Made available in DSpace on 2014-06-11T19:24:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-01-20Bitstream added on 2014-06-13T20:32:14Z : No. of bitstreams: 1 calcada_ftb_me_guara.pdf: 2051959 bytes, checksum: ca1589717e6afa4ab2801767fb3f5869 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No presente trabalho foi feita a analise quantitativa das superfícies de fratura obtidas através da propagação de trinca em fadiga. As trincas em fadiga são o modo de falha que ocorre por uma carga cíclica e repetida aplicada a um corpo de prova, o que irá causar a nucleação, propagação da trinca até a sua ruptura. Utilizou-se a ferramente da dimensão fractal para analisarmos correlações com a propagação de trincas. Os materiais que foram ensaiados são: liga de alumínio AA7475 e aço 300M, ambos materiais de uso aeronáutico. Foram realizados ensaios de propagação de trinca em fadiga em corpos de prova do tipo C(T) para a obtenção da superfície de fratura para análise. Posteriormente as superfícies foram analisadas em microscopio óptico e em microscópio eletrônico de varredura. Foi realizada a medição da dimensão monofractal (DF), quando a superfície é descrita por um único valor, também os valores de dimensão textural (DT), quando temos macroescalas e a dimensão estrutural (DS), quando temos microescalas. Com os resultados obtidos podemos analisar que o DS é quem melhor representa o comportamento das superfícies de fratura, já que este indica os micromecanismos de fratura presentes. Os valores de DS são menos dispersos na identificação das regiões de fadiga (pré-trinca, propagação estável e propagação instável da trinca),possibilitando a comparação com as imagens obtidas de cada etapa do mecanismo de fratura. Os valores de DT são melhores representados pelas reconstruções em microscópio óptico, pois estas permitem descrição mais precisa da topografia do material, considerando que o DT é característico em macroescalas. Já os valores de DS são melhores descritos em análises de microscopia eletrônica de varredura, já que esta apresenta melhor definição para a observação... / In this paper we make quantitative analysis of fracture surfaces obtained through from fatigue crack propagation. The fatigue cracks are in the mode of failure that occurs for a repetead cycling loading and applied to a specimen, which will cause the nucleation, crack propagation until rupture. We will use the tool of fractal dimension to analyze correlations with the crack propagation. The materials that were tasted are: AA7475 aluminum alloy and 300M steel, both materials for aeronautical use. Tested were performed in fatigue crack propagation inspecimens of type C(T) to obtain the fracture surface for analysis. Subsequently the surfaces were examines in optical microscope and scanning electron microscope. Was performed to measure the monofractal dimension (DF), when the surface is described by a single value, so the textural dimension values (DT), and when we involved macroescale and finally structural dimension (DS) when was presente microscale. With the results we can analyze the DS is who represents the best value for the fractal fracture surface, as this indicates the micromechanics of fracture surfaces. The DS values are less dispersed in the identification of regions of fatigue (pre-crack propagation stable and unstable crack propagation), allowing comparison with the images obtained from each step of the mechanism of fracture. The values of DT are better represented when we do analysis in an optical microscope, because it a achieves the best results of the topography of the material, whereas the DT is characteristic macroscale. The values of DS are best described in the analysis of scanning electron microscopy, since it show better the micromechanics of fracture. So we can say the the DS would be the best representative of the fractal dimension to the analysis of micromechanics of fracture surfaces to their good representation at the microscale

Fracture conductivity and the effects of treatment variables can be studied in the laboratory. We conducted experiments based on scaling down the field conditions to laboratory scale by matching Reynold’s and Peclet numbers. Experiments conducted were comprised of three stages: dynamic etching, surface characterization of etched cores, and conductivity measurement. The effect of initial condition of fracture surfaces on the etching pattern and conductivity were investigated in this study. Another area of interest is the variation of conductivity along the fracture due to acid spending. We also investigated the contact time, acid system type, and treatment temperature effects on conductivity using San Andres dolomite cores. The results from these studies showed that rough-surface fractures generate higher conductivity by an order of magnitude compared with a smooth-surface fracture at low-closure stress. Also, conductivity generated on rough-surface fractures by smoothing peaks and deepening valleys which widen the gap between the fracture surfaces after closure and acid creates conductivity on smooth-surface fractures by differential etching that creates asperities. The results suggest that an increase in acid spending does not automatically result in lower conductivity; and etched volume alone is not adequate to predicate the conductivity. Conductivity results from a combination of etching pattern, etched volume, and rock compressive strength after etching. In-situ crosslinked acid was found to be more effective in etching rock and controlling acid leakoff compared with linear-gelled acid. Also, crosslinked acid reduces the number of pits and the pit diameters. Based on conductivity tests, linear-gelled acid is more favorable at higher temperatures while in-situ crosslinked acid showed higher conductivity at lower temperatures. For a rough-surface fracture, shorter contact time created high conductivity compared to longer contact while injecting the same volume of acid, suggesting the existence of an optimum contact time.

