In 2016, an inflatable arch wreaked havoc during the Tour de France cycle race when it deflated and collapsed on a cyclist, throwing him off his bike and delaying the race while officials scrambled to clear debris from the road. Officials blamed a passing spectator’s wayward belt buckle for the arc collapse, but the real culprit was physics.
Today’s inflatables, used for everything from field hospitals to sports complexes, are monostable, which means they need constant pressure to maintain their inflated state. Lose this pressure and the structure returns to its only stable form – flat.
But what if these structures had more than one stable state? What if the arch was just as stable inflated as it was flat on the ground?
Now, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed bistable inflatable structures inspired by origami.
The research is published in Nature.
“This research provides a direct path for a new generation of large-scale rugged inflatable systems that lock into place after deployment and do not require continuous pressure,” said Katia Bertoldi, William and Ami Kuan Danoff professor of applied mechanics at SEAS and main author of the article.
Inspired by origami and guided by geometry, the research team developed a library of triangular building blocks that can appear or fold flat and be combined in different configurations to create closed, multistable shapes.
“We rely on the geometry of these building blocks, not the characteristics of the materials, which means we can make these building blocks from almost any material, including inexpensive recyclable materials,” said Benjamin Gorissen, partner in materials science and mechanical engineering at SEAS and co-first author of the article.
Taking their design process in the real world, the researchers designed and built an 8ft by 4ft inflatable shelter from thick plastic sheets.
“You can imagine these shelters being deployed as part of the emergency response in the disaster area,” said David Melancon, doctoral student at SEAS and co-first author of the article. “They can be stacked flat on a truck and you only need one source of pressure to inflate them. Once they are inflated, you can remove the source of pressure and move on to the next tent. “
The shelter can be set up by one or two people, as opposed to the roughly a dozen needed to deploy current military field hospitals.
The building blocks of these origami structures can be mixed and matched to create a structure of any shape or size. Researchers built a range of other structures, including an archway, an extendable spire, and a pagoda-style structure. The researchers also designed shapes with more than two stable shapes.
“We have unlocked an unprecedented design space for large-scale inflatables that can fold flat and retain their deployed shape without the risk of catastrophic failure,” said Chuck Hoberman, Pierce Anderson Professor of Design Engineering at the Graduate School of Design and co-author of the article. “By using the inflatable and reversible actuation to make hard-walled structural enclosures, we see important applications, not only here on Earth, but potentially as habitats for lunar or Martian exploration.”
This research was supported by the National Science Foundation under grants DMR-2011754 and DMR-407 1922321.