Most e orts on High Temperature Shape Memory Alloys (HTSMAs), have focused on improving their work characteristics by thermomechanical treatment methods. However, the in uence of transformation induced plasticity (TRIP) and viscoplasticity during actuation has not been studied. The objective of this dissertation work was to study the in uence of plasticity and viscoplasticity on the transformation characteristics that occur during two common actuation-loading paths in TiPdNi HTSMAs. Thermomechanical tests were conducted along di erent loading paths. The changes in the transformation temperature, actuation strain and irrecoverable strain during the tests were monitored. Transmission Electron Microscopy (TEM) studies were also conducted on select test specimens to understand the underlying microstructural changes. The study revealed that plasticity, which occurs during certain actuation load paths, alters the transformation temperatures and/or the actuation strain depending on the loading path chosen. The increase in the transformation temperature and the irrecoverable strain at the end of the loading path indicated that the rate independent irrecoverable strain results in the generation of localized internal stresses. The increased transformation temperatures were mapped with an equivalent stress (which corresponds to an internal stress) using the as-received material's transformation phase diagram. A trend for the equivalent internal stress as a function of the applied stress and accumulated plastic strain was established. Such a function can be implemented into thermomechanical models to more accurately capture the behavior of HTSMAs during cyclic actuation. On the contrary, although the viscoplastic strain generated during the course of constant stress thermal actuation could signi cantly reduce actuation strain depending on the heating/cooling rate. Additional thermomechanical and microstructural tests revealed no signi cant change in the transformation behavior after creep tests on HTSMAs. Comparing the thermomechanical test results and TEM micrographs from di erent cases, it was concluded that creep does not alter the transformation behavior in the HTSMAs, and any change in the transformation behavior can be attributed to the retained martensite which together with TRIP contributes to the rate independent irrecoverable strain. As a consequence, a decrease in the volume fraction of the martensite contributing towards the transformation must be considered in the modeling.

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Recent advances in materials engineering have given rise to a new class of materials known as active materials. These materials when used appropriately can aid in development of smart structural systems. Smart structural systems are adaptive in nature and can be utilized in applications that are subject to time varying loads such as aircraft wings, structures exposed to earthquakes, electrical interconnections, biomedical applications, and many more. Materials such as piezoelectric crystals, electrorheological fluids, and shape memory alloys (SMAs) constitute some of the active materials that have the innate ability to response to a load by either changing phase (e.g., liquid to solid), and recovering deformation. Active materials when combined with conventional materials (passive materials) such as polymers, stainless steel, and aluminum, can result in the development of smart structural systems (SSS). This Dissertation focuses on characterization of SMAs and structures that incorporate SMAs. This characterization is based on a hybrid analytical, computational, and experimental solutions (ACES) methodology. SMAs have a unique ability to recover extensive amounts of deformation (up to 8% strain). NiTiNOL (NOL: Naval Ordinance Lab) is the most commonly used commercially available SMA and is used in this Dissertation. NiTiNOL undergoes a solid-solid phase transformation from a low temperature phase (Martensite) to a high temperature phase (Austenite). This phase transformation is complete at a critical temperature known as the transformation temperature (TT). The low temperature phase is softer than the high temperature phase (Martensite is four times softer than Austenite). In this Dissertation, use of NiTiNOL in representative engineering applications is investigated. Today, the NiTiNOL is either in ribbon form (rectangular in cross-section) or thin sheets. In this Dissertation, NiTiNOL is embedded in parent materials, and the effect of incorporating the SMA on the dynamic behavior of the composite are studied. In addition, dynamics of thin sheet SMA is also investigated. The characterization is conducted using state-of-the- art (SOTA) ACES methodology. The ACES methodology facilitates obtaining an optimal solution that may otherwise be difficult, or even impossible, to obtain using only either an analytical, or a computational, or an experimental solution alone. For analytical solutions energy based methods are used. For computational solutions finite element method (FEM) are used. For experimental solutions time-average optoelectronic holography (OEH) and stroboscopic interferometry (SI) are used. The major contributions of this Dissertation are: 1. Temperature dependent material properties (e.g., modulus of elasticity) of NiTiNOL based on OEH measurements. 2. Thermomechanical response of representative composite materials that incorporate NiTiNOL“fibers". The Dissertation focuses on thermomechanical characterization of NiTiNOL and representative structures based on NiTiNOL; this type of an evaluation is essential in gainfully employing these materials in engineering designs.

