Experimental results of damage development in and mechanical response of heat-treated NicaloniCAS-II laminates subjected to monotonic flexure and axial loading and to cyclic tensile loading are reported. The specimens were subjected to post-processing heat treatments at 900°, 1000°, and l100°C in air for 100 hours. Changes at the fiber/matrix interface/interphase due to post-processing heat treatments were also characterized. The combined effect of fiber debonding and transverse matrix cracking in both 90° and 0° plies plays an important role in damage development in [0/90]₄₅ Nicalon/CAS-II laminates, especially in developing the secondary damage modes such as longitudinal matrix cracking and delamination. Frictional wear effects found in cyclically loaded specimens may be responsible for the observed temperature profiles during the intermediate stage of fatigue life. It is also believed that frictional wear is critical to the failure of notch sensitive fibers. Different damage modes such as "brittle" matrix crack propagation and "quasi-brittle" matrix crack propagation were observed in heat-treated specimens. Results obtained from microanalysis using an analytical scanning transmission electron microscope equipped with an energy dispersive spectrometer, and microindentation indicated that the changes of damage and failure modes were directly related to the changes of characteristics at the fiber/matreix interface/interphase. / Ph. D.

Al-Mg alloys were infiltrated into porous alumina preforms at temperatures greater than 950°C where significant amount of nitride forms in the matrix. The present work aims to obtain a process window for growing A1N rich composites over uniform thicknesses so that bulk fabrication of these composites could be carried out. Initial experiments were carried out in a thermo-gravimetric analyser (TGA) to establish suitable conditions for growing useful thicknesses. Al- 2wt% Mg alloy, alumina preforms of particle size 53-63μm and N2 - 2% H2 (5ppm O2) were used for the present study based on previous work carried out in the fabrication of MMCs at low temperatures. Experiments carried out in the TGA indicate that oxygen in the system has to be gettered for the growth of nitride rich composites. Infiltration heights of about 8mm were obtained using an external getter (Al - 5wt%Mg) alloy in addition to the base alloy used for infiltration. The above process conditions were subsequently employed in a tube furnace to fabricate bulk composites and to study the effect of temperature on the volume fraction of aluminium nitride in the matrix. The volume fraction of nitride in the composite varied between 30 and 95 vol % with increase in process temperature from 950°C to 1075°C. Microstructures of these composites indicate that A1N starts to form on the particle surface and tends to grow outwards. The metal supplied through channels adjacent to the particle surface nitride until a point is reached when the composite growing from the adjacent particles meet each other and isolate the melt underneath from nitrogen thereby leading to a metal rich region underneath. Increase in temperature results in an increased nitridation rate resulting in reduced metal pocket size. Composites fabricated at 975°C had a minor leak at the O-rings, which seal the tube. This led to infiltration under conditions of varying oxygen partial pressure leading to different nitride fractions in the composite. The above fact was confirmed by conducting an experiment with commercial purity nitrogen, which has an oxygen content of about 5000ppm. The composite had an A1N content of about 30% whereas the composite fabricated with N2 -2%H2 (5ppm oxygen) showed a nitride content of 64%. This suggests that one can vary the nitride content in the composite by varying the oxygen content in the system at a particular process temperature. The hardness of the matrix increases with increase in process temperature from 3.5 ± 0.7 GPa at 975°C to about 9.8 ± 0.9 GPa at 1075°C. Porosity was observed in the composite processed at 1075°C. This increased porosity leads to decreased hardness though the nitride content in the composite has increased by 11%. The scatter in the data is attributed to variations in the microstructure as well as due to interference from underlying metal pockets or particles as well as due to porosity introduced in the composite at high processing temperatures.

