No description available.

No presente trabalho, peças com gradiente funcional de Al2O3 com reforço de NbC foram planejadas com o intuito de obter um MGF (material com gradiente funcional) com uma alta dureza e boa tenacidade à fratura a partir de diferentes técnicas de sinterização. Os MGFs apresentam-se como uma excelente alternativa quando é necessária a união de materiais com propriedades térmicas ou mecânicas muito diferentes, já que possuem uma transição suave de propriedades ao longo do corpo, como consequência de uma mudança gradual do teor das fases. No planejamento dos MGFs foram utilizadas análises dilatométricas para compatibilizar o comportamento durante a sinterização de cada camada e assim minimizar as tensões que ocorrem durante a retração, responsáveis por trincas e delaminações. Nos ensaios de dilatometria observou-se que a diferença máxima de retração entre os compósitos de teor de NbC variando de 5 a 30 %p é de 4,85%, assim, foram projetados MGFs com um passo de 5% de NbC, reduzindo esta diferença para 2,73%. Compósitos monolíticos de Al2O3 com diferentes teores de NbC foram sinterizadas a 1500ºC num forno convencional sob atmosfera de grafite. As densidades das peças sinterizadas foram inferiores a 90% da densidade teórica (DT), o que comprometeu a dureza dos compósitos (10 a 14 GPa), inferiores que as durezas dos materiais originais. Uma das maiores dificuldades no processamento destes compósitos foi sua densificação, prejudicada devido à presença de partículas de alta refratariedade na matriz de alumina, pelo que foi realizado um estudo do efeito da nióbia (Nb2O5) como auxiliar de sinterização nos compósitos Al2O3-NbC. Utilizando 0,5 %mol deste aditivo foi possível melhorar as densidades dos compósitos que, segundo os resultados da microscopia eletrônica de varredura (MEV), devido a uma densificação em presença de fase líquida. No entanto, a melhora na densidade é efetiva para temperaturas inferiores a 1450°C devido provavelmente à sobrequeima. Devido às dificuldades para obter peças densas a partir desses compósitos, foi utilizado o processo de Spark Plasma Sintering (SPS), o qual foi bem sucedido para obter peças com gradiente funcional com boa densidade (> 98 %TD) e livres de trincas. O gradiente projetado foi mantido com sucesso após a sinterização e, graças à alta densidade das peças, foi possível atingir altas durezas (até 24,3 GPa) e tenacidade à fratura ~5 MPa.m1/2, fazendo com que estes materiais apresentem potencial de aplicação como ferramentas de corte. / In the present work, Al2O3/ NbC graded composites were designed in order to obtain a FGM with a high hardness and good fracture toughness from different sintering techniques. Functionally graded materials (FGM) present enormous potential on matching materials that have different mechanical and thermal properties via a gradual transition throughout the body, as a consequence of a gradual transition of the phase content. For designing of FGMs, a dilatometric analysis was used for matching the sintering behavior of each layer in order to minimize the thermal strains occurring during shrinkage and that are responsible for cracking and delamination. It was observed that the maximum difference in shrinkage between these composites is 4.85%, which could be reduced to 2.73% if a FGM with step of 5% NbC is produced. Monolithic composites of Al2O3 with different amounts of NbC were sintered at 1500°C in a conventional oven under an atmosphere of graphite, the density of the sintered pieces were less than 90 %TD, compromising the hardness of the composites (10 to 14 GPa) that were lower than the hardness of the original materials. Due to the fact that one of the greatest difficulties in processing these composites is a densification, which is impaired due to the presence of high refractory particles in the alumina matrix, a study of the effect of the niobia (Nb2O5) as a sintering aid in the composite Al2O3-NbC was conducted, with addition of 0.5 mol% was possible to improve the density of the composites, due to the liquid state sintering according to the SEM results. However, this effect is only effective until a temperature of 1450°C probably due to the overfiring. In order to obtain dense bodies from these composites, Spark plasma sintering (SPS) was used. This process was successful for producing functional graded bodies with good density (> 98% TD) and crack free. The designed gradient was successfully maintained after sintering and due to the high density of FGMs, it was possible to attain high hardness (up to 24.3 GPa) and a fracture toughness of ~ 5 MPa.m1/2, showing that these materials have a good potential application as cutting tools.

