In material science, thermal expansion is a very well understood concept. However, in most cases it’s regarded as somewhat of a nuisance. It’s the kind of thing that gives engineers headaches, and entire subsystems of machines are often designed specifically to combat it. But a group of students at MIT have come up with an ingeniously simple way of taking advantage of thermal expansion to create shape-changing composites.
Their project is a method of creating shape-shifting composites, called uniMorph. It works by using resistive heating (or simply ambient temperature) to change the temperature of a sandwich composite. The composite is made of two different materials, and the copper traces to heat them. The two materials themselves aren’t particularly important, what’s important is that they have vastly different thermal expansion rates.
When the composite is heated, one material will expand more or less than the other material. Depending on the relative shapes of the two materials, this causes the composite to bend or twist in predetermined ways. How much it bends, for example, is just a matter of how the layers are cut, and how much they’re heated.
The concept itself isn’t exactly new – bimetallic composites have existed for ages. We even covered a similar idea that works based on moisture content. But, the methods used for uniMorph are very well thought out. It’s very inexpensive to produce, and the students seem to have devised reliable techniques for designing the layers in order to produce a desired shape change.