Sma ppt

SHAPE MEMORY ALLOY
AND ITS STRUCTURAL
APPLICATIONS
GUIDED BY,
Ms . AMRITHA E K
ASSISTANT PROFESSOR
CIVIL ENGINEERING DEPARTMENT
UEC
PRESENTED BY,
KRISHNA PRIYA V V
ROLL NO : 02
S3, M Tech
UEC
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SHAPE MEMORY ALLOYAND ITS STRUCTURALAPPLICATIONS
CONTENT
Introduction
History
Properties
Types of SMAs
Working principle
Application

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 A shape-memory alloys (SMA, smart metal, memory metal,
memory alloy, muscle wire, smart alloy) are metal alloys that
can be deformed at one temperature but when heated or
cooled, return to their “original” shape
 The alloy appears to have a memory
 The most effective and widely used alloys are NiTi, CuZnAl,
and CuAlNi
 SMA also exhibits superelastic (pseudoelastic) behavior
INTRODUCTION

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CONTD…
Extraordinary properties are due to the temperature and stress
dependent phase transformation from a low-symmetry to a
highly symmetric crystallographic structure
Very high actuation strain, stress, and work output
Excellent self-centering ability, good energy dissipation
capacity, high corrosion resistance, and high fatigue life
Applications of SMAs in various disciplines including
biomedical, aerospace, automotive, and other industries

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)
Fig 1 (a) Shape memory effect; (b) superelastic effect
(Ozbulut et al.2015)

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HISTORY
1932: Chang and Read recorded the first observation of the shape
memory transformation
1938: Greninger and Mooradian observed the formation and
disappearance of martensitic phase by varying the temperature of a
Cu-Zn alloy
1951: Shape memory effect was observed
1962-63: Ni-Ti alloys were first developed by the United States
Naval Ordnance Laboratory
Mid-1990s – Memory metals start to become widespread in
medicine and soon move to other applications

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PROPERTIES OF SMA
Figure 2 Transformation temperatures
(Motavalli et al.2009)

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CONTD…
Temperatures at which the SMA changes its crystallographic
structure are characteristic of the alloy and can be tuned by
varying the elemental ratios
Ms-the temperature at which the structure starts to change from
austenite to martensite upon cooling
Mf-the temperature at which the transition is finished
As and Af are the temperatures at which the reverse
transformation from martensite to austenite start and finish,
respectively

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Pseudo-Elasticity
Occurs without temperature change
Based on stress induced mechanism
This property allows the SMA’s to bear large amounts of stress
without undergoing permanent deformation.
CONTD…

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TYPES OF SMAs
Alloy Composition
Transformation temperature(K)
Mf Ms As Af
Ni–Ti 50.5, 49.5 277.0 306.0 317.0 335.0
Ni–Ti 50.8, 49.2 227.0 252.0 270.0 284.0
Ni–Ti 50.9, 49.1 157.4 242.5 275.1 317.8
Ni–Ti 50.0, 50.0 245.2 310.7 321.4 351.0
Ni–Ti–Cu 40.0,50.0,10.0 294.1 314.6 325.9 339.8
Cu–Zn–Al 25.6, 4.2, 70.2 288.5 292.3 293.2 298.3
Cu–Al–Ni 82.0, 14.0, 4.0 252.0 246.0 274.0 285.0
Cu–Al–Be 11.6, 0.6, 87.8 157.0 179.0 169.0 195.0

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Table 1. Property values of selected shape memory alloys
CONTD…

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BASIC WORKING PRINCIPLE
A molecular
rearrangement in the
SMA’s austenite and
martensite phase is
responsible for its
unique properties
Martensite is relatively
soft and occurs at lower
temperatures
Fig 3 : Temperature vs Load graph

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CONTD…
The shape of austenite structure is cubic
No change in size or shape is visible in shape memory alloys
until the Martensite is deformed
To fix the parent shape, the metal must be held in position and
heated to about 500°C
The high temperature causes the atoms to arrange themselves
into the most compact and regular pattern possible resulting in a
rigid cubic arrangement (austenite phase)

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APPLICATIONS
Applications in civil engineering/ structure
1. Reinforcement
 SMA’s are particularly beneficial for construction in
seismic regions.
 If SMA is used as reinforcement, it will yield when
subjected to high seismic loads but will not retain
significant permanent deformations.

