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Thermomechanical Characterization Of Ti Rich Tini Shape MemoryalloysYasar, Fatih 01 December 2006 (has links) (PDF)
Titanium-nickel is a unique class of material known as Shape Memory Alloy (SMA). A thermoelastic martensitic phase transformation is responsible for its extraordinary properties such as shape memory effect and superelasticity. The near equiatomic Ti-Ni alloys are the commercially most exploited SMAs because of the unique combination of these properties and superior ductility, strength, fatigue resistance and corrosion resistance. The properties of Ti-Ni SMAs are very sensitive to composition and the processing parameters. The properties of Ti-Ni SMAs can be modified to a great extent by choice of composition, mechanical working and heat treatment.
Thermo-mechanical treatments are required to strengthen the matrix and improve the shape memory characteristics. Plastic deformation and subsequent annealing is the common way to improve shape memory properties.
In the present study, Ti- 50 at% Ni wire specimens are produced and used for the investigation of the effect of different heat treatment and cold working processes on shape memory characteristics. To investigate the thermomechanical behavior of differently processed wire specimens, a fully computerized servo hydraulic thermomechanical testing machine was designed and constructed. Testing machine was capable to perform different types of tests that are selected by the user. It can both heat and cool the specimen automatically according to the testing sequence by applying DC current directly through the SMA wire or by sending liquid nitrogen into the cooling chamber. Temperature is measured by a K-type thermocouple directly mounted on the wire specimen with a glass tape. Force that is applied to the specimen is produced by hydraulic power unit with a double action cyclinder and it is controlled by a controller which takes the feedback from the loadcell and LVDT (Linear Variable Distance Transducer). During performig thermomechanical-tests all the data of loadcell, LVDT and thermocouple are collected by a data acqusition system integrated with a host computer that operates the program XPC Target.
Ti-Ni alloy with equiatomic composition is prepared in vacum induction furnace. Specimen cast in the form of rod was then hot swaged. Subsequent to swaging, cold wire drawing, intermediate annealing at 500 & / #61616 / C and water quenching was applied to obtain SMA wire with a diameter of 1.52 mm. Ti-Ni wires produced were subjected to four different processes. All the samples were initially solution heat treated at 925 & / #61616 / C for 30 minutes prior to water quenching. Some of the samples were further treated by an intermediate anneal at 500 & / #61616 / C. To see the effect of cold working / prior to intermediate annealing, 20 % or 40 % cold work was applied to another group of specimens.
To study the shape memory characteristics of specimens subjected to the above mentioned processes, four types of test, namely constant stress free recovery test, constant strain free recovery test, constant stress constrained recovery test and constant strain constrained recovery test, were designed and applied cyclically.
The tests have shown that the stress plateau observed in the first cycle of the tests disappear upon cycling and the shape memory characteristics improve and stabilize with cycling. Once trained by cycling, fractional free recovery was observed to reach to 100 % and recovery stress to reach 120% of the applied stress if shape recovery is prevented.
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Computational modelling of a smart impeller actuated by shape memory alloysFuhnwi, Godwin Fonguh January 2011 (has links)
Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2011 / Smart (SMA-Shape Memory Alloy) Technology continues to advance rapidly
as engineers move closer to and understand better the industrial and
commercial needs for SMA. As a matter of fact, all types of products, which
exercise some type of control over their function, are rapidly making their way
into the marketplace [36] Nonetheless, nowhere has been evidence in the
development of a SMA impeller.
Unlike traditional impellers with no control over their function and sometimes
fixed angle of attack, this paper demonstrates numerical investigations using
analytical algorithms (Matrix laboratory programming and excel spread sheet)
and advanced computer simulation package, Engineering Fluid dynamics
(EFD) into the feasibility of using a smart impeller to study the performance of
a pumping system and the best angle of attack for a Shape Memory Impeller.
Primarily, Bench mark data and dimensions are obtained from a standard
centrifugal pump run on a FM21 demonstration unit. Using the same standard
centrifugal pump, and keeping all other dimensions the same but altering the
angle of attack, EFD simulations where made.
From analytical algorithm and EFD comparison, it was evident that the best
angle of attack is 12 degree at the outlet angle with respect to the inlet angle.
From EFD results, it is palpable that, by increasing the angle of attack from 35
degree to 45 degree at the outlet there will be huge increase in flow rate by
63.47%
There is also a slight decrease in the impeller Torque from 35 degrees to 42
degrees by 0.72%.
It is economically feasible to work at an outlet angle of 42 degrees due to
increase in efficiency of 62.1% and a drop in torque of 0.72% by varying the
outlet angle from 35 degrees to 42 degree.
Understanding how critical actuator design is, it should be suggested that any
shape memory impeller should never be used in critical components without a
prior history of thermal and mechanical loading.
Therefore, a NiTi impeller constitutive model can be designed, with impeller
blades made from NiTi plates, trained to remember its best angle of attack
(Martensitic phase). NiTi shape memory metal alloy (plates-blades) can exist
in a two different temperature-dependent crystal structures (phases) called
martensite [9](lower temperature-normal pumping condition) and austenite [9]
(higher temperature or parent phase-trained best angle of attack.)
