Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-07-16T13:34:47Z No. of bitstreams: 1 ECLYS DE OLIVEIRA SOARES MONTENEGRO - DISSERTAÇÃO (PPGEM) 2016.pdf: 5996362 bytes, checksum: 84827496654dcae4004aea6958439570 (MD5) / Made available in DSpace on 2018-07-16T13:34:47Z (GMT). No. of bitstreams: 1 ECLYS DE OLIVEIRA SOARES MONTENEGRO - DISSERTAÇÃO (PPGEM) 2016.pdf: 5996362 bytes, checksum: 84827496654dcae4004aea6958439570 (MD5) Previous issue date: 2016-09-01 / Estudos recentes têm mostrado que as telas de titânio estão sendo utilizadas para auxiliar na recuperação de fraturas ósseas em diversas partes do corpo humano, como face, mandíbula, crânio e joelho. Esses componentes apresentam como vantagens uma elevada resistência mecânica somada a uma baixa espessura, necessária para a ancoragem de partes fraturadas e importante para prevenir a irritação no processo pós-operatório, buscando ainda reduzir a taxa de re-operação. Assim, vislumbrando uma melhor eficiência futura dessa aplicação, surge o interesse em analisar o comportamento termomecânico desse tipo de implante, porém fabricado a partir das ligas com memória de forma (LMF), que são materiais que apresentam propriedades funcionais como o efeito memória de forma (EMF) e a superelasticidade (SE). Estas peculiaridades, aliadas a biocompatibilidade das LMF Ni-Ti tem levado à sua utilização no desenvolvimento de dispositivos médicos implantáveis. Nesse contexto, aplicar telas de LMF Ni-Ti, com boa resistência mecânica e deformações reversíveis, para potencializar aplicações biomédicas em substituição a telas de titânio, é um desafio tecnológico atual. Sendo assim, o presente trabalho teve por objetivo realizar a caracterização termomecânica de telas de LMF Ni-Ti e Ni-Ti-Cu produzidas por fundição de precisão com três geometrias celulares distintas (circular, hexagonal e quadrada) e em três estados (brutas de fundição, tratadas termicamente e laminadas). Os resultados obtidos mostraram que as telas produzidas apresentaram a transformação de fase característica dos fenômenos de EMF e SE, além de deformações reversíveis em tração da ordem de até 5%. O tipo de geometria celular foi o fator de maior influência nos valores de resistência mecânica e os melhores resultados foram verificados nas telas de geometria circular. Nos ensaios termomecânicos de flexão, além do tipo de célula, os resultados foram bastante influenciados pela espessura das telas e tratamentos térmicos utilizados. Dessa forma, as telas produzidas apresentam características funcionais adequadas para potencializar aplicações biomédicas a partir de LMF Ni-Ti em substituição as telas de titânio puro, que não se beneficiam de propriedades funcionais de EMF e SE. / Recent studies have shown that titanium meshes are being used to assist in the recovery of bone fractures in various parts of the human body such as the face, jaw, skull and knee. These components have advantages as a high strength coupled with a low thickness required for anchoring of fractured parts important to prevent irritation postoperatively process still looking to reduce the rate of re-operation. Thus, by anticipating a future better efficiency of this application, arises interest in analyzing the thermomechanical behavior of this type of implant, but manufactured from alloys with shape memory (SMA), which are materials that exhibit functional properties such as shape memory effect (SME) and superelastic (SE). These peculiarities, coupled with biocompatibility of LMF NiTi has led to their use in the development of implantable medical devices. In this context, apply SMA meshes, with good mechanical strength and reversible deformation to enhance biomedical applications replacing titanium screens, it is a current technological challenge. Therefore, this study aimed to carry out the thermomechanical characterization of Ni-Ti and Ni-Ti-Cu SMA meshes produced by precision casting with three different cell geometries (circular, hexagonal and square) and three states (as foundry, thermally treated and laminated). The results showed that the screens produced showed the phase transformation phenomena characteristic of EMF and SE, and reversible deformation in order draw up to 5%. The type of cell geometry was the most influential factor in the strength values and the best results were obtained in the circular geometry screens. In the thermomechanical bending tests, and the type of cell, results were greatly influenced by the thickness of the screens and thermal treatments. Thus, the meshes produced had enough features to enhance biomedical applications from SMA to replace the titanium meshes, which do not benefit from functional properties.