PowerPoint Presentation
Special Technologies
An Introduction to Shape Memory Alloys (SMAs)
Mehrshad [email protected]
University of RomeDepartment of Mechanical and Aerospace
Engineering
Department of Mechanical and Aerospace Engineering
Special TechnologyTypes of Materials
- Metals- Ceramics- Polymers- Composites- Semiconductors
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Department of Mechanical and Aerospace Engineering
Special TechnologyPiezoelectric materialsShape memory
alloysMagnetic shape memory alloysMagnetorheologicalPH sensitive
polymersHalochromic materialsThermochromic materialsChromogenic
systemsElectrochromicSmart Grease
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Department of Mechanical and Aerospace Engineering
Special TechnologyWhat are Shape Memory Alloys? Shape Memory
Alloys (SMAs) are metallic alloys that undergo a solid-to-solid
phase transformation which can exhibit large recoverable strains.
Example: Nitinol
Department of Mechanical and Aerospace Engineering
Special Technology
Department of Mechanical and Aerospace Engineering
Special TechnologyTimeline of Memory Metals1932 - A. lander
discovers the pseudoelastic properties of Au-Cd alloy.1949 - Memory
effect of Au-Cd reported by Kurdjumov & Kandros.1967 At Naval
Ordance Laboratory, Beuhler discovers shape memory effect in nickel
titanium alloy, Nitinol, which proved to be a major breakthrough in
the field of shape memory alloys.1970-1980 First reports of
nickel-titanium implants being used in medical
applications.Mid-1990s Memory metals start to become widespread in
medicine and soon move to other applications.
Department of Mechanical and Aerospace Engineering
Special TechnologyNumber of publications per year
Department of Mechanical and Aerospace Engineering
Special TechnologyGeographic distribution
Department of Mechanical and Aerospace Engineering
Special TechnologyShape Memory Alloys
AlloyTransformation CompositionTransformation Temp. Rang
(C)Hysteresis (C)Ag-Cd44/49 at % Cd-190 to -50~15Au-Cd46.5/50 at %
Cd30 to 100~15Cu-Al-Ni14/14.5 wt %Al, 3/4.5 wt %Ni-140 to
100~35Cu-Sn~15 at % Sn-120 to 30Cu-Zn38.5/41.5 wt % Zn-180 to
-10~10Cu-Zn-X (X=Si,Sn,Al)few wt % X-180 to 200~10In-Ti18/23 at %
Ti60 to 100~4Ni-Al36/38 at % Al-180 to 100~10Ni-Ti~49/51 at % Ni-50
to 110~30Fe-Pt~25 at % Pt~-130~4Mn-Cu5/35 wn % Cu-250 to
180~25Fe-Mn-Si32 wt % Mn-200 to 150~100
Department of Mechanical and Aerospace Engineering
Special TechnologyFerromagnetic shape-memory alloysShows
shape-memory effect in response to a magnetic field Deformation due
to magnetic field is known as magnetoelastic deformation.Ni-Ti is
non-magnetic Examples of ferromagnetic SMAs: Ni2MnGa, Fe-Pd,
Fe3Pt
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Special TechnologyMaterial behavior in Micro-size
Department of Mechanical and Aerospace Engineering
Special Technology
MfMsAsAfAusteniteMartensiteTEMPERATURE
MfMsAsAfAusteniteMartensite
TEMPERATURE(twinned)(twinned)Characteristic
temperatures:Mf=Martensitic FinishMs=Martensitic StartAs=Austenitic
StartAf=Austenitic FinishThermally Induced Phase Transformation in
SMAs
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Special Technology
How are SMAs working?
Department of Mechanical and Aerospace Engineering
Special TechnologyTriggers for Martensitic Transformation
(MT)StressTemperature
Department of Mechanical and Aerospace Engineering
Special TechnologyHow does it work? Step 1: Austenite PhaseHigh
TemperatureThe atoms arrange themselves in their permanent
shape
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Special Technology
Step 2: Martensite PhaseLow temperatureCubic structure becomes
folded or twined
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Step 3:Bend the WireIt remains in its Martenesite Phase
Department of Mechanical and Aerospace Engineering
Special TechnologyStep 4: Austenite PhaseHeat the wire above the
transition temperature of 50 degrees It moves back to its original
position!
