-situ behaviour of the brittle rocks. The two most common methods of detecting damage thresholds are the Acoustic Emission method and the strain measurement method. Apparent discrepancy that exists between the accuracy of these methods was the author’s motivation for comparing these two methods on Stanstead and Smaland granites. The author introduced two new parameters based on the measured strains for improving the strain measurement method. Based on the comparisons, the author is of the opinion that the Acoustic Emission method is a more accurate method of detecting damage thresholds. Numerical models are an important tool in the design of underground structures. The numerical methods that are able to simulate fractures explicitly have the ability to predict the brittle failure, the density and the extension of the microcracks around the opening. Itasca’s Particle Flow Code (PFC) was used in this study due to its potential to simulate fractures explicitly. Calibration of PFC models to Unconfined Compressive Strength properties of the rock does not mean that the model will behave correctly under other confining stresses or in tension. The author has tried to solve this problem by different methods and developing new procedures. Improvements in the model behaviour have been achieved but more work is required. The definition, and detection and calibrated simulation of rock damage thresholds for calibration of numerical models is helpful for a successful design of underground excavations and long term, lower bound strength, a critical design parameter for deep geological repositories for the storage of nuclear wastes, for example. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2010-09-23 13:59:28.795

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Osteoporosis is a significant healthcare issue due to the increasing elderly population. Bisphosphonates are used to treat osteoporosis by reducing the rate of resorption, increasing bone mineral density (BMD) and thereby reducing fracture risk. Long-term bisphosphonate treatment, however, has been associated with low-energy fractures. Bone microdamage may provide a partial explanation for one of the mechanisms responsible for these fractures since it has been shown to reduce bone toughness, fracture resistance, and bone strength. The goal of this study was to quantify the changes in bone microdamage parameters with the duration of bisphosphonate treatment. This study selected, stained, and histomorphometrically analyzed 40 iliac crest bone biopsies from controls and female patients with osteoporosis treated with bisphosphonates for varying durations (up to 12 years). All subjects were matched for age and low turnover. The results showed that microcrack density and microcrack surface density were significantly greater in patients who took bisphosphonates for at least 5 years compared to those who took bisphosphonates for less than 5 years or not at all. These results reveal novel, clinically relevant information linking microdamage accumulation to long-term bisphosphonate treatment without influences from age or turnover.

Wellbore seismic measurements were recorded in the Lake Bosumtwi impact structure, Ghana, in 2004. A full range of petrophysical measurements were also performed in the laboratory on core samples from the same boreholes. The Vertical Seismic Profile shows low velocities for both P and S waves in the hardrock basement of the crater. Although we were expected to locate fractures within the rock, no upgoing waves were detected. Density and porosity measurements on the core samples indicate higher than normal porosity in the impact damaged rocks. Mercury porosimetry and SEM analysis characterized the pores as impact induced microcracks. These microcracks are most likely the reason for the low velocities observed on the seismic profiles, the in situ sonic logs, and the seismic velocity measurements on the core samples. Furthermore our laboratory P and S velocities measurements indicate a strong heterogeneity within the impactites. / Geophysics

