Topological transitions of a deformed kagome lattice by uniform soft twisting. Two types of triangles (red and blue) are connected by free hinges at their corners, forming a deformed kagome lattice with primitive vectors a1, a2. The angle θ between the triangles defines the twisting coordinate. The blue curve shows (defined in equation (1)) as a function of θ. The 3 white dots on the θ axis represent three critical angles (, and ) where sides of the triangles form straight lines (yellow stripes on the lattices) and topological polarization RT (shown as black arrows above the axes) changes.
University of Michigan researchers have developed a new way to design a “metamaterial” that allows the material to switch between being hard and soft without damaging or altering the material itself. Metamaterials are human-made materials that get their properties – in this case, whether a material is hard or soft – from the way the material is constructed rather than the material that constructs it. This allows researchers to manipulate a metamaterial’s structure in order to make the material exhibit a certain property.
They composed a metamaterial that can be easily manipulated to increase the stiffness of its surface by orders of magnitude – the difference between rubber and steel. Since these properties are “topologically protected,” ie the material’s properties come from its total structure, they’re easily maintained even as the material shifts repeatedly between its hard and soft states.
Xiaoming Mao, assistant professor of physics said: “Usually, it’s hard to change the stiffness of a traditional material. It’s either hard or soft after the material is made.” For example, a dental filling cannot be changed after the dentist has set the filling without causing stress, either by drilling or grinding, to the original filling. A guitar string cannot be tightened without putting stress on the string itself.
Mao says the way an object comes in contact with the edge of the metamaterial changes the geometry of the material’s structure, and therefore how the material responds to stress at the edge. But metamaterial’s topological protection allows the inside of the metamaterial remains damage free. The material could one day be used to build cars or rocket launch systems. In cars, the material could help absorb impacts from a crash. “When you’re driving a car, you want the car to be stiff and to support a load,” Mao said. “During a collision, you want components to become softer to absorb the energy from the collision and protect the passenger in the car.”
The researchers also suggest the material could be used to make bicycle tires that could self-adjust to ride more easily on soft surfaces such as sand, or to make damage-resistant, reusable rockets. http://www.ns.umich.edu/new/releases/24476-new-metamaterial-can-switch-from-hard-to-soft-and-back-again
http://www.nature.com/articles/ncomms14201
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