If you follow The SMART Tire Company, by now you’ve heard a lot about shape memory alloys (“SMAs”). Sounds fancy, but what are they? It is like memory foam? Was it invented by aliens? Well, no. And probably not. But it is a big part of our special sauce at SMART tire, so let’s dig a little deeper.
What is a Shape Memory Alloy?
Shape memory alloys have the ability to sustain large deformations; however, they return to their original undeformed shape upon removal of stress (superelastic SMA) or with the application of heat (shape memory effect) [1]
Sounds interesting, but what do we mean by “deformation”, “superelastic” and why is that special? Here’s me, taking an ordinary SMA spring, and crushing + twisting it in my hand with quite a bit of force:
This particular piece of metal has been through 100s if not 1000s of demos, and I tell people to be as rough as they want. Every time, it goes back to its original shape. Now imagine doing that with a paper clip, a coat hanger, or any steel wire. It will be permanently ruined (“deformed”) on your first attempt.
Imagine a material that is light and strong like titanium, but also incredibly elastic (“superelastic”) like this spring. That material is called nitinol, and it’s what we use to make strong, lightweight and superelastic SMART (“Shape Memory Alloy Radial Technology”) tires.
What is Nitinol, and How Does It Work?
Nitinol is a particular shape memory alloy made from nickel titanium, and first discovered at the Naval Ordnance Laboratory (ni = nickel, ti = titanium, nol = naval ordnance laboratory).
How nitinol works is pretty remarkable. When you apply stress to the material, it actually spontaneously changes its crystal structure as pictured below:
When you deform ordinary metals, you are stretching chemical bonds. When you stretch nitinol, it actually rearranges itself at a molecular level to fit the new shape. Amazing! For a longer explanation, Wikipedia breaks down more of the basics here.
The size of this effect is easy to see compared to steel:
Are SMART Tires Really the Future?
Yes! But it does require new thinking to understand why. Shape memory alloys are more than just metals (in fact, they are actually intermetallic compounds), and even among SMAs superelastic nitinol is special. If you’ve seen our latest bicycle prototypes, they are fully encased in thin polymers and fitted with high quality rubber treads for road use. The result? Strong, light, smooth riding tires that no longer rely on air pressure to perform. Someday nobody will question the metal inside tires, because it will just be normal for them to perform that way.
Learn More
Shape memory alloys are a complex subject, and this is just a basic primer, but as you can see they are pretty amazing. A few other cool applications include:
- Self-expanding heart stents
- Flexible eyeglass frames
- Heating & cooling systems
Want to learn more? Post your questions below about this “magic metal” that is transforming the transportation industry.
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