Η παρούσα διδακτορική διατριβή πραγματεύεται την κατασκευή και τον έλεγχο ενός καινοτόμου τεχνητού χεριού, για προσθετικές κυρίως εφαρμογές, κάνοντας χρήση βιομιμητικών ενεργοποιητών και πιο συγκεκριμένα ειδικά κατεργασμένων λεπτών κυλινδρικών αγωγών από μορφομνήμονα μεταλλικά κράματα νικελίου-τιτανίου. Εκμεταλλευόμενοι τα συγκριτικά πλεονεκτήματα των ενεργοποιητών αυτών έναντι των αντίστοιχων συμβατικών, αναπτύσσεται μια πλήρως λειτουργική συσκευή με μικρό μέγεθος και βάρος, ανθρωπομορφική εμφάνιση, αθόρυβη λειτουργία και χαμηλό κόστος κατασκευής και συντήρησης, ικανή να εκπληρώσει σε μεγάλο βαθμό τις απαιτήσεις των ατόμων με αναπηρία στα άνω άκρα. Για τη φυσική υλοποίηση του σκελετού του τεχνητού αυτού χεριού χρησιμοποιείται η τεχνολογία της ταχείας προτυποποίησης. Καθένα από τα πέντε δάκτυλά του ελέγχεται ανεξάρτητα μέσω ενός υπο-ενεργοποιούμενου μηχανισμού κίνησης με τεχνητούς τένοντες. Για τον έλεγχο θέσης κάθε δακτύλου, αναπτύσσεται και εφαρμόζεται μία νέα μέθοδος ελέγχου βασισμένη στην έμφυτη δυνατότητα ανάδρασης θέσης των προαναφερθέντων ενεργοποιητών μέσω μέτρησης της ηλεκτρικής τους αντίστασης. Επιπλέον, αναπτύσσεται κατάλληλος αλγόριθμος για τον σχηματισμό διαφόρων θέσεων και συλλήψεων του τεχνητού χεριού. Για τη βελτίωση του ελέγχου, το χέρι εξοπλίζεται με αισθητήρες αφής στα ακροδάκτυλα, καθώς και με τη δυνατότητα οδήγησης συσκευών οπτικής και απτικής ανάδρασης. Όλα τα ηλεκτρονικά κυκλώματα που είναι απαραίτητα για την οδήγηση των ενεργοποιητών και τον έλεγχο του χεριού αναπτύσσονται και ενσωματώνονται στο εσωτερικό του φυσικού πρωτοτύπου. Με τη βοήθεια ειδικού προγραμματιστικού πακέτου, σχεδιάζεται μία γραφική διεπαφή ελέγχου μέσω της οποίας μελετάται και αξιολογείται η δυνατότητα του αναπτυχθέντος χεριού σε πειράματα σύλληψης διαφόρων αντικειμένων. Τέλος, προτείνονται διάφορες τεχνικές ελέγχου του χεριού από τους χρήστες του, ενώ αναπτύσσεται και κατάλληλος αλγόριθμος ελέγχου βασισμένος στη χρήση ηλεκτρομυογραφικών σημάτων. / This doctoral thesis presents the development and control of an innovative artificial hand, mostly for use in prosthetic applications, utilizing biomimetic actuators, and, more specifically, specially processed thin cylindrical wires made of shape memory nickel-titanium alloys. By exploiting the comparative advantages of these actuators over the conventional ones, a fully functional device is developed, of low size and weight, anthropomorphic appearance, silent operation, low fabrication and maintenance cost, which is capable of satisfying to a great extent the needs of the upper limb amputees. The physical implementation of the chassis of this artificial hand has been performed using rapid prototyping technology. Each of its five digits is independently controlled via a tendon-driven underactuated mechanism. For the position control of each digit, a novel control scheme is devised and implemented based on the inherent position feedback capability of these actuators via the measurement of their electrical resistance. In addition, the necessary algorithm is developed for the formation of various hand postures and prehension patterns. In order to improve the overall hand control, the hand is equipped with tactile sensors at its fingertips, and is also capable of driving optical and tactile feedback devices. All the necessary electronics for driving the actuators and controlling the hand are developed and embedded inside the physical prototype. Using a special programming package, a graphical user interface is designed, through which the grasp capabilities of the developed hand are studied and evaluated for various objects. Finally, several user control techniques of the hand are proposed, and a control algorithm based on the use of electromyographic signals is also developed.