Shape memory materials have been known for many years to possess the unique ability of memorising their shape at some temperature. If these materials are pre-strained into the plastic range, they tend to recover their original un-strained shapes via phase transformation when subjected to heat stimulation. In recent years, this shape memory effect (SME) or strain recovery capability has been explored in aerospace structures for actuating the real-time movement of structural components. Among all the shape memory materials, the nickel-titanium based shape memory alloy (SMA) has by far received the most attention because of its high recovery capabilities. Since SMAs are usually drawn into the form of wires, they are particularly suitable for being integrated into fibre-reinforced composite structures. These integrated composite structures with SMA wires are thus called smart adaptive structures. To achieve the SME, these wires are normally embedded in the host composite structures. In returning to their unstrained shape upon heat application, they tend to exert internal stresses on the host composite structures in which they are embedded. This action could result in a controlled change in shape of the structural components. Although there has been a significant amount of research dedicated to characterising and modelling the SME of SMA wires, little experimental work had been done to offer an in-depth understanding of the mechanical behaviour of these smart adaptive polymeric composite structures. This project examined the deflection and shape change of carbon/epoxy and glass/epoxy cantilever beams through heating and cooling of internal nitinol SMA wires/strips. The heat damage mechanism and cyclic behaviour are major factors in the operation of such a system and need to be clearly understood in order to develop and gain confidence for the possible implementation of future smart actuating systems. Therefore, the objectives of the proposed research were to investigate (i) effect of embedding SMA, wires on mechanical properties of host composite, (ii) assessment of single-cycle and multiple-cycle actuation performance of smart beams, and (iii) thermal effects of excessive heat on the surrounding composite matrix.

Despite progress that has been made in the areas of maternal acculturation and internalizing symptoms in Hispanic youth, much remains to be learned about the relation between maternal acculturation and youth anxiety. The inclusion of cognitive vulnerabilities such as anxiety sensitivity (AS) further adds to the understanding the development of anxiety in Hispanic youth. Examining the role that youth age and youth sex play in the relation between AS and youth anxiety symptoms also can further understanding of the development of youth anxiety. Thus, the specific aims of this dissertation were to examine whether: (1) a confirmatory factor analysis (CFA) would yield a two factor structure of the Stephenson Multigroup Acculturation Measure (SMAS; Stephenson, 2000); (2) maternal acculturation as measured by the SMAS is related to youth anxiety symptoms; (3) mother country of origin (i.e, Cuban or another Latin country) moderates the relation between youth AS and youth anxiety symptoms; (4) youth age moderates the relation between youth AS and youth anxiety symptoms; (5) youth sex moderates the relation between youth AS and youth anxiety symptoms. In addition, research has shown Hispanic youth report more anxiety symptoms than non-Hispanic youth. The Revised Children’s Manifest Anxiety Scale’s (RCMAS; Reynolds & Richmond, 1978) Lie Scale was included to examine whether it relates to Hispanic youths’ reporting of anxiety symptoms in the current sample. There were no significant differences in youth anxiety associated with the mother country of origin. Specifically, Cuban mothers and mothers from other Hispanic countries of origin did not significantly differ in their ratings of their child’s anxiety symptoms. Mother country of origin did not moderate the relation between AS and youth anxiety symptoms. Also, no significant findings were found with respect to effects of age on the relation between anxiety sensitivity and anxiety. The study’s main contributions and potential implications on theoretical, empirical, and clinical levels are further discussed.

Den industriella revolutionen kom med behovet av att bygga byggnader och broar, till en början förstod man inte vikten av armering och förstärkning av konstruktion. Men med tiden behövde man komma på någon strategi att göra konstruktionen starkare och mer hållbar, och det var då man började använda sig av förstärkning. I dagens moderna samhälle är det vanligare att bygga med betong, betong är det viktigaste byggmaterialet i världen. Det har flera egenskaper som garanterar en lång livslängd för konstruktionen; dess hållbarhet och styvhet är av störst intresse för att designa betongkonstruktioner. Andra egenskaper såsom täthet och bearbetbarhet är också viktiga. För att utnyttja betongegenskaperna korrekt måste nästan alla strukturer förstärkas på ett eller annat sätt. Därför har man under en lång period gjort stora forskningar på hur man kan göra betong starkt i draghållfasthet och inte bara i tryck. Moderna komplicerade konstruktionsformer kräver nya förstärkningsmetoder, komplexiteten i den nya strukturen både när det gäller höjd och bredd har nödvändiggjort behovet av nya metoder för betongarmering. En metod är användningen av järn-baserade minneslegeringar (Fe-SMA), genom forskning har det visat sig vara en effektiv metod för armering av stål. SMAs har unika egenskaper och det mest speciella är att det återgår till sin ursprungliga form även när det har deformerats. Som ett resultat av detta möjliggör det förstärkning av betong av vilken form och storlek som helst, de goda limegenskaperna hos betong och järn gör installationen komplett. Detta examensarbete resulterade att SMA har väldigt unika egenskaper som kommer att göra stora skillnader i byggbranschen. Detta gäller främst hos broar och är en väldigt aktuell metod som har förmågan att anpassa sig till den omgivande miljön. Utöver det kan den även justera sig själv för att säkerställa optimal och säker drift under normala och svåra belastnings villkor och det minimala kravet för underhåll.

