  A great flourish of interest in the development of new high-strength and
high-toughness materials is taking place in contemporary materials science,
with the aim of surpassing the mechanical properties of commercial
high-performance fibres. Recently, macroscopic buckypapers, nanotube bundles
and graphene sheets have been manufactured. While their macroscopic strength
remains 1-2 orders of magnitude lower than their theoretical strength, and is
thus comparable to that of current commercial fibres, recent progress has been
made in significantly increasing toughness. In particular, researchers have
produced extremely tough nanotube fibres with toughness modulus values of up to
570 J/g, 870 J/g and very recently, including graphene, reaching 970 J/g, thus
well surpassing that of spider silk (170 J/g, with a record for a giant
riverine orb spider of 390 J/g and Kevlar (80 J/g). In this letter, thanks to a
new paradigm based on structural mechanics rather than on materials science, we
present the Egg of Columbus for making fibres with unprecedented toughness: a
slider, in the simplest form just a knot, is introduced as smart frictional
element to dissipate energy and in general to reshape the fibre constitutive
law, showing evidence of a previously hidden toughness, strictly related to the
specific strength of the material. The result is a nearly perfectly plastic
constitutive law, with a shape mimicking that of spider silk. The proof of
concept is experimentally realized making the world toughest fibre, increasing
the toughness modulus of a commercial Endumax fibre from 44 J/g up to 1070 J/g.
The maximal achievable toughness is expected for graphene, with an ideal value
of 100000 J/g.
