Strength of nanotubes and megacables

Invited lecture, Int. Conf. Nanoscience & Nanotechnology, Frascati (ITA), Nov. 6-9, 2006. --- In this chapter my findings [mainly reported in N. Pugno, J. Phys.– Condens. Matter, 18, S1971–S1990 (2006); N. Pugno, Acta Mater. 55, 5269–5279 (2007); N. Pugno, Nano Today 2, 44–47 (2007)] on the mechanical strength of nanotubes and megacables are reviewed, with an eye to the challenging project of the carbon nanotube-based space elevator megacable. Accordingly, basing the design of the megacable on the theoretical strength of a single carbon nanotube, as originally proposed at the beginning of the third millennium, has been demonstrated to be naïve. The role on the fracture strength of thermodynamically unavoidable atomistic defects with different size and shape is thus here quantified on brittle fracture both numerically (with ad hoc hierarchical simulations) and theoretically (with quantized fracture theories), for nanotubes and nanotube bundles. Fatigue, elasticity, non-asymptotic regimes, elastic-plasticity, rough cracks, finite domains and size-effects are also discussed.