NiTi is the most commonly used shape memory alloy (SMA) and has been widely used for bio-medical, electrical and mechanical applications. Nickel rich NiTi shape memory alloys are coming into prominence due to their distinct superelasticity and shape memory properties as compared to near equi-atomic NiTi shape memory alloys. Besides, their lower density and higher work output than steels makes these alloys an excellent candidate for aerospace and automotive industry. Shape memory properties and phase transformation behavior of high Ni-rich Ni54Ti46 (at.%) polycrystals and Ni-rich Ni51Ti49 (at.%) single-crystals are determined. Their properties are sensitive to heat treatments that affect the phase transformation behavior of these alloys. Phase transformation properties and microstructure were investigated in aged Ni54Ti46 alloys with differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) to reveal the precipitation characteristics and R-phase formation. It was found that Ni54Ti46 has the ability to exhibit perfect superelasticity under high stress levels (~2 GPa) with 4% total strain after 550°C-3h aging. Stress independent R-phase transformation was found to be responsible for the change in shape memory behavior with stress. The shape memory responses of [001], [011] and [111] oriented Ni51Ti49 single-crystals alloy were reported under compression to reveal the orientation dependence of their shape memory behavior. It has been found that transformation strain, temperatures and hysteresis, Classius-Clapeyron slopes, critical stress for plastic deformation are highly orientation dependent. The effects of precipitation formation and compressive loading at selected temperatures on the two-way shape memory effect (TWSME) properties of a [111]-oriented Ni51Ti49 shape memory alloy were revealed. Additionally, aligned Ni4Ti3 precipitates were formed in a single crystal of Ni51Ti49 alloy by aging under applied compression stress along the [111] direction. Formation of a single family of Ni4Ti3 precipitates were exhibited significant TWSME without any training or deformation. When the homogenized and aged specimens were loaded in martensite, positive TWSME was observed. After loading at high temperature in austenite, the homogenized specimen did not show TWSME while the aged specimen revealed negative TWSME.

The objective of this work is to understand the structure-property relationships in a pseudoelastic composition of polycrystalline NiTiPt (Ti-42.7 at% Ni-7.5 at% Pt). Structural characterization of the alloy includes grain size determination and texture analysis while the thermo-mechanical properties are explored using tensile testing. Variation in heat treatment is used as a vehicle to modify microstructure. The results are compared to experiments on Ni-rich NiTi alloy wires (Ti-51.0 at% Ni), which are in commercial use in various biomedical applications. With regards to microstructure, both alloys exhibit a <111> fiber texture along the wire drawing axis, however the NiTiPt alloy's grain size is smaller than that of the Ni-rich NiTi wires, while the latter materials contain second phase precipitates. Given the nanometer scale grain size in NiTiPt and the dispersed, nanometer scale precipitate size in NiTi, the overall strength and ductility of the alloys are essentially identical when given appropriate heat treatments. Property differences include a much smaller stress hysteresis and smaller temperature dependence of the transformation stress for NiTiPt alloys compared to NiTi alloys. Potential benefits and implications for use in vascular stent applications are discussed.

