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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 1
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
2. Review of Smart Materials and Structures
(part 1)
RVIT Sensor
Torsional Spring
Power Supply
for RVIT
Power Amplifier
Rotor with
SMA Wire
LPACT
52
14
BaseBay
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 2
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
2.1 What are Smart Materials
No official definition.
A lot of names: intelligent materials, adaptive materials, among others.
Smart materials refer to the materials that are "responsive". Often theresponse is the conversion of one form of energy into another in useful
quantities.
For example, piezoelectric ceramic material will generate voltage
when it is subjected to strain. Commonly used smart materials include piezoelectric ceramics, shape
memory alloy, magneto-rheological or MR fluids, electro-rheological
or ER fluids, and fiber Bragg Grating optics.
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 3
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Some Examples of Smart Materials
SMA Springs SMA Rods SMA Thin Wire
PZT Patches Flexible Piezo Actuator Piezos
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 4
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Types of Smart Materials
Electric
Field
Magnetic
Field
Thermal
EnergyLight
Chemical
Energy
Actuation
Piezoceramics
Piezopolymers
Electrostrictors
Electrorheological(ER) fluids
Magnetostrictors
Magnetorheological(MR) fluids
Shape memoryalloys, ceramics,
Polymers, Mecha-nocalories
Special gelsPhotostrictors
Mechanophoto-
chemics
Mechanochemics
Ionic polymeric gels
Piezoceramics
Piezopolymers
Electrostrictors
Electrorheological
(ER) fluids
Magnetostrictors
Magneto-rheological(MR) Fluids
Shape memory
alloys, ceramics,
polymers
Fiber optical
sensors Ionic polymeric gelsSensing
mechanical force, displacement
Resistance
Capacitycharge
Resistance
Inductance ResistanceLight
intensity
Concen-tration
pH
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 5
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Comparison of Smart Material Actuators
PZT-5H PVDF PMN Terfenol D Nitinol
Actuator Type Piezo-
ceramics
Piezo Polymer
Film
Electro-
strictive
Magneto-
strictive
Shape Memory Alloy
Max Free Strain
Micro Strain1000 700 1000 2000 80000 (single cycle)
50000 (many cycles)
Modulus
10^6 psi10 .3 17 7 4 (Martensite)
13 (Austenite)
Bandwidth High High High Moderate Low
Linearity Linear Linear Nonlinear Nonlinear Nonlinear
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 6
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
2.2 What are Smart Structures
No official definition.
Even more names: intelligent structures, multifunctional
structures, adaptive structures, adaptronics, etc.
Smart structures refer to the structures that employ embedded
actuators and sensors, and microprocessors that analyze the
responses from the sensors and use control theory to command
the actuators to apply localized strains to insure the systemrespond in a desired fashion. The actuators and sensor are
often made of smart materials. Smart structures have the
capability to respond to a changing external environment (such
as loads or shape change) as well as to a changing internalenvironment (such as damage or failure). Smart actuators are
used to alter system characteristics (such as stiffness or
damping) as well as of system response (such as strain or
shape) in a controlled manner.
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 7
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Position Control of an SMA Actuator under a Constant Load
Smart Structures: Example 1 An SMA Linear Actuator
Linear Bearing
Linear Variable
Differential Transformer
(LVDT) Sensor
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 8
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Position Control of an SMA Actuator under aConstant Load Experimental Results
Open Loop Testing
0 5 10 15 20 25 30-45
-40
-35
-30
-25
-20
-15
-10
-5
0
5Position(mm)
Time(sec)
Position(mm)
Red = Desired Position, Blue = Actual Position
0 5 10 150
0.5
1
1.5
2
2.5
3
3.5
4
4.5Position (cm) Vs Voltage (V)
Position(cm)
Voltage (V)
With PD Control
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 9
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Smart Structures: Example 2 An SMA Rotary Servo
The Rotary SMA Servo
Nickel-Titanium SMA wire (73.66cm in length, 0.381 mm in diameter).
dSPACE Data Acquisition and Real Time Control system
RVIT Sensor
Torsional Spring
Power Supply
for RVIT
Power Amplifier
Rotor with
SMA Wire
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 10
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
RVIT Sensor
Torsional Spring
Power Supply
for RVIT
Power Amplifier
Rotor with
SMA Wire
Achieving Two-Way Rotary Motion with a
SMA Wire and a Biasing (steel) Spring
By utilizing SMAs shape memory
property, a rotary servo actuated by a
Nitinol type SMA wire is designed andfabricated. An SMA wire winds along the
thread on the rotor. One end of the SMA
wire is fixed to base plate and the other end
is fixed to rotor. The rotor is connected
with a torsional spring with pre-tension.The rotor has a diameter of 1.15 inch. The
Nitinol wire has a diameter of 0.015 inch
and a total length of 29 inch. It is obvious
that this rotor design is a space-saving
solution for using SMA wire actuators.Upon heating of the SMA wire using
electric current, the wire contracts and
rotates the rotor since the other end of the
SMA wire is rigidly connected to the base
plate. During this process, the torsional
spring will be loaded. Upon cooling, the
torsional spring will return the rotor to its
original position and the SMA wire returns
to its original length.
