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From the same paper as the previous 8 images.
Fig. 16: Similarly to bending situations, SWNTs under torsion exhibit a sudden morphological change at a critical torque, transforming into a straight-axis helical shape. The crucial difference from bending cases is that, under torsion, the critical buckling torque of SWNTs depends on the loading direction, i.e., whether the tube is twisted in a right-handed or left-handed manner [186,187]. This load-direction dependence originates from the tube chirality, which breaks the rotational symmetry about the tube axis. For example, the twisting failure strain of chiral SWNTs in one rotational direction may even be 25% lower than that in the opposite direction [187]. Moreover, symmetry breaking causes coupling between axial tension and torsion, giving rise to an axial-strain-induced torsion of chiral SWNTs [188]. This intriguing coupling effect shows that a chiral SWNT can convert motion between rotation and translation, thus promising a potential utility of chiral SWNTs as electromechanical device components.
Figure 16. Morphological changes for a (8, 3) nanotube under torsion. Applied strain and its direction are indicated beneath the diagram; the digit 0.05, for example, corresponds to the strain of 5%, and the sign + (−) indicates right(left)-handed rotation. Under right-handed rotation, the tube buckles at a critical buckling strain γcr = 7.6%, whereas it buckles at γcl = 4.3% under left-handed rotation. Reprinted from Reference [186]:
186. Chang, T. Torsional behavior of chiral single-walled carbon nanotubes is loading direction dependent. Appl. Phys. Lett. 2007, 90, 201910.
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