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Dutch researchers develop materials that buckle on demand

14 June 2015

Small structural variations in the material single out regions that buckle selectively under external stress, whereas other regions remain unchanged.

The structure is made of flexible beams, and can be compressed on demand (image courtesy of Leiden University)

Researchers from Leiden University in the Netherlands, have designed a novel metamaterial that buckles on demand. Their research is published in The Proceedings of the National Academy of Sciences.

The promise of metamaterials is to realise artificial structures with unusual properties that would be hard to come by in nature. Their unconventional properties can be programmed by suitable design of their geometry or topology. The Leiden researchers created a 3D-printed working prototype of a novel metamaterial that displays selective and tunable buckling.

The research was carried out in the Topological Mechanics Lab (Leiden), led by Vincenzo Vitelli. The lab is investigating the mechanical analogues of so-called topological insulators, a recently discovered exotic quantum state of matter. When applied to macroscopic structures, the topological ideas underlying these exotic states give rise to materials with unusual mechanical properties.

"The design begins with a general idea, a physical ‘hunch’, based on this analogy," says co-author Jayson Paulose. "The major strength of using these topological ideas in metamaterials design is that a topological material is guaranteed to have interesting behaviour at the boundaries."

The next step is to predict the response of the mechanical analogue with the imposed topological design. The ultimate test is to build it and investigate what happens under various kinds of external stress. That resulted in a flexible plastic prototype that displayed the localised buckling response the researchers were looking for.

"We were expecting some trial and error before getting the design to work," adds Jayson Paulose. "But the first batch that we got back from the 3D printing firm worked right out of the box."

Selective buckling materials have a wide range of potential applications in engineering and medicine. The buckling behaviour can be tuned without changing other physical properties such as electromagnetic or heat conduction.

A typical application would be in shape-memory materials, in which shape-transitions usually take place when the temperature is changed. Selective buckling regions in such materials would show dramatically different shape transitions from the rest of the structure, without affecting the heat flow, enabling engineers to tune such devices.

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