2. GUIDED BY : PRESENTED BY:
MANJU GEORGE ELDHO PETER
Dept. of Civil Engg. S7 CE
ROLL NO:21
MBITS
3. INTRODUCTION
Shape Memory Alloys are materials that “remember”
their original shape.
If deformed, they recover their original shape upon
heating.
They can take large stresses without undergoing
permanent deformation.
They can be formed into various shapes like
bars, wires, plates and rings thus serving various
functions.
Shape Memory Alloy 3
4. HISTORY
1938: Arne Olande observed shape and
recovery ability of Au-Cd alloy.
1938: Greninger and Mooradian observed
the formation and disappearance of
martensitic phase by varying the temperature of
a Cu-Zn alloy.
1962-63: Ni-Ti alloys were first developed
by the United States NavalOrdnance
Laboratory.
Nitinol – Nickel Titanium Naval Ordnance
Laboratories.
Shape Memory Alloy 4
5. PROPERTIES
SMA’s exhibit 2 important properties.
1. Shape Memory Effect
2. Pseudo-Elasticity
Shape Memory Effect
Austenite and Martensite – Two phases
exhibited by SMA’s in solid state.
SMA moulded into parent shape in
austenite phase.
Shape Memory Alloy 5
8. 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.
Shape Memory Alloy
8
9. Pseudo-Elasticity
Occurs without temperature change.
This property allows the SMA’s to bear large amounts
of stress without undergoing permanent deformation.
Applications: Reading glasses.
Shape Memory Alloy 9
10. Temperature of
SMA is maintained
above transition
temperature.
Load is increased
until austenite
transforms to
martensite.
When loading is decreased, martensite transforms
back of austenite.
SMA goes back to original shape as temperature is still
above transition temperature.
Shape Memory Alloy 10
11. WORKING OF SMA’S
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.
Austenite occurs at higher temperatures.
The shape of austenite structure is cubic.
Shape Memory Alloy 11
12. The un-deformed Martensite phase is the same size and
shape as the cubic Austenite phase on a macroscopic scale.
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).
Shape Memory Alloy 12
13. APPLICATIONS
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.
The seismic performance of reinforced concrete and
steel columns with SMA bars was investigated by
Wang (2004).
Shape Memory Alloy 13
14. 2. Bolted Joints
Beam-column and column-foundation joints are the
weakest links in a structure during an earthquake.
SMA materials can be effectively employed in such
joints to reduce their vulnerability by dissipating
greater energy through large plastic deformation and
then recovering it on removal of load.
Shape Memory Alloy 14
15. 3. Prestressing
The benefits of employing SMAs in prestressing include:
i. Active control on the amount of prestressing
ii. No involvement of jacking or strand-cutting
iii. No elastic shortening, friction, and anchorage losses ove
time
SMA strands are used in pre tensioning and post
tensioning.
SMA’s in prestressing have the potential for creating
smart structure.
Shape Memory Alloy 15
16. 4. Restrainers
One of the main problems of bridges during earthquakes
is their unseating because of excessive relative hinge
opening and displacement
. Limitations of existing unseating-prevention devices
include small elastic strain range,
limited ductility, and no recentering
capability.
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
Shape Memory Alloy 16
17. CONCLUSION
SMA’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.
Shape Memory Alloy 17
18. REFERENCE
1. K Otsuka, C M Wayman, Shape Memory
Materials, Cambridge University press, 1999.
2. Kauffman, George and Isaac Mayo, (1996) The Story of
Nitinol: The Serendipitous Discovery of the Memory
Metal and Its Applications, The Chemical Educator, VOL.
2, pp1430-4171.
3. Peter Filip and Karel Mazanec, (1995) Influence of work
hardening and heat treatment on the substructure and
deformation behaviour of TiNi shape memory
alloys, Scripta Metallurgica et Materiala, Volume 32, Issue
9, 1 May 1995, pp 1375-1380.
4. Rogers, Craig., (1995), Intelligent Materials, Scientific
American Sept. 1995:, pp154-157.
5. Lin, Richard., Shape Memory Alloys And Their
Applications, (Created: January 21, 1996. Last modified:
February 22, 2008), <www.stanford.edu>, (July 17, 2011).
Shape Memory Alloy 18