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Shape Memory Based Self-Powered Fluid PumpKatzenburg, Stefan, Spanke, Nina, Langhoff, Moritz, Faller, Clemens 13 February 2024 (has links)
In the range of 25°C - 80°C (ultra-low grade heat), a large quantity of waste heat from various processes
is available unused. Special alloys made of nickel and titanium, so-called Shape Memory Alloys
(SMA), could be an alternative technology to Organic Rankine Cycles to make this energy usable
in the low power range. The 'THEAsmart 2' research project is therefore investigating the service
life and energy lifecycle of this material to test the benefits of shape memory alloys in energy recovery
and the efficiency levels that can be achieved.
To this end, a demonstration prototype is being built that converts thermal energy into rotary motion.
The next step is to link the demonstration prototype with a conventional fluid pump to create
an SMA fluid pump that is driven by the thermal energy of the fluid to be pumped. The advantage of
such a pump would be that it would be energy-independent, i.e. it would be operated solely by the
thermal energy of the fluid without an electrical connection. Furthermore, such a pump could contribute
to energy savings if it is used in cooling circuits in which the thermal energy of the fluid is the
waste product from another process. In this case, it replaces an electric pump and utilizes the 'waste
product' heat.
The aim of the project is to investigate how and whether coil springs made of shape memory alloy
are suitable for energy recovery. This is considered via the energy lifecycle: if more energy is required
to manufacture a spring than this spring can convert kinetic energy from thermal energy in
its lifecycle, then its use for energy recovery does not make sense in principle. As a secondary result
of this research, statements about the efficiency of shape memory alloy coil springs and statements
about their service life are expected.
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[en] MODELING OF THERMOMECHANICAL BEHAVIOR OF SHAPE MEMORY ALLOYS / [pt] MODELAGEM DO COMPORTAMENTO TERMOMECÂNICO DAS LIGAS COM MEMÓRIA DE FORMAALBERTO PAIVA 28 May 2004 (has links)
[pt] O estudo de materiais inteligentes tem instigado várias
aplicações nas mais diversas áreas do conhecimento (da
área médica à industria aeroespacial). Os materiais mais
utilizados em estruturas inteligentes são as ligas com
memória de forma, as cerâmicas piezoelétricas, os
materiais magneto-estrictivos e os fluidos eletro-
reológicos. Nas últimas décadas, as ligas com memória de
forma vêm recebendo atenção especial, sendo utilizadas
principalmente como sensores ou atuadores. Existe uma
gama de fenômenos associados a estas ligas que podem ser
explorados. Visando uma análise mais precisa do
comportamento destes materiais, tem se tornado cada vez
maior o interesse no desenvolvimento de modelos
matemáticos capazes de descrevê-los de maneira adequada,
permitindo explorar todo o seu potencial. O objetivo
deste trabalho é propor um modelo constitutivo
unidimensional que considera quatro variantes de
microconstituintes (austenita, martensita induzida por
temperatura, martensita induzida por tensão trativa e
martensita induzida por tensão compressiva) e diferentes
propriedades para cada fase. O efeito das deformações
induzidas por temperatura é incluído na formulação. O
modelo contempla ainda o efeito das deformações plásticas
e o acoplamento entre os fenômenos de plasticidade e
transformação de fase. Além disso, são introduzidas
modificações na formulação que permitem o alargamento
do laço de histerese da curva tensão-deformação,
fornecendo resultados mais coerentes com dados
experimentais. Por fim, incorpora-se a assimetria no
comportamento tração-compressão. A validação do modelo é
obtida comparando os resultados numéricos obtidos através
do modelo com resultados experimentais encontrados na
literatura para ensaios de tração a diferentes
temperaturas e para a assimetria no comportamento tração-
compressão. / [en] The study of intelligent materials has instigated many
applications within the various knowledge areas (from
medical field to aerospace industry). The most
used materials in intelligent structures are the shape
memory alloys (SMA), the piezoelectric ceramics, the
magnetostrictive materials and the electrorheological
fluids. In the last decades, SMAs have received special
attention, being mainly used as sensors or actuators. There
is a number of phenomena related to these alloys that can
be explored. Aiming a more precise analysis of SMA
behavior, the interest on the development of mathematical
models capable of describing these phenomena properly has
grown, allowing to explore all their potential. The aim of
this work is to propose a unidimensional constitutive model
which considers four microconstituent variants (austenite,
martensite induced by temperature, martensite induced by
tensile loading and martensite induced by compressive
loading) and different material properties for each phase.
The effect of thermal strains is included in the
formulation. The model considers the effect of plastic
strains and the plastic-phase transformation coupling.
Besides, some changes are introduced in the formulation in
order to enlarge the stress-strain hysteresis loop,
resulting in better agreements with experimental data.
Eventually, the tensioncompression asymmetry is
incorporated. The model validation is obtained through
the comparison between the numerical results given by the
model and experimental results found in the literature for
tensile tests at different temperatures and for tension-
compression asymmetry.
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Prestressing concrete beams using shape memory alloy tendonsOrtega, Rosales Juan 01 April 2003 (has links)
No description available.
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Design And Analysis Of A Linear Shape Memory Alloy ActuatorSoylemez, Burcu 01 January 2009 (has links) (PDF)
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 TÜ / BiTAK-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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