A programmable current amplifier is used to power the
SMA wire. To study the forced cooling effect on the SMA
actuator, a cooling fan is installed underneath the rotor. A
Rotary Variable Inductance Transformer (RVIT) is used to
measure the wire displacement.
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 11
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
The Control Block Diagram
KD
Robust
Comp.
R Gain
Command
Saturation
Feedback Signal
Command Signal
Programmable
Power Supply
Real-Time Control System
Bias
t
RVIT Sensor
FlexibleCoupling
TorsionalSpring
Rotor with
SMA Wire
Amplified Command Signal
Low Pass
Filter
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 12
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
EXPERIMENTAL RESULTS
Experiment: the rotor is instructed to rotate from its initial position of 39.5
degree to 60 degree and then return to 0 degree.
Angular position with robust control (Desired and actualposition)
Steady state error =
.2 degree at 60 degree
and.1 degree at 0 degree
0 10 20 30 40 50 60
-40
-30
-20
-10
0
10
20
30
40
50
60
70
position(mm)
Time (second)
AngularPosition(degree)
Desired Position
Ac tual Pos itionRobust Control
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 13
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Comparison of Angular Positions with and without Cooling (PD control)
0 20 40 60 80 100 120-45
-40
-35
-30
-25
-20
-15
-10
-5
0
AngularPosition(degree)
Time (second)
Desired Position
With Cooling
Without Cooling
14
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 14
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Example3 A cantilevered beam with piezo sensors and actuators..
Power Amplifier
Piezo Actuator
Oscilloscope
Cantilevered Flexible Beam
Piezo Sensor
Sensor SignalSensor Signal
Actuating SignalPC with DataAcquisition &Real TimeControl
System
Example 4 Active vibration control of a composite I-beam.
C l f S S 2 R i f S M i l d S (P 1) 15
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 15
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Use Piezoceramic Patch as an Actuator
- + -+No Voltage
Direction
of Polarity
Applied Voltage
opposite polarityApplied Voltage
same as polarity
Direction
of Polarity
Direction
of Polarity
(a) Beam being bent upwards (b) No bending (c) Beam being bent downwards
C t l f S t St t 2 R i f S t M t i l d St t (P t 1) 16
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 16
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Use Piezoceramic Patch as a Sensor
-+ - +
No voltage generated
Direction
of Polarity
Voltage generatedsame as polarity
Voltage generatedopposite polarity
Direction
of PolarityDirection
of Polarity
F F
C t l f S t St t 2 R i f S t M t i l d St t (P t 1) 17
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 17
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Example 4: Strain Measurement using Fiber Bragg
Grating Optic Sensor
Optical fiber
Bragg gratings
Control of Smart Str ct res 2 Re ie of Smart Materials and Str ct res (Part 1) 18
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 18
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
About Fiber Bragg Grating Optic Sensor
Writing
Grating
With
Pulsed
Excimer
Laser
Period (
)
Coherent UV
beams
Holographically
Induced index
Modulation
( grating)
Fiber core
UV interference
pattern
IR
IIO
Principle: Write a grating on fiber by constructively interfering two high powerlasers. This corrugates index of refraction at a known wavelength.
Project broad band light down the fiber. Light at a Bragg wavelength
proportional to grating spacing is partially reflected: =2 n.
If the fiber grating is strained, the Bragg wavelength of reflected light changes
slightly. /= ~0.74 By detecting frequency shifts in reflected power spectrum, one can infer
strains in the grating region. Detectable resolution ~6 nano-stains.
Control of Smart Structures 2 Review of Smart Materials and Structures (Part 1) 19
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 19
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Experimental Results
Sensor Output When the Beam Vibrates
Sensor Output When Beam Is Subjected to a Constant Strain
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 20
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Example 5: Vibration Isolation using
an Ultra Quiet Platform
Disturbance Vibration
Caused by Shaker
Signal
Conditioner
Vibration Controller
for Each Strut
Bias Voltage
Trek 50/750
Power Amp.
Geophone
SensorOutputs
LowpassFilter
(Anti-Aliasing)
dSpace Real Time Data
Acquisition and Control
A/D Converter
+
D/A Converter
Piezoelectric
Actuator Inputs
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 21
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Example 6: Beam Shape Control using
Embedded Shape Memory Alloy Wires
Composite beam with
embedded SMA wires
Programmablepower supply
DC power supply
for manual control
Laser range sensor
OscilloscopePower supply for
laser range sensor
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 22
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
5.08cm
30.48 cm
Shape memory composite beam
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 23
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Low Pass
Filter
Programmable
Current/Voltage Amp.