Orientador: Luis Rogério de Oliveira Hein / Banca: Marcelo dos Santos Pereira / Banca: Miguel Justino Ribeiro Barboza / Resumo: No presente trabalho foi feita a analise quantitativa das superfícies de fratura obtidas através da propagação de trinca em fadiga. As trincas em fadiga são o modo de falha que ocorre por uma carga cíclica e repetida aplicada a um corpo de prova, o que irá causar a nucleação, propagação da trinca até a sua ruptura. Utilizou-se a ferramente da dimensão fractal para analisarmos correlações com a propagação de trincas. Os materiais que foram ensaiados são: liga de alumínio AA7475 e aço 300M, ambos materiais de uso aeronáutico. Foram realizados ensaios de propagação de trinca em fadiga em corpos de prova do tipo C(T) para a obtenção da superfície de fratura para análise. Posteriormente as superfícies foram analisadas em microscopio óptico e em microscópio eletrônico de varredura. Foi realizada a medição da dimensão monofractal (DF), quando a superfície é descrita por um único valor, também os valores de dimensão textural (DT), quando temos macroescalas e a dimensão estrutural (DS), quando temos microescalas. Com os resultados obtidos podemos analisar que o DS é quem melhor representa o comportamento das superfícies de fratura, já que este indica os micromecanismos de fratura presentes. Os valores de DS são menos dispersos na identificação das regiões de fadiga (pré-trinca, propagação estável e propagação instável da trinca),possibilitando a comparação com as imagens obtidas de cada etapa do mecanismo de fratura. Os valores de DT são melhores representados pelas reconstruções em microscópio óptico, pois estas permitem descrição mais precisa da topografia do material, considerando que o DT é característico em macroescalas. Já os valores de DS são melhores descritos em análises de microscopia eletrônica de varredura, já que esta apresenta melhor definição para a observação... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this paper we make quantitative analysis of fracture surfaces obtained through from fatigue crack propagation. The fatigue cracks are in the mode of failure that occurs for a repetead cycling loading and applied to a specimen, which will cause the nucleation, crack propagation until rupture. We will use the tool of fractal dimension to analyze correlations with the crack propagation. The materials that were tasted are: AA7475 aluminum alloy and 300M steel, both materials for aeronautical use. Tested were performed in fatigue crack propagation inspecimens of type C(T) to obtain the fracture surface for analysis. Subsequently the surfaces were examines in optical microscope and scanning electron microscope. Was performed to measure the monofractal dimension (DF), when the surface is described by a single value, so the textural dimension values (DT), and when we involved macroescale and finally structural dimension (DS) when was presente microscale. With the results we can analyze the DS is who represents the best value for the fractal fracture surface, as this indicates the micromechanics of fracture surfaces. The DS values are less dispersed in the identification of regions of fatigue (pre-crack propagation stable and unstable crack propagation), allowing comparison with the images obtained from each step of the mechanism of fracture. The values of DT are better represented when we do analysis in an optical microscope, because it a achieves the best results of the topography of the material, whereas the DT is characteristic macroscale. The values of DS are best described in the analysis of scanning electron microscopy, since it show better the micromechanics of fracture. So we can say the the DS would be the best representative of the fractal dimension to the analysis of micromechanics of fracture surfaces to their good representation at the microscale / Mestre

The design of polyethylene (PE) pipelines for applications in the gas, water and chemical process industries has been based on data mainly obtained from stress rupture testing pipes only. In practice, installations are composed of both extruded pipe and injection moulded fittings which are joined by a fusion welding technique and are very often subjected to internal pressures of a fluctuating nature. Several makes of PE pipe systems were therefore obtained and work was undertaken to fully characterise mechanical performance in terms of internal pressure loadings. Butt-welded test specimens comprising pipe lengths and fittings were subjected to both static and fluctuating conditions at 80°C, at pressures resulting in brittle fractures (below the knee on stress rupture curves) and at frequencies not exceeding 7.5 cpm (0.125 Hz). Resulting fracture surfaces were examined to identify sources of crack initiation and mechanisms of failure. Mechanical behaviour of the PE pipe samples was found to be markedly influenced by the grade of plastics compound, the pipe system dimensions, mould designs and methods of processing. Fatigue loading was the most aggressive test method and significant reductions in lifetimes were observed in fittings or joints between pipes and fittings with only modest increases in the frequency of pressurisation. It was also demonstrated that improved stress rupture behaviour did not necessarily lead to better fatigue performance. For the square-wave loading profiles used, an idea of the relevant failure mechanisms in any given system was obtained by comparing experimental Nf values with those predicted from cumulative damage principles based on Nf=τSR/τmax. In all types of system, failure was initiated at a defect residual from processing or jointing. Over 95% of all small diameter pipe fractures originated from inclusions at or close to the inside wall. They were geometrically and elementally analysed and suggestions made as to their possible origin and means of elimination. For one PE a reasonable correlation was obtained, between lifetime under stress rupture or fatigue and the inclusion size as measured in the fracture plane.

Nondestructive evaluation techniques were employed to fully characterize three 2.3L camshafts tested in an engine simulator for an equivalent of 100,000 miles. Optical microscopy, acoustic microscopy (SAM), and profilometry were used to characterize wear and fatigue, crack depth, and surface roughness, respectively. Results show cracking to occur mainly in the opening ramp of the most abusively ground cam lobes. No clear evidence was found for subsurface cracking at depths as great as 200 μm from the lobe's surface. Profilometry results show no evidence of any major tribological effect due to the sliding friction of the follower. Fractography studies show a difference between fracture surfaces among the cracks examined; straight cracks exhibit features resembling fatigue propagation, while fracture surfaces from pitted cracks show a more brittle behavior. Small grinding cracks (approximately 300 μm in length) were found in the opening ramps of the most abusively ground lobes prior to testing. Knoop and Nanoindenter microhardness indicate a near-surface rehardening for the most abusively ground lobe (confirmed by metallography), and temper burn for the remaining lobes. X-ray residual stress results made in the opening ramp of the tested lobes show evidence of residual stress relaxation. X-ray line width data as a function of depth does not correlate with residual stress. / Master of Science