The exciting thermomechanical properties of nickel-titanium shape memory alloys have sparked significant research efforts seeking to exploit their exotic capabilities. Until recently, the performance capabilities of nickel-titanium devices have been inhibited by the retention of only one thermomechanical characteristic. However, laser processing technology promises to deliver enhanced material offerings which are capable of multiple functional responses. Presented in this thesis, is an investigation of the effects of laser processing on the thermomechanical behaviour of nickel-titanium shape memory alloys. In the context of this work, laser processing refers to removal of alloy constituents, as in the case of laser ablation, or alternatively, addition of elements through laser alloying. The effects of laser ablation on the composition, crystallography and phase transformation temperatures of a nickel-titanium strip have been studied. Application of laser energy was shown to ablate nickel constituents, induce an austenite-martensite phase change and cause an increase in phase transformation onset temperatures, which correlated well with reported findings. Laser processing of a nickel-titanium wire was shown to locally embed an additional thermomechanical response which manifested as unique shape memory and pseudoelastic properties. Localized alloying of ternary species via laser processing of nickel-titanium strip was investigated. Synthesis of a ternary shape memory intermetallic within the laser processing region was achieved through melting of copper foils. Results from thermoanalytical testing indicated that the ternary compound possessed a higher phase transformation temperature and reduced transformation hysteresis in comparison to the reference alloy. Indentation testing was used to demonstrate the augmented thermomechanical characteristics of the laser processed shape memory alloy. In order to demonstrate the enhanced functionality of laser processed nickel-titanium shape memory alloys, a self-positioning nickel-titanium microgripper was fabricated. The microgripper was designed to actuate through four different positions, corresponding to activation of three embedded shape memory characteristics. Thermoanalytical and tensile testing instrumentations were used to characterize the thermomechanical performance of the laser processed nickel-titanium microgripper. Results indicated that each of the laser processed microgripper components possessed unique mechanical and shape memory recovery properties.

Shape memory alloys are a class of alloys that display the unique ability to undergo large plastic deformations and return to their original shape either through the application of heat (shape memory effect) or by relieving the stress causing the deformation (superelastic effect). This research takes advantage of the unique characteristics of shape memory alloys in order to provide a moment resisting connection with recentering capabilities. In this study, superelastic Nitinol, a nickel-titanium form of shape memory alloy that exhibits a flag-shaped stress versus strain curve, is used as the moment transfer elements within a partially restrained steel beam-column connection. Experimental testing consists of a one-half scale interior connection where the loading is applied at the column tip. A pseudo-static cyclic loading history is used which is intended to simulate earthquake loadings. The energy dissipation characteristics, moment-rotation characteristics, and deformation capacity of the connection are quantified. Results are then compared to tests where A36 steel tendons are used as the moment transfer elements. The superelastic Nitinol tendon connection showed superior performance to the A36 steel tendon connection, including the ability to recenter without residual deformation.

M. Tech. Metallurgical Engineering. / Studies the corrosion behavior of sintered Ni-Ti shape memory alloys containing Cu and Nb additions.Objectives are: 1. Investigate structural and phased interactions occurring during the sintering of the allloys. 2. Study the effects of niobium and copper addition on the general corrosion behavior of the sintered nickel-titanium alloys in sodium chloride and sulphuric acid. 3. Study the effects of copper and niobium addition on localized corrosion behavior of the alloys in chloride environments.

M. Tech. Metallurgical Engineering. / StudIes the tribocorrosion behaviour of copper-nickel-titanium shape memory composite reinforced by zirconia,synthesized through powder metallurgy process. The research aims to achieve the following objectives: 1. Study the tribocorrosion mechanisms of the composites in NaCl solution (typical human body fluid). 2. Investigate the tribocorrosion mechanisms of the composites in other environments typical of some engineering applications.The proposed study on incorporating zirconia into the matrix NiTiCu through powder metallurgical process and investigations of the phenomenon of joint wear-corrosion synergism occurring in sodium chloride considered typical of human body system and sulphuric acid environment typical of wide range engineering applications is therefore very novel. It is therefore aimed that information on the tribocorrosion behaviour of NiTiCu as well as with zirconia incorporation will form basis for typical compositional formulation approaches for improved bio-tribocorrosion improvement in biomedical applications and actuators used in other engineering applications.