Department of Mechanical and Aerospace Engineering
Special TechnologyAustenite & Martensite Phases
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Special Technology
SMAs
Pseudoelasticity or Superelasticity (SE)
Shape Memory Effect (SME)
Department of Mechanical and Aerospace Engineering
Special TechnologyShape Memory Alloys
Pseudoelasticity or Superelasticity (SE)When the metal is
changed to the martensite phase simply by strain. The metal becomes
pliable and can withstand strains of up to 8%.
Shape Memory Effect (SME)These materials have an ability to
remember its austenite phase. As the metal is cooled to the
martensite phase, it can be easily deformed. When the temperature
is raised to the austenite phase, it reforms to the original shape
of the material.A mix of roughly 50% nickel and 50% titanium is the
most common SMA. Also CuZnAl and CuAlNi are widely used.
Department of Mechanical and Aerospace Engineering
Special TechnologySuperelastic behavior (SE)SMAs deformed above
a critical temperature show a large reversible elastic deformation
(recoverable strains up to 10%. much exceeding the elasticity) as a
result of stress-induced martensitic transformation.
Superelastic behaviorT > AfHysteresis loop means energy
dissipation, hence vibration dampingStress
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Special TechnologyApplications of superelastic
behaviorOrthodontal bracesFrames for eyeglassesUnderwires for
brassieresAntennas for cellular phones
Department of Mechanical and Aerospace Engineering
Special TechnologyShape Memory Effect (SME)Martensitic phase
transformation that occurs as a result of stress or temperature
change
Department of Mechanical and Aerospace EngineeringThe Shape
Memory Effect
se
T
Cooling
Detwinning
Heating/Recovery
Department of Mechanical and Aerospace Engineering
Special TechnologyApplications of shape memory effect
Self-expandable cardiovascular stentBlood clot
filtersEnginesActuators for smart systemsCouplingsFlaps that change
direction of airflow depending upon temperature (for air
conditioners)
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Special Technology
SHAPE MEMORY ALLOY (NITINOL)Inactive
Active - Bending
Active - Twist
Department of Mechanical and Aerospace Engineering
Special Technology
Department of Mechanical and Aerospace Engineering
Special TechnologyBEFORE TRANSFORMATION
DURING TRANSFORMATION
AFTER TRANSFORMATION
SHAPE MEMORY POLYMERS
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Special Technology
AFTER TRANSFORMATION
BEFORE TRANSFORMATION
DURING TRANSFORMATION
SHAPE MEMORY POLYMERS
Department of Mechanical and Aerospace Engineering
Special Technology SHAPE MEMORY POLYMERS
Department of Mechanical and Aerospace Engineering
Special TechnologyTypes of shape-memory behaviorOne-way shape
memory: transformation to the desired shape occurs only upon
heating, i.e., memory is with the austenite phase.
