A scientist from the University of Trento in Italy claims to have made the world's toughest material. But this isn't some kind of exotic super material—it's just made from strands of fibre with knots tied in them.
The material, created by Nicola Pugno, is formed from strands of Endumax polymer fibre with a simple slip knot tied into them. For those who missed out on a youth in scouting, a slip knot's incredibly simple: it's just a loop of rope passed through a bight—that's a u-shaped section of the same rope—and you probably tie one without thinking about it. But how the hell does that give rise to a super-tough material?
Before diving into exactly how it works, it's worth pointing out what toughness actually is. Crucially, it's not strength—that's a measure of how much force a material can handle before it breaks. Toughness is instead a measure of how much energy a material can absorb So, glass is strong, not tough; rubber is tough, not strong; steel is a bit of both. For some perspective, kevlar is considered incredibly tough, and can handle 80 joules per gram before breaking.
So, Pugno took those Endumax fibers—which usually exhibit a toughness of 44 joules per gram without a knot—and tied his slip knots. Then he loaded them up, and found that they could absorb an astronomical quantity of energy before breaking. The reason? Well, when loaded, the knot dissipates large quantities of energy through friction as it's pulled. Once the knot slips open, the fiber fails—but by that point it's absorbed 1,070 joules of energy per gram.
For comparison, that's more than the theoretical values calculated for graphene, which we think can only withstand 1,000 joules per gram. So Pugno's material could—could—be the toughest material in the world. He also theorises that a knotted thread of graphene could absorb 100,000 joules per gram, which is just insane.
But easy there, tiger. There are caveats. First, it's not clear how a single fibre with a knot tied in it translates to a real, practical piece of material: a sheet of kevlar contains thousands of fibres, each of which would need knots tied in them somehow. Second, this work is preliminary—it's not yet appeared in a peer-reviewed journal—so it's not clear that it's 100 percent reproducible.
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