Watch: New Structures Shrink Instead of Stretching When Pulled

Researchers in the Netherlands have developed innovative mechanical structures that, surprisingly, contract — or more precisely, snap inward — rather than expand when pulled.

The Science Behind the Phenomenon

While it may sound counterintuitive, this unexpected behavior is the result of a creative approach that combines geometry and mechanics, devised by scientists at the AMOLF physics institute. The concept may help address unwanted instabilities in various applications.

“This type of behavior — which we’re calling ‘countersnapping’ — has never been observed experimentally before,” said Bas Overvelde, lead researcher of the Soft Robotic Matter group. “It has the potential to revolutionize how we design everything from medical robotic devices to earthquake-resistant buildings.”

You can see the structure in action in the video below.

Fascinating, right? The countersnapping effect, recently described in the journal PNAS, emerges from the design and assembly of mechanical structures that leverage geometric nonlinearities. The main idea is to create systems with self-intersecting force–displacement relationships — meaning they suddenly contract under increasing tension, or require more force unexpectedly when stretched.

Building the Structures

To achieve this, the team combined three different types of nonlinear mechanical building blocks — each with a specific force-extension behavior — into a network. In the demonstrated example, the components were 3D printed.

These countersnapping structures offer several remarkable mechanical properties:

• Unidirectional stick–slip motion: Unlike regular snapping, which results in back-and-forth motion under cyclic loading, countersnapping produces incremental movement in a single direction.
• Switchable stiffness: The structure can shift between different stiffness levels at a specific point, maintaining the same extension and applied force.This design lets users alter the resistance to deformation without changing the system’s size or load.
• Passive resonance avoidance: Because users can change the stiffness without affecting equilibrium, the structure automatically shifts its natural vibration frequency — helping protect it against harmful vibrations at certain frequencies.
• Sequential stiffness switching: When users arrange multiple countersnapping units side-by-side (in parallel), they can adjust the stiffness of each unit one at a time.
• Instantaneous collective switching: When connected end-to-end (in series), all units can switch simultaneously — like a chain reaction.

The researchers see potential for this technology in protective equipment and prosthetics that switch between soft and rigid states (similar to motorcycle safety gear), vibration damping in buildings and aircraft, and even in soft medical robots that navigate the body safely by advancing forward without slipping backward.

Read the original article on: New Atlas

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