SHAPE MEMORY ALLOYS

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.

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.

TYPES OF MEMORY EFFECT Most common effects are one-way memory effect and two way

memory effect

ONE-WAY MEMORY EFFECT The material is deformed at a lower temperature. When heated, the material attains its pre-deformed shape.

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).

2 way memory is achieved with the aid of “training”. Training dictates the shape the alloy will remember when heated.

MANUFACTURE

ByCasting using Vacuum Arc Melting or Induction Melting

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.

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.

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.

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.

ADVANTAGES High power/weight ratio. High corrosion resistance.

Can be electrically controlled.

DISADVANTAGES Has poor fatigue properties.

Highly expensive.

More response time.

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