Thesis (M.Sc.)--City University of Hong Kong, 2006. / "Master of Science in Materials Engineering & Nanotechnology dissertation." Title from title screen (viewed on Nov. 23, 2006) Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 127-134).

Thesis (M.Sc.)--City University of Hong Kong, 2005. / At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Aug. 31, 2006) Includes bibliographical references.

Thesis (M.Sc.)--City University of Hong Kong, 2005. / At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Aug. 31, 2006) Includes bibliographical references.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 101-106). Also available in electronic version.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 249-257).

Submitted by FREDERIC CONRAD JANZEN null (fcjanzen@utfpr.edu.br) on 2016-11-13T01:59:49Z No. of bitstreams: 1 Positioning and vibration control of a flexible structure in slewing motion by applying Shape Memory Alloys.pdf: 10393447 bytes, checksum: 905f7c805c63133af1f576ad7ebbfd4b (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-11-17T18:09:27Z (GMT) No. of bitstreams: 1 janzen_fc_dr_bauru.pdf: 10393447 bytes, checksum: 905f7c805c63133af1f576ad7ebbfd4b (MD5) / Made available in DSpace on 2016-11-17T18:09:27Z (GMT). No. of bitstreams: 1 janzen_fc_dr_bauru.pdf: 10393447 bytes, checksum: 905f7c805c63133af1f576ad7ebbfd4b (MD5) Previous issue date: 2016-09-19 / Estruturas flexíveis com movimento de rastreamento tem sido encontradas com frequência cada vez maior em diversos tipos de aplicações, por serem mais eficientes do que suas concorrentes rígidas. O estudo desses sistemas é importante por conta das vibrações advindas da redução de massa das estruturas. Muitos trabalhos têm sido publicados apresentado técnicas de controle aplicadas na redução dos efeitos dessas vibrações. Vários trabalhos demonstram a aplicação de materiais inteligentes como atuadores para esse tipo de aplicação. Sendo assim, o presente trabalho apresenta uma proposta para o controle do posicionamento angular e da vibração de uma estrutura flexível em movimento de rastreamento. Para tal, atuadores compostos de um material inteligente conhecido como Liga com Memoria de Forma são empregados para o controle da vibração da estrutura flexível. Com relação ao controle, a técnica de controle conhecida como Equações de Ricatti Dependentes dos Estados (SDRE) é aplicada para o controle. Com o objetivo de analisar a dinâmica do sistema com o controle proposto considera-se a modelagem matemática do sistema e sua validação através do desenvolvido de um protótipo experimental. Simulações numéricas são realizadas para analisar a viabilidade do controle proposto e testes experimentais são realizados com a finalidade de validar o modelo teórico e a proposta de controle. / Flexible structures with slewing motion has been found with increasing frequency in various types of applications, because they are more efficient than their rigid competitors. The study of these systems is important because of the vibrations coming from the mass reduction of structures. Many works have been published presenting control techniques applied in reducing the effects of these vibrations. Several studies demonstrate the application of intelligent materials as actuators for this application. This paper presents a proposal for controlling the angular positioning and vibration of a flexible structure in slewing motion. For such compounds an intelligent actuator materials known as Shape Memory Alloy is employed to control the vibration of the flexible structure. To control the system, the control technique known as State Dependent Ricatti Equation (SDRE), is applied to the control. In order to analyse the dynamics of the system with the proposed control the mathematical modelling of the system is considered and its validation by developed an experimental prototype. Numerical simulations are carried out to analyse the viability of the control and experimental tests are performed in order to validate the theoretical model and the proposed control.

Thesis submitted in fulfilment of the requirements for the degree Magister Technologiae: Mechanical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2008 / The increasing requirement for light weight constructions and the unsatisfactory performances of traditional metals and conventional engineering materials, especially in their failure to positively respond to environmental stimuli, in a demanding environment have made the search for the development of alternative materials inevitable. Such alternative materials being sought, which are the so-called adaptive, multifunctional, smart or intelligent composites would facilitate the realization of some engineering applications that are simply difficult to achieve with the existing conventional materials. Composite materials have found increasing applications in construction, aerospace and automotive industries due to their good characteristics of light weight, improved strength, corrosion resistance, controlled anisotropic properties, and reduced manufacturing and maintenance costs. However, there is a growing demand to improve on composite materials to have “smart" capabilities so as to be able to sense, actuate and respond to the surrounding environment. Shape memory alloys (SMAs) are metallic alloys that can undergo martensitic phase transformations as a result of applied thermomechanical loads and are capable of recovering permanent strains when heated above a certain transformation temperature. SMAs possess sensing and actuating functions and have the potential to control the mechanical properties and responses of their hosts due to their inherent unique characteristics: shape memory effect (SME) and pseudoelasticity. When integrated into structural components, they perform sensing, diagnosing, actuating and repair or healing functions, thereby enhancing improved performance characteristics of their hosts. Amongst the commercially available SMAs, NiTi (Nickel-Titanium) alloys in forms of wires, ribbons, bars, particles and porous bulks are the most widely used because of their excellent mechanical properties and superior material characteristics. Embedding SMAs into composite materials can create smart or intelligent hybridized composites. This thesis details an investigation of the mechanical properties and behaviour of the hybridized composites formed by embedding NiTi SMA wires into 60D polyurethane. The composites were produced by the vacuum process of manufacturing. The properties of the implanted SMA wires were enhanced by ageing and pre-straining. Uniaxial tensile and four point bending tests were conducted to ascertain the significance of embedding SMA wires into the polyurethane host matrix. It was found that the embedded SMA results in an increasing in elastic modulus, tensile strength and bending stiffness. It was found that these improvements in the properties can not be sustained at high temperature owing to degradation of interfacial strength between the SMA and polyurethane as a result of the high recovery stress generated by the SMA upon activation. Some measures that can ameliorate the interfacial breakdown were suggested.

