Shape memory alloys (SMAs) are a smart material that can ‘remember’ a shape. SMAs will try an return to a remembered shape when heated.
SMAs work because of their unique chemical structure and have a wide range of applications. They are special because when heated to very high temperatures (these vary depending on the composition) they are programmed to remember the shape they are currently in (if they previously had a shape memorized it is lost and replaced with the new shape). They can then be bent into new shapes but if you ever want to return to the original shape you only have to heat the SMA (often around 80-90 degrees Celsius) and it will try to return and maintain it’s original shape with a not inconsiderable force. This can be repeated over and over again if necessary. The are a number of SMA types out there all differing in their function the main difference between them is that some can retain a memorized shape in the cold state and warm state and some only remember their warm state configuration. Above is an example of a two state SMA and the bottom video is of a single state SMA.
- Can remember shapes and return to them even after excessive bending.
- Can be programmed with a new shape at very high temperatures
- Are superelastic meaning they can undergo exceptional amounts of bending without weakening. (Most metal when bent repeatedly will become damaged through work hardening)
- Is suitable for medical applications
- Exerts force to return to original shape and can even unknot itself while returning to its original shape.
- Can have electric current passed through to induce a shape change.
- Cannot be easily reprogrammed in average consumer homes
- Heat level required to return to shape often makes material dangerous to touch.
- Fatigue in cool shape causes warping
Shape memory alloys are present in high end glasses using their super elastic nature to reduce the chances of them being damaged.
Often used in medical and engineering applications, these are self extending stents.
Found in a lot of actuators SMAs can pull objects by being activated by small amounts of current. They are desirable because they can be manipulated very finely by changes in current.
This video does a great summary of what is possible.
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