Researchers turn to origami and Lego to build a better spacecraft

Cells mimicking folded paper can improve safety in a wide range of applications. Mark Bruer reports.

Identical impact-resistant “cells” are combined to dramatically reduce the damaging force of impacts.

Kiyomi Taguchi/University of Washington

Scientists are turning to the Japanese art of origami to design impact-resistant material that may make spacecraft reusable, helmets more effective and cars safer.

Researchers at the University of Washington, US, have used centuries-old paper-folding techniques to create a prototype material that reduces the compression stress of impacts.

This “metamaterial” – that is, a material engineered to have a property not found in nature – could be used to soften the force delivered to the legs of a spacecraft on landing. This would remove one impediment to reusable rockets.

Lead researcher Jinkyu Yang describes metamaterials as being “like Lego”.

“You can make all types of structures by repeating a single type of building block, or unit cell as we call it,” he says.

The team designed the unit cell for their new material prototype by using origami principles, and then built it with three-ply drawing paper.

Each cell is laser-cut and folded so that after it is compressed by an impact, it quickly bounces back into shape.

The researchers then connected 20 cells together in a line and used a device to strike a blow at one end of the chain.

Using six GoPro cameras, Yang and colleagues tracked the compression wave caused by the impact travelling through the chain. They also tracked as the cells bounced back into shape, causing an opposing wave of tension – known as a rarefaction wave – along the chain.

And here is where the payoff is: the rarefaction wave moved more quickly than the compression wave and overtook it, so that by the far end of the chain there was no impact force, just tension pulling away from the last cell.

“If you were wearing a football helmet made of this material and something hit the helmet, you'd never feel that hit on your head,” Yang says. “By the time the energy reaches you, it's no longer pushing. It's pulling.”

The researchers say that it had been mathematically predicted that a rarefaction wave would overtake a compression wave in a line of cells, but theirs is the first practical demonstration of the phenomenon.

“Impact is a problem we encounter on a daily basis, and our system provides a completely new approach to reducing its effects,” Yang explains.

“For example, we'd like to use it to help both people and cars fare better in car accidents.”

While the prototype is made of paper, the architecture could be reproduced in a range of materials appropriate to each application.

“We believe that this architecture of volumetric origami cells can be used as a versatile building block for a wide range of applications such as impact/shock mitigation, vibration filtering, and energy harvesting,” the researchers conclude.

The study is published in the journal Science Advances.

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Mark Bruer is a freelance journalist based in Adelaide, Australia. He is a former Features Editor of The Age newspaper in Melbourne, and Online Editor of The Australian and in Sydney.
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