Shape memory alloys (SMAs) are widely used in a broad variety of applications in multiscale devices ranging from nano-actuators used in nano-electrical-mechanical systems (NEMS) to large energy absorbing elements in civil engineering applications. This research introduces a multiscale analysis for SMAs, particularly Nickel-Titanium alloys (NiTi). SMAs are studied in a variety of length scales ranging from macroscale to nanoscale. In macroscale, a phenomenological constitutive framework is adopted and developed by adding the effect of phase transformation latent heat. Analytical closed-form solutions are obtained for modeling the coupled thermomechanical behavior of various large polycrystalline SMA devices subjected to different loadings, including uniaxial loads, torsion, and bending. Thermomechanical responses of several SMA devices are analyzed using the introduced solutions and the results are validated by performing various experiments on some large SMA elements. In order to study some important properties of polycrystalline SMAs that the macroscopic phenomenological frameworks cannot capture, including the texture and intergranular effects in polycrystalline SMAs, a micromechanical framework with a realistic modeling of the grains based on Voronoi tessellations is used. The local form of the first law of thermodynamics is used and the energy balance relations for the polycrystalline SMAs are obtained. Generalized coupled thermomechanical governing equations considering the phase transformation latent heat are derived for polycrystalline SMAs. A three-dimensional finite element framework is used and different polycrystalline samples are modeled. By considering appropriate distributions of crystallographic orientations in the grains obtained from experimental texture measurements of NiTi samples the effects of texture and the tension-compression asymmetry on the thermomechanical response of polycrystalline SMAs are studied. The interaction between the stress state (tensile or compressive), number of grains, and the texture on the thermomechanical response of polycrystalline SMAs is also studied. For studying some aspects of the thermomechanical properties of SMAs that cannot be studied neither by the phenomenological constitutive models nor by the micromechanical models, molecular dynamics simulations are used to explore the martensitic phase transformation in NiTi alloys at the atomistic level. The martensite reorientation, austenite to martensite phase transformation, and twinning mechanisms in NiTi nanostructures are analyzed and the effect of various parameters including the temperature and size on the phase transformation at the atomistic level is studied. Results of this research provide insight into studying pseudoelasticity and shape memory response of NiTi alloys at different length scales and are useful for better understanding the solid-to-solid phase transformation at the atomistic level, and the effects of this transformation on the microstructure of polycrystal SMAs and the macroscopic response of these alloys.

The exciting thermomechanical properties of nickel-titanium shape memory alloys have sparked significant research efforts seeking to exploit their exotic capabilities. Until recently, the performance capabilities of nickel-titanium devices have been inhibited by the retention of only one thermomechanical characteristic. However, laser processing technology promises to deliver enhanced material offerings which are capable of multiple functional responses. Presented in this thesis, is an investigation of the effects of laser processing on the thermomechanical behaviour of nickel-titanium shape memory alloys. In the context of this work, laser processing refers to removal of alloy constituents, as in the case of laser ablation, or alternatively, addition of elements through laser alloying. The effects of laser ablation on the composition, crystallography and phase transformation temperatures of a nickel-titanium strip have been studied. Application of laser energy was shown to ablate nickel constituents, induce an austenite-martensite phase change and cause an increase in phase transformation onset temperatures, which correlated well with reported findings. Laser processing of a nickel-titanium wire was shown to locally embed an additional thermomechanical response which manifested as unique shape memory and pseudoelastic properties. Localized alloying of ternary species via laser processing of nickel-titanium strip was investigated. Synthesis of a ternary shape memory intermetallic within the laser processing region was achieved through melting of copper foils. Results from thermoanalytical testing indicated that the ternary compound possessed a higher phase transformation temperature and reduced transformation hysteresis in comparison to the reference alloy. Indentation testing was used to demonstrate the augmented thermomechanical characteristics of the laser processed shape memory alloy. In order to demonstrate the enhanced functionality of laser processed nickel-titanium shape memory alloys, a self-positioning nickel-titanium microgripper was fabricated. The microgripper was designed to actuate through four different positions, corresponding to activation of three embedded shape memory characteristics. Thermoanalytical and tensile testing instrumentations were used to characterize the thermomechanical performance of the laser processed nickel-titanium microgripper. Results indicated that each of the laser processed microgripper components possessed unique mechanical and shape memory recovery properties.

