An introduction to shape memory alloys

2009 January 9

I just received my Flexinol Deluxe kit, a box full of samples and little experiments to discover the great world of shape memory alloys (SMA). I have been fiddling with this stuff before but I never got farther than the regular “amazing spring” setup: you stretch a spring beyond its point of deformation, then if you heat it up it goes back to its original shape quite vigorously!

The kit contains a mixture of stuff, cheap demos and gimmicks, but the nicest things in my opinion are the little leaflets that explain the qualities and characteristics of SMA. The text introduces the SMA, the strengths of this technology (compared to servos and solenoids) and some typical setups for how to use SMA properly and fully.

I won’t copy all the good text from the manual, but in short, SMAs rearrange their crystal structure and shrink (~4% for Flexinol) when heated to a specific transition temperature (wikipedia page). One common way to heat the alloy is to run an electrical current through it for a short time. The tiny wires can create relatively quite strong forces, silently and with lifelike movement. Over the years, I have seen some very clever usage of SMA for building actuated interfaces or devices. Ivan Poupyrev and Marcelo Coelho have the most interesting projects I’ve seen so far: Lumen, Sprout I/O, Shutters and Surflex. I have a lot of ideas I would like to try with SMAs: shape-morphing shells, shifting the center of mass in handheld devices, soft-haptic stimuli, etc.

Well, first things first. I have to start with the basics and learn how to harness the power of these floss-like space-age filaments.



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