Here, we report the production of silk incorporating graphene and carbon nanotubes directly by spider spinning, after spraying spiders with the corresponding aqueous dispersions. We observe a significant increment of the mechanical properties with re
spect to the pristine silk, in terms of fracture strength, Youngs and toughness moduli. We measure a fracture strength up to 5.4 GPa, a Youngs modulus up to 47.8 GPa and a toughness modulus up to 2.1 GPa, or 1567 J/g, which, to the best of our knowledge, is the highest reported to date, even when compared to the current toughest knotted fibres. This approach could be extended to other animals and plants and could lead to a new class of bionic materials for ultimate applications.
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.
We have discovered that the influence of the surrounding nanotubes in a bundle is similar to that of a liquid having surface tension equal to the surface energy of the nanotubes. This surprising behaviour is confirmed by the calculation of the self-c
ollapse diameters of nanotubes in a bundle. Other systems, such as peapods, fullerites, are similarly treated, including the effect of the presence of a solvent. Finally, we have evaluated the strength and toughness of the nanotube bundle, with or without collapsed nanotubes, assuming a sliding failure.
In this paper we solve the multiple peeling problem by applying a fracture mechanics approach to a complex system of films, adhering to the substrate and having a common hinge, where the pulling force is applied. The simplest V-shaped system, consist
ing of two identical peeling tapes is considered as a case study (to be solved coupling six nonlinear equations); an optimal peeling angle, at which adhesion is maximal, is discovered.
In this paper the new concept of super-bridges, i.e. kilometre-long bridges suspended over carbon nanotube cables, is introduced. The analysis shows that the use of realistic (thus defective) carbon nanotube bundles as suspension cables can enlarge the current limit main span by a factor of 3.
