Torsional response and stiffening of individual multi-walled carbon   nanotubes
  We report on the characterization of torsional oscillators which use multi-walled carbon nanotubes as the spring elements. Through atomic-force-microscope force-distance measurements we are able to apply torsional strains to the nanotubes and measure their torsional spring constants and effective shear moduli. We find that the effective shear moduli cover a broad range, with the largest values near the theoretically predicted value. The data also suggest that the nanotubes are stiffened by repeated flexing. 
P. A. Williams, S. J. Papadakis, A. M. Patel, M. R. Falvo, S.   Washburn, R. Superfine