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MART MATERIAL AND EN OR
ABSTRACT
Now days, smart materials have found an important place in the
modern engineering applications. Smart materials or intelligent materials
system include integration of sensors, actuators and control with a material
or structural component possesses intelligent and life features .The
development of smart material is inspired by the biological structure
systems and their basic characteristics of functionality, efficiency, precision,
self - repair and durability. Smart materials are not only singular materialsbut also Hybrid composites or integrated systems of materials.
Shape Memory Alloys are one of the maor categories of smart
materials which after being strained at certain temperature revert bac! to
the original shape because of uni"ue properties such as Shape Memory
effect, Pseudo elasticity and high damping capacity . These properties in
smart hybrid composites provide them the tremendous potential for creating
new paradigms for material-structural interactions and demonstrate various
successes in engineering applications li!e Aeronautical engineering, in
medical fields li!e Vascular stents and Osteosynthesis etc., and in
commercial fields also.
The main advantages of shape memory alloys are, they are Bio-
compatible, strong and good corrosion resistant . They generally have high
power to weight ratio and can withstand large amount of recoverable strain
and when heated above transition temperature, they can e#ert high recovery
stresses of 700MPa which can be used to perform wor!.
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$n this paper, we are presenting one of the maor categories of smart
materials, SMAs, their properties, different types of SMAs and their
applications in various fields
.
HAPE MEMORY ALLOY
INTRODUCTION:
Shape memory alloys are metals that, after being strained, at a certain temperature
revert back to their original shape. A change in their crystal structure above their
transformatations temperature causes them to return to their original shape.
SMAs enable large forces (generated when encountering any resistance during theirtransformation) and large movements’ actuation, as they can recover large strains.
SMAs ehibit two very uni!ue properties pseudo-elasticity and the shape memory
effect. "ypical Alloys which ehibit these properties are #i$"i alloy, %ron base SMA
alloy, &opper base SMA alloy, Super 'lastic glasses etc.,
SHAPE EOR! E""ECT:
"he ability of SMAs to return to their original shape after heating to their
transformation temperature after having been deformed is termed as #shape memory
e$$ect%& "his is due to the change in the crystalline structure during the transition from
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martensitic phase to austenitic phase.
Martensite is the relatively soft and easily deformed phase of shape memory alloys,
which eists at lower temperatures. "he molecular structure in this phase is twinned as
shown in the middle of figure. pon deformation this phase takes on the second form
shown in figure, on the right. Austenite, the stronger phase of shape memory alloys,
occurs at higher temperatures. "he shape of the Austenite structure is cubic, shown on the
left side of figure."he un$deformed Martensite phase is the same si*e and shape as the
cubic Austenite phase on a macroscopic scale, so that no change is visible in shape
memory alloys until the Martensite is deformed.
"he Shape Memory effect is observed when the temperature of SMA is cooled to
below the temperature Mf. At this stage the alloy is completely composed of Martensite
which can be easily deformed. "he original shape of SMA can be recovered simply by
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heating the SMA above the temperature Af.
"he shape memory effect is currently being implemented in+
Co$$eepots
The Space Shuttle
Thermostats
'ascular Ste(ts
Hydraulic "itti() *$or Airpla(es+
PSEUDO-E,ASTICIT!+
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Pseudo-elasticity occurs i( SAs he( the alloy is completely composed o$
Auste(ite. %t occurs without change in temperature. "he load on the SMA is increased
until the Austenite becomes transformed into Martensite due to the loading (as shown).
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"he loading is absorbed by the softer
Martensite, but as soon as loading is decreased the Martensite begins to transform back to
Austenite since the temperature of the SMAs is still above Af, and the wire springs back to
its original shape.
Some Applications of pseudo$elasticity is used are+
Eye)lass "rames
edical tools
Cellular pho(e A(te((a
Orthodo(tic Arches
"E. SHAPE EOR! A,,O!S+
!"#$%-&!&A!'M A%%O()
#i$"i alloys are the most used SMA. %t is an e!uiatomic compound of #i$"i, whose
transformation temperature can range between -/00 1 //0C& %t has great shape$memory
strain (up to 23+4is thermally stable and has ecellent corrosion resistance. ecause of
the reactivity of "i, all melting of it must be done in a vacuum.
"OPP$* BAS$ SMA A%%O( +"u-n-Al "u-Al-i.)
&u$-n$Al and &u$Al$#i alloys are commercially available SMAs. "heir
transformation temperature ranges between -/20 1 500C a(d -/60 1 /00 C
respectively. "hey are cheaper than #i$"i alloys can be melted in air with ease and have a
shape$memory strain up to 6-73& ot work in air is well suitable, while cold work is
suitable only for low Al content alloys *893 t+&
S'P$* $%AS&!" /%ASS$S +
"hese glasses are made from a super elastic metal alloy. "herefore, they
can be bended !uite drastically without permanent damage. The )lasses
utilie the super elastic property o$ Ni-Ti alloys.
!*O BAS$ SMA A%%O(S)
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"he most important %ron based shape memory alloy is "e-(-Si. "hey base shape$
memory effect on a different physical principle than conventional SMAs. "hey can
recover only less tha( 63 strai(&
APP,ICATIONS:
"he pseudo elasticity and Shape memory effect are being applied to a wide variety
of applications in a number of different fields. Some of them are+
Aero(autical E()i(eeri()
edical Applicatio(s
Commercial applicatio(s
AERONAUTICS:
Aircraft maneuverability depends heavily of flaps found at the rear or trailing edges
of the wings.Aircrafts at present operate these flaps using etensive hydraulic systems. %n
order to maintain reliability of operation, multiple hydraulic lines must be run to each set
of flaps. "his comple system is often relatively difficult and costly to maintain. Some of
the most promising alternatives to this comple system are+
Pieoelectric $i;res
Electrostricti<e ceramics
Shape emory Alloys
/Smart0wings, which incorporate shape memory alloys, are shown.
