SMILE You have entered a Shape Memory Alloy Site

1
SMILE You have entered a Shape Memory Alloy
Site
Picture from http//www.wonderwire.com/pgs/lnk5.h
tm
2
What is an Shape Memory Alloy??

• A shape memory alloy(SMA) is a material that has
  the ability to return to its previous shape after
  being deformed(bent) by applying heat or in some
  cases just releasing the stress.
• Shape memory alloys were discovered in 1932,
  however it was not until 1961 when the most
  common form was discovered - nickel-titanium
  (NiTi)
• Several NiTi products are can be seen in the
  picture to the right.

Picture from http//www.fitec.co.jp/ftm/nt-e/
3
How do Shape Memory Alloys Work?

• In order to understand the way in which the shape
  memory effect occurs it is useful to understand
  the crystal structure of a SMA. All shape memory
  alloys exhibit two very distinct crystal
  structures. Which phase is present depends on the
  temperature and the amount of stress being
  applied to the SMA. These phases as known as
  martensite which exists at lower temperatures and
  austenite for higher temperatures. The properties
  of an SMA depends on which the amount of each
  crystal phase present.

This figure shows the different shapes the
crystal structure of the two phases.
Picture from smart.tamu.edu
4
Shape Memory Alloy NiTiNOL

• The name Nitinol comes from the chemical symbol
  of its two component metals nickel (Ni) and
  titanium (Ti) and the laboratory where it was
  discovered, Naval Ordinance Laboratory (NOL).
  When nickel and Titanium are mixed eqiatomically
  then it is possible to create a SMA by proper
  annealing.

5
Shape Memory Alloy CuZnAl

• Copper-base alloys can be readily hot worked in
  air. With low aluminum content (alloys can be cold finished with annealing,
  however high aluminum content makes cold working
  harder.

6
Forms of Shape Memory Alloys

• The first form of an SMA that was used in
  industry was One-way trained. That is that the
  shape change can only be done one way, that
  usually is by heating the material. The first
  commercial use of a SMA was in forming coupling
  in the hydraulic lines of aircraft

• Another type of training a can go though SMA
  two-way training. This is done by repeatedly
  putting the material under a stress, thus
  deforming it, heating it to the austenite phase
  to recover the shape, and then cooling it to
  martensite. This is used to make SMA actuators.

7
More Forms of Shape Memory Alloys

• Still another form of an SMA is called a
  Superelastic Material. A good example of this is
  the glasses with the frame that can be twisted
  around a finger and as soon as it is released
  they glasses go back to their original shape.

• The newest form of an SMA is still under
  research. They are High Temperature SMAs, for
  possible use in aircraft engines and other
  elevated temperature environments.