Shape memory alloys (SMA) offer several advantages over traditional electro-mechanical devices, including: smooth, silent, clean operation; linear actuation; high power/weight ratio; scalability; and reduced part counts. These unique characteristics make them an attractive option when developing actuators, particularly at the meso- and micro-scales. However, SMAs do not typically display cyclic actuation and, therefore, require some reset force or bias mechanism in order to achieve this behaviour. Additionally, the micro-assembly of SMA material with a reset mechanism becomes increasingly difficult as the dimensions of actuators are scaled down. Therefore, actuators have been developed in which the actuation and reset mechanism are fabricated from a single piece of material. These actuators are referred to as monolithic actuators. Monolithic actuators are fabricated from a single piece of SMA material in which local annealing is used to selectively impart the shape memory effect (SME), while the remainder of the material acts as the bias mechanism. This work proposes an extension to monolithic actuators that locally varies the material composition of the monolithic component to exhibit different mechanical properties in select regions. This eliminates the need for local annealing by introducing regions of material unaffected by the annealing process. Additionally, incorporating regions of superelastic material to act as the bias mechanism greatly increases the actuator’s range of motion. These actuators are referred to as hybrid monolithic actuators. The creation of hybrid monolithic SMA actuators requires the development of both a fabrication technique and design tool. Varying the composition locally is accomplished by utilizing powder metallurgy fabrication techniques, specifically tape casting. Tapes of different compositions are cut, stacked, and sintered resulting in a monolithic component with mechanical properties that vary spatially. Tape casting NiTi from elemental powders is studied in this work, and tape recipes and sintering profiles are developed. In order to model the SMA behaviour of complex geometries, a finite element implementation of an existing lumped-element SMA model is developed. This model is used to design and simulate a prototype hybrid monolithic actuator. The prototype is fabricated and its performance used to illustrate the advantages of hybrid design over typical monolithic actuators.

Shape memory alloys (SMA) offer several advantages over traditional electro-mechanical devices, including: smooth, silent, clean operation; linear actuation; high power/weight ratio; scalability; and reduced part counts. These unique characteristics make them an attractive option when developing actuators, particularly at the meso- and micro-scales. However, SMAs do not typically display cyclic actuation and, therefore, require some reset force or bias mechanism in order to achieve this behaviour. Additionally, the micro-assembly of SMA material with a reset mechanism becomes increasingly difficult as the dimensions of actuators are scaled down. Therefore, actuators have been developed in which the actuation and reset mechanism are fabricated from a single piece of material. These actuators are referred to as monolithic actuators. Monolithic actuators are fabricated from a single piece of SMA material in which local annealing is used to selectively impart the shape memory effect (SME), while the remainder of the material acts as the bias mechanism. This work proposes an extension to monolithic actuators that locally varies the material composition of the monolithic component to exhibit different mechanical properties in select regions. This eliminates the need for local annealing by introducing regions of material unaffected by the annealing process. Additionally, incorporating regions of superelastic material to act as the bias mechanism greatly increases the actuator’s range of motion. These actuators are referred to as hybrid monolithic actuators. The creation of hybrid monolithic SMA actuators requires the development of both a fabrication technique and design tool. Varying the composition locally is accomplished by utilizing powder metallurgy fabrication techniques, specifically tape casting. Tapes of different compositions are cut, stacked, and sintered resulting in a monolithic component with mechanical properties that vary spatially. Tape casting NiTi from elemental powders is studied in this work, and tape recipes and sintering profiles are developed. In order to model the SMA behaviour of complex geometries, a finite element implementation of an existing lumped-element SMA model is developed. This model is used to design and simulate a prototype hybrid monolithic actuator. The prototype is fabricated and its performance used to illustrate the advantages of hybrid design over typical monolithic actuators.