In this study the plane linear elastic problem of a functionally graded layer which contains periodic cracks is considered. The main objective of this study is to determine the thermal stress intensity factors for edge cracks. In order to find an analytic solution, Young&rsquo / s modulus and thermal conductivity are assumed to be varying exponentially across the thickness, whereas Poisson ratio and thermal diffusivity are taken as constant. First, one dimensional transient and steady state conduction problems are solved (heat flux being across the thickness) to determine the temperature distribution and the thermal stresses in a crack free layer. Then, the thermal stress distributions at the locations of the cracks are applied as crack surface tractions in the elasticity problem to find the stress intensity factors. By defining an appropriate auxiliary variable, elasticity problem is reduced to a singular integral equation, which is solved numerically. The influence of such parameters as the grading, crack length and crack period on the stress intensity factors is investigated.

No description available.

An elastic FGM layer bonded to a semi-infinite linear elastic, isotropic, homogeneous half plane is considered. The half plane contains periodic cracks perpendicular to the interface. Mechanical loading is applied through crack surface pressure, resulting in a mode I crack problem. The plane elasticity problem described above is formulated by using Fourier transforms and Fourier series. A singular integral equation is obtained for the auxiliary variable, namely derivative of the crack surface displacement. Solution is obtained, and stress intensity factors are calculated for various values of crack period, crack length, crack location, layer thickness and material gradation.

Made available in DSpace on 2016-06-02T19:11:48Z (GMT). No. of bitstreams: 1 dissABML.pdf: 4339605 bytes, checksum: b2fcb2bbac41c9e9cc7c77720f7b0b4c (MD5) Previous issue date: 2007-03-01 / Universidade Federal de Sao Carlos / The search for alternatives sources to fossil fuel has stimulated the technological development of solid oxide fuel cell. Hydrogen is the ideal fuel for this application. However, due to technical reasons, alternatives fuels to hydrogen such as methanol and natural gas has been tested. Therefore, the use of these fuels makes necessary the substitution of the anode materials that are normally used with hydrogen. The anode materials substitution must be based on the knowledge about the relationship between anode microstructure and its performance during cell operation. This knowledge makes possible introduce new materials besides new fabrication process for solid oxide fuel cell anodes. The main characteristics of anode are: high chemical activity and durability. The durability of the anode can be attained using FGM material that makes possible to match the thermal expansion of the interfaces. Ni-8YSZ cermet is normally used as anode material. In this work it was studied the cermets Ni-8YSZ as electrodes on the YSZ electrolyte. Two types of electrodes were prepared: with and without compositional gradient along the electrode thickness. This work was developed in two steps. The first one was the development of the powder 8YSZ-NiO suspension with the appropriated rheological characteristics. The second one was the electrodes characterization by impedance spectroscopy and scanning electron microscopy. It was found that electrodes containing layers with ≤30 vol% Ni are inefficient to promote the reactions because de Ni particles are not percolated. / A busca por fontes alternativas aos combustíveis fósseis para geração de energia tem estimulado a tecnologia para a fabricação de células a combustível (CaC). Gás hidrogênio é o combustível ideal para CaC porém outros combustíveis, tais como metanol e gás natural, são testados. O material de anodo utilizado, quando se emprega hidrogênio como combustível, é o compósito Ni-8YSZ. O anodo deve atender dois requisitos: alta atividade química das reações e durabilidade. O conceito de material FGM (gradação funcional) é aplicado a eletrodo com o objetivo de aumentar a durabilidade pela compatibilização da expansão térmica do eletrólito e coletor de corrente. Nesta dissertação foram estudados eletrodos compósitos Ni-8YSZ, em eletrólitos de 8YSZ, com e sem gradiente composicional ao longo da espessura. Este trabalho foi realizado em duas etapas: desenvolvimento do processamento cerâmico e caracterização elétrica dos eletrodos. A primeira etapa consistiu no desenvolvimento de suspensões da mistura 8YSZ-NiO com características adequadas ao processo de deposição por jato de suspensão e cujo filme granular resultante fosse livre de defeitos. A segunda etapa consistiu na caracterização dos eletrodos, com e sem gradação de composição, por espectroscopia de impedância e microscopia eletrônica. Eletrodos contendo camadas ≤30%vol Ni são ineficientes para promover as reações de anodo pois as partículas de níquel não estão percoladas.

