Shape memory alloys are alloys that remember their original shape and return to it when heated. The two main types are copper-aluminum-nickel and nickel-titanium alloys, with nickel-titanium preferred for its stability and performance. Shape memory alloys exhibit either one-way or two-way memory effects. They are manufactured by casting and have applications in bone plates, aircraft maneuverability, and reinforcing arteries and veins where they expand when heated. Advantages include high power-to-weight ratio and corrosion resistance while disadvantages are poor fatigue properties, high cost, and slower response time.
2. WHAT IS A SHAPE MEMORY ALLOY?
A shape memory alloy(SMA) is an alloy that remembers its
“original shape” and that when deformed returns to its original
“pre-deformed” shape when heated.
3. TYPES OF SMA
Two main types are
Copper-Aluminium-Nickel and Nickel-Titanium(Ni-Ti)
alloys.
Ni-Ti alloys are preferred because of their stability, practicability
and superior thermo-mechanic performance.
4. TYPES OF MEMORY EFFECT
Most common effects are one-way memory effect and two way
memory effect
5. ONE-WAY MEMORY EFFECT
The material is deformed at a lower temperature.
When heated, the material attains its
pre-deformed shape.
6.
7. TWO-WAY MEMORY EFFECT
The material remembers 2 different shapes;
one at a lower temperature and the other at
a higher temperature.
The material is cooled, gets deformed(intrinsic) and then heated to
reach an alternate shape.
Even a slight increase in the higher temperature, makes the SMA
to forget its shape(Amnesia).
8. 2 way memory is achieved with the aid of “training”.
Training dictates the shape the alloy will remember when heated.
11. VACUUM INDUCTION MELTING
Uses Electromagnetic Induction to melt metal in vacuum.
Electromagnetic induction generates eddy current in the alloy.
Eddy current generated heats the alloy and melts it.
12.
13. APPLICATIONS
Bone Plates
Ni-Ti is used.
Same procedure as that of conventional bone plates like stainless
steel or Ti.
Plates are set at a temperature below their higher temperature.
When the body gets heated, the plates contract inducing sustained
pressure, making the recovery fast.
14.
15.
16. AIRCRAFT MANEUVRABILITY
Used in flaps of aircrafts.
When using metals other than SMA, a complex network of
hydraulic systems is used.
This hydraulic system weighs more.
When using a SMA the complex and heavy hydraulic system can
be easily replaced by electric circuits.
When these circuits get activated, heat is generated as per Joule’s
law of heating.
This heat deforms the SMA and the flaps move for ascend/descend
of the flight.
17.
18. REINFORCING OF ARTERIES & VEINS
Clogged arteries and veins can be
strengthened.
SMA are crushed and are placed inside
these arteries and veins.
When they reach body temperature, they
expand opening the arteries and veins.