Shape Memory Alloy is an amazing material, which can “remember” and return to its original shape when heated due to its temperature dependent phase transformation. Shape Memory Alloy wire has significant potential for application in the automobile industry due to its high ratio of energy / weight and silent actuation. However, a dependable method to measure the operating temperature of SMA wire and a reliable heat transfer model to characterize the dynamics of the SMA wire limit its widespread use in the automobile industry. This thesis presents a detailed description of the work performed to develop a reliable method for determining surface temperature of current carrying SMA wires and the development of a heat transfer correlation for natural convection cooling of heated SMA wires. The major findings of the research are as follows: When a spot welded thermocouple measures the temperature of a current carrying SMA wire, there is a “spurious voltage” ΔV added to the thermo electro-motive force (EMF) of the thermocouple as a result of a voltage drop across the two points of contact that the thermocouple wires make with the SMA wire. This leads to an erroneous temperature reading that can be higher or lower than the actual temperature depending on the direction of current flow. When the carrying current is reversed in direction, the “spurious voltage” becomes –ΔV allowing a correct temperature reading to be obtained by averaging the readings based on opposed current flow. A two-step spot welding procedure for attaching thermocouples to SMA wire can eliminate the influence of the “spurious voltage” in the temperature reading. By spot welding the thermocouple wires onto the SMA wire one by one, the thermocouple lead offset is eliminated and the thermocouple provides an accurate point source reading. Infrared thermal imaging can be a good supplement in the experiment to monitor errors in temperature readings from thermocouples. Due to the curvature of the SMA wire, the temperatures of the locations on the SMA wire that are the closest to the infrared camera represent the temperature of the SMA wire. So a line analysis across the SMA wire on the software “ThermaCAM” is required to determine the temperature of the SMA wire by infrared thermal imaging and the highest temperature on the line is the temperature of the SMA wire. A new natural convective heat transfer correlation comprising the inclination angle φ is developed based on experimental results, which can be used to predict the temperature of a SMA wire given its diameter and inclination angle. The comparisons show that the new correlation agrees with existing correlations in a vertical orientation and for small Rayleigh numbers (0.001 < RaD < 0.05) in the horizontal orientation. The correlation developed in this work for horizontal orientation tends to overestimate values of Nusselt numbers as predicted in other correlations when the Rayleigh number is high (0.05 < RaD < 0.6). It is speculated that this overestimation can be attributed to a temperature distortion associated with thermocouple measurement at or near ambient pressure conditions.

The objective of this study is to reduce the interstory drifts, floor accelerations, and shear forces experienced by masonry houses subject to seismic excitation. Ambient vibration testing was performed on a case study structure in Maip�, Chile, to identify characteristics of the system. Upon creating a multiple degree-of-freedom (MDOF) model of the structure, the effect of implementing several base isolation techniques is assessed. The isolation techniques analyzed include the use of friction pendulum systems (FPS), high-damping rubber bearings (HDRB), two hybrid systems involving HDRB and shape memory alloys (SMA), and precast-prestressed pile (PPP) isolators. The dynamic behavior of each device is numerically modeled using analytical formulations and experimental data through the means of fuzzy inference systems (FIS) and S-functions. A multiobjective genetic algorithm is utilized to optimize the parameters of the FPS and the PPP isolation systems, while a trial-and-error method is employed to optimize characteristic parameters of the other devices. Two cases are studied: one case involves using eight devices in each isolation system and optimizing the parameters of each device, resulting in different isolated periods for each system, while the other case involves using the number of devices and device parameters that result in a 1.0 sec fundamental period of vibration for each baseisolated structure. For both cases, the optimized devices are simulated in the numerical model of the case study structure, which is subjected to a suite of earthquake records. Numerical results for the devices studied indicate significant reductions in responses of the base-isolated structures in comparison with their counterparts in the fixed-base structure. Metrics monitored include base shear, structural shear, interstory drift, and floor acceleration. In particular, the PPP isolation system in the first case reduces the peak base shear, RMS floor acceleration, peak structural shear, peak interstory drift, and peak floor acceleration by at least 88, 87, 95, 95, and 94%, respectively, for all of the Chilean earthquakes considered. The PPP isolation system in the second case (yielding a 1.0 sec period) and the FPS isolation systems in both cases also significantly reduce the response of the base-isolated structure from that of the fixed-base structure.

The work presents investigations into the development of a fuel-powered compact SMA actuator system. For the final SMA actuator, the K-alloy SMA strip (0.9 mm x 2.5 mm), actuated by a forced convection heat transfer mechanism, was embedded in a rectangular channel. In this channel, a rectangular piston, with a slot to accommodate the SMA strip, ran along the strip and was utilized to prevent mixing between the hot and the cold fluid in order to increase the energy density of the system. The fuel, such as propane, was utilized as main energy source in order to achieve high energy and power densities of the SMA actuator system. Numerical analysis was carried out to determine optimal channel geometry and to estimate maximum available force, strain and actuation frequency. Multi-channel combustor/heat exchanger and micro-tube heat exchanger were designed and tested to achieve high heat transfer rate and high compactness. The final SMA actuator system was composed of pumps, valves, bellows, multi-channel combustor/heat exchanger, micro-tube heat exchanger and control unit. The experimental tests of the final system resulted in 250 N force with 2 mm displacement and 1.0 Hz actuation frequency in closed-loop operation, in which the hot and the cold fluid were re-circulated by pumps.

