Shape memory alloys (SMA) offer several advantages over traditional electro-mechanical devices, including: smooth, silent, clean operation; linear actuation; high power/weight ratio; scalability; and reduced part counts. These unique characteristics make them an attractive option when developing actuators, particularly at the meso- and micro-scales. However, SMAs do not typically display cyclic actuation and, therefore, require some reset force or bias mechanism in order to achieve this behaviour. Additionally, the micro-assembly of SMA material with a reset mechanism becomes increasingly difficult as the dimensions of actuators are scaled down. Therefore, actuators have been developed in which the actuation and reset mechanism are fabricated from a single piece of material. These actuators are referred to as monolithic actuators. Monolithic actuators are fabricated from a single piece of SMA material in which local annealing is used to selectively impart the shape memory effect (SME), while the remainder of the material acts as the bias mechanism. This work proposes an extension to monolithic actuators that locally varies the material composition of the monolithic component to exhibit different mechanical properties in select regions. This eliminates the need for local annealing by introducing regions of material unaffected by the annealing process. Additionally, incorporating regions of superelastic material to act as the bias mechanism greatly increases the actuator’s range of motion. These actuators are referred to as hybrid monolithic actuators. The creation of hybrid monolithic SMA actuators requires the development of both a fabrication technique and design tool. Varying the composition locally is accomplished by utilizing powder metallurgy fabrication techniques, specifically tape casting. Tapes of different compositions are cut, stacked, and sintered resulting in a monolithic component with mechanical properties that vary spatially. Tape casting NiTi from elemental powders is studied in this work, and tape recipes and sintering profiles are developed. In order to model the SMA behaviour of complex geometries, a finite element implementation of an existing lumped-element SMA model is developed. This model is used to design and simulate a prototype hybrid monolithic actuator. The prototype is fabricated and its performance used to illustrate the advantages of hybrid design over typical monolithic actuators.

Metal foams have found increasing applications in a wide range of structural and functional products, due to their exceptional mechanical, thermal, acoustic and electrical properties and offer great potential for lightweight structures for energy absorption in packaging during impact at high velocities. Metal foam structures have densities only fractions of that of a solid structure and have high specific strength and higher stiffness than other contemporary packaging materials. Therefore, the metal foam in particular “Aluminium Foam” has an important application as packaging material for transportation of Reactor fuels and Radioactive samples. Nuclear materials are transported in packages which should meet stringent safety standards like impact resistance, thermal shock etc. Therefore, in the transportation of the above materials, aluminium foam can play a key role in providing a cushion for absorption of shock and impact. The aim of this work is to develop a process for fabrication of aluminum foam. Two methods are experimented to manufacture metal foams. The first method involves mixing of a foaming agent in a liquid aluminium pool and the subsequent cooling of the melt while hydrogen is released from the foaming agent. The second method of metal foaming process is based on a procedure consisting of a base metal and a foaming agent, which are milled for homogeneous mixing and then pre-compacted by cold isostatic pressing. This is followed by cold/warm extrusion. The extruded piece is then heated up to a certain foaming temperature. The heating process leads to partial metal melting as well as to the release of the hydrogen gas and consequently to the formation of metal foam in the semi-solid state. In this thesis, the technology for fabrication of Al foam having a density of around 0.2-0.3 g/cm3 has been made & discussed in detail. The effects of various fabrication parameters like compaction pressure, extrusion ratio and foaming temperature on the formation of the Al foam are discussed. The quality of fabricated Al foams is characterized in terms of density, microstructure, porosity content etc. The various mechanical properties like yield strength, tensile strength and impact energy of the Al foams are evaluated in order to understand their behavior under different conditions. The typical values of Young’s modulus, plateau stress, densification strain and energy absorbed for the foam tested are tabulated. The observations, which are made from the data, can be briefly quoted as under: a) As the length of the specimen increases, plateau stress increases which increases the energy absorption. b) The energy absorption for Al-20% Mg alloy has been found to be minimum. The foam exhibited brittle behaviour and crumbled under load application. c) Young’s modulus varies in the range of 0.057 – 0.13 GPa for the foam. d) As density increases, Young’s modulus also increases and correspondingly the energy absorption value increases for Al-foam. It is found that the variation in the plateau stress with density is marginal. But the strain value was found to be dependent on the alloy composition and the density. The strain obtained for all cases was found to be very near to 75-90%. Al-20%Mg alloy showed an inferior behaviour compared to pure Al. It showed a lesser plateau stress and crumbled while testing. This shows that this alloy is highly brittle in nature. Also, the Al-Mg foam obtained did not exhibited good luster.

