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Prothero, Lori Michelle Gross Robert Steven. "Shape memory alloy robotic truss." Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SUMMER/Aerospace_Engineering/Thesis/Prothero_Lori_16.pdf.
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Lafontaine, Serge R. "Fast shape memory alloy actuators." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0004/NQ44482.pdf.
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Lafontaine, Serge R. "Fast shape memory alloy actuators." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=34990.
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In this thesis techniques for fabricating fast contracting and relaxing shape memory alloy (SMA) fibers are presented. Shape memory alloy fibers have demonstrated the largest stress and highest power to mass ratio of any known actuator technology. However their practical application has been plagued by three major drawbacks, namely: (1) relatively slow expansion of the material despite rapid contraction; (2) problems of mechanically and electrically connecting to the material due to the violent nature of their contractions; and (3) low efficiency in the conversion of electrical energy or heat into mechanical energy. The work associated with this thesis has led to solutions to the first two problems allowing even sub-millisecond contraction-expansion cycle times, and fibers to be attached via light weight but high strength and high conductivity joints. The properties of these fibers are extensively studied. Both linear and rotary actuators are built using these fibers.A new technique is presented to mount nickel-titanium (NiTi) SMA fibers. NiTi alloys are not readily bonded, soldered, brazed or welded to other materials. The new method employs metal deposited on the fiber or between two fibers or between fibers and other parts, creating metallic attachments that are mechanically sound and electrically conductive. Furthermore a new process for the three-dimensional microfabrication by localized electrodeposition and etching has also been developed. This latter process, combined with the first process, can be used to integrate NiTi alloys in micro-mechanisms. The good electrical contacts as well as mechanical contact provided by the new attachment mechanisms are important, since they allow the rapid methods to be employed.
Several apparatus were built to study the response of NiTi fibers, in particular to very fast current pulses. Experimental results were obtained to describe the response of the fibers, such as their speed, hysteresis, stiffness and resistivity, and show how these variables change dynamically as a function of time, temperature and stress. Other measurements important for the design of new actuators were done, such as those of efficiency when fast actuation with large current pulses is used.
In the third part of the thesis a novel application for fast fiber actuators is presented in the form of a fast rotary motor for in-the-wheel car rotary motors.
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Santiago, Anadón José R. "Large force shape memory alloy linear actuator." [Gainesville, Fla.] : University of Florida, 2002. http://purl.fcla.edu/fcla/etd/UFE1001179.
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Yoshikawa, Shuji. "Global solutions for shape memory alloy systems /." Sendai : Tohoku Univ, 2007. http://www.gbv.de/dms/goettingen/538059052.pdf.
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Prince, A. G. "Refrigeration effects in shape memory alloy systems." Thesis, University of Bristol, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425093.
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Orvis, Skye M. "Prestressing Concrete with Shape Memory Alloy Fibers." DigitalCommons@CalPoly, 2009. https://digitalcommons.calpoly.edu/theses/120.
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Concrete is considerably stronger in compression than it is in tension. When cracks form in concrete members, the flexural stiffness of the member decreases and the deflection increases which increases the overall size of the member. Prestressing concrete remedies this problem by inducing a compressive stress in the concrete thereby reducing the net tension in the member and increasing the load required to crack the member. Traditional prestressing is generally limited to large, straight members. During the last decade, shape memory alloys (SMA) have become more prevalent in engineering and civil engineering applications. The shape memory effect refers to the contraction of the SMA when it is heated to its austenite phase. When a prestrain is induced in the SMA, it can be recovered when it goes through the phase change. Nitinol, a NiTi shape memory alloy was used in this research. Thin, steel cables were also tested to provide a comparison. Two different Nitinol alloys were studied in this research. The alloy M wires were elongated to 8% stain while the alloy X wires were prestrained by the manufacturer. The wires were cast into thin concrete beams and once cured, the beams were heated and a phase change from martensite to austenite occurred in the Nitinol. As a result, the Nitinol contracted and compressed the concrete. The SMA fibers are randomly oriented and allow prestressing to occur along all three axis. This is ideal for thin, curved specimens. Third-point bending tests showed that the SMA fibers prestressed the concrete and upon reheating the cracked specimens, the shape memory effect provides partial crack closure.
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Walls-Bruck, Marcus. "Shape adaptive self-fixing structures using shape memory alloy actuation." Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556738.
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Shape changing or morphing structures enable optimisation of structural configuration to suit current operating conditions. Conventional techniques for achieving shape change often result in weight and complexity penalties, which may outweigh the potential benefits of greater shape changing ability. The research presented in this thesis focuses on the use of shape memory materials to achieve a reversible change in shape of an innovative compliant composite structure, which may enable shape change without the drawbacks of conventional shape changing techniques. An initial concept was evaluated using a glass fibre reinforced shape memory polymer which was heated and deformed locally to fix the actuated shape. It was found that a large change in shape can be achieved. However, due to the high shear strain between the fibres during large deformations, fibre/matrix debonding occurred and propagated with repeated cycling. An alternative topology, consisting of a shape memory polymer reinforced with comparatively large diameter precured CFRP composite rods, was proposed and successfully demonstrated to reduce matrix shear strains, thereby reducing damage during deformation. The increased reinforcement size also improved load carrying ability when the shape memory polymer was in its low stiffness state. Initial testing of a rod reinforced composite beam with a low stiffness elastomer matrix indicated that shape memory alloy actuators wound helically around the composite beam could be effectively used to provide Significant rotational actuation. A constitutive model of the shape memory alloy thermo-mechanical behaviour was compared to the experimental findings for different configurations of shape memory alloy winding around the composite beam. A composite beam with a shape memory polymer matrix was found capable of 'locking' and 'releasing' mechanically introduced rotational shape change. The composite beam topology used initially consisted of circular rods and relied upon an adhesive for torsional rod restraint within the end alignment fittings, often resulting in failure of the adhesive and large non- returnable rotations at the temperatures required for softening of the shape memory polymer matrix. Rectangular cross section rods were used to enable the end fittings to mechanically restrain the rods in torsion. The rectangular rod topology also gave a large increase in bending stiffness compared to circular rods, with both topologies having similar torsional rigidities. A key aspect of the actuator performance was found to be the rate at which the shape memory materials could be activated by heating or cooling. This was found to be a particular problem for the shape memory polymer. To increase the rate of heating for the composite beam with a shape memory polymer matrix, efforts were made to incorporate carbon nanotubes to improve the thermal response of the material. However, only a modest change in thermal properties was achieved, combined with some undesirable detrimental effects on mechanical and therrno- mechanical properties. Further work is needed to optimise this combination. A final composite beam demonstrator combining both helically wound shape memory alloy wires for actuation and a shape memory polymer matrix for shape fixing was constructed. The shape memory polymer matrix was heated using an embedded heating element. By activating the shape memory alloy actuators when the shape memory polymer matrix was in its soft state, a rotation was achieved. Cooling the shape memory polymer matrix before the shape memory alloy actuators fixed the rotated, which was returned upon reheating the shape memory polymer matrix.
