Microactuators are needed to convert energy into mechanical work at the microscale. Thermal microactuators can be used to produce this needed mechanical work. The purpose of this research was to design, fabricate, and test thermal microactuators for use at the microscale in microelectromechanical systems (MEMS). The microactuators developed were tested to determine the magnitude of their deflection and estimate their force. Five groups of thermal microactuators were designed and tested. All of the groups used the geometrically constrained expansion of various segments to produce their deflection. The first group, Thermal Expansion Devices (TEDs), produced a rotational displacement and had deflections up to 20 µm. The second group, Bi-directional Thermal Expansion Devices (Bi-TEDs) were similar to the TEDs. The difference, as the name implies, was that the Bi-TEDs deflected up to 6 µm in two directions. Thermomechanical In-plane Micromechanisms (TIMs) were the third group tested. They produced a linear motion up to 20 µm. The fourth group was the Rapid Expansion Bi-directional Actuators (REBAs). These microactuators were bi-directional and produced up to 12 µm deflection in each direction. The final group of thermal microactuators was the Joint Actuating Micro-mechanical Expansion Systems (JAMESs). These thermal microactuators rotated pin joints up to 8 degrees. The thermal microactuators studied can be used in a wide variety of applications. They can move ratchets, position valves, move switches, change devices, or make connections. The thermal microactuator groups have their own unique advantages. The TIMS can be tailored for the amount of deflection and output force they produce. This will allow them to replace some microactuator arrays and decrease the space used for actuation. The Bi-TEDs and REBAs are bi-directional and can possibly replace two single direction micro-actuators. The JAMESs can be attached directly to a pin joint of an existing mechanism. These advantages allow these thermal microactuator groups to be used for a wide variety of applications.

Neste trabalho, foi investigado o efeito do tamanho do abrasivo e do pH do meio na resistência ao desgaste abrasivo do aço H-13 com matriz martensítica e do aço Hadfield com matriz austenítica. Ensaios de abrasão foram realizados utilizando o equipamento roda de borracha a úmido, variando o tamanho do abrasivo entre 0,15 e 2,40 mm e o pH do meio entre 5,5 e 12,8. As microestruturas dos materiais estudados foram analisadas utilizando microscopia óptica, as superfícies de desgaste e as partículas de desgaste foram analisadas em microscópio eletrônico de varredura. A macrodureza e a microdureza, antes e após os ensaios, foram obtidas utilizando durômetro Vickers. A topografia da região central da superfície de desgaste foi obtida utilizando Perfilometria 3D, visando obter valores de profundidade de penetração do abrasivo. Os resultados mostraram que o aço Hadfield é mais resistente do que o aço H-13 em todos os valores de pH e tamanhos de abrasivo utilizados. Para os dois materiais, a perda de massa aumenta linearmente até um tamanho crítico de abrasivo (TCA) e, após este, a mesma continua a aumentar, mas com uma intensidade menor. Para os dois materiais e para todos os tamanhos de abrasivo, o aumento do pH do meio resultou em menores perdas de massa, sendo este efeito maior para os dois menores tamanhos de abrasivo. Para maiores valores de pH, foram observadas menores profundidades de penetração do abrasivo. A microdureza da superfície de desgaste do aço H-13 sofreu um pequeno aumento com o aumento do tamanho do abrasivo enquanto que para o aço Hadfield esse aumento foi mais intenso. A análise das partículas de desgaste mostraram que, para todas as condições ensaiadas, os debris do aço H-13 tinham duas morfologias, contínuas e descontínuas enquanto que os cavacos do aço Hadfield foram sempre descontínuos. Para os dois materiais, foram observados dois micromecanismos de desgaste, sendo eles microcorte e microsulcamento. Por fim, os resultados apresentados neste trabalho sugerem que a análise de desempenho do aço Hadfield em serviço deve considerar o pH do meio bem como a granulometria do abrasivo em contato. / In this work, the effects of abrasive particle size and pH value of the aqueous solution on abrasive wear resistance of the H-13 steel with martensitic matrix and the Hadfield steel with austenitic matrix were investigated. Abrasive wear tests, using a wet rubber wheel abrasion tester, were carried out using abrasive sizes between 0.15 and 2.40 mm and pH values of the aqueous solution between 5.5 and 12.8. The microstructures of the materials studied were analyzed by optical microscopy and the wear surfaces and wear particles were analyzed by scanning electron microscopy. The hardness and microhardness before and after the tests were measured using a Vickers hardness tester. The topography of the middle of wear scars, were obtained by a noncontact 3D profiler in order to measure the depth of abrasive penetrations.The results show that the Hadfield steel is more wear resistant than the H-13 steel at all pH values and abrasive sizes conditions tested. For both materials, mass loss increases linearly up to a critical abrasive size, and after this the mass loss continues to increase, but with a lower intensity. Moreover, for both materials and all the abrasive sizes, increases in the pH values of the aqueous solution resulted in lower mass losses, and this effect is greater for the two smaller grain sizes. For higher pH values, lower depths of penetration of abrasive were observed. The microhardness in the wear scar surface of the H-13 steel presented a slight increase with the abrasive size, while for the Hadfield steel, this microhardness increases in a more intense form with the abrasive size. The analysis of the wear particles showed that, for all test conditions, the chips of H-13 steel has two types of morphologies, continuous or discontinuous, and for Hadfield steel only discontinuous. For both materials, two abrasive wear micromechanisms were observed, microcutting and microploughing. Finally, the results presented in this work suggest that the wear performance analysis of the Hadfield steel, to be used in an abrasive environment, must consider the effects of pH of the aqueous solution and particle size.

