Source: Engineering & Technology

A team of researchers from the University of Massachusetts Amherst has engineered a new rubber-like solid substance with surprising qualities: it can absorb and release very large quantities of energy and it is programmable.

The new material holds great promise for a wide array of applications, from enabling robots to have more power without using additional energy to new helmets and protective materials that can dissipate energy much more quickly.

Alfred Crosby, professor of polymer science and engineering at UMass Amherst, and the paper’s senior author, said: “Imagine a rubber band. You pull it back and when you let it go, it flies across the room. Now imagine a super rubber band. When you stretch it past a certain point, you activate extra energy stored in the material. When you let this rubber band go, it flies for a mile.”

This hypothetical rubber band is made out of a new metamaterial – a substance engineered to have a property not found in naturally occurring materials – that combines an elastic, rubber-like substance with tiny magnets embedded in it. This new ‘elasto-magnetic’ material takes advantage of a physical property known as a phase shift to greatly amplify the amount of energy the material can release or absorb.

A phase shift occurs when a material moves from one state to another, such as water turning into steam, or liquid concrete hardening into a road or pavement. Whenever a material shifts its phase, energy is either released or absorbed. Phase shifts aren’t limited to changes between liquid, solid and gaseous states – a shift can also occur from one solid phase to another. A phase shift that releases energy can be harnessed as a power source, but getting enough energy has always been the difficult part.

“To amplify energy release or absorption, you have to engineer a new structure at the molecular or even atomic level,” said Crosby. However, this is challenging to do and even more difficult to do in a predictable way. By using metamaterials, Crosby suggested that he and his team has “overcome these challenges and have not only made new materials, but also developed the design algorithms that allow these materials to be programmed with specific responses, making them predictable”.

The team was inspired by some of the lightning-quick responses seen in nature, such as the snapping shut of Venus flytraps and trap-jaw ants. “We’ve taken this to the next level,” said Xudong Liang, the paper’s lead author, and a professor at Harbin Institute of Technology, Shenzhen (HITSZ) in China, who completed this research while a postdoc at UMass Amherst.

“By embedding tiny magnets into the elastic material, we can control the phase transitions of this metamaterial. And because the phase shift is predictable and repeatable, we can engineer the metamaterial to do exactly what we want it to do: either absorbing the energy from a large impact or releasing great quantities of energy for explosive movement.”

The research – which was supported by the US Army Research Laboratory, the US Army Research Office and HITSZ – has applications in any scenario where either high-force impacts or lightning-quick responses are needed.

The research paper – ‘Phase-transforming metamaterial with magnetic interactions’ – has been published in the journal Proceedings of the National Academy of Sciences.

Source: Engineering & Technology