The Two-Way Shape Memory Effect (TWSME)

Nitinol Springs

If the shape memory effect hasn’t
completely blown your mind, now you can learn
about the two-way shape memory effect (TWSME).
The TWSME occurs when a second memory shape
is programmed into the nitinol, which the nitinol takes upon
cooling. In real life, it looks like the part has the
shape memory effect on heating, as is normal for
nitinol, but it automatically takes on a second shape
upon cooling. This means that your nitinol parts
can move back and forth between the two shapes
without any external forces!

So, how do you make your own TWSME
parts? There are effectively three different methods of
programming the TWSME, although two of them are quite similar. The first method is to
over-deform martensitic (low temperature state)
nitinol. The second method is very similar to the
first in that you over-deform austenitic (high
temperature state) nitinol. It is important to note
that deforming the nitinol in its austenite phase will
cause it to operate backwards from if you had done
the same deformation in martensite.

The third method to achieve TWSME is to constrain or clamp the nitinol into the
shape that you want the second shape to be and then
cycle the temperature until the second memory
shape is taken on.
For example, program
a TWSME nitinol rod (or spring) that expands on
cooling and contracts on heating.

Read more about the two-way effect in our free ebook : Nitinol in Plain Language

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