When you stretch an elastic band, it gets longer. But imagine a material that actually becomes shorter when you pull on it. Sounds strange, doesn't it? Yet that's exactly what physicists from Leiden University, AMOLF, and ARCNL have managed to create.
A structure that 'snaps' inwards when stretched could one day be useful in smart devices or to help buildings withstand earthquakes. The researchers discovered this unexpected motion - which they call 'countersnapping' - while working on new ways to position parts precisely in a special type of robot.
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More than 6,5 M views: This mechanism shrinks when pulled by Veritasium.
More than 300 K views: These structures shrink when pulled: Counter-snapping instabilities by AMOLF (above).
Clever design
The team started with small, simple components and cleverly connected them. This created a structure with surprising behaviour: when pulled, it snaps inward rather than stretching outwards.
'We're showing that mechanical systems can behave in ways that go against our intuition,' says Martin van Hecke, professor at the Leiden Institute of Physics. According to him, this is the first time countersnapping has ever been observed in an experiment.
Real-world uses in the future
We already see snapping mechanisms in nature - like the Venus flytrap that snaps shut when an insect lands on it. Humans have also designed snapping objects, such as pop-up tents and slap bracelets. But countersnapping could open the door to a whole range of smart, adaptable technologies. The team has already come up with several possible applications:
- Soft robots with no motors: Imagine a robot that can move forward without sliding back - useful, for example, for medical robots that need to move safely through the body. Countersnapping could convert a back-and-forth motion into movement in just one direction.
- Smart materials with adjustable stiffness: Think of an exoskeleton or prosthetic that stays flexible while walking but stiffens instantly during a sudden movement.
- Vibration dampers: Structures that absorb vibrations on their own, without needing electronics. This could be valuable in aircraft, wind turbines, or buildings in earthquake-prone areas.
Combining structures
The researchers are now experimenting with combinations of these soft robotic structures. Van Hecke believes this could unlock even more potential: 'This could lead to materials that behave almost like a computer.'
The research was published in the journal Proceedings of the National Academy of Sciences.
'Exotic mechanical properties enabled by countersnapping instabilities', by Paul Ducarme, Bart Weber, Martin van Hecke and Johannes T.B. Overvelde.