Two types of rotary gate microvalves are developed for flow modulation in a microfluidic system that operates at high flow rate and/or uses particulate flow. This research work encompasses design, microfabrication, and experimental evaluation of these microvalves in three distinct areas compliant micromechanism, microfluidics, and electromagnetic actuation. The microvalve consists of a suspended gate that rotates in the plane of the chip to regulate flow through the orifices. The gate is suspended by a novel fully-compliant in-plane rotary bistable micromechanism (IPRBM) that advantageously constraints the gate in all other degrees of freedom. Multiple inlet/outlet orifices provide flexibility of operating the microvalve in three different flow/port configurations. The suspended gate is made of a soft magnetic material and is electromagnetically actuated like a rotor in a variable-reluctance stepper motor. Therefore, an external electromagnetic (EM) actuation at the integrated set of posts (stator) causes the gate mass to switch from its default angular position to a second angular position. The microvalve chip is fabricated by electroplating a soft magnetic material, Permalloy (Ni80Fe20) in a sacrificial photoresist mold on a Silicon substrate. The inlet/outlet orifices are then etched into the Silicon substrate from the back-side using deep-reactive ion etch process. Finally, the gate structure is released by stripping the PR and seed layers. This research work presents the realization of a new microvalve design that is distinct from traditional diaphragm-type microvalves. The test results are encouraging and show the potential of these microvalves in effectively modulating flow in microfluidic systems that may not require a tight seal. The microvalve uses a novel in-plane rotary bistable micromechanism that may have other applications such as optical shutters, micro-locks, and passive check valves.

Neste trabalho, foi investigado o efeito do tamanho do abrasivo e do pH do meio na resistência ao desgaste abrasivo do aço H-13 com matriz martensítica e do aço Hadfield com matriz austenítica. Ensaios de abrasão foram realizados utilizando o equipamento roda de borracha a úmido, variando o tamanho do abrasivo entre 0,15 e 2,40 mm e o pH do meio entre 5,5 e 12,8. As microestruturas dos materiais estudados foram analisadas utilizando microscopia óptica, as superfícies de desgaste e as partículas de desgaste foram analisadas em microscópio eletrônico de varredura. A macrodureza e a microdureza, antes e após os ensaios, foram obtidas utilizando durômetro Vickers. A topografia da região central da superfície de desgaste foi obtida utilizando Perfilometria 3D, visando obter valores de profundidade de penetração do abrasivo. Os resultados mostraram que o aço Hadfield é mais resistente do que o aço H-13 em todos os valores de pH e tamanhos de abrasivo utilizados. Para os dois materiais, a perda de massa aumenta linearmente até um tamanho crítico de abrasivo (TCA) e, após este, a mesma continua a aumentar, mas com uma intensidade menor. Para os dois materiais e para todos os tamanhos de abrasivo, o aumento do pH do meio resultou em menores perdas de massa, sendo este efeito maior para os dois menores tamanhos de abrasivo. Para maiores valores de pH, foram observadas menores profundidades de penetração do abrasivo. A microdureza da superfície de desgaste do aço H-13 sofreu um pequeno aumento com o aumento do tamanho do abrasivo enquanto que para o aço Hadfield esse aumento foi mais intenso. A análise das partículas de desgaste mostraram que, para todas as condições ensaiadas, os debris do aço H-13 tinham duas morfologias, contínuas e descontínuas enquanto que os cavacos do aço Hadfield foram sempre descontínuos. Para os dois materiais, foram observados dois micromecanismos de desgaste, sendo eles microcorte e microsulcamento. Por fim, os resultados apresentados neste trabalho sugerem que a análise de desempenho do aço Hadfield em serviço deve considerar o pH do meio bem como a granulometria do abrasivo em contato. / In this work, the effects of abrasive particle size and pH value of the aqueous solution on abrasive wear resistance of the H-13 steel with martensitic matrix and the Hadfield steel with austenitic matrix were investigated. Abrasive wear tests, using a wet rubber wheel abrasion tester, were carried out using abrasive sizes between 0.15 and 2.40 mm and pH values of the aqueous solution between 5.5 and 12.8. The microstructures of the materials studied were analyzed by optical microscopy and the wear surfaces and wear particles were analyzed by scanning electron microscopy. The hardness and microhardness before and after the tests were measured using a Vickers hardness tester. The topography of the middle of wear scars, were obtained by a noncontact 3D profiler in order to measure the depth of abrasive penetrations.The results show that the Hadfield steel is more wear resistant than the H-13 steel at all pH values and abrasive sizes conditions tested. For both materials, mass loss increases linearly up to a critical abrasive size, and after this the mass loss continues to increase, but with a lower intensity. Moreover, for both materials and all the abrasive sizes, increases in the pH values of the aqueous solution resulted in lower mass losses, and this effect is greater for the two smaller grain sizes. For higher pH values, lower depths of penetration of abrasive were observed. The microhardness in the wear scar surface of the H-13 steel presented a slight increase with the abrasive size, while for the Hadfield steel, this microhardness increases in a more intense form with the abrasive size. The analysis of the wear particles showed that, for all test conditions, the chips of H-13 steel has two types of morphologies, continuous or discontinuous, and for Hadfield steel only discontinuous. For both materials, two abrasive wear micromechanisms were observed, microcutting and microploughing. Finally, the results presented in this work suggest that the wear performance analysis of the Hadfield steel, to be used in an abrasive environment, must consider the effects of pH of the aqueous solution and particle size.