Submitted by Alison Vanceto (alison-vanceto@hotmail.com) on 2017-08-30T12:06:28Z No. of bitstreams: 1 DissMRS.pdf: 7292710 bytes, checksum: b518987951bcfa31933df3cece2f16cf (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-09-06T18:24:26Z (GMT) No. of bitstreams: 1 DissMRS.pdf: 7292710 bytes, checksum: b518987951bcfa31933df3cece2f16cf (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-09-06T18:33:14Z (GMT) No. of bitstreams: 1 DissMRS.pdf: 7292710 bytes, checksum: b518987951bcfa31933df3cece2f16cf (MD5) / Made available in DSpace on 2017-09-06T18:34:27Z (GMT). No. of bitstreams: 1 DissMRS.pdf: 7292710 bytes, checksum: b518987951bcfa31933df3cece2f16cf (MD5) Previous issue date: 2017-02-10 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Shape memory alloys (SMA) are alloys that undergo martensitic transformation due to an external solicitation (temperature, stress, strain or magnetic field) and are capable of recovering permanent deformation when heated above a critical temperature. The most used shape memory alloys are Ti-Ni- and Cu-based. Cu-based SMA have some advantages due to better thermal and electrical conductivity, lower production cost and are easier to process. The main disadvantage of Cu-based SMA is its low ductility. This property is improved by decreasing the grain size and by a reduction of microstructural heterogeneities. This can be achieved at the surface of structural components after LASER remelting, through which the surface of the material is remelted by a LASER beam and solidifies under extremely high cooling rates. In this context, the aim of the present work is to investigate the influence of LASER surface remelting in the microstructure, thermal stability and mechanical properties of Cu-11.8Al-3.2Ni-3Mn (wt. %) SMA plates obtained by suction casting. The samples were characterized by optical and scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction, X-ray computed tomography, X-ray diffraction, differential scanning calorimetry as well as by tensile and microhardness tests. The results show that small shifts in the transformation temperatures occur due to the LASER treatment. It was observed that only the monoclinic β’1 martensitic phase formed in the as cast and LASER treated samples. The LASER treatment provided an improvement in mechanical properties with an increase of up to 162 MPa in fracture stress, up to 2.2% in fracture strain and up to 21 HV in microhardness when compared with the as-cast sample. This makes the surface remelting treatment a promising method for improving the mechanical properties of Cu-based SMA. / Ligas com memória de forma (LMF) sofrem transformação martensítica devido a uma solicitação externa (temperatura, tensão, deformação ou campo magnético) e são capazes de recuperar deformações permanentes quando aquecidas acima de uma temperatura crítica. Dentre as LMF mais utilizadas se destacam aquelas à base de Ti e Ni e aquelas à base de Cu. As à base de Cu apresentam vantagens devido a melhor condutividade térmica e elétrica, menor custo de produção e maior facilidade de processamento. A principal desvantagem das LMF à base de cobre é a baixa ductilidade. Uma forma de melhorar essa propriedade é promovendo uma diminuição no tamanho de grão e uma redução das heterogeneidades microestruturais. Isso pode ser obtido no tratamento de refusão superficial a LASER, no qual a superfície do material é refundida por um feixe de LASER e solidificada sob altas taxas de resfriamento. Nesse contexto, o objetivo da presente dissertação de mestrado é analisar a influência do tratamento de refusão superficial a LASER na microestrutura, na estabilidade térmica e nas propriedades mecânicas de placas da LMF Cu-11,8Al-3,2Ni-3Mn (% peso) obtidas através de fundição por sucção. As amostras foram caracterizadas por microscopia óptica e eletrônica de varredura, espectometria de energia dispersiva de raios X, difração de elétrons retroespalhados, tomografia computacional por raios X, calorimetria diferencial de varredura, difração de raios X, ensaio de tração e microdureza. A análise dos resultados mostrou que as temperaturas de transformação sofreram pequenas variações e nenhuma nova fase foi observada após o tratamento de refusão a LASER, sendo observada apenas a presença da fase monoclínica martensítica β’1. O tratamento propiciou uma melhoria nas propriedades mecânicas das placas obtidas por fundição por sucção, com um aumento em até 162 MPa na tensão de fratura, em até 2,2 % na deformação de fratua e em até 21 HV na microdureza, fazendo deste tratamento um método promissor para melhorar as propriedades mecânicas das LMF à base de Cu. / CNPq: 132132/2015-0 / FAPESP: 2015/04134-7