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Fung, Cheung Kwan. "Thermal mechanical behaviour of NiTi shape memory alloy." access abstract and table of contents access full-text, 2004. http://libweb.cityu.edu.hk/cgi-bin/ezdb/dissert.pl?msc-ap-b21174076a.pdf.
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Thesis (M.Sc.)--City University of Hong Kong, 2004.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.
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Machado, Luciano G. "Shape memory alloy for vibration isolation and damping." Texas A&M University, 2007. http://hdl.handle.net/1969.1/85772.
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This work investigates the use of shape memory alloys (SMAs) for vibration isolation
and damping of mechanical systems. The first part of this work evaluates the nonlinear
dynamics of a passive vibration isolation and damping (PVID) device through
numerical simulations and experimental correlations. The device, a mass connected
to a frame through two SMA wires, is subjected to a series of continuous acceleration
functions in the form of a sine sweep. Frequency responses and transmissibility of the
device as well as temperature variations of the SMA wires are analyzed for the case
where the SMA wires are pre-strained at 4.0% of their original length. Numerical
simulations of a one-degree of freedom (1-DOF) SMA oscillator are also conducted
to corroborate the experimental results. The configuration of the SMA oscillator is
based on the PVID device. A modified version of the constitutive model proposed
by Boyd and Lagoudas, which considers the thermomechanical coupling, is used to
predict the behavior of the SMA elements of the oscillator.
The second part of this work numerically investigates chaotic responses of a 1-
DOF SMA oscillator composed of a mass and a SMA element. The restitution force
of the oscillator is provided by an SMA element described by a rate-independent,
hysteretic, thermomechanical constitutive model. This model, which is a new version
of the model presented in the first part of this work, allows smooth transitions
between the austenitic and the martensitic phases. Chaotic responses of the SMA oscillator are evaluated through the estimation of the Lyapunov exponents. The Lyapunov
exponent estimation of the SMA system is done by adapting the algorithm
by Wolf and co-workers. The main issue of using this algorithm for nonlinear, rateindependent,
hysteretic systems is related to the procedure of linearization of the
equations of motion. The present work establishes a procedure of linearization that
allows the use of the classical algorithm. Two different modeling cases are considered
for isothermal and non-isothermal heat transfer conditions. The evaluation of
the Lyapunov exponents shows that the proposed procedure is capable of quantifying
chaos in rate-independent, hysteretic dynamical systems.
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Karjalainen, T. (Teemu). "Nitinol shape memory alloy in flexor tendon repair." Doctoral thesis, Oulun yliopisto, 2012. http://urn.fi/urn:isbn:9789514299803.
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Abstract Early motion is crucial for tendon healing and functional results after flexor tendon repair in the fingers. Motion, however, causes stress in the repair site, which can result in failure of the repair. A flexor tendon repair is made with fine calibre sutures, which sets exceptional requirements for the suture materials used in flexor tendon repair. Nitinol (nickel-titanium alloy) is a shape memory alloy, which can exist in two temperature-dependent forms, soft martensite and stiff austenite. It is possible to fabricate a nitinol wire that is soft and pliable, yet has high tensile strength. It also has excellent biocompatibility. Therefore, it is a potential candidate flexor tendon repair suture material. This study evaluates biomechanical aspects of martensite nitinol wire as a flexor tendon repair suture material. The study hypothesis was that nitinol wire improves the strength of the repairs compared with the repairs made with conventional suture materials. It was found that nitinol core repairs and circumferential repairs performed significantly better when compared with repairs made with commonly used braided polyester and polypropylene of equal calibre. To further optimise the performance of the nitinol wire in tendon surgery, two experimental models were developed to study the suture-tendon interface. The aim was to prevent pull-out of the suture loop so that surgeons could have full advantage of the tensile strength of the nitinol suture. First, it was tested whether it is possible to improve the suture’s ability to grip the tendon tissue by changing the suture type from monofilament to multifilament. Multifilament suture loops reached higher pull-out strength when compared with round monofilament loops when a locking loop was used. Subsequently, the grip of four different previously reported core repair loops was tested. Based on their failure mechanism, two novel loops were developed. The novel loops demonstrated superior ability to grip the tendon. The novel loops can be useful with high tensile strength suture materials and in repairs, which are prone to suture pull-outTiivistelmä Varhainen korjauksen jälkeinen aktiivinen kuntoutus on osoittautunut hyödylliseksi jänteen paranemiselle. Varhainen liike altistaa korjauksen kuormitukselle, joka voi johtaa korjauksen pettämiseen. Korjaukset tehdään ohuilla langoilla. Tämä asettaa erityisiä vaatimuksia jännekorjauksessa käytettävälle ommelainemateriaalille. Nikkeli-titaani (nitinoli) on nk. muistimetalli. Sillä on kaksi lämpötilariippuvaista muotoa: pehmeä martensiitti ja jäykkä austeniitti. Nitinolista voidaan valmistaa ohutta pehmeää ja taipuisaa lankaa, jonka vetolujuus on suuri. Nitinolin siedettävyys jännekudoksessa on todettu hyväksi, minkä vuoksi se on lupaava materiaali käytettäväksi jännekorjauksissa. Tässä tutkimuksessa kokeiltiin martensiittisen nitinolilangan käyttöä jänteen ydinompeleena ja pintaompeleena. Olettamuksena oli, että nitinolilangalla saadaan kestävämpiä korjauksia kuin nykyään käytössä olevilla langoilla. Tulosten mukaan nitinolilangalla tehdyt korjaukset olivat kestävämpiä, kun niitä verrattiin saman paksuiseen punottuun polyesteriin ja polypropyleeniin. Lisäksi kehitimme kaksi mallia, joiden tarkoituksena oli parantaa nitinolilankasilmukan pitoa jännekudoksesta. Tarkoituksena oli löytää keinoja, joilla langan otetta jännekudoksesta voidaan parantaa ja langan hyvät vetolujuusominaisuudet pääsevät oikeuksiinsa. Ensin muutimme langan muotoa perinteisestä yksisäikeisestä pyöreästä monisäikeiseen muotoon. Monisäikeisen langan läpileikkausvoima oli huomattavasti suurempi kuin yksisäikeisen pyöreän langan. Ero oli havaittavissa vain, kun käytettiin lukitsevaa silmukkaa. Tämän jälkeen testasimme neljän perinteisesti käytetyn korjaustekniikan silmukan pitokykyä ja tulosten perusteella kehitimme kaksi uutta silmukkaa. Työssä kehitetyt silmukat pitivät kiinni jänteestä huomattavasti paremmin kuin perinteiset silmukat. Työssä kehitetyillä silmukoilla voidaan optimoida vahvojen ommelainemateriaalien suorituskyky jännekirurgiassa
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Zhao, Peng. "Magnetoelastic coupling in NiMnGa ferromagnetic shape memory alloy." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/4129.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Material Science and Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Leong, Siu Loong. "Using shape memory alloy as dampers : design methodology." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33693.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2005.Includes bibliographical references (p. 141-143).