Tez (Doktora) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, Makina Mühendisliği Anabilim Dalı, 2007. / Kaynakça var.

The preliminary goal of this study is to determine the effects of processing conditions, compositions and microstructural morphologies of the constituents on the physical and thermo-mechanical properties of alumina (Al_2O_3) reinforced aluminum (Al) composites. Composites with 0, 5, 10, 20 and 25 vol% Al_2O_3 were manufactured using powder metallurgy method. The elastic properties (Young's and shear modulus) and the coefficient of thermal expansion (CTE) of the composites were determined using Resonant Ultrasound Spectroscopy (RUS) and Thermo Mechanical Analyzer (TMA) respectively at various temperatures. Increasing compacting pressure improved relative density (or lowered porosity) of the composites. Furthermore, increasing the Al_2O_3 vol% in the composite increased the elastic moduli and reduced the CTE of the composites. Increasing the testing temperature from 25 to 450 oC, significantly reduced the elastic moduli of the composites, while the CTE of the composites changed only slightly with temperatures. Secondly, the goal of this study is to determine the effect of microstructures on the effective thermo-mechanical properties of the manufactured Al-Al_2O_3 composites using finite element (FE) method. Software OOF was used to convert the SEM micrographs of the manufactured composites to FE meshed models, which were then used to determine the effective elastic modulus and CTE. It was observed that, effective modulus dropped by 19.7% when porosity increased by 2.3%; while the effective CTE was mildly affected by the porosity. Additionally, the effect of residual stress on the effective thermo-mechanical properties was studied, and the stress free temperature of the composites was determined. Another objective of this study is to examine the stress-strain response of Al-Al_2O_3 composites due to compressive loads at various temperatures. Elastic modulus, yield stress and strain hardening parameters were determined from the stress-strain curves and their dependency on temperature, porosity and volume fraction were studied. The experimental results were compared with the numerical results. It was observed that high-localized stresses were present near the pores and at the interfaces between Al and Al_2O_3 constituents. Finally, functionally graded materials (FGMs) with varying Al_2O_3 concentration (0, 5and 10 vol%) in Al were manufactured; and their stress-strain response and CTE were determined at various temperatures.

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O presente trabalho objetiva o estudo, obtenção e caracterização da liga magnética macia Fe-Si-P produzida por metalurgia do pó convencional visando à futura aplicação em núcleos de máquinas elétricas, atualmente fabricados por estampagem de chapas. Escolheu-se com base em testes prévios a liga Fe-3%Si-0,75%P. Para a obtenção da liga, foi utilizada a rota de mecâno-síntese com diferentes tempos de moagem: 1 h, 3 h e 9 h, além do material sem moagem para comparação. Na sequência compactaram-se uniaxialmente a frio os corpos de prova a 600 MPa seguido de sinterização a 1150 ºC em atmosfera de gás argônio. A análise da influência do tempo de moagem nas propriedades físicas, mecânicas, magnéticas e elétricas no material sinterizado foi a meta central deste trabalho. A caracterização das propriedades físicas mostrou uma redução da densidade aparente do pó moído, um aumento da distribuição do tamanho de partícula e redução do mesmo com o aumento do tempo de moagem. No que se refere às propriedades magnéticas, evidenciou-se que o material moído durante 3h apresentou os melhores resultados de indução de saturação (1,15 T), apesar do aumento na coercitividade já previsto devido ao processo de mecâno-síntese. Além disso, a difração de raios-X detectou a formação da liga através da solução sólida dos elementos P e Si na matriz ferrita. A análise metalográfica revelou a diminuição do tamanho de grãos com o aumento do tempo de moagem. Por fim, realizou-se a simulação do protótipo para análise do desempenho do material visando à aplicação futura. Esta, realizada pelo método de elementos finitos em um núcleo de um gerador síncrono com ímãs permanentes de NdFeB resultou em uma densidade de fluxo (1,95T) para o material com 3h de moagem e um torque de apenas 13% inferior se comparado ao gerador convencional produzido com núcleos de chapas de aço elétrico. / The present work aims to study, obtaining and characterization of Fe-Si-P soft magnetic alloy produced by conventional powder metallurgy intended for the future application in electrical machines cores, currently manufactured by sheet metal forming. The alloy Fe-3%Si-0,75%P was chosen based on previous tests. To obtain the alloy was used mechanical alloying route with different milling times: 1 h, 3 h and 9 h, and the material without milling for comparison. In the sequence, the specimens were uniaxially cold compacted at 600 MPa followed by sintering at 1150 ° C in an atmosphere of argon. The analysis of the influence of milling time on the physical, mechanical, magnetic and electric properties of the sintered material was the central goal of this work. The physical properties characterization showed a reduction in the bulk apparent density of the milled powder, an increase in particle size distribution and reduction thereof with increasing milling time. As regards magnetic properties, it was observed that the milled material for 3 hours showed the best results of saturation induction (1.15 T), despite the increase in the coercivity as expected due to the inherent mechanical alloying process. Furthermore, the X-ray diffraction detected the alloy formation through the solid solution of P and Si elements in the ferrite matrix. The metallographic analysis showed the decrease in grain size with increasing milling time. Finally, were performed a simulation prototype for analysis of material performance in order to future implement. This, held by finite element method on a synchronous generator core with NdFeB permanent magnets, resulting in a flux density (1.95 T) for the material with 3h of milling and a torque of only 13% lower compared to conventional generator produced with cores of electric steel sheet.