Signal
Conditioner
Laser
Range Sensor
Composite Beam
with Embedded
Shape Memory
Alloy (SMA)
Wires
Current
Command
SaturationReal Time Control System
KD
Robust
Compensator R Gain
FeedforwardTerm
t
re
SMA beam
control strategy
along with theexperimental
setup
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 24
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
-50 0 50 100 150 200 250 300 350 400 450 5004
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
Desired Position
Beam Tip Response
P gain=20, D gain=20, Robust gain =10
BeamT
ipPositio
n(mm)
time (s)
Tip position control of the composite
beam with robust compensation
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1) 25
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Shape Memory Alloys (SMA's) are novel metal materials
which have the ability to return to a predetermined shape
when heated.
When an SMA is cold, or below its transformation
temperature, it has a very low yield strength and can bedeformed quite easily into any new shape. However, when
the material is heated above its transformation temperature
it undergoes a change in crystal structure which causes it to
return to its original shape.
If the SMA encounters any resistance during this
transformation, it can generate extremely large forces. This
phenomenon provides a unique mechanism for remote
actuation.
SMA Spring
After being Elongated at Cold
SMA Spring
After being heated
For example, the SMA spring shown in the figures can be
easily elongated when it is cold, but the SMA spring
returns to its original shape once heated.
2.3 Shape Memory Alloy Materials
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Control of Smart Structures 2. Review of Smart Materials and Structures (Part 1)
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
How SMA Works
Shape Memory Effect (SME) (One Way)The shape memory effect is a unique property of certain alloys exhibitingmartensitic transformations. These materials can be deformed in the lowtemperature phase, and they will recover their original shape by the reversetransformation upon heating to a critical temperature called the reverse
transformation temperature. This shape change is due to a change in the atomiccrystal structure of the alloy.
Heat
High Temperature
Cool
Remove Force
Force Force
Low Temperature
Deformed SMA Spring Deformed SMA Spring
SMA Spring
Deform
One Way Shape
Memory Effect of a
SMA Spring.
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( )
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Austenite and Martensite:
The high temperature crystal structure is called austenite and is cubic and strong. When cooled,
the material transforms to a structure called martensite, with a monoclinic lattice structure
which looks like a parallelogram in two dimensions and it is weak.
High Temperature
Cubic Structure
- Austenite
Low Temperature
Structure
- Martensite
How SMA Works (cont)
Nitinol Crystal Structures: Austenite and Martensite
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( )
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
How SMA Works (cont)
Twinning Process:
When a piece of shape memory material containing many atoms is cooled below a
transformation temperature, the atoms do not all tilt in the same direction. Instead, the atoms
form alternating rows of atoms tilting either left or right (shown in the figure). Any four atomsin the low temperature structure have the martensite parallelogram shape. The alternating rowsin the figure is called twinning, because the atoms form mirror images of themselves, or twins,through a plane of symmetry.
High Temperature Low Temperature
Twinned Martensite
Twinning Process: Nitinol Atomic Rearrangement upon Cooling
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( )
Department of Mechanical Engineering
Dr. G. Song, Associate Professor
De-twinning Process:
When a stress is applied to the twinned low temperature SMA, the stress will deform, or
accumulate strain, as the twins are reoriented so they all lie in the same direction. This is
called de-twinning, and in shape memory alloys, the stress required to reorient twins is
relatively low. This de-twinning process is shown in the figure.
How SMA Works (cont)
As Cooled Deformed by
Applied Force
Force
Force
De-twinning Process: Deformation of Low Temperature Nitinol Structure
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30Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Return to Austenite Upon HeatingHeating the material above a certain temperature will cause the deformed martensite to return to
austenite and the original shape of the piece will be obtained. This occurs because the original
atomic positions are always maintained in the austenite phase.
How SMA Works (cont)
Phase Transformation of Nitinol Shape Memory Alloy
High Temperature Austenite
Low Temperature Martensite
Twinned Structure
Deformed Low Temperature Martensite
Detwinned Structure
Deform
HeatingCooling
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31Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Phase Transformation of the SMA Spring (Macro and Micro Views)
How SMA Works (cont)
Heat
High Temperature
Cool
Remove Force
Force Force
Low Temperature
Deformed SMA Spring Deformed SMA Spring
SMA Spring
Deform
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32Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Two-Way Shape Memory Effect (SME)
Two-way shape memory effect: the shape memory
material will return to a low temperature shape on
cooling, as well as to a high temperature shape on
heating. But the recovery stress of a two-way SMA is
much lower than that of a one-way SMA.In both the one-way and two-way shape memory
effects, only during heating work can be generated.
During cooling with the two-way effect, the material
simply recovers its low temperature shape and cannot
provide a force to external mechanical components.
Heating Cooling
Deformation
One-Way SME
Cooling
Heating
Two-Way SME
The one-way shape
memory effect
requires a force to
deform the material
while it is cool, butwill recover its shape
when heated.
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33Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Transformation Hysteresis of SMAs
The phase transformation of SMAs exhibits hysteresis, i.e., transformations on heating and oncooling do not overlap.
Hysteresis, a nonlinearity, adversely affect precision control of the structures activated by SMAactuators.
To design control methods to compensate for the nonlinearities associated with SMA actuators
poses a challenge for control engineers and researchers.