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2. Prestressing
 The benefits of employing SMAs in prestressing
include:
-No involvement of jacking or strand-cutting
-No elastic shortening, friction, and anchorage losses
over time
 SMA strands are used in pre tensioning and post
tensioning
CONTD…

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3.Braces for frame structures
 The SMA wire braces are installed diagonally in the
frame structures.
 As the frame structures deform under excitation, SMA
braces dissipate energy through stress-induced
Martensite transformation (in the superelastic SMA
case) or Martensite reorientation (in the Martensite
SMA case)
CONTD…

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Fig. 4 Schematic of the setup of the SMA
brace reinforced frame structure
CONTD…
Fig. 5. Schematic of the SMA braces
for a two-story steel frame
(Motavalli et al.2009)(Motavalli et al.2009)

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CONTD…
Fig 6 Schematic of the SMA braces for a frame
structure

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4.Damping element for Bridges(restrainer)
 One of the main problems of bridges during earthquakes is
their unseating because of excessive relative hinge opening
and displacement
 These limitations can be overcome by introducing SMA
restrainers as they have larger elastic strain range and can
be brought back to its original position even after
deformation
CONTD…

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Fig. 7 Schematic of the SMA damper for a
stay-cable bridge
CONTD…

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Fig. 8. Schematic of the setup of SMA restrainer for a
simple-supported bridge
CONTD…

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5.SMA for structural self-Rehabilitation
 The IRC(Intelligent Reinforced Concrete ) uses stranded
Martensite SMA wires for post-tensioning
 By monitoring the electric resistance change of the SMA wires,
the strain distribution inside the concrete can be obtained
 This self-rehabilitation can handle macro-sized cracks
 The concrete structure is intelligent since it has the ability to
sense and the ability to self-rehabilitate
CONTD…

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6.SMA as FRP
 SMA-FRP reinforcing bars behave in a ductile manner
and are capable of dissipating energy
 It was found that SMA-FRP bars have more potential to
improve the ductility and energy dissipation capability
of concrete structures compared to conventional FRP
bars
CONTD…

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7.SMA as fibers
 Due to the propagation of micro-cracks, strength of
concrete decreases
 This may be prevented by using prestrained SMA wires
that are embedded in the concrete matrix
 Upon activation, these wires regain their original shape,
and consequently, initial compressive stresses are
transmitted to the concrete matrix
CONTD…

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EXPERIMENTAL PROGRAM ON SMA
1. Buckling Control Using Shape-memory Alloy Cables
 To provide additional insight into the high potential shown
by SMAs for new structural applications, namely in bracing
systems
 Achieved by using original cable-restraining systems based
in SMAs
 The proposed cable-restraining systems take advantage of
either superelasticity or the SME

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CONTD…
Passive Control Of Buckling With SMAs
• The system that is analyzed in this section is based on a
simply supported aluminium column with a total height (l) of
500 mm and a rectangular cross section of 15 × 2 mm2
•In this system, two SE cables, each having a circular cross
section with a 0.406-mm diameter, laterally restrain the column
•The system has a horizontal deviator at mid height, which is
equipped with two pulleys, one in each extremity

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CONTD…
)
Fig 9 The proposed cable restrained system (Santos et al.2016)

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CONTD…
)
Fig 10 . Critical buckling mode shapes(Santos et al.2016)

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 Active Control Of Buckling With SMAs
•A restrained column with martensitic NiTi wires is used with
the 36-mm deviator
•The compressive force is introduced with the same
experimental apparatus as in the passive control system
•The system is also provided with two laser-displacement
sensors to monitor the vertical and horizontal displacements of
the column
CONTD…

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•The stress in the wire is applied to the system by temperature-
induced phase transformations in a two-way NiTi SMA, martensitic
actuator wire, which can remember both high- and low-temperature
shapes
•A Sorensen programmable direct-current (DC) power supply
(PPS), model XHR 40–25 (Sorensen Systems,
Northborough,Massachusetts), was used to allow the Joule heating
of the NiTi wire actuators
CONTD…

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)
Fig. 11 A view of the experimental setup(Santos et al.2016)