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-04-26T19:19:12Z No. of bitstreams: 1 HENRIQUE MARTINNI RAMOS DE OLIVEIRA - DISSERTAÇÃO PPGEM 2014..pdf: 5119070 bytes, checksum: 23504b03a49c79c4f4d5a4f8815ee9ac (MD5) / Made available in DSpace on 2018-04-26T19:19:12Z (GMT). No. of bitstreams: 1 HENRIQUE MARTINNI RAMOS DE OLIVEIRA - DISSERTAÇÃO PPGEM 2014..pdf: 5119070 bytes, checksum: 23504b03a49c79c4f4d5a4f8815ee9ac (MD5) Previous issue date: 2014-08-01 / CNPq / Capes / As Ligas com Memória de Forma (LMF) devem seu comportamento único a uma transformação de fase reversível entre duas estruturas cristalinas: martensita (baixa temperatura e menor rigidez) e austenita (alta temperatura e maior rigidez). Essa transformação pode ocorrer em consequência de dois estímulos diferentes: uma mudança de temperatura ou aplicação de tensão mecânica, ambos acima de valores críticos característicos desses materiais. Do segundo caso resulta o fenômeno da superelasticidade, que é a capacidade de recuperar totalmente a deformação após o carregamento e descarregamento mecânico na fase de mais alta temperatura (austenita). No decorrer dessa deformação ocorre a transformação de fase induzida por tensão da austenita para a martensita. Esta transformação é exotérmica e tende a se estabilizar após certo número de ciclos de deformação. Estudos sobre as propriedades dinâmicas das LMF mostram que o comportamento superelástico é dependente da taxa de deformação, ou em outras palavras, da frequência de excitação. Este comportamento resulta da combinação complexa entre tensão mecânica, temperatura e taxa de dissipação do calor latente gerado no material. Observou-se também que altas frequências diminuem a capacidade de dissipação de calor latente, resultando no aumento de temperatura do material e valores de tensão de transformação de fase maiores. Considerações como estas são importantes para a modelagem do comportamento dinâmico do material, aplicável, por exemplo, em sistemas de absorção de vibração de construções civis. Nesse contexto, o objetivo deste trabalho é estudar experimentalmente a influência da frequência sobre o comportamento dinâmico superelástico de fios de LMF Ni-Ti pré-estabilizados, assim como os efeitos da geração de calor sobre as propriedades mecânicas avaliadas. Os testes realizados corresponderam a ensaios dinâmicos de tração uniaxial em fios superelásticos de LMF Ni-Ti com variação de freqüência e simultâneo acompanhamento de temperatura do material, usando uma máquina de ensaios da marca MTS modelo MTS 793 series. / Shape Memory Alloys (SMA) owe their behavior unique to a reversible phase transformation between two crystalline structures: martensite (low temperature and stiffness) and austenite (high temperature and stiffness). This phase change can occur as a result of two distinct stimuli: a change in temperature or an applied mechanical stress, both over certain critical values, characteristic of this materials. From the latter it results the phenomenon of the superelasticity, which is the ability to totally recover a deformation after simply ceasing the load. During this deformation occurs a stressinduced martensitic transformation from austenite to martensite, being it an exothermal process and that tends to stabilize after a certain number of cycles. Investigation concerning dynamic properties of SMA demonstrate that its superelastic behavior depends on the strain rate, or in other words, on the excitation frequency. This behavior results from the complex combination of mechanical stress, temperature and rate of latent heat dissipation generated in the material. It was also observed that high frequencies diminish the capacity of dissipation of latent heat, resulting in an increase in the material temperature and, therefore, in higher values of phase transformation stresses. This kind of consideration is fundamental in dynamic behavior modeling, applicable for instance, in vibration absorption systems in civil building. In this context, the objective of this work is experimentally study the influence of the frequency on superelastic behavior of pre-stabilized Ni-Ti SMA superelastic wires, as well as the effects of heat generation on the evaluated mechanical properties. Dynamical tests were performed in a uniaxial tensile mode in Ni-Ti SMA superelastic wires varying the frequency and simultaneously monitoring sample’s temperature, using a test machine from MTS, model MTS 793 series.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2013. / This thesis outlines a proposed mechanical design, prototyping and testing of a five fingered artificial hand made of 15 articulated joints actuated by Shape Memory Alloys (SMAs) mimicking muscular functions. SMAs Artificial muscles were incorporated in the forearm and artificial tendons made of nylon wires passing through a hollow palm transmit the pulling force to bend the fingers. Torsion springs set in each joint of the fingers create enough restoring force to straighten the finger when the actuators are disengaged. Nickel-Titanium (NiTi) wires were intrinsically embedded within the hand structure allowing significant movements mimicking human hand-like gestures. A control box made of switches connected to the artificial hand helps to control each gesture. A modular approach was taken in the design to facilitate the manufacture and assembly processes. Nickel-Titanium wires were used as actuators to perform the artificial muscle functions by changing their crystallographic structures due to Joule's heating. Rapid prototyping techniques were employed to manufacture the hand in ABS plastic.