Orientador: Gustavo Luiz Chagas Manhães de Abreu / Resumo: Diversos estudos relacionados à atenuação de vibrações utilizando materiais inteligentes vem sendo amplamente explorados no meio acadêmico. Neste âmbito, as Ligas de Memória de Forma (LMF) se destacam por apresentarem dissipação de energia vibratória devido ao seu comportamento histerético promovido pelo efeito pseudoelástico. No presente trabalho, dois sistemas com um e dois graus de liberdade, contendo mola helicoidal de LMF como elemento resiliente, são implementados numericamente para demonstrar a atenuação de vibrações ocasionada pelas transformações de fase presentes no material. Para cada um dos sistemas mecânicos investigados, dois modelos termomecânicos são confrontados numericamente visando a obtenção das características de cada modelo em representar a atenuação de vibrações dos sistemas submetidos à carregamentos termo-mecânicos. O trabalho termina comentando as potencialidades da proposta apresentada, discutindo as facilidades e dificuldades encontradas na sua implementação e apontando para o desenvolvimento de futuros estudos. / Mestre

The aim of the thesis is the mathematical and computer modelling of thin films of martensitic materials. We derive a thermodynamic thin-film model on the meso-scale that is capable of capturing the evolutionary process of the shape-memory effect through a two-step procedure. First, we apply dimension reduction techniques in a microscopic bulk model, then enlarge gauge by neglecting microscopic interfacial effects. Computer modelling of thin films is conducted for the static case that accounts for a modified Hadamard jump condition which allows for austenite--martensite interfaces that do not exist in the bulk. Further, we characterize $L^p$-Young measures generated by invertible matrices, that have possibly positive determinant as well. The gradient case is covered for mappings the gradients and inverted gradients of which belong to $L^\infty$, a non-trivial problem is the manipulation with boundary conditions on generating sequences, as standard cut-off methods are inapplicable due to the determinant constraint. Lastly, we present new results concerning weak lower semicontinuity of integral functionals along (asymptotically) $\mathcal{A}$-free sequences that are possibly negative and non-coercive. Powered by TCPDF (www.tcpdf.org)

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-10-09T13:44:00Z No. of bitstreams: 1 ANTÔNIO ARISTÓFANES DA CRUZ GOMES - DISSERTAÇÃO (PPGEM) 2018.pdf: 3128879 bytes, checksum: 1a0aaa662fd3e47d06a1e3545ab63f87 (MD5) / Made available in DSpace on 2018-10-09T13:44:00Z (GMT). No. of bitstreams: 1 ANTÔNIO ARISTÓFANES DA CRUZ GOMES - DISSERTAÇÃO (PPGEM) 2018.pdf: 3128879 bytes, checksum: 1a0aaa662fd3e47d06a1e3545ab63f87 (MD5) Previous issue date: 2018-08-07 / CNPq / Os procedimentos cirúrgicos de reconstrução crânio facial vêm se desenvolvendo significativamente e grande parte desse progresso se deve às inovações nas técnicas cirúrgicas e ao emprego de novos materiais na fabricação dos dispositivos de fixação. O objetivo principal é tornar os procedimentos mais eficientes e menos invasivos aos pacientes, consequentemente haverá diminuição nos índices de retrabalhos. O emprego de Ligas com Memória de Forma (LMF) pode ser uma alternativa interessante nesses casos, uma vez que esses materiais possuem um comportamento adaptativo, com a capacidade de reagir a estímulos externos de natureza térmica ou mecânica. As LMF da família Ni-Ti lideram o interesse das pesquisas devido ao maior número de aplicações comerciais, principalmente nas áreas médica e odontológica. Essas LMF Ni-Ti, além de serem biocompatíveis possuem também módulo de elasticidade inferior ao de ligas de titânio, como o Ti-Al-V, e dos aços inoxidáveis. Neste contexto, o objetivo deste trabalho é desenvolver um protótipo de placa de fixação óssea, que poderá ser destinada a procedimentos de trauma e reconstrução mandibular, utilizando uma LMF Ni-Ti com características superelásticas. Foi escolhido um elemento de fixação, tipo placa, como modelo para os protótipos e as dimensões foram baseadas em componentes fornecidos comercialmente. Para a fabricação dos dispositivos optou-se pelos processos de fundição de precisão: Plasma Skull Push-Pull (PSPP), e fusão por indução com injeção por centrifugação (FIC), os quais se mostraram bastante eficazes. Foram realizados ensaios de caracterização para determinar as propriedades térmicas e mecânicas do dispositivo fabricado. Os principais resultados foram um componente de rigidez variável com a temperatura, módulo de elasticidade da ordem de 50 GPa na temperatura corpórea e vida em fadiga ente 103 e 106 para amplitudes de deslocamento em flexão entre 0,5 mm e 2,5 mm. Estes resultados de caracterização termomecânica indicam o potencial das LMF Ni-Ti e dos processos de fundição de precisão para a produção de placas de fixação óssea. / Surgical procedures for facial skull reconstruction have been developing significantly and much of this progress is due to innovations in surgical techniques and the use of new materials in the manufacture of fastening devices. The main objective is to make the procedures more efficient and less invasive to the patients, consequently there will be a decrease in the rates of reworking. The use of Shape Memory Alloys (SMA) may be an interesting alternative in these cases, since