Landing is stressful on a rocket’s legs because they must handle the force from the impact with the landing pad. One way to combat this is to build legs out of materials that absorb some of the force and soften the blow. Inspired by the paper-folding art of origami, researchers 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.
Many types of structures can be made of metamaterials by repeating a single type of building block or unit cell. Depending on how the unit cell is designed, a material can be created with unique mechanical properties that are unprecedented in nature. By changing where creases are introduced into flat materials, researchers can design materials that exhibit different degrees of stiffness when folded and unfolded. A unit cell was created that softens the force it feels when someone pushes on it and accentuates the tension that follows as the cell returns to its normal shape.
Just like origami, the unit cell prototypes are made out of paper. A laser cutter was used to cut dotted lines into paper to designate where to fold. The paper was folded along the lines to form a cylindrical structure, and then acrylic caps were glued on either end to connect the cells into a long chain; 20 cells were lined up and one end was connected to a device that pushed and set off a reaction throughout the chain.
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 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. The unit cells at the end of the chain only felt the tension force pulling them back.
The chain could be made out of a composite material that could help both people and cars fare better in accidents.