Shape Memory Alloy is an amazing material, which can “remember” and return to its original shape when heated due to its temperature dependent phase transformation. Shape Memory Alloy wire has significant potential for application in the automobile industry due to its high ratio of energy / weight and silent actuation. However, a dependable method to measure the operating temperature of SMA wire and a reliable heat transfer model to characterize the dynamics of the SMA wire limit its widespread use in the automobile industry. This thesis presents a detailed description of the work performed to develop a reliable method for determining surface temperature of current carrying SMA wires and the development of a heat transfer correlation for natural convection cooling of heated SMA wires. The major findings of the research are as follows: When a spot welded thermocouple measures the temperature of a current carrying SMA wire, there is a “spurious voltage” ΔV added to the thermo electro-motive force (EMF) of the thermocouple as a result of a voltage drop across the two points of contact that the thermocouple wires make with the SMA wire. This leads to an erroneous temperature reading that can be higher or lower than the actual temperature depending on the direction of current flow. When the carrying current is reversed in direction, the “spurious voltage” becomes –ΔV allowing a correct temperature reading to be obtained by averaging the readings based on opposed current flow. A two-step spot welding procedure for attaching thermocouples to SMA wire can eliminate the influence of the “spurious voltage” in the temperature reading. By spot welding the thermocouple wires onto the SMA wire one by one, the thermocouple lead offset is eliminated and the thermocouple provides an accurate point source reading. Infrared thermal imaging can be a good supplement in the experiment to monitor errors in temperature readings from thermocouples. Due to the curvature of the SMA wire, the temperatures of the locations on the SMA wire that are the closest to the infrared camera represent the temperature of the SMA wire. So a line analysis across the SMA wire on the software “ThermaCAM” is required to determine the temperature of the SMA wire by infrared thermal imaging and the highest temperature on the line is the temperature of the SMA wire. A new natural convective heat transfer correlation comprising the inclination angle φ is developed based on experimental results, which can be used to predict the temperature of a SMA wire given its diameter and inclination angle. The comparisons show that the new correlation agrees with existing correlations in a vertical orientation and for small Rayleigh numbers (0.001 < RaD < 0.05) in the horizontal orientation. The correlation developed in this work for horizontal orientation tends to overestimate values of Nusselt numbers as predicted in other correlations when the Rayleigh number is high (0.05 < RaD < 0.6). It is speculated that this overestimation can be attributed to a temperature distortion associated with thermocouple measurement at or near ambient pressure conditions.

Concrete-filled buckling restrained braces (BRBs) was first developed in 1988 in Tokyo, Japan, to prevent the steel plates in the core portion from buckling, leading the steel core to exhibiting a more stable and fully hysteretic loop than conventional steel braces. However, past studies have shown that buckling restrained braced frames (BRBFs) have a large residual deformation after a median or high seismic event due to steel’s residual strain. In order to address this issue, innovative self-centering SMA braces are proposed and installed in the originally unbraced bays in existing BRBFs to become a hybrid frame system where the existing steel BRBs dissipate energy induced by external forces and the newly added self-centering SMA braces restore the building configuration after the steel BRBs yield. A case study of conventional three-story BRBF retrofitted by the proposed self-centering SMA braces is carried out to develop systematic retrofit strategies, to investigate the structural behavior, and to probabilistically assess their seismic performance in terms of interstory drifts, residual drifts, and brace deformation, as compared to the original steel BRB frames. Finally, the developed brace component fragility curves and system fragility curves will be further used for the assessment of downtime and repair cost.

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.

abstract: Space systems such as communication satellites, earth observation satellites and telescope require accurate pointing to observe fixed targets over prolonged time. These systems typically use reaction wheels to slew the spacecraft and gimballing systems containing motors to achieve precise pointing. Motor based actuators have limited life as they contain moving parts that require lubrication in space. Alternate methods have utilized piezoelectric actuators. This paper presents Shape memory alloys (SMA) actuators for control of a deployable antenna placed on a satellite. The SMAs are operated as a series of distributed linear actuators. These distributed linear actuators are not prone to single point failures and although each individual actuator is imprecise due to hysteresis and temperature variation, the system as a whole achieves reliable results. The SMAs can be programmed to perform a series of periodic motion and operate as a mechanical guidance system that is not prone to damage from radiation or space weather. Efforts are focused on developing a system that can achieve 1 degree pointing accuracy at first, with an ultimate goal of achieving a few arc seconds accuracy. Bench top model of the actuator system has been developed and working towards testing the system under vacuum. A demonstration flight of the technology is planned aboard a CubeSat. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2016