these materials have an adaptive behavior, with the ability to react to external stimuli of a thermal or mechanical nature. The SMA of the Ni-Ti family lead the research interest due to the greater number of commercial applications, mainly in the medical and dental areas. In addition to being biocompatible, these Ni-Ti SMAs also have lower modulus of elasticity than titanium alloys, such as Ti-Al-V, and stainless steels. In this context, the objective of this work is to develop a prototype bone fixation plate, which can be used for trauma and mandibular reconstruction procedures, using a Ni-Ti SMA with superelastic characteristics. A plate-type fastening element was chosen as the prototype model and the dimensions were based on commercially supplied components. In order to manufacture the devices, it was chosen the precision casting processes: Plasma Skull Push-Pull (PSPP) and induction fusion with centrifugal injection (FCI), which proved to be quite effective. Characterization tests were performed to determine the thermal and mechanical properties of the fabricated device. The main results were a variable stiffness component with temperature, modulus of elasticity of the order of 50 GPa at body temperature and fatigue life between 103 and 106 for flexural displacement amplitudes between 0.5 mm and 2.5 mm. These thermomechanical characterization results indicate the potential of Ni-Ti SMA and precision casting processes for the production of bone fixation plates.

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-10-09T14:06:57Z No. of bitstreams: 1 ARMANDO WILMANS NUNES DA FONSECA JÚNIOR - DISSERTAÇÃO (PPGEM) 2018.pdf: 5713433 bytes, checksum: aba957d62b27260ecd8141ce8547fa05 (MD5) / Made available in DSpace on 2018-10-09T14:06:57Z (GMT). No. of bitstreams: 1 ARMANDO WILMANS NUNES DA FONSECA JÚNIOR - DISSERTAÇÃO (PPGEM) 2018.pdf: 5713433 bytes, checksum: aba957d62b27260ecd8141ce8547fa05 (MD5) Previous issue date: 2018-08-31 / Capes / No decorrer dos anos, com a construção de pontes cada vez mais longas e leves, o comportamento dinâmico passa a ser um fator limitante no projeto dessas estruturas. Portanto, é de grande interesse que sistemas de controle de vibrações estruturais sejam desenvolvidos. Entre os vários materiais utilizados atualmente para supressão de vibrações, estão as ligas com memória de forma (LMF). Estas vêm ganhando popularidade graças a sua capacidade de sofrer grandes deformações reversíveis, aliadas às suas propriedades de dissipação de energia. Neste contexto, este trabalho tem como objetivo realizar o controle passivo de vibrações num protótipo de ponte estaiada, em escala reduzida, utilizando molas superelásticas de uma LMF Ni-Ti (Nitinol). Foram realizadas análises dinâmicas na estrutura utilizando ferramentas analíticas, numéricas e experimentais. Nos resultados experimentais, obteve-se uma redução de até 75% de transmissibilidade de força em vibração livre, em comparação com a estrutura com molas equivalentes, de aço. Em vibração forçada, o valor de redução de transmissibilidade de força chegou a um máximo de 85,5%. Os resultados numéricos mostraram boa coerência na determinação dos parâmetros modais da estrutura e na resposta em vibração livre, com maior erro associado aos resultados em vibração forçada, mais especificamente no segundo modo de vibrar do sistema. Concluiu-se que as molas de LMF têm capacidade de dissipação de energia vibracional para a aplicação em estruturas de pontes e os modelos numéricos permitem uma boa previsão da resposta da estrutura. / Over the years, with the construction of increasingly longer and lighter bridges, dynamic behavior becomes a limiting factor in the design of these structures. Therefore, it is important that structural vibration control systems are developed. Among the various materials currently used for vibration suppression are the shape memory alloys (SMA). These have been gaining popularity as a result of their ability to undergo large reversible deformations, coupled with their energy dissipating properties. In this context, the objective of this dissertation is to perform the passive vibration control of a cable-stayed bridge prototype, in small scale, using SMA Ni-Ti (Nitinol) superelastic springs. Dynamic analyses were performed using analytical, numerical and experimental tools. In the experimental results, a reduction of 75% of force transmissibility in free vibration was obtained, compared to the structure with equivalent steel springs. In forced vibration, the value of reduction of force transmissibility reached a maximum of 85.5%. The numerical results showed good coherence in the determination of the modal parameters of the structure and the response of the latter in free vibration, with the largest error associated to the second mode of vibration of the structure, in forced vibration. It was concluded that the SMA springs have the capacity to dissipate vibrational energy, for the application in bridges structures, and the numerical models allow a good prediction of the structure response.

