The team is said to have has created a paper model of a metamaterial that uses ‘folding creases’ to soften impact forces and instead promote forces that relax stresses in the chain. The team’s results are published in Science Advances.
"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. By the time the energy reaches you, it's no longer pushing. It's pulling," said corresponding author Jinkyu Yang, a UW associate professor of aeronautics and astronautics.
"Metamaterials are like Legos. You can make all types of structures by repeating a single type of building block, or unit cell as we call it," said Yang. "Depending on how you design your unit cell, you can create a material with unique mechanical properties that are unprecedented in nature."
The researchers turned to origami to create their unit cell.
"Origami is great for realising the unit cell," said co-author Yasuhiro Miyazawa, a UW aeronautics and astronautics doctoral student. "By changing where we introduce creases into flat materials, we can design materials that exhibit different degrees of stiffness when they fold and unfold. Here we've created a unit cell that softens the force it feels when someone pushes on it, and it accentuates the tension that follows as the cell returns to its normal shape."
The unit cell prototypes are made from paper. The researchers used a laser cutter to cut dotted lines into paper to designate where to fold. The team folded the paper along the lines to form a cylindrical structure, and then glued acrylic caps on either end to connect the cells into a long chain.
The researchers reportedly lined up 20 cells and connected one end to a device that pushed and set off a reaction throughout the chain. Using six cameras, the team tracked the initial compression wave and the following tension wave as the unit cells returned to normal.
According to the University of Washington, the chain composed of the origami cells showed the counterintuitive wave motion: even though the compressive pushing force from the device started the whole reaction, that force did not reach the other end of the chain. Instead, it was replaced by the tension force that started as the first unit cells returned to normal and propagated faster and faster down the chain. The unit cells at the end of the chain only felt the tension force pulling them back.
"Impact is a problem we encounter on a daily basis, and our system provides a completely new approach to reducing its effects. For example, we'd like to use it to help both people and cars fare better in car accidents," Yang said. "Right now it's made out of paper, but we plan to make it out of a composite material. Ideally, we could optimise the material for each specific application."