Heating
Wire Contracts
Cooling
Wire Extends
Weight
Shape Memory Alloy Wire Actuator
Current
Current
Current
An SMA Wire ActuatorTemperature
Length
Martensite%
100
0
Austenite
Start
Austenite
FinishMartensite
Start
Martensite
Finish TransformationHysteresis
As
Af
Mf
Ms
Mf< Ms < As < Af
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34Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Hysteresis of an SMA Wire Actuator
A programmable current amplifier is used to electrically heat the SMA wire.
A linear variable differential transformer (LVDT) is placed aganst the slider to detect theactuators displacement.
The electrical heating of the wire causes a phase transformation, which is seen as a contractionof the wire. The wires contraction places additional tension on the spring. Once the current iscut off and heat is removed, the bias spring will pull the SMA wire actuator back to its coldlength.
Shape Memory Alloy Wire Actuator
LVDT Position
Sensor
Current Amplifier
Bia SpringLinear
Bearing
A Nickel-Titanium shape memoryalloy wire (30.48 cm in length and
0.381 mm in diameter) is used. In this SMA test stand, the shape
memory alloy wire is attachedbetween two wire supports. One wiresupport is attached to a slider that isfree to slide through a linear bearing.The slider is attached to a biasingspring which pretensions the shapememory alloy wire.
Experimental Setup
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35Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Motion Obtained by the SMA Wire Actuator
SMA at low temperature.
L1
Stretch the wire at low temperature
by the bias spring.
L2
Remove force, new length at low
Temperature.
Apply heat, regain original length
L1
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36Department of Mechanical Engineering
Dr. G. Song, Associate Professor
0 0.5 1 1.5 2 2.5 3 3.5 40
2
4
6
8
10
12
14Displacement v/s Voltage
Voltage (volt)
Displacement(mm)
The shape memory alloy wire is excited using asinusoidal signal. Though input voltage is puresinusoidal, the displacement is not.
The hysteresis loops observed have an average width of2 volts. The curves are not very smooth, and this can be
attributed to the uncontrolled ambient conditions. The shape memory alloy wire actuator is not fully
repeatable due to the uncontrolled ambient condition.0 50 100 150 200 250 300
0
0.5
1
1.5
2
2.5
3
3.5
4Applied Voltage and Current - Training Signal
.....Voltage _____Current
Time (sec)
Voltage(volt)andCurrent(amp)
0 50 100 150 200 250 3000
2
4
6
8
10
12
14Displacement - Training Signal
Time (sec)
D
isplacement(mm)
The Applied Sinusoidal Voltage and Measured Current
Displacement of the SMA Wire ActuatorRelationship between the Applied Voltage and
Displacement
Hysteresis
Loops
Hysteresis Loop:
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37Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Stress-Strain Relationship of SMA
The Stress-Strain relationship of shape memory alloys shows strong temperature dependence,because of the reversible Austenite to Martensite transformation.
This figure shows the stress-strain relationship of a shape memory alloy at or below the Mf
temperature. It is assumed that the SMA is cooled from the Austenite without applying stress.
Stress
Strain
Detwinning
Elastic
RegionElastic
Region
Plastic
Deformation
O
BA
CStress-strain Relationship at or below Mf
OA: The initial curve segment representselastic deformation and the microstructure
consists of randomly oriented Martensite
twins.
A: Detwinning starts. At this point, the stress
level is sufficient to start the twins to reorient
according to the applied stress field.AB: Detwinning. The twins reorient until
they all lie in the same crystallographic
direction.
B: Detwinning is complete at point.
BC: The Martensite undergoes mostly elastic
deformation again in segment BC. At point
C: The stress level is sufficient to start plastic
deformation of the Martensite.
Beyond C: The shape memory effect is
destroyed or severely diminished by plastic
deformation of the Martensite.
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38Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Stress
Strain
Stress induced Martensite
Elastic
RegionElastic
Region
Plastic
Deformation
O
BA
CStress-strain Relationship above Afbelow Md
Md: temperature at which non-elastic deformation is due toslip (plastic yielding) at stress induced Martensite.
O: The material is fully austenitic.
OA: Elastic deformation.
A: Martensite begins to form from
the austenite, this material isreferred to as stress inducedmartensite.
AB: Stress induced Martensite..
BC: Represents elastic deformation.
C: Plastic deformation starts to occur.
AB: When the material is unloaded in this segment with stress
induced Martensite, the Martensite becomes unstable and the
material returns to austenite and its original shape. The material can
experience 8% of strain change. Superelasticity occurs.
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At temperatures above Md, non-elastic deformation is entirely due to
plastic yielding, and no stress induced Martensite is formed.
Stress
ElasticRegion
Plastic
Deformation
Strain
Stress-strain Relationship above Md
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40Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Superelasticity Definition: the behavior of certain alloys to return to their original shape upon unloading after a
substantial deformation has been applied.
The superelastic mode takes place under constant temperature conditions.