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-07-09T12:28:39Z No. of bitstreams: 1 MATHEUS JOSÉ CUNHA DE OLIVEIRA - DISSERTAÇÃO (PPGCEMat) 2016.pdf: 9296942 bytes, checksum: a273053730345dafcd282de1fc0bf6f1 (MD5) / Made available in DSpace on 2018-07-09T12:28:39Z (GMT). No. of bitstreams: 1 MATHEUS JOSÉ CUNHA DE OLIVEIRA - DISSERTAÇÃO (PPGCEMat) 2016.pdf: 9296942 bytes, checksum: a273053730345dafcd282de1fc0bf6f1 (MD5) Previous issue date: 2016-02-16 / CNPq / As Ligas com Memória de Forma (LMF) foram descobertas nos anos 60 e o desenvolvimento de vários sistemas (NiTi, CuAlNi, CuAlBe, CuZnAl) vem sendo explorado desde então, sendo aquelas do sistema NiTi as mais utilizadas. Devido às suas excelentes propriedades mecânicas, ótima resistência a corrosão e biocompatibilidade, além de apresentarem as melhores propriedades funcionais de efeito de memória de forma e superelasticidade, as LMF NiTi e suas variações ternárias passaram a ser objeto de estudos para várias aplicações nas mais diferentes áreas. Um dos maiores problemas das LMF NiTi ainda está relacionado a dificuldades de conformação mecânica e usinagem. Por esse motivo, o processo de soldagem pode ser uma boa ferramenta alternativa para se conseguir obter peças de geometrias mais complexas, envolvendo a união das LMF NiTi com metais convencionais, como o aço inoxidável. O aço inoxidável é uma opção importante de união com LMF NiTi pois possui igualmente propriedades desejadas de resistência mecânica, biocompatibilidade e resistência a corrosão. A união por soldagem destas duas ligas encontra barreiras diversas, sendo a principal delas a formação de intermetálicos frágeis na junta soldada limitando sua resistência mecânica e consequente aplicação. Nesse contexto, o presente trabalho teve como objetivo geral avaliar a soldabilidade de chapas finas (espessura de 1 mm) de uma LMF NiTi com aço inoxidável (INOX) AISI 304 utilizando o processo micro GTAW e compreender a metalurgia da soldagem na variação das propriedades mecânicas e metalúrgicas das juntas. O processo GTAW foi escolhido por ser mais econômico que os processos usuais de soldagem para estas ligas NiTi, como a soldagem a laser (LBW). As juntas dissimilares NiTi-SS obtidas foram caracterizadas pelas técnicas de MO, MEV, EDS, DSC, ensaios de tração à ruptura e de dureza Vickers. Estas juntas foram soldadas utilizando a própria LMF NiTi e também o Inconel 625 como metais de adição. No geral, constatou-se que as juntas apresentam comportamento frágil, porém ao se utilizar camada intermediária de Inconel 625 na união entre os metais dissimilares e após tratamento térmico para alívio de tensões, é possível aumentar a resistência mecânica da junta para valores da ordem de 150MPa. As juntas apresentaram uma poça de fusão heterogênea devido a formação de elementos fragilizantes ao longo do metal de solda. Observou-se a formação de uma zona parcialmente diluída (ZPD) correlacionada a um aumento excessivo da dureza nesta região e composição química distinta. / Shape Memory Alloys (SMA) were discovered in the 60s and the development of various systems (NiTi, CuAlNi, CuAlBe, CuZnAl) has been explored since then, with those of the NiTi system the most commonly used. Due to its excellent mechanical properties, good corrosion resistance and biocompatibility, in addition to having the best functional properties of shape memory effect and superelasticity, the NiTi SMA and its ternary variations have become the subject of studies for various applications in different areas. One of the main problems of NiTi SMA is also related to difficulties in forming and machining. For this reason, the welding process can be a good alternative tool to achieve more complex geometry parts, involving the union of NiTi SMA with conventional metals, such as stainless steel. Stainless steel is an important option for union with NiTi SMA, since it also has desired properties of mechanical strength, biocompatibility and corrosion resistance. The union by welding between these two alloys find various barriers, the main one being the formation of