Resumo: 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. / Abstract: 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. / Orientador: Vicente Lopes Junior / Coorientador: Carlos de Marqui Junior / Banca: Gustavo Luiz Chagas Manhães de Abreu / Banca: Álvaro Martins Abdalla / Mestre

O seguinte trabalho visa o estudo, desenvolvimento e teste de um controlador de impedância genérico, que seja adequado para controle de exoesqueletos e outros sistemas robóticos, e que permita a utilização de um atuador de liga de memória de forma (SMA), entre outros tipos de atuador. Um segundo objetivo é avaliar a viabilidade da utilização de atuadores de SMA em aplicações de exoesqueletos para humanos, partindo dos resultados obtidos com o controlador e atuador propostos. Para atingir estas metas, foi projetado e construído um protótipo de exoesqueleto de membro inferior com um grau de liberdade, sendo que um atuador baseado em fios de liga de memória de forma foi utilizado. O algoritmo de controle de impedância foi desenvolvido e testes foram realizados primeiro por meio de simulações e posteriormente em ensaios práticos com o protótipo. Os resultados experimentais confirmaram a expectativa indicada pelos resultados numéricos. Embora o controlador de impedância haja funcionado como se pretendia, o atuador deixou a desejar devido, sobretudo, à sua lentidão de resposta. O texto apresenta uma breve revisão teórica sobre controle de impedância, exoesqueletos biomecatrônicos e ligas de memória de forma. Ademais, detalha o modelo matemático do problema e o aparato experimental projetado para realizar os ensaios que serviram de base para a análise do problema. Após apresentação e discussão dos resultados, é feita uma análise da viabilidade de aplicação destes conceitos a exoesqueletos para uso em humanos, concluindo que ainda há desafios tecnológicos importantes a serem vencidos antes da implementação prática de exoesqueletos com atuadores de SMA; contudo, esta implementação não pode ser descartada. Detalhes construtivos e programas desenvolvidos para simulações e controle do protótipo são apresentados nos apêndices. / This work proposes the study, development and test of a generic impedance controller, which must be adequate to control exoskeletons as well as other robotic systems, and must allow the use of a shape memory alloy (SMA) actuator, among others kinds of actuation. A second objective is to evaluate if it is possible to use SMA actuators in exoskeletons for humans, taking into account the results obtained with the proposed controller and actuator. To achieve such goals, a one degree of freedom, lower limb exoskeleton prototype was designed and built, while an actuator based on SMA wires was used. The impedance control algorithm was developed and tests were made, first by means of simulations and later by tests on the prototype. Experimental data confirmed the expected results obtained by simulations. Although the impedance controller has worked as desired, the actuator did not meet the expectations, especially because of its slow response. The text brings a brief theoretical review about impedance control, biomechatronic exoskeletons and shape memory alloys. In addition, it details the mathematical model of the problem and the experimental apparatus, designed to the execution of tests which would serve as a foundation to the problem analysis. After the results are presented and discussed, the viability of use of the proposed concepts to SMA-actuated-exoskeletons is analyzed, concluding that there are still important technological challenges to be overcome before the practical implementation of exoskeletons with SMA actuators; however, this implementation cannot be discarded. Constructive details of the prototype and the programs developed to simulate and control it are presented in the appendixes.

