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Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2014-11-10T11:55:57Z No. of bitstreams: 0 / Made available in DSpace on 2014-11-10T11:55:57Z (GMT). No. of bitstreams: 0 / Os moinhos de bolas são equipamentos presentes em plantas de mineração, sendo uma máquina importante no circuito de cominuição de minérios. Em função de inúmeros fatores como, por exemplo, projeto, fabricação, sobrecarga no equipamento, falta de manutenção e procedimentos de operação inadequados, são desenvolvidas descontinuidades nos componentes estruturais desse equipamento. Os componentes estruturais dos moinhos, basicamente, corpo, tampas e munhões, além do custo elevado, possuem prazos de fabricação que podem variar de dois a três anos dependendo da demanda do mercado. Portanto é cada vez mais necessário que as descontinuidades detectadas nesses componentes sejam corretamente avaliadas. Neste trabalho analisaram-se pela mecânica da fratura a criticalidade de descontinuidades, tais como trincas constatadas em um munhão de um moinho de bolas e compararam-se os valores teóricos de taxa de propagação (crescimento) dessas descontinuidades com valores reais obtidos por meio de inspeções periódicas realizadas neste componente. A nucleação das trincas foi causada por falta de lubrificação nos mancais do moinho, gerando esforços térmicos circunferenciais no munhão, em que a temperatura estimada do contato munhão e bucha atingiu a faixa de 100 °C a 150 °C. No período analisado, os resultados obtidos por meio da norma BS7910 mostraram-se mais próximos dos valores reais do que a norma ASME Seção XI, Apêndice A. O tamanho da trinca mais crítica foi aceito pelos critérios da norma BS7910 e aprovado apenas na condição de emergência da norma ASME Seção XI, Apêndice A. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Cancellous bone constitutes much of the volume of bone which makes up axial skeletal sites such as the vertebrae of the spine and the femoral neck. However the increased vascularity of cancellous bone compared with cortical bone means that it is more prone to drug, endocrine and metabolic related effects and therefore these skeletal sites are more prone to the bone condition osteoporosis. With the bone condition osteoporosis increasing in prevalence it is becoming far more important not only for those at risk of having the condition to be diagnosed earlier, but also for the effects of the condition to be better understood. There is a need for the better clinical management of fractures and for therapies and medical practices that will best avoid the low trauma fractures that are seen as a consequence of the condition. This study is in two separate sections, the first constitutes an investigation into the diagnostic abilities of the CUBA Clinical and Sunlight Omnisense quantitative ultrasound systems; and on the other hand an examination of the osteoporotic risk factor questionnaires, Osteoporosis Risk Assessment Instrument (ORAI), Osteoporosis Index of Risk (OSIRIS), Osteoporosis Self-assessment Tool (OST), Patient Body Weight (pBW), Simple Calculated Osteoporosis Risk Estimation (SCORE) and the Study of Osteoporotic Fractures (SOFSURF). The skeletal status was assessed by DXA at the axial skeleton. The aim was to differentiate between the systems that could rationally be used to screen populations to identify those who needed DXA densitometry investigations, on the basis of ability. The second section of the study focused on the biomechanics of cancellous bone, with the initial studies examining the compressive properties of both osteoporotic and osteoarthritic cancellous bone and the effects that the conditions have on the compressive mechanics of the bone. The later section is the first ever study into the K, G and J-integral fracture mechanics of cancellous bone. It used osteoporotic and osteoarthritic cancellous bone from the femoral head of a cohort of ultrasound scanned patients and of some equine vertebral cancellous bone. The study focused on the identification of the dominant independent material variables which affected the compressive and fracture mechanics of cancellous bone, and the differences that were seen between the two different skeletal conditions. In addition to the independent variables, quantitative ultrasound (QUS) scans were performed on the donors of the femoral heads which enabled investigation into QUS’s ability to predict either the compressive or fracture mechanics of bone in-vivo. The study demonstrated that the investigation of the calcaneus using the CUBA clinical system provided the highest level of diagnostic accuracy (AUC: 0.755 - 0.95), followed by the questionnaires, of which the OSIRIS questionnaire was the best performer (AUC: 0.74 – 0.866), and lastly the Sunlight Omnisense results. The best option for the prediction of the lowest feasible DXA T-score was a combination of the CUBA Clinical results, the individual’s weight and the OSIRIS questionnaire (r2 = 45.5%), with potential minor, but significant, support also added by the OST and SOFSURF questionnaires (r2 = 46.8%). The compressive testing demonstrated that osteoporotic and osteoarthritic bone both performed differently with respect to the apparent density, with the osteoporotic bone adhering to the previously published power function relationships, but with the osteoarthritic bone having lower power functions. The stress intensity factor for plane strain testing (KQ or KC) and the critical strain energy release rate results were both influenced primarily by the apparent density with the K values obeying a power relationship to the power of 1.5 and G a relationship to the power 2. However, both the composition and integrity of the collagen network, (demonstrated by collagen cross-link analysis), played roles in the explanation of the fracture mechanics results. The J-integral results were distinctly different to those of the K and G results with regard to their dependence on composition and it is hypothesised that this is due to the structure of the bone having more dominant effects than the apparent density. In conclusion, the fracture mechanics of cancellous bone are contributed to by a complex combination of a number of variables, but with apparent density dominating the K and G fracture mechanics to a power function of between 1 and 2. Currently available QUS systems demonstrated an ability to relate to the Young’s modulus and strength but also, in this study, to the fracture mechanics variables of the cancellous bone from the hip. This relationship is a profound outcome which may help the clinical management of the condition and the fractures when they occur. The dependence on fracture mechanic variables points to a clear causal relationship between the bone fracture parameters and bone condition as underlying factors of osteoporotic fractures.

The objective of this study is to present the mode I stress intensity factor distribution (SIF) along the crack-front for a wide array of semicircular and semi-elliptical surface cracks inside of a pressurized thick-walled cylinder. A three-dimensional finite element package ANSYS is used to evaluate the SIF for multicracked cylinder with number of cracks from n=1 to 128, the ratio of crack-depth to the wall thickness a/t=0.05 to 0.6, the ellipticity of the crack (the crack-depth to the semi-crack length) a/c=0.2 to 1.5, the ratio of the outer to the inner radius ro/ ri=2. A substructuring technique is introduced which solved a coarse model meshed with ten-node isoparametric elements and applied the resulting displacements in the boundary surface of a submodel which is built employing singular elements along the crack-front to produce the 1/√r singularity . The SIF is evaluated using nodal-displacement method. To validate the modeling and analysis procedure of the present results various configurations were solved using this method and compared to other finite element solutions. The present results were in very good agreement: less than 5 % comparing with Raju and Newman's results and within 8 % of Kirkhope's results. An empirical equation to calculate the maximum SIF, was developed in this study. The equation was obtained by nonlinear fitting of the finite element results and the error was within ± 5.7 %.

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Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

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