brittle intermetallic compounds on the welded joint, limiting its mechanical strength and consistent application. In this context, this study aimed to assess the weldability of thin sheet metal (1 mm thick) of a NiTi SMA with AISI 304 stainless steel (SS) using the micro process GTAW, and study the influence of welding metallurgy in mechanical and metallurgical properties of the joints. The GTAW process was chosen because it is more economical than the usual welding processes for these NiTi alloys such as the laser beam welding (LBW). The NiTi-SS dissimilar joints obtained were characterized by optical microscopy techniques, SEM, EDS, DSC, tensile test to rupture and Vickers hardness. These joints were welded using NiTi SMA and also the Inconel 625 as filler metals. Overall, it was found that the joints have brittle behavior, but when using an intermediate layer of Inconel 625 at the junction between dissimilar metals and after heat treatment for stress relief, it is possible to increase the mechanical strength of the joint for values in the order of 150MPa. The joints exhibited a heterogeneous molten weld pool due to formation of elements along the embrittlement of the weld metal. It was observed the formation of a partially diluted zone (PDZ) correlated to an excessive increase of the hardness in that region and different chemical composition.

Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-07-27Bitstream added on 2014-06-13T19:55:32Z : No. of bitstreams: 1 faria_ct_me_ilha.pdf: 2001879 bytes, checksum: 8c06397bc7d8057b53383eaa08ea1d01 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O projeto de aeronaves convencionais, em geral, apresentam uma série de dificuldades de se realizar de maneira eficiente um amplo número de missões, uma vez que para atender esses requisitos estas aeronaves deveriam ser capazes de realizar grandes alterações em sua geometria. Surge então um novo conceito de projeto de aeronaves, as chamadas aeronaves adaptativas, as quais são capazes de alterar sua geometria, de modo a adaptar a aeronave a um dado tipo de missão. Este novo conceito se tornou ainda mais atrativo com os avanços tecnológicos promovidos pelo estudo de novos materiais, os chamados materiais inteligentes, que apresentam alta densidade de energia, vantagem que leva a uma redução de peso nos mecanismos atuados desta maneira. Este trabalho apresenta um novo modelo adaptativa, utilizando fios atuadores de ligas de memória de forma para realizar uma rotação relativa entre duas seções de um aerofólio, este mecanismo possibilitaria a variação da linha de arqueamento de uma seção aeronáutica. Neste trabalho uma modelagem matemática para se descrever o comportamento deste sistema é apresentada, bem como um modelo aerodinâmico para se verificar o comportamento do sistema em funcionamento. Um controlador do tipo nebuloso é ainda projetado para se controlar a forma do perfil, e ensaios experimentais são conduzidos para se verificar a modelagem termo-mecânica apresentada. / Conventional airplane design, in general, has a large difficulty to attend in an efficient way several mission requirements, once that to attend these requirements the airplane has to perform great shape changes in its structure. Motivated by this problem a new concept in airplane design arise, one called morphing airplanes, which are air vehicles capable of changing its shape to adapt it self to a defined mission. This new concept became even more attractive with the development of active smart material, which can be a high power density actuator, reducing the weight of such morphing mechanism. This work proposes a novel model for morphing wings, using a pair of shape memory alloy wires to create a rotation between two wing sections, this mechanism allows the airfoil to change its camber line. A mathematical model is derived to describe the thermo-mechanical structure behavior, and also an aerodynamic model is investigated. A fuzzy controller is designed to control the system shape, and some experimental tests are used to verify the thermo-mechanical modeling proposed.