Made available in DSpace on 2016-12-08T17:19:39Z (GMT). No. of bitstreams: 1 pre-textuais.pdf: 99837 bytes, checksum: 26af6e9b202afa9fa60be43b442df83a (MD5) Previous issue date: 2011-07-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The finite element method has been traditionally applied in solving problems of elasticity and heat transfer, being widely used in cases with homogeneous isotropic materials. With the advent of new technologies, it has been more frequent to use components with more than one material, aiming to get the most out of each phase. A common example is the application of coating films, with optimal properties, on a substrate. These coating films may be homogeneous or functionally graded (FGM). The latter presents a continuous variation of properties through the geometry, allowing to reduce differences at the interface with the substrate. It is important to analyze the behavior of stresses along the interface between film and substrate, a region prone for the occurrence of failure. As current commercial finite element programs have limitations to handle FGM's, especially at the interfaces, one of the motivations of this dissertation is to develop a method for stress and flux nodal recovery, adequate to work with this type of material. The work presents the analysis of a component made of steel or aluminum coated with a titanium nitride film (homogeneous or FGM) under thermo-mechanical loading. The thermal part of the problem is set in an Eulerian description, leading to heat transfer by conduction and convection in the solid. The mechanical (elasticity) part is set in the usual Lagrangean description. A staggered thermo-mechanical approach is implemented and promising results are obtained. / O método de elementos finitos tem sido tradicionalmente aplicado na solução de problemas de elasticidade e transferência de calor, sendo amplamente utilizado em casos com materiais homogêneos e isotrópicos. Com o advento de novas tecnologias tem sido mais freqüente a utilização de componentes com mais de um material, onde se procura obter o máximo proveito de cada fase. Um exemplo comum é a aplicação de filmes de revestimento com propriedades ótimas sobre um substrato. Estes filmes de revestimento podem ser homogêneos ou funcionalmente gradados (FGM), sendo que o último tem variação continua de propriedades ao longo da geometria, permitindo atenuar diferenças na interface com o substrato. A análise do comportamento das tensões ao longo da interface entre filme e substrato é de suma importância, pois esta é uma região potencial para ocorrência de falhas. Dado que programas comerciais de elementos finitos atuais apresentam limitações para lidar com FGM s, principalmente na região de interface, uma das motivações desta dissertação é desenvolver um método de pós-processamento de tensões e fluxos capaz de trabalhar adequadamente com este tipo de material. O trabalho apresenta a análise de um componente de aço ou alumínio revestido com filme de nitreto de titânio (homogêneo ou funcionalmente gradado), sob carregamento termomecânico. A parte térmica do problema é descrita usando uma abordagem Euleriana, que resulta em condução de calor por convecção e condução no sólido. A parte mecânica (elasticidade) é descrita pela tradicional abordagem Lagrangeana. Um procedimento de solução termomecânica aninhada (staggered) é implementado e resultados promissores são obtidos.

No presente trabalho, peças com gradiente funcional de Al2O3 com reforço de NbC foram planejadas com o intuito de obter um MGF (material com gradiente funcional) com uma alta dureza e boa tenacidade à fratura a partir de diferentes técnicas de sinterização. Os MGFs apresentam-se como uma excelente alternativa quando é necessária a união de materiais com propriedades térmicas ou mecânicas muito diferentes, já que possuem uma transição suave de propriedades ao longo do corpo, como consequência de uma mudança gradual do teor das fases. No planejamento dos MGFs foram utilizadas análises dilatométricas para compatibilizar o comportamento durante a sinterização de cada camada e assim minimizar as tensões que ocorrem durante a retração, responsáveis por trincas e delaminações. Nos ensaios de dilatometria observou-se que a diferença máxima de retração entre os compósitos de teor de NbC variando de 5 a 30 %p é de 4,85%, assim, foram projetados MGFs com um passo de 5% de NbC, reduzindo esta diferença para 2,73%. Compósitos monolíticos de Al2O3 com diferentes teores de NbC foram sinterizadas a 1500ºC num forno convencional sob atmosfera de grafite. As densidades das peças sinterizadas foram inferiores a 90% da densidade teórica (DT), o que comprometeu a dureza dos compósitos (10 a 14 GPa), inferiores que as durezas dos materiais originais. Uma das maiores dificuldades no processamento destes compósitos foi sua densificação, prejudicada devido à presença de partículas de alta refratariedade na matriz de alumina, pelo que foi realizado um estudo do efeito da nióbia (Nb2O5) como auxiliar de sinterização nos compósitos Al2O3-NbC. Utilizando 0,5 %mol deste aditivo foi possível melhorar as densidades dos compósitos que, segundo os resultados da microscopia eletrônica de varredura (MEV), devido a uma densificação em presença de fase líquida. No entanto, a melhora na densidade é efetiva para temperaturas inferiores a 1450°C devido provavelmente à sobrequeima. Devido às dificuldades para obter peças densas a partir desses compósitos, foi utilizado o processo de Spark Plasma Sintering (SPS), o qual foi bem sucedido para obter peças com gradiente funcional com boa densidade (> 98 %TD) e livres de trincas. O gradiente projetado foi mantido com sucesso após a sinterização e, graças à alta densidade das peças, foi possível atingir altas durezas (até 24,3 GPa) e tenacidade à fratura ~5 MPa.m1/2, fazendo com que estes materiais apresentem potencial de aplicação como ferramentas de corte. / In the present work, Al2O3/ NbC graded composites were designed in order to obtain a FGM with a high hardness and good fracture toughness from different sintering techniques. Functionally graded materials (FGM) present enormous potential on matching materials that have different mechanical and thermal properties via a gradual transition throughout the body, as a consequence of a gradual transition of the phase content. For designing of FGMs, a dilatometric analysis was used for matching the sintering behavior of each layer in order to minimize the thermal strains occurring during shrinkage and that are responsible for cracking and delamination. It was observed that the maximum difference in shrinkage between these composites is 4.85%, which could be reduced to 2.73% if a FGM with step of 5% NbC is produced. Monolithic composites of Al2O3 with different amounts of NbC were sintered at 1500°C in a conventional oven under an atmosphere of graphite, the density of the sintered pieces were less than 90 %TD, compromising the hardness of the composites (10 to 14 GPa) that were lower than the hardness of the original materials. Due to the fact that one of the greatest difficulties in processing these composites is a densification, which is impaired due to the presence of high refractory particles in the alumina matrix, a study of the effect of the niobia (Nb2O5) as a sintering aid in the composite Al2O3-NbC was conducted, with addition of 0.5 mol% was possible to improve the density of the composites, due to the liquid state sintering according to the SEM results. However, this effect is only effective until a temperature of 1450°C probably due to the overfiring. In order to obtain dense bodies from these composites, Spark plasma sintering (SPS) was used. This process was successful for producing functional graded bodies with good density (> 98% TD) and crack free. The designed gradient was successfully maintained after sintering and due to the high density of FGMs, it was possible to attain high hardness (up to 24.3 GPa) and a fracture toughness of ~ 5 MPa.m1/2, showing that these materials have a good potential application as cutting tools.