The modeling, analysis and experimental verification of a two-degree-of-freedom typical aeroelastic section with superelastic shape memory alloy springs are presented. The focus is to investigate the effects of the phase transformation of the shape memory alloy springs on the flutter and post-flutter behaviors of the typical section. The shape memory alloy phase transformation kinetics is described by a modified version of well-known phenomenological models. The shape memory alloy spring model is based on classical spring design (with the pure shear assumption) and modified to account for the nonlinear effects of phase transformation. The cross-section of the shape memory alloy wire is represented by a linear radial distribution of shear strain and nonlinear radial distributions of shear stress and martensitic fraction. The equations of motion of a linear typical section are modified to include the shape memory alloy springs. A linear unsteady aerodynamic model is employed to determine the aerodynamic loads. The proposed model is cast into state-space representation and solved with a Runge-Kutta method. It is numerically and experimentally shown that the phase transformation of shape memory alloy springs can be effectively exploited to enhance the aeroelastic behavior of a typical section by replacing unstable flutter oscillations by stable oscillations of acceptable amplitudes over a range of airflow speeds, providing a useful method of passive aeroelastic control. Since the modified aeroelastic behavior is attractive for wind energy harvesting purposes, electromechanical coupling is also modeled in the plunge degree-of-freedom along with a resistive load in the electrical domain for electrical power estimation. The exploitation of the shape memory alloy phase transformation is more attractive for airfoil-based wind energy harvesting performance than the use of typical concentrated nonlinearities (e.g., hardening steel) in terms of enhanced electrical power output. / A modelagem, análise e verificação experimental de uma seção típica aeroelástica com dois graus de liberdade e molas com memória de forma superelásticas são apresentadas. O foco é investigar os efeitos da histerese pseudoelástica das molas com memória de forma nos comportamentos de flutter e pós-flutter da seção típica. A cinética das transformações de fase nas molas com memória de forma é descrita por uma versão modificada de modelos fenomenológicos amplamente conhecidos. O modelo de molas helicoidais com memória de forma é baseado em teoria clássica de molas (com a hipótese de cisalhamento puro) e modificado para representar os efeitos não lineares de transformação de fase. A seção transversal do fio da mola com memória de forma é representada por uma distribuição radial e linear de deformações de cisalhamento e por distribuições radiais e não lineares de tensões cisalhantes e de frações martensíticas. As equações de movimento de uma seção típica linear são modificadas para incluir as molas com memória de forma. Um modelo aerodinâmico linear não estacionário é utilizado para se determinar as cargas aerodinâmicas. O modelo proposto é representado em espaço de estados e resolvido com um método Runge-Kutta. Mostra-se, numérica e experimentalmente, que a histerese pseudoelástica de molas com memória de forma pode ser efetivamente explorada para melhorar o comportamento aeroelástico de uma seção típica ao transformar oscilações instáveis de flutter em oscilações estáveis e de amplitudes aceitáveis em uma faixa de velocidades do escoamento, provendo um método útil de controle aeroelástico passivo. Como o comportamento aeroelástico modificado (pela histerese pseudoelástica) é atrativo para a coleta de energia do escoamento, um acoplamento eletromecânico é modelado no grau de liberdade de deslocamento linear, juntamente com uma carga resistiva no domínio elétrico do problema para se estimar a potência elétrica gerada. A exploração da histerese pseudoelástica das molas com memória de forma é mais atrativa para a performance da coleta aeroelástica de energia do que o uso de não linearidades concentradas típicas (como o enrijecimento não linear do aço) em termos de melhoria na potência elétrica gerada.

