Pugno used three slip knots to make fiber tougher. By applying this simple trick to a commercial polymer fiber called Endumax, he has increased its toughness from 44 Joules per gram to a remarkable 1070 Joules per gram.
Kevlar, for example, can absorb some 80 Joules per gram before breaking but this is dwarfed by certain natural materials which are much tougher. The silk produced by the giant riverine orb spider, for instance, can absorb around 390 Joules per gram before breaking.
That’s better even than fibers made from nanotubes which materials scientists are just beginning to make. The strongest of these, made from carbon nanotubes, has a toughness of 970 Joules per gram.
Pugno says his work is just the beginning and that it ought to be possible to use his slip-knot technique to make graphene fibres with a toughness of 100,000 Joules per gram.
Further improvements are expected for the Endumax fiber, up to a toughness modulus close to the fiber specific strength that we have measured as 1600 J/g.
Arxiv – The “Egg of Columbus” for making the world’s toughest fibres
The mechanism is straightforward. When the fibre is placed in tension, the slip knot begins to tighten and the extra material passes through the knot, dissipating energy through friction.
Of course, the fibre eventually breaks but only after all the material in the loop has passed through the slip knot.
Clearly this doesn’t make the material any stronger (toughness and strength are different properties that are generally uncorrelated). However, it’s not hard to see how the energy dissipation would dramatically increase the amount of energy the fibre absorbs before it breaks, thereby increasing its toughness.
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