When a shape memory alloy is deformed above Afand below Md (the temperature above whichstress-induced martensite can no longer be formed). stress-induced martensite is formed. When
the material is unloaded, the martensite becomes unstable and the material returns to austeniteand its original shape. Superelasticity occurs. The stress-strain relationship is shown in thefigure.
The unloading curve occurs ata lower stress due to
transformational hysteresis
which is closely related to the
thermal hysteresis in shape
memory behavior. The loading
plateau is the result of the
martensite accommodating the
applied stress by forming the
crystallographic twin variant
most favorably inclined to the
applied stress field.
Unloading plateau
Loading plateau
STAIN
STRESS
Sl: loading stress Su: unloading stress
t: total strain
Sl
Su
t
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41Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Superelasticity: Effect ofTemperature on loading and
Unloading Stresses
Loading and unloading stress increase with increasing
temperature within the Superelastic window.
Unloading
plateau
Loading
plateau
Temperature
Stress
MaterialElastic
Strain
Steel 0.8%
Cu-Zn-AI 5.0%
Ni-Ti 10.0%
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42Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Superelastic Window
In the left portion of the figure, the plastic strain is large and due to the Martensitic
transformation associated with the shape memory event (i.e. it can be recovered by
heating above Af,). To the right of the minimum point there exists a relatively flat portion which defines the
superelastic window since the permanent plastic strain is small.
To the right of the superelastic window the permanent plastic strain increases
dramatically and is therefore not acceptable for superelastic applications.
% set
after8%Shape memory
zone
(recover strain
by heating)
Superelastic + plastic
Deformation
(permanent set)
Temperature
Superelastic
zone
This figure shows theuseable temperaturerange for superelastic
behavior, commonlyreferred to as the"superelastic window".
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43Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Narrow Superelastic Window Limits Application
An approximately 40C window, starting at the Aftemperature, can be
obtained by strengthening the alloy--through a combination of cold
work, aging, and annealing. Still, this functional temperature range is too narrow for most industrial
and consumer applications. Automobile springs, for example,
generally require elasticity from -30 to 200C. Moreover, the stiffness
of a superelastic device changes with temperature according to the
Claussius-Clapeyron equation, at a rate of approximately 4-8 MPa/C.
The variability of superelasticity with temperature, and therefore its
narrow superelastic window, limits the general use of superelastic
materials.
Superelastic Window (cont)
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44Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Types of Shape Memory Alloy
Materials There are many known alloy systems which exhibit the shape memory effect, but only three
have shown promise for commercial applications. They are Nickel-Titanium (Ni-Ti), Copper-
Zinc-Aluminum (Cu-Zn-Al), and Copper-Aluminum-Nickel (Cu-Al-Ni).
The copper-zinc-aluminum alloys have a typical composition of 15 25 weight percentage Zn
/ 6 9 weight percentage Al / balance Cu. Cu-Zn-Al alloys are lower in cost than nickel
titanium, but they possess some inferior characteristics. Transformation temperatures can drift
slightly during cycling (particularly at service temperatures greater than 100 oC) and to a
significant extent if the alloy is not processed properly. These alloys are susceptible to stress
corrosion cracking when exposed to certain corrosive agents.
The copper-aluminum-nickel alloys have a typical composition of 13 14 weight percentage
Al / 3 4 weight percentage Ni / balance Cu. Cu-Al-Ni alloys possess lower ductility than
either Ni-Ti or Cu-Zn-Al. Their corrosion resistance is inferior to Ni-Ti and their cost is
higher than Cu-Zn-Al. Cu-Al-Ni alloys undergo less degradation in shape memory properties
than Cu-Zn-Al, after exposure to temperatures in the 100 to 350O C range. In addition, Cu-Al-
Ni alloys have the highest transformation temperatures of the three alloys.
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Nitinol The nickel titanium alloys (Nitinol) they have typical compositions of approximately 50
atomic percentage Ni / 50 atomic percentage Ti, and may have small additions of copper,
iron, cobalt, or chromium.
Nickel-titanium is about four times the cost of Cu-Zn-Al alloys.
It has several advantages over Cu-Zn-Al and Cu-Al-Ni: greater ductility
more recoverable motion
excellent corrosion resistance (comparable to series 300 stainless steels)
stable transformation temperatures
high biocompatability
the ability to be electrically heated for shape recovery.
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High electrical resistivity (~80 micro ohm-cm) enables Ni-Ti to be heated by electric
current.
Time response highly dependents on: the amount of current, the ambient temperature,
the wire diameter and mechanical configuration. AC or DC may be applied, care must be taken to avoid exceeding 250C.
The thicker the wire the longer the cooling time.
Electrical Actuation for Ni-Ti
SMA
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47Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Superelastic Nitinol
The enormous elasticity of this alloy is the most dramatic advantage afforded by
this material.
While many metals exhibit superelastic effects, only Ni-Ti-based alloys appear to
be chemically and biologically compatible with the human body. Although a largenumber of Ni-Ti ternary alloys have been introduced, none has been objectively
shown to be superior to simple binary Ni-Ti with between 50.6 and 51.0 atomic
percent nickel.