In this thesis, I present studies in the field of terahertz (THz) spectroscopy. These studies are divided into three areas: Development of a narrowband THz source, the study of carrier transport in metal thin films, and the exploration of coherent dynamics of quasi-particles in semiconductor nanostructures with both broadband and narrowband THz sources. The narrowband THz source makes use of type II difference frequency generation (DFG) in a nonlinear crystal to generate THz waves. By using two linearly chirped, orthogonally polarized optical pulses to drive the DFG, we were able to produce a tunable source of strong, narrowband THz radiation. The broadband source makes use of optical rectification of an ultra-short optical pulse in a nonlinear crystal to generate a single-cycle THz pulse. Linear spectroscopic measurements were taken on NiTi-alloy thin films of various thicknesses and titanium concentrations with broadband THz pulses as well as THz power transmission measurements. By applying a combination of the Drude model and Fresnel thin-film coefficients, we were able to extract the DC resistivity of the NiTi-alloy thin films. Using the narrowband source of THz radiation, we explored the exciton dynamics of semiconductor quantum wells. These dynamics were made sense of by observing time-resolved transmission measurements and comparing them to theoretical calculations. By tuning the THz photon energy near exciton transition energies, we were able to observe extreme nonlinear optical transients including the onset of Rabi oscillations. Furthermore, we applied the broadband THz waves to quantum wells embedded in a microcavity, and time-resolved reflectivity measurements were taken. Many interesting nonlinear optical transients were observed, including interference effects between the modulated polariton states in the sample. / Graduation date: 2012

Le tricotage est une technique d'obtention de textiles ancestrale qui est encore couramment utilisée de nos jours. Cette technique permet de produire des textiles possédant une forte déformation élastique, un comportement mécanique anisotrope modifiable simplement en jouant sur la géométrie de la maille, la possibilité d'obtenir des formes générales (préformes) ou internes (trous) durant le procédé de fabrication, rendant ces textiles particulièrement attractifs et rentables. Plus récemment, l’utilisation des alliages à mémoire de forme (AMF), en particulier de fils de Nickel-Titane (Ni-Ti), pour produire ces tricots a permis de proposer des textiles aux fonctionnalités nouvelles, telles qu'une très grande déformation élastique, un changement de forme sous l'effet d'un échauffement, une forte capacité d’amortissement, etc.Cependant, le comportement mécanique de tels tricots AMF reste encore assez mal connu, et bien qu'un certain nombre d'études aient déjà été proposées dans la littérature concernant la caractérisation du comportement mécanique de ces tricots, l'application aux tricots NiTi reste insuffisamment faite.Dans ce travail, un ensemble d’outils expérimentaux et numériques a été mis en place pour étudier la déformation des tricots NiTi, en particulier pour évaluer l'influence des paramètres matériaux, géométrie, frottements, etc., sur le comportement mécanique. Un montage expérimental a été développé pour caractériser le textile en traction biaxiale. Il s'inspire des techniques utilisées pour les membranes souples visant à obtenir un champ de déformation le plus uniforme possible dans la zone déformée. De plus, sa conception ainsi qu’un programme de traitement d'images permettent la mesure de la distribution des efforts aux frontières ainsi que la mesure de la morphologie des mailles du tricot au cours de la déformation.Le comportement mécanique du tricot a été modélisé par homogénéisation numérique en réalisant des simulations numériques par éléments finis sur une maille représentative sous conditions périodiques. Les prédictions des simulations sont validées en regard des résultats expérimentaux obtenus sur les tricots NiTi, en traction simple et traction biaxiale suivant les directions chaine et trame. Elles sont ensuite utilisées pour analyser l'importance des différents mécanismes de déformation en fonction de la sollicitation étudiée. / Knitting is an ancestral textile manufacturing technique which is still commonly used nowadays. This method allows to manufacture textiles possessing high recoverable strains, an anisotropic mechanical behavior easily tuned by varying the knit loop dimensions, the ability to obtain general forms (preforms) or internal forms (holes) during the manufacturing process, and more, making those textiles particularly attractive and cost-efficient. More recently, the use of Shape Memory Alloys (SMA), notably