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•A passive control restraining solution that uses the SE cables
to increase the buckling resistance of a compressed column
while employing the SE effect to dissipate energy and promote
recentering
•The critical buckling load was increased by a factor of 2.0
and 2.85
•An active control system based on a PID control algorithm
that detected the onset of buckling and applied control forces
in the cables that counteracted the buckling motion
CONTD…

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CONTD…
•This control approach enabled the increase of the critical
buckling load by a factor of 2.6
•These two promising control approaches can be further
combined in hybrid restraining solutions for subsequent
studies

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2. Bond Behavior Of Smooth And Sand-coated Shape
Memory Alloy (SMA) Rebar In Concrete
The experimental program conducted in this study involved a
series of 56 push out test specimens (concrete cylinders) with
different parameters
 Push out test was selected since it was simple to conduct
Ni–Ti SMA rebar (nitinol) has been used as reinforcement to
investigate the bond behaviour
 4different concrete mixes were evaluating the effect of
concrete compressive strength on the bondbehavior of SMA rebar

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Fig. 12 Test setup for bond behavior SMA rebar with concrete (Billah et al. 2015)

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)
Fig.13 Specimens (smooth) (a) before testing, (b) after testing and (c) inside view
(Billah et al. 2015)

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The results from 56 pushout tests lead to the following
conclusions:
1. The stress–slip curve of SMA rebar can be divided/idealized
into four stages: elastic stage, ascending stage, linearly
descending stage and residual stage
Fig. 14. Load–slip curves for pushout test of smooth SMA rebar (Billah et al. 2015)

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2. The bond strength of both smooth and sand coated SMA rebar
is significantly influenced by the concrete strength, bar diameter
and embedment length but is independent of concrete cover
3. The application of sand coating increased the bond strength
between concrete and SMA rebar by developing friction and
interlocking forces in addition to the adhesion mechanism
4. The coarser the sand size, the more is the improvement in bond
strength
CONTD…

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5. The surface roughness of SMA rebar significantly affects the
failure pattern as well as the bond strength
6. Concrete with smooth SMA rebars resulted in simple push
out failure whereas sand coated rebars resulted in splitting
failure
CONTD…

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3. Experimental Results of A Niti Shape Memory Alloy (SMA)-
based Recentering Beam-column Connection
Use of superelastic nickel–titanium (NiTi) shape memory
alloys (SMAs)to induce the recentering force on the connection
with the goal of creating a simplified ductile recentering system
The connection was designed to recenter under large drift
demands to fully exploit the unique ability of NiTi to
spontaneously recover up to 8% strain

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CONTD…
Four experimental tests were carried out
 Test A was performed using ordinary steel tendons to set a
benchmark to compare performance
Test B was performed using martensitic NiTi tendons, which
do not revert to their initial shape until heat is applied
Test C was performed using superelastic SMA tendons,
which revert to their initial shape spontaneously
Test D was performed using superelastic SMA tendons in
parallel with low-strength aluminium bars
The aluminium bars were added to provide additional energy
dissipation

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The results demonstrated that a NiTi SMA-based connection can
be developed to have excellent ductility, energy dissipation, and
recentering
For the test connection layout, a 0.5% prestrain was applied to all
NiTi tendons.
Prestraining of the NiTi SMA tendons was effective in increasing
the recentering capability, and the overall behaviour of the
connection
• NiTi tendons possess significant superelastic properties that can
fully recenter a connection at drift levels below 1% and adequately
recenter a connection at drift levels above 1%

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4. RC Beams Reinforced With SMA Rebars
A concrete beam reinforced with shape memory alloys (SMA)
wires was tested and compared with a conventionally reinforced
concrete (RC) beam
For the tests, NiTi (Nickel/Titanium) wires approximately
4.3mm in diameter were used to reinforce the underside of a
concrete beam with a span of 1.14m
The surfaces of the SMA wires were sand-blasted and coated
with quartz sand using an epoxy adhesive

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Figure 15.Beam reinforced with SMA wires in the test set-up (Motavalli et al.2009)

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Figure 16.MTest cycles on the test beams (Motavalli et al.2009)

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REAL WORLD APPLICATION OF SMA
1.Retrofitting Of The Basilica Of San Francesco At Assisi,
Italy
Earthquake induced vibrations may cause severe damage in
particular to historical buildings, like the Basilica of San
Francesco at Assisi
The Basilica was restored after being strongly damaged by an
earthquake of 1997
The structural interaction of the basilica’s transept south gable
with the main structure needed to be modified

