University of Washington researchers have developed a way to reduce impact forces encountered on reusable space vehicles such as SpaceX’s Falcon 9. Inspired by the paper folding art of origami, the team created a paper model of a metamaterial that uses folding creases to soften impact forces and promote forces that relax stresses.
Jinkyu Yang, a UW associate professor of aeronautics and astronautics explains, “Metamaterials are like Legos. You can make all types of structures by repeating a single type of building block or unit cell. Depending on how you design your unit cell, you can create a material with unique mechanical properties unprecedented in nature.”
UW aeronautics and astronautics doctoral student Yasuhiro Miyazawa adds, “By changing where we introduce creases into flat materials, we can design materials that exhibit different degrees of stiffness when they fold and unfold. 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.”
Researchers laser-cut dotted lines into paper to designate folds. 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 lined up 20 cells and connected one end to a device that pushed and set off a reaction throughout the chain. Using six video cameras, the team tracked the initial compression wave and the following tension wave as the unit cells returned to normal.
The chain composed of the origami cells showed counterintuitive wave motion: Even though the compressive pushing force from the device started the whole reaction, that force never made it to 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, so the unit cells at the end of the chain only felt the tension force pulling them back.
“Impact is a problem we encounter daily, and our system provides a completely new approach to reducing its effects,” Yang says. It’s made from paper now, but the team plans to make it out of a composite material. Ideally, they could optimize the material for specific applications.