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"his system is much more compact and efficient, in that the shape memory wires
only re!uire an electric current for movement.
"he shape memory wire is used to manipulate a fleible wing surface. "he wire on
the bottom of the wing is shortened through the Shape Memory 'ffect, while the top wire
is stretched bending the edge downwards, the opposite occurs when the wing must be
bent upwards. "he shape memory effect is induced in the wires simply by heating them
with an electric current, which is easily supplied through electrical wiring, eliminating the
need for large hydraulic lines.
y removing the hydraulic system, aircraft weight, maintenance costs and repair
time are all reduced. "he smart wing system is currently being developed cooperatively
through the efense Ad1anced *esearch Pro2ect Agency (1A23A, a branch of the
nited States 1epartment of 1efense) and oeing.
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EDICA, APP,ICATIONS:
S'*/!"A% &OO%S)
one plates are surgical tools, which are used to assist in the healing of broken and
fractured bones. "hey are often applied to fractures occurring to facial areas such as nose,
4aw or eye sockets. 2epair like this fall into an area of medicine known as
Osteosynthesis3
Curre(tly osteotemy e=uipme(t is made primarily o$ tita(ium a(d stai(less
steel. "he broken bones are first surgically reset into their proper position. "hen a plate is
screwed onto the broken bones to hold them in place, while the bone heals back together.
The dra;ac> o$ this process is a$ter i(itially paci() the plate o the ;rea> or
$racture the ;o(es are compressed to)ether a(d held u(der some sli)ht pressure
hich helps to speed up the heali() process o$ the ;o(e& U($ortu(ately4 a$ter o(ly a
couple o$ days the te(sio( pro<ided ;y the steel plate is lost a(d the ;rea> or
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$racture is (o lo()er u(der compressio(4 sloi() do( the heali() process. f
"he bone plates can also be fabricated using SMAs, in particular #i$"i alloys. sing
a bone plate made out of #i$"i, which has a transformation temperature of around Af
much greater than /7 C& the #i$"i plates are first cooled to well below their
transformation temperature, then they are placed on the set break 4ust like "i plates.
owever when the body heats the plate upto the body temperature the #i$"i attempts to
contract applying sustained pressure on the break or fracture for far longer than stainless
steel or "itanium. "his steady pressure assists the healing process and reduces recovery
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time.
VAS"'%A* S&$&S)
A vascular stent is a device which is implanted in a blood vessel (veins and
arteries) to provide structural reinforcements of the vessel wall. "he introduction of SMA
to stent manufacture allows greater recovery strains for use in wider vessels, or stronger
recovery force in narrower vessels.
COERCIA, APP,ICATIONS:
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A&!S"A%$ $V!"$S)
asically an etension which fits between the shower head and the water pipe,
containing a "i$based SMA element which epands if water becomes too hot, choking off
the flow. A very cheap, easy and effective alternative to more epensive technologies."O$"&!/ *!/S)
2ings and cylinders of SMA which are austenite at ambient temperature can provide
significant constraining force around their inner circumference, ensuring a strong 4oint
which can be released by cooling couplings.
"O44$$PO& &5$*MOS&A&)
A #i$"i spring in coffeepots marketed in 5apan is trained to open a valve and
release hot water at the proper temperature to brew a perfect pot of coffee.4AS&$!/ 4'"&!OS)
Shape Memory 'ffect 'lements (SM''), in a variety of shapes can be used for
fastening and coupling purposes, e&)& ;uildi() e()i(eeri()4 aero(autics a(d i(
assem;ly operatio(s. y epanding or shrinking at preset temperatures 4 SEE ca(
per$orm hi)h $orces a(d assure ti)ht $aste(i()4 either perma(e(t or temporary. %n
temporary fastening, the fiation can be released by means of the two$way$memory
effect.
RO?OTICS APP,ICATIONS:
S&$& 4O* V$!S)
"he stent is used for reinforcing weak vein walls and for widening narrow veins.
"he chilled stent is brought into position through a probe, and epands to its original si*e
when warmed up to body temperature. "he stent replaces similar steel stents that are
epanded with a little balloon.
AD'ANTA@ES O" SHAPE EOR! A,,O!S: Some of the main advantages of shape memory alloys include+
?io-compati;ility
Di<erse "ields o$ Applicatio(
@ood echa(ical Properties *stro()4 corrosio( resista(t+
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Hi)h Poer to .ei)ht Ratio
I( marte(site phase they ca( ithsta(d lar)e amou(ts o$ reco<era;le strai(
*upto 23+
.he( heated a;o<e the tra(sitio( temperature they ca( eert hi)h reco<ery
stress o$ B00Pa&
CONC,USION:
"hus, the shape memory Alloys are etensively used in Aeronautics, 6steosynthesis and
in some commercial products. Still they have got some drawbacks(7ess efficient,
epensive etc,). 8e can hope that the ongoing researches in SMAs will rectify these
drawbacks so that they will emerge as a universally accessible one.
?I?,IO@RAPH!:
9. 'ngineering Aspects of Shape Memory Alloys$1uerig ".8., Melton :.#.,
Stoeckel 1, 8ayman &.M.
. 'ngineering Aspects of Shape Memory Alloys$1.'. odgson, M.. 8u, and 2.5.
iermann.
;. "itanium$#ickel Shape Memory Alloys$ 1uerig ".8., A.2. 1elton.
.E?SITES:
9. Shape Memory Applications %nc.,
. #itinol devices and components %nc.,