Nickel-Titanium (Ni-Ti) wires, for producing those textiles allowed to propose textiles with new functional properties, such as very high recoverable strains, shape-shifting effects under temperature changes, high damping capacity, etc.However, such SMA knitted textiles mechanical behavior remains relatively unknown, and even if a certain number of studies have dealt with the knitted textiles mechanical characterization, the application to NiTi knitted textiles remains insufficiently done.In this work, a set of experimental and numerical tools have been developed to study knitted NiTi textiles deformation, especially to evaluate the influence of material parameters, knit geometry, friction, etc., on the mechanical behavior. An experimental setup has been developed to characterize such textiles in biaxial tension. It is inspired by methods developed for soft membranes aiming at obtaining strain fields as uniform as possible in the sample working area. Furthermore, its conception as well as a dedicated image processing software allow measuring boundary forces distributions and knit loops morphology during deformation.The knitted textile mechanical behavior has been modeled using numerical homogenization method by performing finite elements numerical simulation of a representative knit loop under periodic conditions. Simulations predictions are validated in regard to experimental results obtained on knitted NiTi textiles, in simple tension and biaxial tension in course and wale directions. They are then used to analyze the importance of different deformation mechanisms depending on the loading case studied.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho tem como objetivo avaliar a influência da conicidade de instrumentos de níquel-titânio acionados a motor, na flexibilidade; na resistência a fratura por torção à direita e na resistência a fratura por flexão rotativa, analisando ainda por meio de microscopia eletrônica de varredura a superfície de fratura dos instrumentos ocorridas por torção e por flexão rotativa, bem como a configuração das hélices das hastes de corte helicoidais dos instrumentos junto ao ponto de fratura. Foram utilizados sessenta instrumentos fabricados em níquel-titânio acionados a motor da marca K3 (Sybron Dental Specialties-Kerr, México), valores nominais de 25mm de comprimento, e de 0,25mm de diâmetro em Do, nas conicidades de 0,02 0,04 e 0,06mm/mm. Dez instrumentos endodônticos de cada conicidade foram avaliados por meio do ensaio não destrutivo de flexão em cantilever e dez instrumentos endodônticos de cada conicidade foram avaliados por meio dos ensaios destrutivos de torção à direita e de flexão rotativa. Diante das metodologias empregadas, dos resultados obtidos e após a execução dos testes estatísticos: Análise de variância no nível de significância de 5%, e do teste de comparações múltiplas de Student-Newman-Keuls a 5%, podemos concluir que: A flexibilidade dos instrumentos ensaiados diminui com o aumento da conicidade da haste de corte helicoidal. O ângulo máximo de torção dos instrumentos ensaiados por torção diminui com o aumento da conicidade da haste de corte helicoidal. O torque máximo até a fratura dos instrumentos ensaiados por torção aumentou com o aumento da conicidade da haste de corte helicoidal. O número de ciclos para a fratura em flexão rotativa diminui com o aumento da conicidade e com o aumento da resistência em flexão (diminuição da flexibilidade) dos instrumentos endodônticos ensaiados. E quanto à análise por meio do microscópio eletrônico de varredura, independentemente, da conicidade e do tipo de carregamento, (torção ou flexão rotativa) aplicado ao instrumento endodôntico, podemos concluir que as amostras fraturadas apresentaram superfície de fratura com característica dúctil. No ensaio de torção, observou-se a reversão do sentido das hélices das hastes de corte helicoidais junto ao ponto de imobilização dos instrumentos. No ensaio de flexão rotativa não ocorreu reversão do sentido das hélices das hastes de corte helicoidais (deformação plástica visível) dos instrumentos fraturados. / This work has as purpose to evaluate the influence of motor driven nickel-titanium instruments tapering, in the flexibility, resistance to fracture by twisting to the right by rotating flexure, analyzing also by means of scanning electronic microscopy the instruments fracture surface arising by twisting and rotating flexure, as well as the configuration of helices of helical cutting rods of instruments near the fracture point. Sixty instrument made of nickel- -titanium and motor-driven of K3 brand were used (Sybron Dental Specialties-Kerr, Mexico), nominal value of 25mm long, and 0,25mm diameter in Do, in tapering of 0,02 0,04 and 0,06mm/mm. Ten endodontic