Nitinol superelastic materials has the advantages of elastic deployment,
biocompatibility, kink resistance, constancy of stress, physiological compatibility,dynamic interference, fatigue resistance, hysteresis, and MRI compatibility.
Superelastic nitinol alloys are becoming integral to the design of a variety of new
medical products.
Human bodies have a relatively constant temperature, ideally suited to the use ofsuperelasticity. Furthermore, the 37C temperature of humans is, by chance, easily
achieved in Ni-Ti without having to go to brittle Ni-rich alloys, or to very soft Ti-
rich alloys. Thus, the vast majority of successful superelastic applications are of a
medical nature.
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48Department of Mechanical Engineering
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Properties of Some SMAs NiTi CuZnAl CuAlNi FeNiCoTi Unit
Range of transformation temp -100 to +70 -200 to +100 -150 to +200 -150 to +550 C
Hysteresis width 30 15 20 K
Maximum one-way effect 8 4 6 1 %
Maximum two-way effect 4 0.8 1 0.5 %
Fatigue strength 800-1000 400-700 700-800 600-900 N/mm2
Ultimate tensile strength 700 600 500-800 N/mm2
Admissible stress for
actuator cycling 150 75 100 250 N/mm2
No of cycles >100000 10000 5000 50
Density 6450 7900 7150 8000 kg/m3
Electrical resistivity 80-100 7-12 10-14 10-8m
Youngs modulus, EA 50 70-100 80-100 170-190 GPa
Corrosion resistance very good fair good bad
Thermal conductivity 18 120 30-43 J/m-sec-K
Heat capacity 837 400 373-574 J/kg-K
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49Department of Mechanical Engineering
Dr. G. Song, Associate Professor
SMA Properties: Yield Strength
SMA Transformation Temperature Range
Property Ni-Ti Cu-Zn-Al Cu-Al-Ni
Maximum As Temperature (C) 100 120 200
High Temp Yield Strength (MPa) 415 350 400
Low Temp Yield Strength (MPa) 70 80 130
Temperature [C]
- 100 - 60 - 20 +20 +60 +100 +140 +180 +220
Ni- Ti
Ni- Ti- Cu
Cu- Zn- Al
Cu- Al- Ni
Cu- Al- Ni- Ti- Mn
Ti- Ni- Pd
Ti- Ni- Pt700C
600C
Ni- Ti- Fe [R- Phase]
Ni- Ti [R- Phase]
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Dr. G. Song, Associate Professor
2.4 Shape Memory Alloy Actuators
Comparison of Different Actuators
Types of SMA Actuators
Operating Modes of SMA Actuators
Some Mechanisms Using SMA Actuators Operational Modes and Applications of Superelastic Actuators
Passive Damping Using SMA or Superelastic Materials
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Advantages and Disadvantages of SMA
Actuators
Advantages Disadvantages
Large energy density
Solid state actuator no moving part
Combined sensor and actuator
Bio-compatibility
Various means of activation: electricity, laser,
and heat. Availability in different shapes
Linear and rotational motion
Micro-scalable
Usable in clean room environment
Very good corrosion resistance Low voltage actuation
Silent
Highly nonlinear
Low bandwidth
Large actuation power
Very low efficiency
Limited range of transformation
temperature (< 200OC)
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Comparison of Different
Actuators
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Comparison of Actuators
Type Temperature Motion Characteristics
Solenoid -50 to +120 C Linear, On-Off-simple design
-low cost
Bimetal -40 to +600 C Bending-low cost
-linear response
Wax Motor -40 to +180 C Linear
-high force
-low cost-linear response
Shape
Memory
-100 to +170 C Linear
Torsion
Bending
-high force/size
-simple designs
-Non-linear
-silent operation
-electrical and
thermal control
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Types of SMA Actuators
Actuator strokeMaterial
deformationActuator shape
Translation ContractionTensile wire, bar or tube
Translation Extension Compression bar or tube
Translation Shear
Coil spring
Rotation Bending
Leaf spring
Rotation Bending
Torsion helical spring
Rotation Shear
Torsion wire, bar or tube
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55Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Types of SMA Actuators
One-way motion achieved using
a SMA Spring
Heating
Weight
One-way motion achievedusing a SMA Wire
Heating
Wire Contracts
Cooling
Wire Extends
Weight
Shape Memory Alloy Wire Actuator
Current
Curren
t
Current
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Achieving Two-Way Motion
with a SMA Wire and a Biasing
(steel) Spring
Shape Memory Alloy Wire Actuator
LVDT Position
Sensor
Current Amplifier
Bia SpringLinear
Bearing
SMA Wire Test Platform
LVDT Position sensor
itinol SMA Wire
LinearBearing
Tension Spring
Pulle s
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57Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Achieving Two-Way Motion with a
SMA Spring and a Biasing (steel)
Spring
MOTION
STEEL
SPRINGS.M.A.
SPRING
COLD
HOT
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Operating Modes of SMA
ActuatorsA. Free Recovery
This is the most obvious way to use SME.
