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.

1. SHAPE MEMORY ALLOYS

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.

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.

10. MANUFACTURE
By
Casting using Vacuum Arc Melting or Induction Melting

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.

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.

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.

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.

19. ADVANTAGES
 High power/weight ratio
.
 High corrosion resistance.
 Can be electrically controlled.

20. DISADVANTAGES
 Has poor fatigue properties.
 Highly expensive.
 More response time.

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