Researchers have described a new shape that is rarely seen in nature.
The researchers were trying to design new springs when they happened upon the hemihelix, a Harvard School of Engineering and Applied Science news release reported.
The team "stretched, joined, and then released rubber strips" to see if the shape was naturally occurring and if it could be manipulated.
"Once you are able to fabricate these complex shapes and control them, the next step will be to see if they have unusual properties; for example, to look at their effect on the propagation of light," says Katia Bertoldi associate professor of applied mechanics at the Harvard School of Engineering and Applied Sciences(SEAS).
The shape itself was a hemihelix that had "multiple perversions," the news release reported.
The structure resembles a slinky toy; hemihelices form when the spiral turns, known as a chirality; the reversal of this is called a perversion.
The researchers made two dimensional springs using the rubber strips.
"We expected that these strips of material would just bend-maybe into a scroll. But what we discovered is that when we did that experiment we got a hemihelix and that it has a chirality that changes, constantly alternating from one side to another," David R. Clarke, Extended Tarr Family Professor of Materials at SEAS saidn in the news release.
The researchers found that when a strip is wide relative to its height it creates this type of helix, but there is no set aspect ratio at which the material morphs from a helix to a hemihelix. Other material would break before getting to this point, which could explain why the shape has never been seen before.
"We see deterministic growth from a two-dimensional state-two strips bonded together-to a three-dimensional state," Jia Liu, a graduate student in Bertoldi's group said in the news release. "The actual number of perversions, the diameter, everything else about it is entirely prescribed. There is no randomness; it's fully deterministic. So if you make one hundred of these, they'll always perform exactly the same way."
"From a mechanical point of view you can look at these as different springs with very different behavior. Some of them are very soft and then they stiffen up. Some are more linear. Simply by changing geometry, you can design this whole family of springs with very different behavior with predictable results," Bertoldi said.
The research could help researchers learn how to create these complex shapes from flat surfaces.
"Intellectually, it's interesting-and we believe it is significant too," Clarke said. "There are a variety of complex shapes in nature that arise as a result of different growth rates. We stumbled quite by accident on a way to achieve fully deterministic manufacture of some three-dimensional objects."