Free recovery consists of three steps:
1. Deformation of the shape memory material in the martensitic condition atlow temperature.
2. Release of the deforming stress.
3. Heating to above the transformation temperature to recover the high
temperature shape.
Deployment of an SMA-Wire
Antenna upon solar heating
Example: Collapsible SMA Wire Anntenna
One of the first application ideas for a shape memory device after the
properties of the alloys were realized was to fabricate a collapsibleantenna for a space vehicle from shape memory alloy wire, compress it
into a small package, shoot it into space and with heating from the sun
or by other means cause the antenna to self erect.
Source: Goodyear Aerospace
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59Department of Mechanical Engineering
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B. Constrained Recovery
In this family of applications, the SMA component is cooled to below
its Mfso it can be deformed to give a temporary shape. And it is then
used as part of a system to exert considerable force when heated.
Constrained recovery is the mode of operation used for couplings,
fasteners, and electrical connectors.
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Constrained recovery: Single-Cycle
Operation
Cryofit CouplingsCryofit shape memory couplings are used in the
joining of pipes and tubes, mostly in hydraulic
lines. The couplings are manufactured in the form
of an expanded sleeve, which overlaps the ends of
the tubes to be joined. When the sleeve is in place,
it is heated, and this causes it to shrink indiameter, swaging the tubes slightly, and forming
a strong union. They are used in applications
which require a compact, very reliable coupling,
for example for joining hydraulic tubing in
aerospace applications. They have also been usedin industrial and marine applications. Cryofit
couplings generally have to be shipped to the
customer packed in liquid nitrogen (-196O C)and
require special installation tooling. These
cryogenic couplings shrink and form a joint once
they reach the operating temperature of the
application.
These couplings may have been the largest single
use of Nitinol shape memory material to date.
Since the operating temperature may be as low as -
55 C, the transformation temperature has to be
lowered to about -100C. To achieved this,
sufficient iron (3-4%) is added to the Ni-Ti alloy.
Source: Raychem Corp.
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Cryocon electrical connectors made by Raychem
A family of electrical connectors
developed by Raychem Corp. were
named Cryocon to reflect the fact
that cryogenically cooling themwould open the socket so the pin of
the connector could be easily
withdrawn or inserted. When
warmed, though, the Nitinol ring
would recover its smaller diameterand clamp the socket tight on the
pin.
Source: Raychem Corp.
Constrained Recovery: Multi-cycle
Operation
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Electrical Connector with Zero Insertion Force (ZIF)
1. Low Temperature:Insert I.C. Pin
I.C. Pin
Compliant Contact
Shape Memory
Alloy Driver
2. Heat The SMA Driver ToClamp Pin In Place
Force Applied
by the SMA
Driver
It consists of a compliant contact (made of beryllium-copper), and a shape memory driver. Theshape memory driver is expanded at low temperatures, allowing the contact to open (i.e., the
contact assembly provides a biasing force), so the pin from the electronic chip can be inserted.
The assembly is then allowed to heat to perating temperature and the shape memory driver
shrinks in size, firmly holding the pin in place. Special tooling is required, but unlike the
couplings, the assembly can be opened
and closed many times if the electronic components require replacement. The connectors are
used for connecting dual in-line package integrated circuits. They have the advantage of
providing high clamping force and a zero insertion force.
Constrained Recovery: Multi-cycle Operation
Source: Beta Phase, Inc.US Patents:5,044,980
5,015,193
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63Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Some Mechanisms Using SMA
Actuators SMA Valve
Steel Spring Shape Memory Spring
Expanded
VALVE OPEN
HIGH TEMPERATURELOW TEMPERATURE
VALVE CLOSED
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64Department of Mechanical Engineering
Dr. G. Song, Associate Professor
SMA Valve
Hot Gas In
Biasing Spring Shape Memory spring
Gas
Out
HIGH TEMPERATURE
LOW TEMPERATURE
Valve
ClosedCold Gas In
ValveOpen
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65Department of Mechanical Engineering
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SMA Mixing valve
SMA spring will control the ratio of cold and hot water. It will prevent
extreme changing of water temperature at the begging of flow.
Source: Furukawa Techno Material (FTM)
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66Department of Mechanical Engineering
Dr. G. Song, Associate Professor
A Rice Cooker With SMA Release Valve
SMA spring opens the pressure control valve at the certain high
temperature, and releases excess steam to outside.
