For many years, researchers have been trying to create structures that can take different stable forms as needed. The goal of creating these multistable structures, as they’re known, is to build three-dimensional objects that can change between shapes over and over as needed. This would pave the way for realizing, for example, adaptable elements or large objects that can change shape and take up less space during transport.
But progress has been a long time coming. This is because previous solutions were very complex to produce, could only be reshaped once, or required a continuous supply of energy to maintain their new shape.
A remarkably simple solution
Giada Risso, a PhD student in the Composite Materials and Adaptive Structures Group led by Paolo Ermanni, recently presented a new approach that overcomes these drawbacks in an article in the journal Advanced Science. “One of my main goals was to develop a planar, multistable structure that was easy to manufacture,” he explains. And the solution is remarkably simple: it involves gluing a flat composite frame over a pre-stretched thermoplastic polyurethane film. “A flat surface and a clamp to pre-stretch the film, that’s essentially all that’s needed,” explains Risso.
By holding a structure made in this way in your hands, you can bend it from its original flat state into a shape it will hold without any further help. You can then change its shape again and the structure will once again maintain that new shape on its own. Then you can restore the original shape with an equally simple maneuver.
A carbon fiber frame
But how exactly is it possible to remodel this structure so flexibly into different stable states? Risso found that it all depends on the material you select for the frame: “Our best results have been with a composite material made of carbon fibers. This allows us to produce a structure that can actually assume multiple stable states.” However, making a frame out of fiberglass results in much less stable shapes. Of all the frame materials tested, steel performed the worst, unable to produce a single steady state.