Engineering news
Inspired by the rare combination of strength and flexibility found in structures made of tangled staples, mechanical engineers at the University of Colorado Boulder (CU) are developing the new materials from interlocking particles.
Packed into a tight ball, metal stationery staples can be “surprisingly strong”, the CU researchers said. “Try to pull it apart and the tangled metal resists like a solid object – but with the right movement or vibration, that same bundle can quickly fall back into loose pieces.”
The work is focused on ‘entanglement’, in which multiple particles become intertwined and linked with one another. Natural examples include birds’ nests made of interwoven sticks and fibres, or the interplay of hard minerals and soft proteins in bones.
Particle shape is a key element of the work, which aims to recreate natural entanglement with manufactured materials. “Take sand as an example. Sand is smooth and convex-shaped, meaning it cannot interlock from grain to grain,” said PhD student Youhan Sohn. “However, we found that if we change the shape of a grain of sand, we can drastically affect its behavior and mechanical properties, including the particle’s ability to link with other particles.”
The researchers ran Monte Carlo simulations, a type of computational analysis, to predict exactly how the particles interlock with each other. Their goal was to find the optimal geometry for maximum entanglement.
After finding the optimal shape, the team performed tests to see how the entangled particles behaved. The tests showed that a ‘two-legged’ particle – similar in shape to a staple – had the greatest potential for entanglement.
The team also discovered several unexpected advantages, including its rare blend of tensile strength and toughness – a combination the researchers said conventional materials rarely achieve simultaneously. “Our entangled granular material using the staple-like particle demonstrates both high strength and toughness at the same time,” said PhD student Saeed Pezeshki.
Next was its ability to rapidly assemble, and come apart just as quickly. By applying different vibrational patterns to the material, the team was able to change its level of entanglement on demand. A light vibration could be used to interlock and strengthen the particles, for example, while a larger vibration could cause them to completely unravel.
“It’s a strange material because it’s obviously not a liquid. However, it’s also not quite solid. This opens new and intriguing engineering possibilities,” said laboratory leader Professor Francois Barthelat. “Handling a bundle of these entangled particles feels very remote and exotic.”
The group believes that large buildings and structures could one day be designed using entangled materials, allowing them to be disassembled when no longer needed.
Robotic systems are another potential option, according to Pezeshki. “I was talking with other students who believe this technology can be used in swarm robotics – where small robots can entangle, do a task and then disentangle when they are done.”
Barthelat referenced the liquid metal T-1000 robot seen in Terminator 2, which can change shape and slide through small gaps before retaking humanoid form. “It’s expensive and scaling up is a challenge, but it’s something that’s on everybody’s mind.”
The group is continuing the research and currently testing a new particle shape with added protruding ‘legs’, similar to spiky plant burrs, which could generate even stronger entanglement properties.
The work was published in the Journal of Applied Physics.
Want the best engineering stories delivered straight to your inbox? The Professional Engineering newsletter gives you vital updates on the most cutting-edge engineering and exciting new job opportunities. To sign up, click here.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.