No description available.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-08-04T12:41:31Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação de Mestrado - Natasha Lopes Gomes.pdf: 9410241 bytes, checksum: 569cb64525645737ca47e38f379de72c (MD5) / Made available in DSpace on 2016-08-04T12:41:31Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação de Mestrado - Natasha Lopes Gomes.pdf: 9410241 bytes, checksum: 569cb64525645737ca47e38f379de72c (MD5) Previous issue date: 2016-02-26 / FACEPE / A indústria aeroespacial é um setor que contribui significativamente para o desenvolvimento econômico e social de alguns países. A confiabilidade e a disponibilidade de seus equipamentos são uma preocupação constante, uma vez que estes operam a temperaturas elevadas. Dentre os equipamentos que mais falham prematuramente devido à temperatura, destacam-se os bocais de exaustão das turbinas a gás, compostos por um conjunto de ligas à base de níquel ou à base de cobalto. No entanto, os fabricantes de turbinas tem demonstrado um maior interesse no uso de compósitos cerâmicos para revestimento nas seções quentes, devido sua maior capacidade de suportar altas temperaturas e exigência de menor refrigeração do ar. Mas a fragilidade intrínseca das cerâmicas é ainda um fator limitante para o uso destes materiais em estruturas mecânicas e aplicações industriais. Para reduzir fragilidade e aumentar resistência mecânica e tenacidade, normalmente as cerâmicas são reforçadas com incorporação de aditivos. Estudos vêm sendo realizados acerca da utilização da zircônia incorporada com outros óxidos, pois em comparação com outros cerâmicos, a zircônia tem propriedades mecânicas superiores, tais como alta resistência mecânica, estabilidade química e boa tenacidade à fratura. Neste trabalho foram produzidos compósitos cerâmicos zircônia-titânia (ZrO2-TiO2) reforçados com um óxido de terra rara, lantânio (La2O3), variando o teor de TiO2 em 5%, 10%, 15% e 20% e o teor de La2O3 em 5%, 7% e 10%. Os compósitos foram produzidos por processo termomecânico e sinterizados à 1385°C. Posteriormente, foram caracterizados quanto à estrutura, microestrutura e propriedades mecânicas através de difração de raios X, densidade relativa, microscopia óptica, microscopia eletrônica de varredura, espectroscopia de energia dispersiva e microdureza Vickers. A microestrutura do material sinterizado revelou uma boa homogeneidade em distribuição e tamanho de partículas, e a microdureza Vickers mostrou que o compósito com 15% de TiO2 e 10% de La2O3 obteve um melhor resultado, indicando que este possui boas propriedades físicas que apontam para uma possível aplicabilidade. No entanto, é necessário avaliar outras propriedades mecânicas a fim de garantir sua utilização como revestimento cerâmico de exaustores de turbinas a gás aeroespaciais. / The aerospace industry is a sector that contributes significantly to the economic and social development of some countries. The reliability and availability of your equipment is a constant concern, since they operate at high temperatures. Among the equipment more fail prematurely due to temperature, we highlight the exhaust nozzles of gas turbines, comprising a set of nickel based alloys or cobalt-based. However, turbine manufacturers have shown an increased interest in the use of ceramic composite coating on hot sections due to their greater ability to withstand high temperatures and requiring less cooling air. But the intrinsic brittleness of ceramics is still a limiting factor for the use of these materials in mechanical and industrial applications structures. To reduce brittleness and increase strength and toughness, typically ceramics are reinforced by incorporation of additives. Studies have been conducted on the use of zirconia incorporated with other oxides, as compared to other ceramic, zirconia has superior mechanical properties such as high mechanical strength, chemical stability and good fracture toughness. In this work we were produced composite ceramic zirconia-titania (ZrO2-TiO2) reinforced with a rare earth oxide, lanthanum (La2O3), varying the TiO2 content of 5%, 10%, 15% and 20%, and the La2O3 content 5%, 7% and 10%. The composites were produced by thermomechanical process and sintered at 1385 ° C. Later, they were characterized as to structure, microstructure and mechanical properties through X-ray diffraction, relative density, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and microhardness. The microstructure of the sintered material showed a good homogeneous distribution and particle size, and Vickers microhardness showed that the composite with 15% TiO2 and 10% La2O3 obtained best results, indicating that it has good physical properties which indicate a possible applicability. However, it is necessary to assess other mechanical properties to ensure their use as ceramic coating aerospace gas turbine exhaust.