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Figure 17 .Back view of the historic gable (Photo: FIP Industriale)

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Figure 18. Shape memory alloy device (Photo: FIP Industriale)

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Figure 19. Principal load displacement behavior of SMAD

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2. Retrofitting Of The Bell Tower Of The Church Of
Sangiorgio At Trignano, Italy
Seismic upgrade of the bell tower of the Church of San Giorgio
at Trignano became necessary after being struck by a 4.8 Richter
magnitude earthquake in 1996 and represents one of the first
known applications of SMAs to civil engineering
Retrofit design of the 17 meters tall masonry tower was carried
out under the framework of the ISTECH project
After a 4.5 Richter magnitude earthquake with the same
epicenter in 2000, subsequent investigations of the retrofitted bell
tower found no evidence of damage .

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Figure 18.St. Giorgio bell tower (Motavalli et al.2009)

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Figure 20.Bell tower with tendons and principle load-displacementbehavior of
incorporatedSMA devices (Motavalli et al.2009)

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3. Repair Of A Cracked Region Of A Highway Bridge In
Michigan, Usa
The concerned bridge in Michigan on highway no. US-31
has suffered cracks due to insufficient shear resistance
attributed to improper cut-off of longitudinal flexural
reinforcement
The resulting shear cracks in the web of the reinforced
concrete T-beam had an average width of 0.55 mm
Iron-manganese-silicon-chromium (FeMnSiCr) SMA was
used for the rods of diameter 10.4 mm

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Figure 21.Assembly of SMA rods for external strengthening of a
bridge (Motavalli et al.2009)

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LIMITS OF SMA
1.Cost
Due to the size of civil engineering structures and the acting
of relatively high forces, a large amount of material is needed
Ni-Ti based alloys show an extremely good shape memory
effect but the high material costs prevent it from being used
more extensively

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CONTD…
2. Stress Induced Martensite in Shape Memory Effect
The re-transformation from austenite to martensite and the
associated loss in stiffness is unwanted when using shape
memory effect for permanent tensioning
Stress induced martensite can be avoided by providing a
suitable transformation temperature profile

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CONCLUSIONS
The shape memory effect (SME) enables martensite Nitinol
materials to be used as actuators and also enables their
applications in active and semi-active controls of civil structures
Structural self-rehabilitation using reinforced martensite
SMAs is an example of active structural control
Sand coated SMA rebar shows high bond strength
NiTi SMA-based connection can be developed to have
excellent ductility, energy dissipation, and recentering

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REFERENCE
• Filipe Amarante dos Santos, 2016,”Buckling Control Using
Shape-Memory Alloy Cables”, American Society of Civil
Engineers
• A. H. M. MuntasirBillah, A.M.ASCE; and M. ShahriaAlam,
M.ASCE2, 2016,
“Performance-Based Seismic Design of Shape Memory
Alloy–Reinforced Concrete Bridge Piers. I: Development of
Performance-Based Damage States”, ASCE
• Osman E. Ozbulut, A.M.ASCE1; Sherif Daghash; and
Muhammad M. Sherif,2015,”Shape Memory Alloy Cables for
Structural Applications”, American Society of Civil Engineers

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• Mostafa Tazarv and M. Saiid Saiidi, F.ASCE,.
2014,“Reinforcing NiTi Superelastic SMA for Concrete
Structures “, American Society of Civil Engineers
• Michael V. Nathal and George L. Stefko ,2013,“Smart
Materials and Active Structures”, American Society of Civil
Engineers
• Matthew S. Speicher , Reginald DesRoches, Roberto T.
Leon,2011,”Experimental results of a NiTi shape memory alloy
(SMA)-based recentering beam-column connection”, Elsevier Ltd
• G. Song, N. Ma, H.-N. Li, 2006,” Applications of shape
memory alloys in civil structures”, Elsevier Ltd
• L. Janke , C. Czaderski , M. Motavalli and J. Ruth ,2005,”
Applications of shape memory alloys in civil engineering
structures - Overview, limits and new ideas”, Elsevier Ltd

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THANK YOU

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