Com a crescente ideia de sustentabilidade, surge a necessidade de utilização de recursos renováveis e reaproveitamento de resíduos gerados em processos industriais. Neste trabalho foi avaliada a utilização da cinza pesada oriunda da queima do carvão em usinas termoelétricas no desenvolvimento de um Cermet. O compósito Cinza-Ferro (Cz-10Fe) foi obtido por metalurgia do pó e é composto de cinza pesada moída com adição de 10% em massa de pó de ferro puro. A adição do ferro é justificada para melhoria das propriedades mecânicas do material cerâmico. O compósito foi aplicado como meio suporte para biofilme em filtro biológico percolador, no pós-tratamento de efluentes domésticos. Foram realizados estudos com os principais componentes da cinza, tais como a sílica (SiO2), em forma de pó de quartzo, e a alumina (Al2O3) na versão comercial para avaliação da interação dos mesmos com o ferro e avaliação de suas propriedades mecânicas sob influência da variação da temperatura de sinterização A cinza pesada, obtida na Usina Tractebel de Charqueadas, foi moída durante 2, 4 e 8 horas para determinação do tamanho de partícula ideal para o compósito. Após caracterização, foi selecionada cinza moída por 2 horas para a produção dos compósitos para aplicação. A aplicação se deu utilizando um protótipo no pós-tratamento de efluentes da Estação de Tratamento de Esgotos (ETE) da COMUSA visando a remoção de Demanda Química de Oxigênio (DQO). Obteve-se incremento na eficiência do processo, reduzindo a DQO do efluente final em média 9%, indicando a viabilidade de uso do protótipo no pós- tratamento de esgotos domésticos, com porosidade aproximada de 20%, obtidos na cinza moída por 2 horas e sinterizado com ferro, como meio suporte para biofilme em filtro biológico percolador. / With the crescent idea of sustainability, there is a necessity for the use of renewable resources and the reuse of waste generated in industrial processes. In this work the use of the coal bottom ash from thermoelectric plants was evaluated in the development of a Cermet. The composite Ash-Iron (Cz-10Fe) was obtained by powder metallurgy and is composed of ground heavy ash with addition of 10% by mass of pure iron powder. The addition of iron is justified to improve the mechanical properties of the ceramic material. The composite was applied as biofilm packing media in trickling filter in the post-treatment of domestic effluents. Studies with the main components of the ash, such as silica (SiO2), in the form of quartz powder, and alumina (Al2O3) in the commercial version were carried out to evaluate their interaction with iron and evaluation of their mechanical properties under influence of the sintering temperature variation The bottom ash obtained at Tractebel from Charqueadas was milling for 2, 4 and 8 hours to determine the ideal particle size for the composite. After characterization, milled ash for 2 hours was selected for the production of the composites for application. The application was done using a prototype in the post-treatment of effluents from the Wastewater Treatment Station (ETE) of COMUSA aiming at the removal of Chemical Oxygen Demand (COD). The efficiency of the process was obtained by reducing the COD of the final effluent by a mean of 9%, indicating the viability of the utilization the prototype in the post-treatment of domestic sewage, with approximate porosity of 20%, obtained in ground ash for 2 hours and sintered with iron powder, in biofilm packing media in trickling filter.

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