Orientador: Cecília Amélia de Carvalho Zavaglia / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-18T16:53:54Z (GMT). No. of bitstreams: 1 Galdino_AndreGustavodeSousa_D.pdf: 8544982 bytes, checksum: 9bbd7c8f53578d5a0a79aeec90ea4222 (MD5) Previous issue date: 2011 / Resumo: À medida que há uma melhoria na tecnologia aplicada à saúde humana, a expectativa de vida vem aumentando, mas nem todas as partes do corpo podem manter suas funções com o processo de envelhecimento. É preciso que os ossos e a cartilagem apóiem o envelhecimento do corpo, embora as células que os produzem se tornem menos ativas com o tempo. Outros órgãos, tais como os rins, o coração e o fígado devem ser operados para ter um tempo de vida maior. A engenharia tecidual foi desenvolvida para substituir, reparar ou reconstruir tecidos ou órgãos perdidos ou danificados por acidentes ou doenças graves através da utilização e desenvolvimento de novos materiais, que sejam biocompatíveis, bioabsorvíveis, porosos, entre outras características. Os scaffolds são arcabouços tridimensionais porosos e são utilizados na regeneração de tecidos para seu estado natural e suas funções, que é fundamental para a engenharia tecidual. Eles podem ser classificados em arcabouços que induzem a migração e o crescimento celular e em arcabouços carreadores de células osteogênicas autógenas, que foram colonizadas em biorreatores e subsequentemente reimplantadas no paciente. Tais scaffolds podem ser naturais ou sintéticos. O objetivo deste trabalho é avaliar o compósito poroso de hidroxiapatita - titânia (HATiO2), em três composições diferentes (50% HA - 50% TiO2, 60% HA - 40% TiO2, 70% HA - 30% TiO2) para obter scaffolds utilizados para engenharia tecidual óssea. Os corpos de prova foram produzidos pelo método da esponja polimérica, utilizando bicarbonato de sódio como ligante e floculante. A sinterização foi realizada em três temperaturas: a 1250ºC; 1300ºC e 1350ºC. As propriedades analisadas foram: resistência à compressão e dureza através das normas da ASTM, porosidade aparente, densidade aparente, retração linear de queima e absorção de água, pelo método de Souza Santos para argilas. Os resultados obtidos mostraram-se bastante satisfatórios, onde foi mostrado que os corpos cerâmicos porosos obtiveram valores de resistência à compressão e dureza coerentes com os da literatura e superiores aos da hidroxiapatita pura. Realizou-se também uma caracterização estrutural das amostras via difração de raios - x (DRX), microscopia eletrônica de varredura (MEV) e espectroscopia por infravermelho com transformada de Fourier (FT-IR). Com base nos resultados mecânicos e de caracterização estrutural, foi escolhida a amostra com composição de 50% HA - 50% TiO2 sinterizada a 1350ºC para realização de ensaios in vitro, onde foram avaliadas citotoxicidade e crescimento celular de osteoblastos e fibroblastos de camundongos. Os resultados indicaram que o compósito é biocompatível e que as células cresceram nos scaffolds. De forma geral, pode-se concluir que todas as amostras são indicadas para a utilização como matéria prima para aplicação em engenharia tecidual óssea. A amostra com 50% HA - 50% TiO2 apresentou melhores características para a realização dos ensaios in vitro realizados neste trabalho e pode-se indicar esta para a realização de ensaios in vivo, onde devem ser avaliadas as características de citotoxicidade e crescimento de células ósseas em animais, por um período de 15 e 30 dias, conforme normas da área de saúde / Abstract: As we witness an improvement in the technology applied to human health, life expectancy increases, even though not every part of the body can maintain their functions with the aging process. It is necessary that bones and cartilage support the body's aging, even if the cells that produce them become less active with time. Other organs, such as kidneys, heart and liver must be operated to have a higher lifetime. Tissue engineering has been developed in order to replace, repair or rebuild tissues or organs lost or damaged due to accidents or serious diseases through the use and development of new materials that are biocompatible, bioabsorbable, with porosity among other characteristics. Scaffolds are a kind of porous tridimensional net and they are used on tissues regeneration to their natural state and functions, which is fundamental for tissue engineering. They can be classified as scaffolds that induce migration and cell growth and as carrier scaffolds for autogenous ostheogenic cells, which were colonized inside bioreactors and then redeployed on the patient. Those scaffolds can be natural or synthetic. This research aimed to evaluate hydroxyapatite-titanium oxide (HA-TiO2) with