Materials With a Twist: Shear-induced instabilities in metamaterials
The evolution of human-made materials has begun a new era with the invention of metamaterials made by rationally designed building blocks that allow for unexpected and novel behaviors. I designed metamaterials exhibiting such odd behaviors upon shear deformation (twisting). One of our metamaterials exhibits multiple domains separated by energy barriers, which can move in a controlled manner by shearing. This metamaterial behaves similarly to a ferromagnetic system and can act as a battery-free mechanical memory unit or a mechanical sensor. Our metamaterial is programmable since it can change from soft to stiff and from pulling to pushing vertically upon shearing horizontally. Additionally, we presented cylindrical metamaterials that become thinner when twisted. They show surprising stability by keeping their cylindrical morphology, where more than 360 degrees of twist is achievable. We also developed a generic theory to describe the odd dome-like and saddle-like shape-changing of 2D metamaterials inspired by honeycomb patterns, applicable as novel bio-implants or optical reflector with adaptable focal lengths.