CNTE

• CNTE.zip

• FD.zip

• NN.zip

Pure carbon nanotubes exhibit superlubricity - approximately ZERO friction between neighboring tubes in a bundle. In 2013, Zhang et. al. published a paper on carbon nanotube superlubricity that measured the intershell sliding force of a 1 centimeter double-wall carbon nanotube (DWCNT). Three diameters were measured, and the tiny pullout force matched theory, pa function of outer tube diameter.

Laurent et. al. estimates that the inner tube diameter is 0.34 nM ( d_{s-s} ) less than the outer tube diameter, and that DWCNT density (g/cm³) is:

d_{MW} = 6084 { \Large { ( d_{out} ~ - ~ d_{s-s} ) \over { d_{out}^2 } } } with d_{out} and d_{s-s} in nanometers.

I added my own estimations for perfect hexagonally close packed tube density, Tubes/m² = \sqrt( 3 ) / 2 D^2 = 0.866 / D^2 The pullout pressure P = 866 F / D^2 KPa if F is nanonewtons and D is nanometers. Results:

These strengths for pure, perfect DWCNT are less than 0.2% of the minimum strength needed for a space elevator, and 2% of the strength of Torayca 1100G carbon fiber. Furthermore, given these pullout forces, which will be unevenly distributed in real atomically imperfect materials, the stretch will not recover; these are not spring forces, but disassembly forces. After the material slides apart, it will not go back together, the hysteresis is unity. This is weak taffy, not a strong elastic material like kevlar or carbon fiber, or even a .

The situation is grim but not completely hopeless. In CNT fibers - yarns between the extremes, Dr. Thurid Gspann et. al. suggests that defects create load-sharing crosslinks between tubes, but can reduce strength from the theoretical 100 GPa by 30% to 70%. Even with the theoretical "best defect" maximum of 70 GPa, and a density of 1700 kg/m, this theoretical atomic-precision macro-material will have a strength of 41 Myuri, less than the 48 Myuri (derated by 40% to 34 Myuri) material assumed by the 2013 Space Elevators assessment.

If ≈ 40 Myuri is potentially possible with perfect "precision-defect" CNT (based on current pessimistic knowledge), there may be an atomically-perfect 3D material structure with zero hysteresis and 40 Myuri strength. May be; in 2017, we do not have a scintilla of a clue how to do that. Indeed, these may be pseudo-life-like complex nanostructures that can repair and grow themselves under tension, but are far beyond our current understanding and technological imagination.

Space elevators have assumed diamond-like crystal tethers since the 1970s, and carbon nanotube tethers since the 1990s. The materials necessary have not yet been discovered, or even imagined in practical detail.