Rice is on dinner tables everywhere. Now it is also helping scientists build a material that changes how it behaves when you move it slowly or hit it fast.
An international team led by the University of Birmingham found that tightly packed rice grains act in an unusual way under pressure. When compressed slowly, the grains stay relatively strong. When squeezed quickly, they become weaker.
The researchers reported the findings in the journal Matter.
Experiments showed the packed grains responded differently depending on how quickly a load was applied. At higher loading speeds, the material weakened significantly. The team said this kind of “rate softening” is uncommon in most materials.
The researchers found this happens because friction between individual rice grains drops sharply when forces are applied rapidly. That weakens the internal force networks that normally help support the load.
The team then used that property to build a new metamaterial, an engineered composite structure designed to show behaviors not found in naturally occurring materials.
To make it, the researchers combined rice-based granular units with materials such as sand, which become stronger under rapid loading. They said the result was a granular metamaterial that responds differently to slow movements and sudden impacts.
Depending on the situation, the material can bend, buckle or stiffen in different ways, without electronics, sensors or active control systems.
Dr Mingchao Liu, from the University of Birmingham, said: “Rice might be best known as a staple food globally, but it’s rarely associated with advanced engineering. Our research shows that it can form the basis of a new class of functional materials.
“Rather than treating this phenomenon as curiosity, we turned it into a design principle. This approach enabled us to create a material that can bend, buckle, or stiffen differently under slow movements versus sudden impacts, without electronics, sensors, or active control. Instead of telling a structure how to respond, we let physics decide: fast loads trigger one behavior, slow loads another.”
The researchers said the work shows how common granular materials can be turned into engineered systems that respond through their own mechanical properties.
The University of Birmingham said the speed-sensitive metamaterial could open new possibilities in soft robotics. It said future systems built with these materials could be lighter, safer and more adaptable than traditional metal robots.
The university said those robots could be useful for working alongside people, operating in challenging environments and performing delicate tasks, including assisting with surgery.
The material may also be used in protective equipment. Because it responds differently depending on the speed of an impact, it could absorb energy or deform in a controlled way during a collision, helping reduce the risk of injury.
The study is: Mingchao Liu, Weining Mao, Yiqiu Zhao, Qin Xu, Yixiang Gan, Yifan Wang and K. Jimmy Hsia, “Rate dependence in granular matter with application to tunable metamaterials”, Matter.
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