Le SMA Nitinol est largement utilisé dans de nombreux domaines de recherche récemment ( astronautes, biomédical ) et la combinaison de leurs propriétés dans la structure de conception désirée, en particulier les matériaux de l'architecture, est développé dans la dernière décennie. Des études récentes fabriqués avec succès la structure cellulaire, en particulier nid d'abeil, par processus thermomécanique à partir de tubes ou de barres mais les caractères de la liaison entre les éléments constitutifs ne sont pas clarifiées.Ce travail est consacré à l'étude de la liaison entre NiTi alliage quasi- équatomic qui est créé par le processus frittage des tubes ou des fils et par le procédé de soudage de tubes. Les liaisons obtenues des deux méthodes semblent forts et ils sont analysés par les essais de métallurgique et mécanique. Les résultats ont conduit aux conclusions suivantes :Pour les processus de frittage, les liaisons pour les des fils et des tubes semblent être forte quand ils sont chauffés à 1200oC pendant 1 heure avec les fils et 2 heures avec les tubes, respectivement. Cependant, le traitement entraîne le changement de la composition dans le matière. Le traitement à 900oC peut aider l'homogénéisation de la liaison, mais la phase inattendu TiNi2O est existé. En outre, la diffusion entre le Nitinol et Al2O3 est commencé quand ils sont chauffés à 1200oC.Pour le procédé de soudage, les liaisons entre tubes soudés sont forts avec seulement la phase TiNi mais la microstructure a changé. Il ya 2 nouvelles zones existantes à l'intérieur de la liaison de soudure: la zone de soudage, la zone affectée thermique. Les résistances de traction de la liaison de soudge une fois sont 12N/mm et 50N/mm pour tubes ayant la paroi 0,12 mm et la paroi 0,3 mm, respectivement. L'optimisation des paramètres de soudage montre que l'énergie de soudure a un effet fortement sur la création et la résistance de la liaison. La liaison est amilioré si l'énergie augmente. Charge de soudage a un rôle important pour améliorer la résistance de la liaison, et la charge de soudage est adapté pour le tube est 100N. Le deuxième fois de soudage peuvent améliorer la résistance de la liaison de la paroi du tube de 0,3 mm, mais il diminue après le troixième fois de soudage. En plus, l'addition de fois de soudage sous pression plus que de 100N conduit à la réduction de la résistance de la liaison. Ainsi, les paramètres de soudage doivent être tout d'abord examiné base de l'épaisseur de paroi du tube, puis l' énergie de soudage, la pression de soudure et la soudure fois. / Nickel-Titane shape memory alloys are widely used in many fields (aerospace, biomedical) and the combination of their outstanding properties in designed structures, namely architecture materials, has been considered in last decade. Recent studies successfully fabricated cellular structures, in particular honey combs, by thermo-mechanical processing from tubes or bars but the properties of the bonds created between the components need to be carefully investigated.This work is dedicated to the study of the bonds between NiTi near-equatomic alloy (Nitinol) elements, which are created by sintering together tubes or wires and by welding tubes under load. These bonds are characterized from metallurgical, microstructural and mechanical points of view. The obtained results led to the following conclusions.To provide a reasonably strong bond between wires and between tubes, sintering should be operated at least at 1200°C during one hour under the maximal load allowed by the experimental device, 3.5 N. However, this treatment causes intense compositional changes inside the material. A subsequent aging treatment at 900oC can help in homogenizing the material but prejudicial TiNi2O phase still exists. Besides, the interdiffusion between Nitinol elements and alumina tools at 1200°C perturbs sintering experiments. The sintering route has thus found to be inadequate unless the used device allows applying a higher load, so that the temperature can be set down.Tube welding has been more successful in terms on bond strength and NiTi phase conservation, although important microstructure changes have been observed. Three zones have been identified after welding, the weld zone, with large and long grains, the heat-affected zone, with smaller, spherical grains, and the non-affected zone. The extent of these zones is estimated from local hardness measurement. The tensile resistance of the bonds is about 12 and 50 N/mm for tubes having 0.12 and 0.3 mm thickness, respectively. A standard aging treatment does not significantly change these values although it allows material homogenization. The parameters that mainly influence the resistance and the microstructure of the bond are the weld energy, the rate of release of this energy and the load. Achieving successive welding steps is not clearly beneficial.