three different compositions (50% HA - 50% TiO2, 60% HA - 40% TiO2, 70% HA - 30% TiO2) to obtain scaffolds used for bone tissue engineering. Samples were made by the polymeric sponge method, using sodium bicarbonate as a binder and flocculating agent. Sintering was carried out at 1250ºC; 1300ºC e 1350ºC. It was analyzed compressive strength and Vickers hardness using ASTM Standards, apparent porosity, apparent density, burning linear retraction and water absorption by Souza Santos method used for clays. Results proved satisfactory showing that ceramic bodies obtained compressive strength and Vickers hardness according to literature and higher than those for pure hydroxyapatite. Samples structural characterization was done by x-ray diffraction (XRD), scanning electronic microscopy (SEM) and Fourier transformed infrared (FT-IR). It was chosen 50% HA - 50% TiO2 sintered at 1350ºC based on its mechanical properties and structural characterization and in vitro essays were done to evaluate citotoxicity and mouse osteoblasts and fibroblasts cell growth. Results have shown that the composite is biocompatible and the cell growth above scaffolds surface. In general, samples can be recommended for use as raw material for bone tissue engineering application. The sample with 50% HA - 50% TiO2 showed better characteristics for in vitro essays done and it can be recommended for in vivo essays where citotoxicity and bone cell growth in animals during 15 and 30 days, according to health standards / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

The role of an interfacial barrier at the fiber-matrix interface in the heat conduction behavior of an uniaxial silicon carbide fiber-reinforced reaction-bonded silicon nitride and the effect of fiber orientation on the heat conduction characteristics of carbon fiber-reinforced borosilicate glass was investigated. In the study of the effect of an interfacial thermal barrier, a composite with fibers having a carbon-rich coating of about 3 J.l m was chosen as the reference material. The fiber-matrix interface was then modified by preferential oxidation of the carbon coating on the fibers, using fibers with no carbon coating and using hotisostatic-pressing (HIP) after nitridation. The formation of an interfacial gap at the interface due to thermal expansion mismatch between the fiber and the matrix in reference and HIP'd composites, and removal of carbon coating for oxidized composites, resulted in the dependence of thermal diffusivity/conductivity on the surrounding . atmosphere. This effect was attributed to gaseous heat transfer at the interface. However, no atmospheric effects were observed for composites with fibers without the carbon coating due to very strong bonding between the fiber and the matrix. HIP'ing increased the thermal diffusivity/conductivity of the composites due to densification of the matrix, crystallization of the fibers and increased physical contact at the interface. Removal of the interfacial carbon layer by preferential oxidation lowered the interfacial conductance considerably, due to decrease in the direct thermal contact between the fibers and the matrix. Interfacial contact conductance determined from measurements made in vacuum for reference and HIP'd composites increased rapidly with increasing temperature in accordance with interfacial gap closure. These observations indicate that the heat conduction behavior of all the composites investigated was strongly affected by the existence of an interfacial thermal barrier, for heat transfer transverse to the fiber direction. / Ph. D.

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To achieve satisfactory levels of strength, fracture toughness, and reliability for man-rated systems such as jet engines, fiber reinforced ceramic matrix composites are needed. An elevated temperature axial testing system is developed to investigate and characterize fatigue behavior of Nicalon fiber reinforced enhanced silicon carbide matrix. composites at 1800 of under fully reversed cyclic loading. Notch effect on quasi-static tensile response is also considered. Quasi-static and fatigue damage mechanisms and failure modes are examined using various specimen geometries, load levels, fatigue ratios, and laminates stacking sequences by employing a number of NDE techniques. Issues such as damage tolerance and durability are addressed by conducting interrupted fatigue tests at various stages of life for different load levels. Results are compared to the predictions of remaining strength and life, obtained using a performance simulation code. Initial results indicate existence of a threshold stress value which limits the use of the material system. / Ph. D.