Many shape memory alloy (SMA) material models have been proposed in the literature, but most are suited only to forward analysis and not to design. This project proposes a generalized friction element, the lambda box, to model the stress-strain curve of SMA during pseudoelasticity. Simulation is carried out to study the dynamic response of such a system under harmonic loading. Three kinds of systems were examined, in order of increasing complexity: the friction damper system, the hysteretic damper system, and the hysteretic lambda damper system, which dynamically is equivalent to the SMA damper system. Using the simulation results, various asymptotes on the design space are identified, and design methodologies for the three systems are proposed. As the determination of the system parameters is decoupled from the actual damper design, a design methodology to dimension and configure the SMA damper is then proposed, for two kinds of problems, initial design and retrofit design.
by Siu Loong Leong.
S.M.
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Daverman, R. Dodge (Robert Dodge). "A novel binary actuator using shape memory alloy." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32363.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (p. 95-96).
In situations that demand the use of the high-bandwidth, high-quality sense of vision for interactions with the physical world it would be beneficial to have a wearable tactile display that takes advantage of touch to communicate information to the user without causing visual distractions. This thesis presents the design and development of a novel actuator that can be configured into thin, flexible arrays to meet this need for wearable tactile displays. The actuator presented uses the strain recovery property of the martensitic transformation of Nitinol, a Shape Memory Alloy (SMA), to generate the actuation force. A compliant bistable mechanism provides the restoring force that pre- strains the martensitic Nitinol, and thus makes the actuator binary. Binary actuation alleviates some of the problems that would otherwise limit the effectiveness of Nitinol in wearable haptic systems. To increase the potential for commercial success, manufacturability issues are considered throughout the development cycle to ensure the potential for economical large scale production. The paper concludes with the presentation of three different prototypes. Their successes and failures are discussed along with recommendations for future work.
by R. Dodge Daverman.
S.M.
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Turner, Travis Lee. "Thermomechanical Response of Shape Memory Alloy Hybrid Composites." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/29771.
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This study examines the use of embedded shape memory alloy (SMA)actuators for adaptive control of the themomechanical response of composite structures. Control of static and dynamic responses are demonstrated including thermal buckling, thermal post-buckling, vibration, sonic fatigue, and acoustic transmission. A thermomechanical model is presented for analyzing such shape memory alloy hybrid composite (SMAHC) structures exposed to thermal and mechanical loads. Also presented are (1) fabrication procedures for SMAHC specimens, (2) characterization of the constituent materials for model quantification, (3) development of the test apparatus for conducting static and dynamic experiments on specimens with and without SMA, (4) discussion of the experimental results, and (5) validation of the analytical and numerical tools developed in the study.
The constitutive model developed to describe the mechanics of a SMAHC lamina captures the material nonlinearity with temperature of the SMA and matrix material if necessary. It is in a form that is amenable to commercial finite element (FE) code implementation. The model is valid for constrained, restrained, or free recovery configurations with appropriate measurements of fundamental engineering properties. This constitutive model is used along with classical lamination theory and the FE method to formulate the equations of motion for panel-type structures subjected to steady-state thermal and dynamic mechanical loads. Mechanical loads that are considered include acoustic pressure, inertial (base acceleration), and concentrated forces. Four solution types are developed from the governing equations including thermal buckling, thermal post-buckling, dynamic response, and acoustic transmission/radiation. These solution procedures are compared with closed-form and/or other known solutions to benchmark the numerical tools developed in this study.
Practical solutions for overcoming fabrication issues and obtaining repeatable specimens are demonstrated. Results from characterization of the SMA constituent are highlighted with regard to their impact on thermomechanical modeling. Results from static and dynamic tests on a SMAHC beam specimen are presented, which demonstrate the enormous control authority of the SMA actuators. Excellent agreement is achieved between the predicted and measured responses including thermal buckling, thermal post-buckling, and dynamic response due to inertial loading.
The validated model and thermomechanical analysis tools are used to demonstrate a variety of static and dynamic response behaviors associated with SMAHC structures. Topics of discussion include the fundamental mechanics of SMAHC structures, control of static (thermal buckling and post-buckling) and dynamic responses (vibration, sonic fatigue, and acoustic transmission), and SMAHC design considerations for these applications. The dynamic response performance of a SMAHC panel specimen is compared to conventional response abatement approaches. SMAHCs are shown to have significant advantages for vibration, sonic fatigue, and noise control.Ph. D.
