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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