Veermata Jijabai Technological Institute

MumbaiShape Memory Alloys and

it’s Applications in Civil Engineering

Seminar on

Under The Guidance of Dr. Priyanka Jadhav

ByPankaj DhangareM. Tech I(Structural)Roll No-142040013

Content IntroductionHistoryLiterature reviewsTypes of SMAsPropertiesWorking principleApplicationsCase studyConclusion

Introduction SMAs are the Materials which have the ability to

return to a predetermined shape when heated or cooled.

When it is heated above its transformation temperature it undergoes a change in crystal structure which causes it to return to its original shape.

The most common shape memory material is an alloy of nickel and titanium called Nitinol

This particular alloy has very good electrical and mechanical properties, long fatigue life, and high corrosion resistance

History 1932: Chang and Read recorded the first

observation of the shape memory transforation. 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.

Literature reviews "Applications of Shape Memory Alloys in Civil

Engineering Structures - Overview, Limits and New Ideas” by JANKE, L., et al.(2005). "Materials and Structures” 38(June 2005): 578-592.

A basic description of SMA highly non-linear material behaviour in terms of shape memory effect and superelasticity.

It is followed by a brief introduction to Ni-Ti and Fe-Mn-Si SMAs.

Pre-existing and new applications in the fields of damping, active vibration control and prestressing or posttensioning of structures with fibres and tendons are being reviewed with regard to civil engineering.

New ideas for using SMAs in civil engineering structures are proposed such as an improved concept for the active confinement of concrete members.

Literature reviews…. “Applications of Shape Memory Alloys in Civil

Structures” by Song, G., Ma, N., and Li, H.-N. (2006)., Engineering Structures, 28, 1266-1274.

The shape memory effect (SME) and pseudoelasticity, two major properties of SMA associated with the thermal-induced or stress-induced reversible hysteretic phase transformation between austenite and martensite are reviewed.

These unique properties enable SMA to be used as actuators, energy dissipaters and dampers for civil structure control.

Various applications in civil structures.

Literature reviews…. “APPLICATION OF SMART MATERIALS IN CIVIL

ENGINEERING STRUCTURES,” by T.S. Thandavamoorthy(2013) , Research in Civil Engineering Structures-05 251-263.

He described the characteristics of smart materials, the use of SMA in construction and research, and their beneficial aspects by reviewing the available information.

He considered Shape Memory Alloy as SMART MATERIAL or INTELLIGENT MATERIAL.

Types of SMAsAlloy

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–Cu40.0,50.0,10.0

294.1 314.6 325.9 339.8

Cu–Zn–Al25.6, 4.2, 70.2

288.5 292.3 293.2 298.3

Cu–Al–Ni82.0, 14.0, 4.0

252.0 246.0 274.0 285.0

Cu–Al–Be11.6, 0.6, 87.8

157.0 179.0 169.0 195.0

PropertiesMechanical propertiesTensile and compressive behavior

Properties….Unique properties of shape memory alloys1. Shape Memory Effect2. Pseudo-ElasticityShape Memory Effect

Properties…. Austenite and Martensite – Two phases

exhibited by SMA’s in solid state. If deformed in martensite phase, the

parent shape is regained upon heating. As and Af are the temperatures at which

transformation from martensite to austenite starts and finishes.

Transition dependant on temperature and stress.

Repeated use of shape memory effect leads to functional fatigue.

Properties….Pseudo-Elasticityo Occurs without temperature change.o Based on stress induced mechanism o This property allows the SMA’s to bear large

amounts of stress without undergoing permanent deformation.

Working principleA 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.Austenite occurs at higher

temperatures.

Working principle…..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).

ApplicationsGeneral applications• Eyeglass Frames• Helicopter blades• Dental wires

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.

Applications….2. Prestressing

The benefits of employing SMAs in prestressing include:

i. No involvement of jacking or strand-cuttingii. No elastic shortening, friction, and

anchorage losses over time

SMA strands are used in pre tensioning and post tensioning.

Applications….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).

Applications….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.

Applications….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. In the presence of cracks due to explosions or earthquakes, by electrically heating the SMA wires, the wire strands contracts and reduce the cracks.

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.

Applications….

A small concrete block with SMA post-tensioned wires.

Test Set up of beam reinforced with SMA wire.

A model by G. Song et. al(2006)

Applications….

Cracked block on loading Closure of crack on unloading

Applications….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.

7. SMA as fibers The most crucial limitation of concrete is its low tensile

strength, compared to its compressive strength, which results from the propagation of micro-cracks.

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.

AdvantagesBio-compatibilityDiverse Fields of ApplicationGood Mechanical Properties (strong, corrosion

resistant)DisadvantagesThese alloys are still relatively expensive to

manufacture and machine compared to other materials such as steel and aluminum.

Most SMA's have poor fatigue properties; this means that while under the same loading conditions (i.e. twisting, bending, compressing) a steel component may survive for more than one hundred times more cycles than an SMA element.

Case study1. Retrofitting Of the Basilica

of San Francesco at Assisi, Italy

The Basilica of San Francesco was restored after being strongly damaged by an earthquake of 1997 Umbria-March earthquake (Castellano 2000).

The gable was completely disconnected from the roof and was then linked to the roof again by means of Shape Memory Alloy Devices (SMAD’s). Each SMAD is designed to take both tension and compression forces, while consisting of SMA wires which are only subjected to tension.

In order to reduce the seismic forces transferred to the tympanum, a connection between it and the roof was created using superelastic SMAs

The SMA device demonstrates different structural properties for different horizontal forces. Under extremely intense horizontal loads, the SMA stiffness increases to prevent collapse.

SMA Devices in the Basilica of St Francesco of Assissi

Below figure shows the SMDs used in the retrofit.

Case study2. Retrofitting of the bell tower of the Church of

San Giorgio at Trignano, Italy The S. Giorgio Church, located in Trignano, Italy,

was struck by a 4.8 Richter magnitude earthquake on October 15, 1996, resulting in significant damage to the bell tower within the church.

Following the earthquake, the tower was rehabilitated using SMAs.

The upgrade was carried out linking top and bottom of the tower by means of hybrid tendons.

Four vertical prestressing steel tie bars with SMA devices were placed in the internal corners of the bell tower to increase the flexural resistance of the structure.

Case study•The retrofit was tested by a minor m=4.5 Richter

magnitude earthquake on June 18, 2000, with the same epicenter as the event in 1996. After the main shock, the tower was investigated and no evidence of damage was present (DESROCHES and SMITH 2003).

Bell tower with tendons and SMA devices

ConclusionSMA’s have the potential to be used effectively

in seismic regions.

The high cost of SMAs is a major limiting factor for its wider use in the construction industry.

Their capability to allow the development of smart structures with active control of strength and stiffness and ability of self-healing and self-repairing opens the door for exciting opportunities, making them the construction material of the future.

THANK YOU……….