The unique ability of shape memory alloys (SMAs) to remember and recover their original shape after large deformation offers vast potential for their integration in advanced engineering applications. SMAs can generate recoverable shape changes of several percent strain even when opposed by large stresses owing to reversible deformation mechanisms such as twinning and stress-induced martensite. For the most part, these alloys have been largely used in the biomedical industry but with limited application in other fields. This limitation arises from the complexities of prevailing microstructural mechanisms that lead to dimensional instabilities during repeated thermomechanical cycling. Most of these mechanisms are still not fully understood, and for the most part unexplored. The objective of this work was to investigate these deformation and transformation mechanisms that operate within the low temperature martensite and high temperature austenite phases, and changes between these two states during thermomechanical cycling. This was accomplished by combined experimental and modeling efforts aided by an in situ neutron diffraction technique at stress and temperature. The primary focus was to investigate the thermomechanical response of a polycrystalline Ni49.9Ti50.1 (in at.%) shape memory alloy under uniaxial deformation conditions. Starting with the deformation of the cubic austenitic phase, the microstructural mechanisms responsible for the macroscopic inelastic strains during isothermal loading were investigated over a broad range of conditions. Stress-induced martensite, retained martensite, deformation twinning and slip processes were observed which helped in constructing a deformation map that contained the iv limits over which each of the identified mechanisms was dominant. Deformation of the monoclinic martensitic phase was also investigated where the microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were captured and compared to the bulk macroscopic response of the alloy. This isothermal deformation was found to be a quick and efficient method for creating a strong and stable two-way shape memory effect. The evolution of inelastic strains with thermomechanical cycling of the same NiTi alloy, as it relates to the alloy stability, was also studied. The role of pre-loading the material in the austenite phase versus the martensite phase as a function of the active deformation modes (deformation processes as revealed in this work) were investigated from a macroscopic and microstructural perspective. The unique contribution from this work was the optimization of the transformation properties (e.g., actuation strain) as a function of deformation levels and pre-loading temperatures. Finally, the process used to set actuators, referred to as shape setting, was investigated while examining the bulk polycrystalline NiTi and the microstructure simultaneously through in situ neutron diffraction at stress and temperature. Knowledge gained from the binary NiTi study was extended to the investigation of a ternary Ni-rich Ni50.3Ti29.7Hf20 (in at.%) for use in high-temperature, high-force actuator applications. This alloy exhibited excellent dimensional stability and high work output that were attributed to a coherent, nanometer size precipitate phase that resulted from an aging treatment. Finally, work was initiated as part of this dissertation to develop sample environment equipment with multiaxial capabilities at elevated temperatures for the in situ neutron diffraction measurements of shape memory alloys on the VULCAN Diffractometer at Oak Ridge National Laboratory. The developed capability will immediately aid in making rapid multiaxial v measurements on shape memory alloys wherein the texture, strain and phase fraction evolution are followed with changes in temperature and stress. This work was supported by funding from the NASA Fundamental Aeronautics Program, Supersonics Project including (Grant No. NNX08AB51A). This work has also benefited from the use of the Lujan Neutron Scattering Center at LANSCE, which is funded by the Office of Basic Energy Sciences DOE. LANL is operated by Los Alamos National Security LLC under DOE Contract No. DE-AC52-06NA25396.

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This thesis explores the design, implementation and performance of a new concept for a low-cost, high-resolution, lightweight, compact and highly-portable tactile display. This tactile device is intended to be used in a novel visuo-tactile sensory substitution/supplemen-tation electronic travel aid (ETA) for the blind/visually impaired.Based on the psychophysiology of touch and using Shape Memory Alloys (SMAs) as the actuation technology, a mechatronic device was designed and prototyped to stimulate the sense of touch by creating sensations of contact on the fingertips.The prototype consists of an array of 64 elements spaced 2.6 mm apart that vertically actuates SMA based miniature actuators of 1.5 mm diameter to a height range of 1.4 mm with a pull force of 300 mN up to a 1.5 Hz bandwidth. The full display weights 200 g and its compact dimensions (a cube of 8 cm side-length) make it easy for the user to carry. The display is capable of presenting a wide range of tactile binary information on its 8 x 8 matrix. Moreover, both mechanical and electronic drive designs are easily scalable to larger devices while still being price attractive.Human psychophysics experiments demonstrate the effectiveness of the tactile information transmitted by the display to sighted people and show feasibility in principle of the system as an assistive technology for the blind/visually impaired.