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Wakjira, Jillcha Fekadu. "The VT1 Shape Memory Alloy Heat Engine Design." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/31196.
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The invention of shape memory alloys spurred a period of intense interest in the area of heat engines in the late 70's and early 80's. It was believed that these engines could use heat from low temperature sources such as solar heated water, geothermal hot water and rejected heat from conventional engines as a significant source of power. The interest has since dwindled, largely because small prototype devices developed in the laboratory could not be scaled up to produce significant power. It is believed that the scaled-up designs failed because they were dependent on friction as the driving mechanism, which led to large energy losses and slip. This thesis proposes a new chain and sprocket driving mechanism that is independent of friction and should therefore allow for large-scale power generation.
This thesis begins by presenting properties and applications of shape memory alloys. The proposed design is then described in detail, followed by a review of the evolution that led to the final design. A brief chapter on thermodynamic modeling and a summary chapter suggesting improvements on the current design follow.Master of Science
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Soares, Alcimar Barbosa. "Shape memory alloy actuators for upper limb prostheses." Thesis, University of Edinburgh, 1997. http://hdl.handle.net/1842/21541.
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Despite the technological advances of the twentieth century, we are not yet able to produce artificial limbs which "mimic" perfectly their natural counterparts. In general, artificial limbs are not as dextrous as human limbs, the control is unnatural and there is no proper feedback by which the user can assess the status of the prosthesis. In this thesis the problems related to upper-limb prostheses are considered. The use of a special material known as Shape Memory Alloy (SMA) is investigated towards producing improved joint actuators for small artificial prostheses such as those required by young children. SMA actuators can be very lightweight, their motion is silent and smooth and yet they are capable of delivering considerable power per unit of weight. The Shape Memory phenomenon and the many challenges involved in its application are discussed. The detailed design of an SMA joint actuator for a hand mechanism in an above-elbow prosthesis for young children is given. To assist the design and construction of both the artificial hand and the actuator, a mathematical model was developed and incorporated in a computer program simulating the forces and movements within the hand. The model was used to optimise the hand mechanism and specify the required joint actuator. Suitable SMA elements were identified through laboratory tests. The hand mechanism was constructed and the actuator, control systems and power source were attached to it. Tests were performed to investigate the characteristics of the complete device. The results show that, although SMA actuators must be designed and used with great care, they do offer a viable and more natural alternative to conventional actuators such as pneumatic devices and electric motors in certain applications.
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Buban, Darrick Matthew. "Shape Memory Alloy Fracture as a Deployment Actuator." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/283604.
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Many applications require deployable structures to meet operational objectives such as satellites that unfurl antenna arrays. Typically, most deployment efforts involve the use of explosive and non-explosive actuators (EAs and NEAs respectively) that have implementation drawbacks such as the expense associated with special handling and the bulk encountered with mounting the devices. To mitigate EA and NEA drawbacks, the integration of shape memory alloys (SMA) as a deployment actuator was investigated. SMA specimens were heated and pulled to failure developing an environmental and structural operating envelope for application as deployment mechanisms. A Finite Element Model (FEM) was also created to model the response behavior induced during specimen testing so that modeled performance could be used in lieu of testing when integrating SMA actuators into deployment systems. Experimental results verified that SMAs can be implemented as deployment actuators. Recorded data showed that SMA fracture is possible over a wide range of temperatures and strains, filling a material performance gap not found in the literature. The obtained information allows design engineers to appropriately size SMAs given design requirements achieving the desired deployment effects. The Finite Element Model was partially successful, capable of emulating strained ambient material behavior up to approximately 6.1%. The limited response is due to lack of experimentally derived large stress and strain available for model emulation.
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Brewer, Andrew Lee. "Shape memory response of ni2mnga and nimncoin magnetic shape memory alloys under compression." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1341.
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Andolfato, Luca. "Shape Memory Alloy components: energy-consistent modelling and testing." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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The thesis aims to develop a novel control-oriented model for a Shape Memory Alloy (SMA) actuator and subsequently validate it through experimental tests. The main idea is to exploit energy balancing and exchange, along with proper constitutive equations, to represent SMA dynamical behavior. A SMA wire has been considered as a benchmark. The proposed approach returns equations with macroscopically reconstructable variables, embodying the hidden material’s internal phase state. This has allowed the development of simple test methodologies to characterize the several parameters. Moreover, it is also preparatory to a future control project. The characterization tests have been first validated in a simulation environment and subsequently carried out in the laboratory through an experimental set-up, consisting of a traction machine and ad hoc designed electronics. Promising results concerning the data’s accuracy have been obtained and they must be considered a first step towards more accurate modelling and test techniques.
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Toews, Leslie Marilyn. "The Development of a Monolithic Shape Memory Alloy Actuator." Thesis, University of Waterloo, 2004. http://hdl.handle.net/10012/871.
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Shape memory alloys (SMAs) provide exciting opportunities for miniature actuation systems. As SMA actuators are scaled down in size, cooling increases and bandwidth, improves. However, the inclusion of a bias element with which to cycle the SMA actuator becomes difficult at very small scales. One technique used to avoid the necessity of having to include a separate bias element is the use of local annealing to fabricate a monolithic device out of nickel titanium (NiTi). The actuator geometry is machined out of a single piece of non-annealed NiTi. After locally annealing a portion of the complete device, that section exhibits the shape memory effect while the remainder acts as structural support and provides the bias force required for cycling. This work proposes one such locally-annealed monolithic SMA actuator for future incorporation in a device that navigates the digestive tract. After detailing the derivation of lumped electro-mechanical models for the actuator, a description of the prototyping procedure, including fabrication and local annealing of the actuator, is provided. This thesis presents the experimental prototype actuator behaviour and compares it with simulations generated using the developed models.
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Ryhänen, J. (Jorma). "Biocompatibility evaluation of nickel-titanium shape memory metal alloy." Doctoral thesis, Oulun yliopisto, 1999. http://urn.fi/urn:isbn:9514252217.