This thesis studied the representation of female circumcision by analysing 32 articles published during the 21st century in The Journal for Midwives, the union journal of the Federation of Finnish Midwives. With critical discourse analysis, through post-colonial feminist theory, the thesis researched the ways the journal is contributing to the creation of readers’ bias regarding circumcised women and their sexuality.The articles focused on multicultural healthcare, prevention of female circumcision and the most serious health detriments the practice might have. Human rights, criminal law, andgender equality were the main reasons behind the aversion of the practice. Women from the practicing communities were represented as victims of patriarchy, clueless of their position and unable to decide for themselves. Sexuality of circumcised women was widely excluded, only described through possible negative health consequences. Anthropological approach to sexuality and the role of migration was excluded and discussions about complex ethical questions, racialisation, power relations and bias of healthcare professionals were absent. Female circumcision and the practicing communities were categorised and judged based on Western understanding of sexuality and gender equality.Based on the analysis, the thesis recommends more diversity to the production of texts and to the perspectives of articles. Minorities should be included more in the production of the representation of their health issues and wider socio-cultural explanations behind the practice should be presented. Discussions about health inequalities based on ethnicity and reflections about cultural hegemony of West in relation to sexuality are also recommended subjects to be included in the journal. Most importantly, stereotypical representations of broken womanhood and positioning circumcised women as oppressed victims who need to be rescued by outsiders, should be forgotten. Instead, individual care of women and the importance of personal experiences and meanings of circumcision and sexuality should be highlighted.

Female genital mutilation (FGM) is practiced primarily in many African countries as well as some in Asia and the Arab Peninsula; however, it also takes place elsewhere around the globe among those who migrate from countries to which it is indigenous. This study was designed (a) to investigate the prevalence of FGM among the Igbo women in the Dallas-Fort Worth (DFW) area in Texas and (b) to understand the factors that support the continuation of the practice and the effects on women's sexual health. Using a quantitative approach to examine a variety of social variables aligning with the ecological framework, survey data obtained from a sample of 139 Igbo women living in the DFW area were analyzed using a multivariate analysis. Results of the study demonstrated a decreasing prevalence of FGM from maternal incidence (46%), to second generation incidence (31.3%), and future intention for FGM (25%). Nearly half of the responding participants felt the practice was required by their religion, but over 65% felt the practice should be discontinued. Results supported a high incidence of dangerous complications to women's sexual health with the continued practice of FGM. Significant social influences associated with future intention for FGM among the population were found at the micro- and exosystem ecological levels. The findings of this research provide important information on current prevalence and health effects of FGM in Igbo women living in the DFW area. Understanding the reasons behind the culture of FGM will assist public health professionals in designing appropriate culturally-specific intervention strategies that will help to eliminate inappropriate and unsafe practices associated with FGM.