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SMART MATERIALS - SHAPE MEMORY ALLOY (SMA)

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V. Ryan © 2006 - 2008

 

SMA wire is sometimes called ‘Nitinol’, as it is a composed of nickel and titanium. On first site this special wire looks like ordinary wire and even has many of the same properties. It can be folded to form complex shapes quite easily and it conducts electricity. However, it is very expensive when compared to ordinary steel or even copper wire. However, it has properties that make it very special:

 

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1. The wire has a memory - for example, if it is folded to form a shape and then heated above 90 degrees (centigrade) it returns to its original shape.

   

 

 

2. The material can also be ‘programmed’ to remember a shape. This can be achieved by folding the wire to a particular shape and clamping it in position. The wire is then heated for a approximately five minutes at precisely 150 degrees or pass an electric current through the SMA wire. If the wire is now folded into another shape and then placed in hot water it returns to the original ‘programmed’ shape.

The diagram below shows a steel jig. This is used to fold the SMA wire to shape. A battery is then connected and current is passed through it. The wire has now been ‘programmed’ to its new shape.

   
   
 
   
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