Department of Mechanical and Aerospace Engineering
Special TechnologyTypes of shape-memory behaviorTwo-way shape
memory: the deformed shape is remembered during cooling, in
addition to the original shape being remembered during heating,
i.e., memory is with both austenite and martensite phases (requires
training to attain memory during cooling; formation of favorably
oriented twins during cooling between Ms and Mf)
Department of Mechanical and Aerospace Engineering
Special TechnologyPhysical properties of Nitinol (versus SS)
Department of Mechanical and Aerospace Engineering
Special TechnologyThe applications of SMAs
Department of Mechanical and Aerospace Engineering
Special TechnologyMicro-actuatorsMobile phone
antennasOrthodontic archwiresPenile implantPipe couplingsRobot
actuatorsRock splittingRoot canal drillsSatellite antenna
deploymentScoliosis correctionSolar actuatorsSpectacle framesSteam
valvesStentsSwitch vibration damperThermostatsUnderwired
brasVibration dampersZIF connectorsAids for disabledAircraft
flap/slat adjustersAnti-scald devicesArterial clipsAutomotive
thermostatsBraille print punchCatheter guide wiresCold start
vehicle actuatorsContraceptive devicesElectrical circuit
breakersFibre-optic couplingFilter strutsFire dampersFire
sprinklersGas dischargeGraft stentsIntraocular lens mountKettle
switchesKeyhole instrumentsKey-hole surgery instrumentsCurrent
examples of applications of shape memory alloys
Department of Mechanical and Aerospace Engineering
Special TechnologyExisting and potential SMA applications in the
biomedical domain
Department of Mechanical and Aerospace Engineering
Special TechnologySMAs in Bio-medical Devices
Department of Mechanical and Aerospace Engineering
Special Technology
Bone AnchorsRobotic arms
Medical Stents
Department of Mechanical and Aerospace Engineering
Special TechnologySMA orthodontic wires
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Special Technology
Nitinol is used in medicine for stents: A collapsed stent can be
inserted into a vein and heated (returning to its original expanded
shape) helping to improve blood flow. Also, as a replacement for
sutures where nitinol wire can be weaved through two structures
then allowed to transform into it's pre-formed shape which should
hold the structures in place.
SMAs Stents
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Special Technology
Bone staple
Department of Mechanical and Aerospace Engineering
Special TechnologyPhotographs of (a) brassiere and (b) various
designs of superelastic NiTi underwires.
Department of Mechanical and Aerospace Engineering
Special TechnologyExisting and potential SMA applications in the
automotive domain
Department of Mechanical and Aerospace Engineering
Special TechnologyExisting and potential SMA applications in the
aerospace domain
Department of Mechanical and Aerospace Engineering
Special Technology
Picture of wing with SMA wires The wires in the picture are used
to replace the actuator. Electric pulses sent through the wires
allow for precise movement of the wings, as would be needed in an
aircraft. This reduces the need for maintenance, weighs less, and
is less costly.
Department of Mechanical and Aerospace Engineering
Special Technology
Department of Mechanical and Aerospace Engineering
Special TechnologySMAs Microactuators
Department of Mechanical and Aerospace Engineering
Special Technology
Department of Mechanical and Aerospace Engineering
Special TechnologySMAs Micro-actuatorsSMAs can generate the
mechanical work in shape of large actuation force and displacement
during the phase transformation. This deformation is produced due
to cooling and heating cycle as two significant elements in SMA
actuators. The main parts of the SMA actuators include; SMA part,
mechanical system, electronic control system, the fixture body and
the effective element with recovering capability based on the
employed stress.
Department of Mechanical and Aerospace Engineering
Special TechnologyAdvantages and dis-advantages of shape memory
materials
Department of Mechanical and Aerospace Engineering
Special TechnologySMAs Micro-actuatorsThe most common
applications of NiTi thin films are concentrated on microactuators
due to their particular capabilities in MEMS, such as micropumps,
microvalves, microgrippers, micropositioners, microsprings,
microspacers, and microwrappers, etc.
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Special Technology
The schematic of NiTi microvalve in (a) close position, (b) open
position
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Special Technology
(Left) Scanning electron micrograph of a NiTi micro-gripper
(Right) (1) The sketch of operational mode (2) Thermo-mechanically
cycle (3) The working principle due to heating/cooling
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Special Technology
Magnetic microgripper (a) the schematic of the body, (b)
Gripping a micro-object by the micro-tip
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Special Technology
A NiTi microgripper with a hook structure and two C-shape probes
(a) cooled state (b) heated state
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Special Technology
The micro wrapper based on NiTi thin film
Department of Mechanical and Aerospace Engineering
Special TechnologySchematics of the operation of
MicroSwitches
Department of Mechanical and Aerospace Engineering
Special TechnologyProblems With SMAsFatigue from cyclingCauses
deformations and grain boundariesBegin to slip along
planes/boundariesOverstressA load above 8% strain could cause the
SMA to completely lose its original austenite shapeDifficulty in
machining processDifficulty with computer programmingMore expensive
to manufacture than steel and aluminum
Department of Mechanical and Aerospace Engineering
Special Technology
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