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Abstract
The shape memory effect, superelasticity, and good damping properties, uncommon in other implant alloys, make the nickel-titanium shape memory metal alloy (Nitinol or NiTi) a fascinating material for surgical applications. It provides a possibility to make self-locking, self-expanding and self-compressing implants. The purpose of this work was to determine if NiTi is a safe material for surgical implant applications.
The primary cytotoxicity and the corrosion rate of NiTi were assessed in human osteoblast and fibroblast cell cultures. Comparisons were made with 316 LVM stainless steel (StSt) and pure titanium. The metal ions present in the media were analyzed using atomic absorption spectrometry (GFAAS). Despite the higher initial nickel dissolution, NiTi induced no toxic effects, decrease in cell proliferation or inhibition in the growth of cells in contact with the metal surface.
The general soft tissue responses to NiTi were compared to corresponding responses to StSt and Ti-6Al-4V alloy in rats during a follow-up of 26 weeks. The muscular tissue response to NiTi was clearly non-toxic and non-irritating, as were also the neural and perineural responses. The overall inflammatory response and the presence of immune cells, macrophages and foreign body giant cells were similar compared to the other test materials. At 8 weeks, histomorphometry showed that the encapsule membrane of NiTi was thicker than that of stainless steel, but at 26 weeks the membrane thicknesses were equal.
A regional acceleratory phenomenon (RAP) model was used to evaluate new bone formation, bone resorption and bone (re)modeling after periosteal implantation of NiTi, StSt or Ti-6Al-4V in rats using histomorphometry. Maximum new woven bone formation started earlier in the Ti-6Al-4V group than in the NiTi group, but also decreased earlier, and at 8 weeks the NiTi and StSt groups had greater cortical bone width. Later, no statistical differences were seen. NiTi had no negative effect on total new bone formation or normal RAP during a 26-week follow-up.
The ultrastructural features of cell-NiTi adhesion were analyzed with scanning electron microscopy (FESEM). Cell adhesion and focal contacts showed a good acceptance of NiTi.
Femoral osteotomies of rats were fixed with either NiTi or StSt intramedullary nails. Bone healing was examined with radiographs, peripheral quantitative computed tomography (pQCT) and histologically. The maximum follow-up was 60 weeks. There were more healed bone unions in the NiTi than the StSt group at early time points. Callus size and bone mineral density did not differ between the NiTi and StSt groups. Mineral density in both groups was lower in the osteotomy area than in the other areas along the nail. Density in the nail area was lower than in the proximal part of the operated femur or the contralateral femur. Bone contact to NiTi was close, indicating good tissue tolerance. Determination of trace metals from several organs was done by GFAAS or inductively coupled plasma-atomic emission spectrometry (ICP-AES). There were no statistically significant differences in nickel concentration between the NiTi and StSt groups in distant organs. The FESEM assessment showed surface corrosion changes to be more evident in the StSt implants.
On the basis of this study, the biocompatibility of NiTi seems to be similar to or better than that of stainless steel or Ti-6Al-4V alloy. NiTi appears to be suitable for further use as a biomaterial, because its biocompatibility is good. When NiTi is intended to be used in long-term implants, optimal surface treatment must consider.
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Grant, Danny. "Accurate and rapid control of shape memory alloy actuators." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0020/NQ55336.pdf.
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Allam, Hussein Mohammed. "Development of novel tactile displays using shape memory alloy." Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417498.
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Disko, Jeffry. "In search of martensite : titanium-tantalum shape-memory alloy." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/112500.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 47-48).
There is a broad range of life-saving medical implants and devices that rely on the shape-memory (SME) and superelastic properties of various nickel-based alloys [8]. Unfortunately, there is also serious concern about the toxicity of nickel. Titanium based shape-memory alloys have been noted as potentially non-toxic replacements of the more traditional, nickel-based shape memory alloys. In this thesis I present research concerning the potential of SME-capable titanium-tantalum alloys to replace Ni-based alloys in medical implants. A method for heat treatment of Ti -Ta alloys of varying compositions to induce formation of martensite was developed. Heat-treated alloys were then tested for SME and superelastic behavior by means of hot oil recovery tests and were characterized through optical microscopy. Metallographs of some of the samples were taken throughout the processing and testing procedures in order to directly observe changes in microstructure..
by Jeffry Disko.
S.B.
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Lederlé, Stéphane 1978. "Issues in the design of shape memory alloy actuators." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/16830.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002."June 2002."
Includes bibliographical references (p. 93-96).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
This thesis considers the application of shape memory alloy (SMA) actuators for shape control of the undertray of a sports car. By deforming the shape of the structure that provides aerodynamic stability to the car, we expect to improve the overall performance of the vehicle by adapting its aerodynamics according to the vehicle speed. We then develop a methodology for designing SMA actuators in this application. The methodology is based on the integration of the different models involved: mechanical, thermal, and electrical. The constraints imposed on the device are also incorporated. Unfortunately, the analysis predicts an actuation time that is too slow for this particular application. Still, we use our assembled model to sketch the expected characteristics of SMA actuators. A significant result is that the actuation time is a function of the amount of energy the active material has to provide, and that there is a necessary trade-off between the mass of actuators and the actuation time. In particular, the expected energy density may have to be decreased to achieve acceptable actuation times. Finally, we propose a way to estimate a priori the suitability of SMA actuators for a particular application.
by Stéphane Lederlé.
S.M.
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Chun, Katherine S. (Katherine Shisuka). "Shape memory alloy rotary actuator for CubeSat deployable structures." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127066.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, May, 2020Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 77-82).
Small satellites have lowered the barrier to entry for space-bound science and technology demonstrations. However, the small form factor requires extremely low size, weight, and power for any on-board hardware. Precision actuation of deployable structures has previously been achievable only through low SWaP single-use actuators or motor-driven, high SWaP multiple-use actuators. The Folded Lightweight Actuated Positioning System has the potential to provide an ultra-lightweight multiple-use actuator by using a Joule-heated shape memory alloy-based hinge. The hinge uses two shape memory alloy strips which are trained in opposite directions and mounted into a rotary actuator. Two different shape memory alloy geometries are explored: a rectangular cross-section and a circular cross-section. The rectangular hinge actuates over a range of ±20° with an average power of 0.14 W. The circular hinge actuates over a range of ±23° with an average power of 0.073 W. A closed-loop controller uses pulse width modulation and encoder measurements to actuate the rectangular hinge to within 2' of the desired angle.
by Katherine S. Chun.
