2.Reveiw.smart Part1

7/31/2019 2.Reveiw.smart Part1

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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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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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Some Examples of Smart Materials

SMA Springs SMA Rods SMA Thin Wire

PZT Patches Flexible Piezo Actuator Piezos


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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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Experimental Results

Sensor Output When the Beam Vibrates

Sensor Output When Beam Is Subjected to a Constant Strain



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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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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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5.08cm

30.48 cm

Shape memory composite beam



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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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-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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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)



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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( )



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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( )




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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( )



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.


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


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.


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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Phase Transformation of the SMA Spring (Macro and Micro Views)


Heat

High Temperature

Cool

Remove Force

Force Force

Low Temperature

Deformed SMA Spring Deformed SMA Spring

SMA Spring

Deform



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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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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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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.


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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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One-way motion achieved using

a SMA Spring

Heating

Weight

One-way motion achievedusing a SMA Wire

Heating

Wire Contracts

Cooling

Wire Extends

Weight


Current

Curren

t

Current


A hi i T W M ti


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Achieving Two-Way Motion

with a SMA Wire and a Biasing

(steel) Spring


LVDT Position

Sensor

Current Amplifier

Bia SpringLinear

Bearing

SMA Wire Test Platform

LVDT Position sensor

itinol SMA Wire

LinearBearing

Tension Spring

Pulle s


A hi i T W M ti ith


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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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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.


i d i l l


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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


C t i d R M lti l O ti


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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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Some Mechanisms Using SMA

Actuators SMA Valve

Steel Spring Shape Memory Spring

Expanded

VALVE OPEN

HIGH TEMPERATURELOW TEMPERATURE

VALVE CLOSED



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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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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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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.




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SAM Vent for an Air Conditioning Unit




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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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Robotic Fish: Achieve Fish-like

Locomotion using SMA Wires


SMA Fish Actuation Illustration (Top


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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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Shape Control of a Flexible BeamUsing SMA Actuators

Movie: Beam Shape Control in Air Movie: Beam Shape Control in Water



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Shape Memory Saw-Tooth Bone

Fixator

Chinese Patent No: ZL 94239678.2

Source: SIAI Hi-Tech LTD


Operational Modes of Superelastic


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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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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)


Amplatzer Septal Occluder Shape Restoring


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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

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