instruments of each tapering were evaluated by means of the non destructive test of flexure in cantilever and ten endodontic instruments of each tapering were evaluated by means of destructive tests twisting to the right and rotating flexure. After the performance of statistic test,: variance analysis at significance level of 5%, and multiple comparison test from Student-Newman-Keuls to 5%, Taking into consideration the implemented methodology, the applied statistical techniques (e.g. variance analysis at significance level of .05 and multiple comparison test from Student-Newman-Keuls at significance level of .05), and the obtained results, it was demonstrated that the flexibility of the instruments tested decreases as the tapering of the helices of helical cutting rods increases. The maximum twisting angle of the instruments tested by twisting decreases as the tapering of the helices of helical cutting rods increases. The maximum torque up to the fracture of the tested instruments increased as the tapering of the helices of helical cutting rods increased. The number of cycles for the fracture in rotating flexure decreases as the tapering increase and the increase of the resistance in flexure (flexibility decrease) of the tested endodontic instruments increased. The analysis by scanning electronic microscopy revealed that, independently of the tapering and the rotating type (twisting or rotating flexure) applied to the endodontic instrument, the fractured samples presented fractured surface of ductile characteristics. A reversion of the helical cutting rods course was observed on the twisting test near the immobilization point. A reversion of the helical cutting rods course (visible plastic deformation) on the rotating flexure test of the fractured instruments was not observed.

Orientador: Léa Assed Bezerra da Silva / Banca: Mario Roberto Leonardo / Banca: Jesus Djalma Pécora / Resumo: Foram utilizados 115 dentes pré molares inferiores de humanos, que foram divididos em 5 grupos de 16 dentes cada; sendo 5 grupos com 5 dentes cada, utilizados como controle positivo e, 5 grupos de 2 dentes como controle negativo. Em todos os dentes após a abertura coronária, foi realizado o desbridamento foraminal com uma lima tipo Kerr no 15 até 1mm além do forame apical e o preparo biomecânico a 1mm aquém comprimento real do dente. Foram utilizados para a instrumentação dos canais radiculares, os sistemas de limas rotatórias de níquel titânio ProFile 0.4/.06 e Quantec, e a técnica Clássica Modificada; sendo o batente apical preparado até a lima 45 de cada técnica de instrumentação. A cada troca de lima, foi utilizado o hipoclorito de sódio à 1% como solução irrigadora. Posteriormente os dentes foram obturados pelos sistemas de guta-percha termoplastificada Thermafil, Microseal e pela técnica da Condensação Lateral Ativa; utilizando como cimento obturador; AH Plus. Após as obturações os dentes foram impermeabilizados com esmalte de unha, exceto, o 1mm ao redor do forame apical; imersos no corante de azul de metileno à 2% sob vácuo e fraturados de maneira a serem obtidas duas hemi-partes. A penetração do corante foi medida com auxílio de um perfilômetro, e os dados, após análise estatística mostraram que, o grupo de dentes instrumentados pelo sistema ProFile 0.4/.06 e obturados com o sistema Thermafil, apresentaram menor infiltração apical, quando comparado com os demais grupos. / Abstract: It was evaluated 115 mandibular premolars of humans, that were divided in 5 groups of 16 teeth each; 5 groups with 5 teeth each, used as positive control and 5 groups of 2 teeth as negative control. After coronary acess, the apical patency was accomplished with a file type Kerr no 15 up to 1mm after the apical foramen and prepared to 1mm short of working length. Instrumentation wasdone, using ProFile 0,04 and 0,06 and Quantec, stotary files and the Modified Classic technique; The apical preparation used a file 45 as memory file. After each file change, sodium hypochlorite was used at 1% as irrigation solution. The teeth were filled using systems of thermoplasticized gutta-percha Thermafil, Microseal and the technique of the Active Lateral Condensation. The sealer used was the AH Plus root canal sealer. After obturation the teeth were waterproof with fingernail enamel, except, the 1mm short of the apical foramen; immerged in the coloring of methylene blue at 2% under vacuum and fractured in a way where it was obtained two hemi-parts. The penetration of the coloring was measured with aid of a Nikon Profile Projector, and the data, after statistical analysis showed that, the group of teeth under the system ProFile 0,04 and 0,06 and filled with the system Thermafil, presented lower leakage apical, when compared with other groups. / Mestre