S.M.
S.M. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics
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Tabesh, Majid. "Finite Element Analysis of Shape Memory Alloy Biomedical Devices." University of Toledo / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1271800551.
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Suraneni, Sanhita. "Microwave Assisted Reactive Sintering of TiNi Shape Memory Alloy." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1321628786.
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Speicher, Matthew S. "Cyclic testing and assessment of shape memory alloy recentering systems." Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/33834.
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In an effort to mitigate damage caused by earthquakes to the built environment, civil engineers have been commissioned to research, design, and build increasingly robust and resilient structural systems. Innovative means to accomplish this task have emerged, such as integrating Shape Memory Alloys (SMAs) into structural systems. SMAs are a unique class of materials that have the ability to spontaneously recover strain of up to 8%. With proper placement in a structural system, SMAs can act as superelastic "structural fuses", absorbing large deformations, dissipating energy, and recentering the structure after a loading event. Though few applications have made it into practice, the potential for widespread use has never been better due to improvements in material behavior and reductions in cost. In this research, three different SMA-based structural applications are developed and tested. The first is a tension/compression damper that utilizes nickel-titanium (NiTi) Belleville washers. The second is a partially restrained beam-column connection utilizing NiTi bars. The third is an articulated quadrilateral bracing system utilizing NiTi wire bundles in parallel with c-shape dampers. Each system was uniquely designed to allow a structure to undergo large drift demands and dissipate energy while retaining strength and recentering ability. This exploratory work highlights the potential for SMA-based structural applications to enhance seismic structural performance and community resilience.
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Mirzaeifar, Reza. "A multiscale study of NiTi shape memory alloys." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49071.
Full textAbstract:
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.
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Simon, Anish Abraham. "Shape memory response and microstructural evolution of a severe plastically deformed high temperature shape memory alloy (NiTiHf)." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/3139.
Full textAbstract:
NiTiHf alloys have attracted considerable attention as potential high temperature Shape Memory Alloy (SMA) but the instability in transformation temperatures and significant irrecoverable strain during thermal cycling under constant stress remains a major concern. The main reason for irrecoverable strain and change in transformation temperatures as a function of thermal cycling can be attributed to dislocation formation due to relatively large volume change during transformation from austenite to martensite. The formation of dislocations decreases the elastic stored energy, and during back transformation a reduced amount of strain is recovered. All these observations can be attributed to relatively soft lattice that cannot accommodate volume change by other means. We have used Equal Channel Angular Extrusion (ECAE), hot rolling and marforming to strengthen the 49.8Ni-42.2Ti-8Hf (in at. %) material and to introduce desired texture to overcome these problems in NiTiHf alloys. ECAE offers the advantage of preserving billet cross-section and the application of various routes, which give us the possibility to introduce various texture components and grain morphologies. ECAE was performed using a die of 90º tool angle and was performed at high temperatures from 500ºC up to 650ºC. All extrusions went well at these temperatures. Minor surface cracks were observed only in the material extruded at 500 °C, possibly due to the non-isothermal nature of the extrusion. It is believed that these surface cracks can be eliminated during isothermal extrusion at this temperature. This result of improved formability of NiTiHf alloy using ECAE is significant because an earlier review of the formability of NiTiHf using 50% rolling reduction concluded that the minimum temperature for rolling NiTi12%Hf alloy without cracks is 700°C. The strain level imposed during one 90° ECAE pass is equivalent to 69% rolling reduction. Subsequent to ECAE processing, a reduction in irrecoverable strain from 0.6% to 0.21% and an increase in transformation strain from 1.25% to 2.18% were observed at a load of 100 MPa as compared to the homogenized material. The present results show that the ECAE process permits the strengthening of the material by work hardening, grain size reduction, homogeneous distribution of fine precipitates, and the introduction of texture in the material. These four factors contribute in the increase of stability of the material. In this thesis I will be discussing the improvement of mechanical behavior and stability of the material achieved after various passes of ECAE.
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Giles, Adam R. "Deflection and shape change of smart composite laminates using shape memory alloy actuators." Thesis, Loughborough University, 2005. https://dspace.lboro.ac.uk/2134/7698.
Full textAbstract:
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.
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Kotamala, Sreenath. "PRESTRESSING OF SIMPLY SUPPORTED CONCRETE BEAM WITH NITINOL SHAPE MEMORY ALLOY." Text at OhioLINK ETD Center (Requires Adobe Acrobat Reader for viewing), 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=toledo1091806884.
Full textAbstract:
Thesis (M.S.V.)--University of Toledo, 2004.Typescript. "A thesis [submitted] as partial fulfillment of the requirements of the Master of Science degree in Civil Engineering." Includes bibliographical references (leaves 63-64).
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Lin, Brian E. "Stucture and thermomechanical behavior of nitipt shape memory alloy wires." Thesis, Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28233.
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The objective of this work is to understand the structure-property relationships in a pseudoelastic composition of polycrystalline NiTiPt (Ti-42.7 at% Ni-7.5 at% Pt). Structural characterization of the alloy includes grain size determination and texture analysis while the thermo-mechanical properties are explored using tensile testing. Variation in heat treatment is used as a vehicle to modify microstructure. The results are compared to experiments on Ni-rich NiTi alloy wires (Ti-51.0 at% Ni), which are in commercial use in various biomedical applications. With regards to microstructure, both alloys exhibit a <111> fiber texture along the wire drawing axis, however the NiTiPt alloy's grain size is smaller than that of the Ni-rich NiTi wires, while the latter materials contain second phase precipitates. Given the nanometer scale grain size in NiTiPt and the dispersed, nanometer scale precipitate size in NiTi, the overall strength and ductility of the alloys are essentially identical when given appropriate heat treatments. Property differences include a much smaller stress hysteresis and smaller temperature dependence of the transformation stress for NiTiPt alloys compared to NiTi alloys. Potential benefits and implications for use in vascular stent applications are discussed.