Source: Furukawa Techno Material (FTM)
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67Department of Mechanical Engineering
Dr. G. Song, Associate Professor
SAM Vent for an Air Conditioning Unit
Source: Furukawa Techno Material (FTM)
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68Department of Mechanical Engineering
Dr. G. Song, Associate Professor
SMA Valve
Steel
Spring
SMA Spring at HIGH
TEMPERATURE
SMA Spring at LOW
TEMPERATURE
Valve OPEN
Shape Memory
Alloy Spring
Steel
Spring
Valve BLOCKEDShape Memory Alloy
Spring Expanded
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69Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Robotic Fish: Achieve Fish-like
Locomotion using SMA Wires
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SMA Fish Actuation Illustration (Top
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70Department of Mechanical Engineering
Dr. G. Song, Associate Professor
SMA Fish Actuation Illustration (Top
View)
Wire 1
Bending
1 & 4 actuated
Bending
2 & 3 actuated
Waving
1 & 3 actuated
Waving
2 & 4 actuated
Wire 3
Wire 4
Wire 2
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71Department of Mechanical Engineering
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Shape Control of a Flexible BeamUsing SMA Actuators
Movie: Beam Shape Control in Air Movie: Beam Shape Control in Water
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72Department of Mechanical Engineering
Dr. G. Song, Associate Professor
Shape Memory Saw-Tooth Bone
Fixator
Chinese Patent No: ZL 94239678.2
Source: SIAI Hi-Tech LTD
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Operational Modes of Superelastic
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73Department of Mechanical Engineering
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Operational Modes of Superelastic
Actuators
A. Deformation Resistant ApplicationsThis class of superelastic devices is manufactured with the intent that they may never bedeformed beyond the limits that ordinary metals would tolerate, but if they are then theywill demonstrate superelasticity by undergoing stress induced transformation and will
spring back from the deformation when the stress is removed to restore the design.function of the device.
Cellular telephones antennas
Eyeglass frames
Guide wires to guide catheters
Superelastic Cell
Phone Antenna
Nitinol guide wires
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74Department of Mechanical Engineering
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B. Shape Restoring Applications
Superelasticity allows one to pass a
complex instrument through a
cannula, and have the instrument
elastically return to the deployed
configuration once through. The
figure below shows a comparison of
the smaller "footprint" that is possible
with "hingeless" Nitinol designs
compared to a stainless steel design.
Instruments include right angle
needles, suture passers, retractors,
graspers, baskets, and retrieval bags.
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Atrial Septal-Defect Occlusion System (ASDOS) - Shape Restoring
Application
This device is the first to allow nonsurgical repairs of
occlusions, or holes, in the atrial wall of the heart. This
procedure can treat defects ranging in diameter from 20 to 35
mm. A transcatheter method is used with the entire procedure
conducted through two catheters, in this case 10 french (~3.5
mm) in diameter.
The actual device comprises two small umbrellas consisting of
five nitinol wire loops supporting webs of microporous
polyurethane (see the figurse). The two umbrellas are passed
into the body while folded into two catheters, and arepositioned one each on either side of the defect area. A
guidewire passing directly through the hole is used to ensure
that the two catheters and umbrella devices are positioned
correctly. Once positioned, the umbrellas are pushed forward
from their catheters and screwed together using a specialtorquing catheter. The resulting sandwich forms a patch,
occluding the atrial defect. Available umbrella diameters range
from 20 to 65 mm.Source: Osypka Medizintechnik
(Rheinfelden, Germany)
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Amplatzer Septal Occluder Shape Restoring
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76Department of Mechanical Engineering
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Amplatzer Septal Occluder - Shape Restoring
Application
The Amplatzer Septal Occluder is a self-
expandable, double disc device made
from a Nitinol (Nickel-Titanium Alloy)
wire mesh. The two discs are linked
together by a short connecting waistcorresponding to the size of the ASD. To
increase its thrombogenicity, the device's
discs and waist are filled with polyester
patches. The polyester patches are
securely sewn to the wire frame withpolyester threads.
The Amplatzer Septal Occluders are
provided in a kit containing devices
ranging in size from 4-34mm*. Thedelivery system consists of a delivery
cable, sheath, loading device, pin vise,
and sizing template. Sheath sizes range
from 6 to 12F.
Source: AGA Medical Corporation
U.S. Patent 5,725,552
U.S. Patent 5,846,261
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A & B: Pre Closure
C & D: Complete closure
immediately after device
release.
E & F: Six month TEE
Follow-up, note the
shrinkage in the profile ofthe device with time.
Source: AGA Medical Corporation
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Stents: Shape Restoring Application
The gentle pressure against the vessel wall is controlled by
the unloading arrows, but reclosing of the vessel is resisted
by the stiffness indicated by the loading arrows.
Superelastic medical self-expanding stents are used to support the insidecircumference of a tubular passage such as an esophagus, bile duct, or blood vessel.
Probably the most interesting area of application is in the cardiovascular system, as a
follow-up to balloon angioplasty. The placement of a stent has been shown to
significantly decrease the propensity for restenosis.
4% 8%
MartensiteInducing Stress
Reversion Stress
Strain
Loading
Unloading
Stress
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Use of Shape Memory Alloys for Passive Damping
Shape Memory Hysteresis During Cyclic Motion
Strain %
4 8 12
Martensite deformation Stress
20
60
100
Stress, ksi
Due to the hysteresis, the shadow area represents the energy dissipated during a
cycle.
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Use of Superelasticity for Passive Damping
Due to the hysteresis, the shadow area represents the energy dissipated during a
cycle.
Strain %
12
100
Stress, ksi
4 8
20
60
Martensite Inducing Stress
Reversion Stress