Owing the capability of recovering large deformations through reversible phase transformation, shape memory alloys (SMAs) are well-known for their unique behaviors such as shape memory effect (SME) and superelasticity (SE), which can also be characterized by instrumented indentation techniques. Nickel titanium (NiTi) SMAs have been extensively used for nano/micro-indentation studies and widely applied to biomedical and other elaborate medical devices. In this study, indentation responses of NiTi, NiTiHf, NiTiHfPd and NiTiHfCu alloys were investigated using spherical and Berkovich indenters at room temperature. Spherical and Berkovich indentation hardness, modulus, and work/depth recoverable ratio of these NiTi-based alloys were revealed as a function of maximum loading level at nano and macro scales. It has been revealed that indentation responses are highly composition, aging and load level dependent. Perfect work/depth recovery was observed in superelastic NiTiHfPd alloys using the spherical indenter. Temperature-dependent shape memory properties of equiatomic NiTi, Nickel rich NiTi, and as-received and aged NiTiHf alloys were investigated using a spherical indenter between 30-340 ºC under selected load levels. Ti-6Al-4V was also tested for comparison. Spherical indentation response of aged high temperature NiTiHf alloys showed a clear relationship between the work recoverable ratio and transformation temperatures, superelastic and plastic behavior. It was concluded that indentation response can be used to measure local superelasticity response, determine phase transformation temperatures and reveal the temperature intervals of the deformation mechanisms of shape memory alloys. Spherical indentation hardness and modulus as a function of temperature can be used to exam the phase transformation, but cannot provide sufficient information regarding the superelastic and plastic behavior. Orientation dependence of the shape memory properties in aged Nickel rich Ni50.3Ti29.7Hf20 single crystals were investigated along the [100], [110] and [111] orientations under room and high temperatures through indentation techniques. Indentation hardness, modulus and work /depth recoverable ratio were investigated as a function of temperature and indentation depth/load. It was found that indentation response of work recovery ratio is orientation independent, however, shape memory properties (e.g. transformation temperatures) determined from the indentation responses are almost orientation independent.

Les Alliages à Mémoire de Forme (AMF) possèdent, entre autres, des propriétés de superélasticité et de mémoire de forme remarquables dues à une transformation de phase solide-solide entre l'austénite et la martensite. En particulier, les AMF à base de Nickel-Titane (NiTi) sont aussi utilisés dans l'industrie, pour leur résistance à l'oxydation et leur tenue en fatigue. Leur capacité à dissiper l'énergie incite à leur utilisation au sein de dispositifs amortisseurs dédiés au Génie Civil. En effet, les sources de vibration (trafic routier, séismes, vent, pluie...) affectent la durabilité, vis-à-vis de la fatigue, des câbles de pont. Les amortisseurs de type hydraulique, utilisés jusqu'à aujourd'hui, peuvent transmettre des contraintes néfastes à la structure hors de leur domaine d'utilisation (en fréquence et amplitude). Un nouveau dispositif à base de fils NiTi est étudié au cours de cette thèse. Toutefois, ce matériau adapte son comportement thermomécanique aux conditions de chargement et à l'environnement thermique. Cette étude a permis de mettre au point un outil numérique destiné à caractériser l'influence d'un tel dispositif sur la réponse dynamique d'un système "câble+amortisseur". Pour cela, le matériau est caractérisé expérimentalement afin d'alimenter un nouveau modèle numérique du comportement thermomécanique en superélasticité, à l'échelle du VER. Le modèle proposé est validé selon un critère énergétique. Celui-ci est ensuite étendu à l'échelle du fil par un modèle non-local, afin d'explorer les effets d'hétérogénéité de comportement, dans le but d'une utilisation concrète. Un prototype d'amortisseur, développé au cours de cette thèse, a été testé avec succès sur un câble de pont à l'échelle 1. Le dispositif montre une réelle efficacité à réduire les amplitudes de vibration du câble. L'analyse de différentes configurations d'essais sur le câble fournit des pistes d'optimisation du système. Un modèle d'éléments finis associé, intégrant la loi de comportement du fil, permet de réaliser une analyse dynamique transitoire. Celui-ci est validé, justifiant ainsi la prise en compte des différentes sources de dissipation observées expérimentalement, à savoir : la dissipation intrinsèque, le couplage thermomécanique et la présence d'une phase solide intermédiaire (R-phase). Ces dernières peuvent être découplées, afin d'évaluer leur contribution à l'amortissement du câble.} / Shape memory alloys (SMA) have many interesting properties due to solid-solid phase transformations (usually between austenite and martensite), such as super-elasticity and/or shape memory effects. More particularly, Nickel-Titanium (NiTi) based SMA are currently used in many industrial fields for their oxydation resistance and their fatigue resistance. Furthermore, their dissipation capacities make them particularly suitable for using as dampers dedicated to Civil Engineering issues. Indeed, several phenomena (road traffic, earthquakes, wind, rain...) which are the main causes of structure vibrations, affect the sustainability of bridge cables. Current solutions, consisting in setting-up hydraulic dampers, are not satisfactory out of their working range in terms of amplitude and frequency. A new device based on NiTi wires is studied in this thesis. However, this material adapts its thermomechanical response according to input loading rates or amplitudes and thermal surroundings.In the thesis, we have developed a numerical tool which enables to predict the NiTi wires based damper influence on the dynamical response of the cable. Thus, the specimens are characterized using experimental tests in order to build a numerical thermomecanical model taking into account the superelasticity effect, at the REV scale. The model is validated according to an energetical criterion. The model is then extended to the scale of the structure, using a non-local finite elements model, in order to investigate heterogeneity effects.A damping device, developed during the thesis, is tested successfully on a full-scale bridge cable. Furthermore, the NiTi wires based damping device shows a real damping power effectiveness. The study of several test configurations provides recommendations for optimisation of the system. A related finite elements model is used to realize a transient dynamic analysis. The model, which lies on the superelastic law, is validated. It justifies, afterwards, the consideration of phenomena assumed to be sources of dissipation, such as intrinsic dissipation, thermomechanical coupling and R-phase transformation. These phenomena can be numerically isolated, to evaluate how they take part in the mitigation of cable vibrations.