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Otieno, Timothy. "Shape memory Alloy Actuator for cross-feed in turning operation." Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1012590.
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A shape memory alloy (SMA) is an intermetallic compound able to recover, in a continuous and reversible way, a predetermined shape during a thermal cycle while generating mechanical work. In this thesis, its use in developing an actuator for a machining process is investigated. The actuator is to drive the tool cross feed into an aluminium workpiece in a finishing lathe operation. The actuator structure was designed with an output shaft to transfer the movement and force of the SMA wire outside the device. The actuator was fabricated and the experimental setup was assembled which also included a power supply control circuit, displacement sensor, temperature sensor and current sensor for feedback, and data collection and monitoring within software. PID control was implemented within the software that regulated the power supplied to the SMA, thereby providing the position control. This study covers the mechatronics system design and development of the actuator, the experiments carried out to determine performance and the results. Open loop tests were conducted to determine the maximum stroke, the effect of cooling and response to radial forces. These tests revealed the expected non-linearity of the SMA. The actuator achieved the rated maximum stroke of 3-4 percent. The forced cooling test showed a general improvement of approximately 65 percent with fans. The radial force tests showed the value of the maximum stroke remained unaffected by force. The results from the closed loop tests responses with a tuned PID controller produced a stable system for various displacement setpoints. The actuator had a feed rate of 0.25 mm/s and an accuracy of 0.0153mm, which was within the acceptable accuracy for turning operations. The system was deemed accurate for a conventional lathe machine cross feed.
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Kumar, Guhan. "Modeling and design of one dimensional shape memory alloy actuators." Connect to resource, 2000. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1116879145.
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Soylemez, Burcu. "Design And Analysis Of A Linear Shape Memory Alloy Actuator." Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610340/index.pdf.
Full textAbstract:
Shape memory alloys are new, functional materials used in actuator applications with their high power to weight ratio. The high strength or displacement usage of shape memory alloys makes them suitable for direct drive applications, which eliminate use of power transmission elements.
The aim of this research is to develop the methodology and the necessary tools to design and produce linear shape memory alloy actuators to be used in missile systems, space applications, and test equipments.
In this study, the test apparatus designed and built to characterize shape memory alloy thin wires is described, and then the characterization tests, modeling and control studies performed on a wire are explained. In the control studies, displacement control through strain, resistance and power feedback is investigated and different control strategies (proportional-integral, proportional-integral with feedforward loop, and neural network) are employed. The results of the characterization tests, simulations and experiments are all presented in graphical and tabular form. From the results it is concluded that through careful characterization, the behavior of SMA wire can be closely approximated through models which can be used effectively to test various control strategies in simulations. Also, satisfactory position control of SMA wires can be achieved through both classical and NN control strategies by using appropriate feedback variables and power is found to be a viable feedback variable.
Lastly, a linear SMA wire actuator is designed as a case study. The actuator prototype is produced, suitable control strategies are applied and actuator is experimented to validate the theoretical assumptions.
The actuator developed through this work is a technology demonstration and shows that shape memory alloy elements can be utilized in several defense and space applications contracted to TÜBiTAK-SAGE as well as certification test equipments. The development of shape memory alloy actuators that can be used in defense and later in aeronautical/space applications is a critical research and development project for national defense industry.
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Feng, Ping. "Deformation instability and morphology in shape memory alloy under stress /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?MECH%202005%20FENG.
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Becker, Marcus Patrick. "Thermomechanical training and characterization of shape memory alloy axial actuators." Thesis, Montana State University, 2010. http://etd.lib.montana.edu/etd/2010/becker/BeckerM0510.pdf.
Full textAbstract:
Although considerable work has been performed to understand the key mechanisms of Shape Memory Alloy (SMA) behavior, little of this work follows a standard testing protocol, quantifies a conditioning methodology, or develops data appropriate for design of SMA actuators. One major issue that limits the ability of the material from being used directly as an actuator is the large, non-recoverable strains likely to accrue in the material during each training cycle, mechanical or thermal. When mechanical or thermal cycling is performed, a hysteresis curve develops and reaches a steady state strain recovery response. At the point where permanent plastic strain stops growing, or saturates, the SMA has been successfully trained. The focus of this work is oriented toward SMAs in general, but all testing and experimentation was carried out on Nickel-Titanium (NiTi) alloys. The experimentation and testing was performed on a combination of 4 different sizes and 3 different NiTi alloy compositions. Thermomechanical testing was performed to determine critical values to describe the stress-temperature phase space of the materials and parameters to model the applied stress and transformation strain relationship. All material size and alloy combinations were tested in the as-received, or as-machined, and fully annealed state. The results of the training and actuation strain characterization process developed in this work shows that the samples that experienced Transformation Induced Plasticity (TRIP), greater than 2% during the training process and exhibit Two-Way Shape Memory (TWSM) after being fully trained, share a very similar applied stress versus transformation strain curve. This curve is modeled by the Back Stress formulation derived from the Gibbs Free Energy constitutive model by Bo & Lagoudas. The design space created by the Back Stress formulation, recrystallization temperature, and training stress allows SMA materials to be characterized and implemented as stable 1-D actuators. This research formalized a thermomechanical training and characterization method for uniaxial SMA actuators by addressing the interaction between processing, recoverable and non-recoverable deformation. Using various sizes and NiTi alloy combinations, this research develops and evaluates a method to train and characterize a diverse range of SMAs through a set of thermomechanical and physical property measurements.
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Anders, William S. "Structural acoustic analysis of shape memory alloy hybrid composite panels." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-11012008-063243/.
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Nakamura, Mealani 1978. "A torso haptic display based on shape memory alloy actuators." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/89927.
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Chambers, Joshua Michael. "Design and characterization of acoustic pulse shape memory alloy actuators." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32378.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (p. 175-177).
