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Shaping materials containing porous constituents is a critical issue. This work analyses the process of abrasive water-jet (AWJ) cutting applied to low density metal matrix composites (LD.MMCs) consisting of AA7075 alloy as matrix and porous, foamed particles of SiO2/Al2O3/Fe2O3or vermicular SiO2/Al2O3/MgO, as reinforcements. Results show that although presenting lower density (from 1.09 g/cm3to 1.59 g/cm3, depending on the particle type) and lower strength than the non-reinforced AA7075 alloy, the composites present some difficulties in AWJ cutting. Deflection of the jet was noticed, being more evident on vermiculite-reinforced samples. Anyhow machinability numbers for the composites analyzed are in the order of 20% higher than the AA7075 matrix alone. Jet deflection, surface quality and machinability number showed to be dependent on the internal structure of the porous ceramic particles: vermiculite can pull out under the jet while cinasite is more susceptible to suffer fracture. This mechanisms result in lower jet deflection, better surface and better overall machinability in the case of AA7075 / cinasite LD.MMC.

The work presents an innovative approach to produce metal matrix composites by using thixoforming techniques. The proposed procedure is based on the infiltration of thixotropic semisolid metal into an assembly of loose particles of reinforcing material. Experiments were performed using Al alloys as base metal and SiC and porous ceramic particles (expanded clay known as cinasite) as reinforcement. Process parameters are investigated to observe their influence in the quality of products. Results demonstrate that the process is flexible for the manufacturing of different distributions of reinforcing agents, such as homogeneous or layered composites. Moreover, it is also shown that metallic chips can be used as raw material, meaning an important possibility for materials recycling. It can be concluded that Thixoinfiltration is a simple and low cost technique to produce different types of MMCs, with advantages upon techniques involving metal powders, which usually require long milling and sintering periods. Thixoinfiltration can be also advantageous upon techniques involving liquid processing, once lower temperatures are involved and so lower energy input, as well as less interface reactions.

Orientadores: Maria Helena Robert, Antonio Celso Fonseca de Arruda. Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica Resumo: Este trabalho teve como objetivo estudar o processo de produção de esponjas metálicas e compósitos de baixa densidade por tixoinfiltracao. A liga metálica AA7075 foi submetida a uma analise de tixohabilidade, na qual foi observada sua adequação ao processo e foi definida a temperatura de trabalho para a infiltração. A produção das amostras consistiu em infiltrar a pasta tixotropica da liga AA7075 sobre bloqueadores removíveis (partículas de NaCl), para a produção das esponjas, e sobre bloqueadores não-removíveis de materiais cerâmicos porosos (vermiculita e cinasita), para a produção dos compósitos. Todas as esponjas metálicas e compósitos produzidos foram caracterizados quanto a sua arquitetura interna, propriedades físicas, térmicas e mecânicas. Os resultados mostraram em todos os casos uma boa qualidade geral dos produtos e uma boa repetibilidade do processo. O comportamento de todos os materiais produzidos em compressão estática ou dinâmica se mostrou próximo do comportamento típico de materiais celulares, com grande platô de deformação plástica ocorrendo com valores relativamente baixos de tensão. A analise das curvas obtidas nos ensaios de compressão semi-estática e compressão dinâmica, em conjunto com imagens de amostras parcialmente comprimidas, forneceu informações sobre os prováveis mecanismos de deformação envolvidos, incluindo o papel dos materiais de reforço. Adicionalmente, foi proposto um equacionamento para a condutividade térmica, dos compósitos, cujos resultados se mostraram satisfatoriamente correlacionados com os experimentais Abstract: This work had the objective to study the process of production of open-cell metallic foams and low-density composites by thixoinfiltration. The AA7075 alloy underwent a thixoability analysis, in which it was observed its adequation to the process, and the working temperature for the infiltration was defined. The samples production consisted in infiltrating the thixotropic slurry of AA7075 alloy into removable space-holders (NaCl particles) for the production of the foams, and into non-removable space-holders of porous ceramic materials (vermiculite and expanded clay) for the production of the composites. All the foams and composites produced were characterized according to their internal architecture, physical, thermal, and mechanical properties. The results in all cases showed a good quality of the products in general, and a good repeatability of the process. The behavior of all the produced materials under semi-static and dynamic compression remained similar to the typical behavior of cellular materials, with a large plastic deformation plateau occurring with relatively low stress levels. The analysis of the obtained curves from the semi-static and dynamic tests, together with images from partially compressed samples, gave information about the possible deformation mechanisms involved, including the role of the reinforcement materials. Furthermore, a calculation for the thermal conductivity of the composites was proposed, with their results satisfactorily correlated to experimental data Doutorado Materiais e Processos de Fabricação Doutor em Engenharia Mecânica

Orientadores: Antonio Celso Fonseca de Arruda, Paulo Roberto Gardel Kurka Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica Resumo: Um dispositivo de retenção infantil, a ser certificado pela norma NBR14400, tem como um dos principais requisitos atingir determinados níveis de performance em ensaios de impacto. Durante seu desenvolvimento, o dispositivo deve ser submetido a esse teste várias vezes, até ser aprovado, o que envolve altos custos. Este estudo propõe um teste de impacto simplificado, não para substituir o teste de certificação, mas na condição de teste de desenvolvimento preliminar e eliminatório. O principal equipamento envolvido, neste estudo, é o boneco de testes, que possui simplificações tanto na parte biomecânica quanto na parte de instrumentação. Como vantagem, quando comparado ao boneco instrumentado completo, seu custo é significativamente menor. Neste trabalho são apresentadas as condições de contorno envolvidas no projeto, na construção e no uso desse boneco. Adicionalmente, são reportados os resultados comparativos dos ensaios de impacto entre o boneco construído e o instrumentado completo Hybrid III. Tais resultados validam a proposta do projeto Abstract: A child restraint system, to be certified to NBR 14400 standard, has as one of its main requirements, to reach specific performance levels under impact tests. During its development, the device has to undergo several times such tests, which are expensive, until approval. This study proposes a simplified impact test, not to replace the certification test, but as a preliminary and eliminatory test. The main equipment involved in this study is the test dummy, which has simplifications both on biomechanical and instrumentation aspects. As an advantage, when compared to a complete instrumented dummy, it has a considerably lower cost. In this work, the guiding conditions involved in the project, construction and use of that dummy are presented. Also, the results of comparative impact testes between the projected dummy and the complete instrumented dummy Hybrid III are reported. Such results validate the proposal of the project Mestrado Mestre em Engenharia Mecânica