Les alliages de titane sont actuellement très utilisés comme implants orthopédiques de part leurs bonnes propriétés mécaniques, leur bonne résistance à la corrosion ainsi que leur excellente biocompatibilité. Cependant, l’alliage Ti-6Al-4V qui est le plus utilisé présente un module d'élasticité élevé (110GPa), ce qui peut provoquer le phénomène de « stress shielding » et finalement causer l’échec de l’implantation. De plus, l’utilisation à long terme de ce type d’alliage est remise en question à cause de la présence de certains éléments (Al et V) considérés comme cytotoxiques et/ou allergènes. Les alliages -métastables à base de titane peuvent être des candidats de remplacement intéressants grâce à l’addition d'éléments biocompatibles tel que Nb, Zr et Sn.L'alliage superélastique biocompatible de composition Ti-24Nb-4Zr-8Sn (% massique) a été étudié dans le cadre de cette thèse. Cet alliage montre des propriétés intéressantes telles qu’un bas module d’élasticité, une résistance mécanique élevée et une ductilité relativement importante.Dans ce travail de thèse, différents traitements thermomécaniques ont été réalisés afin d’obtenir des textures cristallographiques différentes. Les influences de changement de texture sur les propriétés mécaniques et la superélasticité ont été ainsi préalablement étudiées. La transformation martensitique a été caractérisée par des essais in situ de diffraction des rayons X sous rayonnement synchrotron (SXRD) pendant une sollicitation mécanique et par analyse mécanique dynamique (DMA) sous différentes contraintes statiques. De plus, les microstructures de déformation ont été observées par EBSD et MET pour caractériser précisément les mécanismes de déformation plastique, en particulier le maclage. / Titanium alloys have already been extensively used as orthopedic implants due to the good mechanical properties, corrosion resistance and excellent biocompability. However, the most widely used Ti-6Al-4V alloy exhibits high elastic modulus (110GPa) which would cause the stress shield effect and eventually lead to the implantation failure. Furthermore, elements of Al and V are proved to be toxic for long-term application. Low modulus metastable  titanium alloy can be a suitable candidate through proper addition of non-toxic alloying element such as Nb, Zr and Sn.The present investigated Ti-24Nb-4Zr-8Sn alloy is a new -type metastable alloy potentially interesting for biomedical applications. This alloy displays high strength, low elastic modulus, high ductility, superelastic property and good biocompatibility according to previous investigations.In this work, the as-cold rolled Ti-24Nb-4Zr-8Sn alloy was subjected to different thermo-mechanical treatments in order to introduce different crystallographic texture. Influences of texture change on mechanical properties and superelasticity have been preliminarily studied. Martensitic transformation which is responsible for the superelasticity has been characterized by both in situ synchrotron X-ray diffraction and dynamic mechanical analysis. Moreover, deformed microstructures have been observed by EBSD and TEM to characterize precisely the plastic deformation mechanisms, and particularly the twinning.

Near equi-atomic nickel titanium (NiTi) shape memory alloys (SMAs) are a class of materials characterized by their unique deformation behavior. In these alloys, deformation mechanisms such as mechanical twinning and stress induced phase transformation between a high symmetry phase (austenite) and a low symmetry phase (martensite) additionally occur and influence mechanical behavior and thus their functionality. Consequently, applications of SMAs usually call for precise phase transformation temperatures, which depend on the thermomechanical history and the composition of the alloy. Instrumented indentation, inherently a mechanical characterization technique for small sampling volumes, offers a cost effective means of empirically testing SMAs in the form of centimeter scaled buttons prior to large-scale production. Additionally, it is an effective probe for intricate SMA geometries (e.g., in medical stents, valves etc.), not immediately amenable to conventional mechanical testing. The objective of this work was to study the deformation behavior of NiTi SMAs using instrumented indentation. This involved devising compliance calibration techniques to account for instrument deformation and designing spherical diamond indenters. Substantial quantitative information related to the deformation behavior of the shape memory and superelastic NiTi was obtained for the first time, as opposed to existing qualitative indentation studies. For the case of shape memory NiTi, the elastic modulus of the B19' martensite prior to twinning was determined using spherical indentation to be about 101 GPa, which was comparable to the value from neutron diffraction and was substantially higher than typical values reported from extensometry (68 GPa in this case). Twinning at low stresses was observed from neutron diffraction measurements and was attributed to reducing the elastic modulus estimated by extensometry. The onset of predominantly elastic deformation of the twinned martensite was identified from the nanoindentation response and the elastic modulus of the twinned martensite was estimated to be about 17 GPa. Finite element modeling was used to validate the measurements. For the case of the superelastic NiTi, the elastic modulus of the parent austenite was estimated to be about 62 GPa. The onset of large-scale stress induced martensite transformation and its subsequent elastic deformation were identified from the nanoindentation response. The effect of cycling on the mechanical behavior of the NiTi specimen was studied by repeatedly indenting at the same location. An increase in the elastic modulus value for the austenite and a decrease in the associated hysteresis and residual depth after the initial few cycles followed by stabilization were observed. As for the case of shape memory NiTi, finite element modeling was used to validate the measurements. This work has initiated a methodology for the quantitative evaluation of shape memory and superelastic NiTi alloys with instrumented spherical indentation. The aforementioned results have immediate implications for optimizing thermomechanical processing parameters in prototype button melts and for the mechanical characterization of intricate SMA geometries (e.g., in medical stents, valves etc.) This work was made possible by grants from NASA (NAG3-2751) and NSF (CAREER DMR-0239512) to UCF.