Previous experimental observations have shown that the pseudoelastic response of NiTi shape memory alloys (SMA) is localized in nature and proceeds through nucleation and propagation of localized deformation bands. It has also been observed that the mechanical response of SMAs is strongly affected by loading rate and cyclic degradation. These behaviors significantly limit the accurate modeling of SMA elements used in various devices and applications. The aim of this work is to provide engineers with a constitutive model that can accurately describe the dynamic, unstable pseudoelastic response of SMAs, including their cyclic response, and facilitate the reliable design of SMA elements. A 1-D phenomenological model is developed to simulate the localized phase transformations in NiTi wires during both loading and unloading. In this model, it is assumed that the untransformed particles located close to the transformed regions are less stable than those further away from the transformed regions. By consideration of the thermomechanical coupling among the stress, temperature, and latent heat of transformation, the analysis can account for strain-rate effects. Inspired by the deformation theory of plasticity, the 1-D model is extended to a 3-D macromechanical model of localized unstable pseudoelasticity. An important feature of this model is the reorientation of the transformation strain tensor with changes in stress tensor. Unlike previous modeling efforts, the present model can also capture the propagation of localized deformation during unloading. The constitutive model is implemented within a 2-D finite element framework to allow numerical investigation of the effect of strain rate and boundary conditions on the overall mechanical response and evolution of localized transformation bands in NiTi strips. The model successfully captures the features of the transformation front morphology, and pseudoelastic response of NiTi strip samples observed in previous experiments. The 1-D and 3-D constitutive models are further extended to include the plastic deformation and degradation of material properties as a result of cyclic loading. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Superelastic Shape Memory Alloys (SMAs) are being explored as alternative reinforcing materials to traditional deformed steel reinforcement for seismic applications. The main advantage is the ability of the SMA to recover large nonlinear strains, which promotes the self-centering phenomenon. The primary objective of this research is to present the performance, before and after repair, of slender reinforced concrete shear walls, one reinforced internally with SMAs in the boundary zones within the plastic hinge region and other control wall reinforced with conventional steel only. The repair procedure included removal of damaged concrete within the plastic hinge region, replacing fractured and buckled reinforcement, followed by shortening of the SMA reinforcement in the boundary zones of SMA wall. The removed concrete was replaced with self-consolidating concrete, while the concrete above the plastic hinge region remained intact. The SMA reinforced concrete shear wall (before and after repair) exhibited stable hysteretic response with significant strength, and displacement and energy dissipation capacities. In addition, the walls exhibited pinching in the hysteretic response as a result of minimizing the residual displacements due to the restoring capacity of the SMA reinforcement. The results demonstrate that SMA reinforced components are self-centering, permitting repairing of damaged areas. Furthermore, the SMA reinforcement is re-usable given its capacity to reset to its original state. The length of the SMA bars in the original and repaired wall, in addition to the presence of starter bars in the original wall, were significant factors in the location of failure of the walls. The conventional steel wall prior to repair was unstable due to large residual displacements experienced during the original test. After repair the wall exhibited ratcheting in hysteretic response but with significant strength. The conventional wall, before and after repair, dissipated more energy than the SMA wall. This was the result of the wider hysteretic loops with reduced punching, but at the cost of large residual displacements. The starter bars in the conventional wall before repair controlled the location of failure, while the presence of couplers in the plastic hinge region was the main factor in determining the failure location in the repaired conventional wall.