Single crystal Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs) are active materials which produce strain when a magnetic field is applied. The large saturation strain (6%) of Ni-Mn-Ga, and material energy density comparable to piezoelectric ceramics make Ni- Mn-Ga an interesting active material. However, their usefulness is limited by the bulky electromagnet required to produce a magnetic field. In this thesis, a novel actuation method is developed for shape memory alloys in their martensitic phase, whereby asymmetric acoustic pulses are used to drive twin boundary motion. Experimental actuators were developed using a combination of Ni-Mn-Ga FSMA single crystals and a piezoelectric stack actuator. In bi-directional actuation without load, strains of over 3% were achieved using repeated pulses (at 100 Hz) over a 30 s interval, while 1% strain was achieved in under 1 s. The maximum strains achieved are comparable to the strains achieved using bi-directional magnetic actuation, although the time required for actuation is longer. No-load actuation also showed a nearly linear relationship between the magnitude of the asymmetric stress pulse and the strain achieved during actuation, and a positive correlation between pulse repetition rate and output strain rate, up to at least 100 Hz. Acoustic actuation against a spring load showed a maximum output energy density for the actuator of about 1000 J/m³, with a peak-to-peak stress and strain of 100 kPa and 2%, respectively.
by Joshua Michael Chambers.
S.M.
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Ueland, Stian Melhus. "Grain constraint and size effects in shape memory alloy microwires." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/80893.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 142-147).
Shape memory alloys exhibit interesting and useful properties, such as the shape memory effect and superelasticity. Among the many alloy families that have been shown to exhibit shape memory properties the ones based on copper are interesting because they are relatively inexpensive and show excellent properties when made as single crystals. However, the performance of these alloys is severely compromised by the introduction of grain boundaries, to the point where they are too poor for commercial applications. This thesis studies the mechanical properties of fine Cubased wires with a bamboo microstructure, i.e., where triple junctions are absent and grain boundaries run perpendicular to the wire axis. These microwires are not single crystals, but their microstructure is not as complex as that of polycrystals either: we call this new class of shape memory alloys oligocrystals. This thesis seeks to better understand the relationship between microstructure and properties in these alloys through a combination of mechanical testing, in situ experiments and modeling. First, in situ scanning electron microscopy, together with finite element modeling, is used to understand the role of grain constraint on the martensitic transformation. Grain constraints are observed to be much less severe in oligocrystalline wires as compared to polycrystals. Oligocrystalline microwires are then thermomechanically tested and shown to exhibit excellent properties that approach those of single crystals. Next, property evolution during cycling is investigated, revealing training effects as well as fatigue life and fracture. Finally, size effects in damping and transformation morphology are studied and it is shown that a transition from a many-domain to a single domain martensite morphology takes place when the wire diameter is decreased.
by Stian Melhus Ueland.
Ph.D.
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Khatsenko, Maxim O. "A rotary shape memory alloy actuator for CubeSat deployable structures." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111751.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 155-158).
Over a decade of continuing CubeSat technology improvements are driving the wide adoption of CubeSats for research and commercial missions. Resource constraints onboard CubeSats still limit their ability to support multi-use actuators, but there is a need for a rotary CubeSat actuator that can be actively commanded to different angles. This type of actuator can be implemented in a CubeSat mechanism for differential drag management, increased power generation, and reconfigurable deployable structures. We propose using a shape memory alloy (SMA) actuator to meet this need. A SMA can be annealed at high temperatures to remember a trained shape. Upon cool down, the SMA element transforms to the martensite phase and is easily deformed. When the element is heated above the transformation temperature it transforms to the stiff austenite phase and assumes its remembered shape, driving the mechanism. Two SMA actuators are trained to different shapes and provide bidirectional rotary motion for use as a space mechanism. The actuators are designed by implementing kinematic, thermal, and bending models to size the SMA element. The models also predict the performance, size, weight, and power of the actuator and ensure it can operate in the CubeSat environment. Then, a prototype of the proposed actuator is manufactured, assembled, and ground tested. Testing is used to validate the models and verify the requirements necessary to operate onboard a CubeSat. The prototype meets all requirements and offers a reduced mass, volume, and complexity alternative to current CubeSat electromagnetic actuators. Future work is necessary to improve the mechanical performance and positional control of the SMA actuator.
by Maxim O. Khatsenko.
S.M.
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Jia, Hongyu. "Impact Damage Resistance of Shape Memory Alloy Hybrid Composite Structures." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30572.
Full textAbstract:
The strain energy absorption of shape memory alloy (SMA) bars and beams under tension and bending loading was studied. A theoretical model is presented that can give quantitative relations between the martensite fraction, the applied load, and the strain energy absorbed in the shape memory alloy (SMA). It was found analytically that the super-elastic SMA demonstrates a high strain energy absorption capability. The closed- form solution of the strain energy absorption capability of SMA bars is a simple and useful tool in the design of energy absorption applications of super-elastic SMA. The nonlinear equations for SMA hybrid composite plates, which can be used for low velocity impact or quasi-static contact loading, are derived. The governing equations include the transverse shear deformation to the first-order, large deformation of the plates, and SMA/epoxy lamina. The equations are derived in the general form with general boundary conditions and general stack of angle ply. The equations can be simplified to special forms in the specific applications.
A theoretical study of the impact force and the strain energy absorption of an SMA/graphite/epoxy composite beam under a low-velocity impact has been performed. The contact deformation, the global bending deformation, the transverse shear deformation, and the martensitic phase transformation of the super-elastic SMA fibers are studied. The energy absorbed by the SMA hybrid composite is calculated for each task of the absorption mechanisms: contact deformation, global bending deformation, and The analysis methods and models developed in this dissertation are the first reported research in modeling SMA composite under low velocity impact and quasi-static loading. The models and methods developed here can be used for further study and design of SMA composites for low velocity impact or quasi-static loading in failure process.Ph. D.
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Li, Yinan. "Design and Analysis of Energy Harvesting with Shape Memory Alloy." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1354872782.
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Eshghinejad, Ahmadreza. "Finite element study of a shape memory alloy bone implant." University of Toledo / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1333726695.
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Hegana, Ashenafi B. "Low Temperature Waste Energy Harvesting by Shape Memory Alloy Actuator." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1461631046.
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Blocher, Richard Paul. "Predictive Tools for the Improvement of Shape Memory Alloy Performance." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1556022653899471.
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