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Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-08-29T22:59:56Z No. of bitstreams: 1 DANIEL HENRIQUE SILVA DE SOUZA – TESE (PPGEPM) 2018.pdf: 6159458 bytes, checksum: 8e4c70574dd865ffa673125938b4f268 (MD5) / Made available in DSpace on 2018-08-29T22:59:56Z (GMT). No. of bitstreams: 1 DANIEL HENRIQUE SILVA DE SOUZA – TESE (PPGEPM) 2018.pdf: 6159458 bytes, checksum: 8e4c70574dd865ffa673125938b4f268 (MD5) Previous issue date: 2018-03-16 / Capes / Bandas de deformação são estruturas geradas por deformação localizada e possuem a capacidade de alterar a porosidade e permeabilidade das rochas sedimentares. As bandas de deformação podem ocorrer na forma individual (singles) ou como nucleação de bandas (clusters). A gênese das bandas de deformação pode estar associada à formação, crescimento e coalescência de estruturas denominadas de “microcracks”. Estas estruturas são geradas e crescem aproximadamente paralelas ao eixo de máxima compressão (σ1). O objetivo principal deste trabalho foi gerar um modelo evolutivo das estruturas rúpteis do “Afloramento 1”, que está relacionado aos arenitos conglomeráticos da Formação Antenor Navarro, baseado no desenvolvimento e coalescência dos microcracks e predizer os locais de nucleação de bandas. A metodologia consiste na análise, mapeamento e coleta de dados de planos e linhas das estruturas rúpteis do afloramento em questão, e no cálculo dos paleotensores que atuaram na sua gênese. Este cálculo foi executado com o auxílio do programa TectonicsFP, que se utiliza dos dados de planos e linhas para fornecer os paleotensores relacionados à formação de tais estruturas. A análise estrutural em afloramento resultou na identificação de dois sistemas de estruturas rúpteis, um E-W e outro NE-SW. Estes sistemas possuem padrões de linkagem entre si, e permitiu inferir que um único conjunto de paleotensores atuou na gênese de ambos. A configuração geométrica do afloramento, juntamente com os padrões de linkagem entre os sistemas de bandas de deformação, se assemelha ao processo de linkagem de microcracks. Pesquisas anteriores, sobre a formação de estruturas pela interação entre microcracks, foram baseadas em análises laboratoriais e microscópicas. Contudo, estudos do seu desenvolvimento em maiores escalas permanecem ausentes. A gênese dos microcracks se daria de forma paralela ao eixo de compressão máxima (σ1), e estaria relacionada à ação do “fator de intensidade de stress” (SIF) tipo I (distensivo), enquanto que a linkagem entre elas se daria pelo fator de intensidade de stress tipo II (cisalhante). Este SIF tipo II formaria uma estrutura denominada de “microcrack de linkagem” que uniria as estruturas coalescentes, no qual uma nucleação maior de bandas de deformação ocorreria no entorno do análogo do microcrack de linkagem na escala de afloramento. Por fim, a configuração geométrica atual do afloramento seria resultante do desenvolvimento fractal da gênese, crescimento e coalescência dos microcracks. / Deformation bands are structures formed by localized deformation and exhibit the capacity of the porosity and permeability changes in sedimentary rocks. Therefore, it has the capacity to change the flow properties on reservoir rocks. Deformation bands may occur in the individual form (singles) and as bands nucleation (clusters). The genesis of deformation bands can be associated to formation, growth and coalescence of structures named “microcracks”. These strutures are formed and grow approximately to the maximum compression axis (σ1). The main objective of this work is create an evolutive model for the brittle structures of “Outcrop 1”, which is related to the Antenor Navarro Fomration, based in the development and coalescence of microcracks and predict the nucleation location of occurrence. The methodology consists in the analysis, mapping and data collect of planes and lines of the aimed outcrop, and compution of paleotensors that acted in its genesis. This compution was made by the utilization of the software TectonicsFP which uses the data of planes and lines to provide the paleotensors related to formation of these structures. The structural analysis in outcrop resulted in the identification of two brittle structures system, one E-W and another NE-SW. These systems own linkage patterns with each other, allowing to infer that only a set of paleotensors acted in the genesis of both of them. The geometric set of the outcrop, along with de linkage patterns between the deformation bands systems, is similar to the process of microcrack linkage. Preview researchs, about formation of structures by the interaction of microcracks, were based in laboratory and microscopy analysis. However, studies about their development in larger scales remains absents. The microcracks genesis would happen parallelly to the maximum compressive axis (σ1), and would be related to the action of “stress intensity factor” (SIF) mode I (tensile), while the linkage of microcracks would be caused by the stress intensity factor mode II (shearing). The SIF mode II would create a structure denominated “linkage microcrack”, which would bond the coalescente structures, which a larger nucleation of deformation bands would occur in the analogous surroundings of linkage microcrack in the outcrop scale. Ultimately, the current geometric configuration of the outcrop would be a fractal resultant of development of genesis, growth and coalescence of microcracks.