Understanding the torsional mechanical behavior of twisting carbon nanotube ribbon with different boundary conditions

Twisting can generate internal stress and store torsional energy, which is widely used as actuators and energy harvesters in electronic and biomedical fields. However, uncovering the effect of internal stress remains unclear. Herein, the experimental and theoretical mechanical model of the twisted ribbon with different boundary conditions was derived and analyzed. The dynamic experimental results indicate that the polymer inclines to constrain the unraveling process of carbon nanotube fiber. Then the elastic/plastic theoretical equations reveal that the internal stress gradually increases as the twisted angle, and the simulated internal stress agrees well with the theoretical results. The simulation results also indicate that the twisting-induced deformation and failure behavior of twisted ribbons are affected by the strain-rate sensitivity of the matrix and the loading velocity. Then, the releasing of the stored energy for twisted ribbons with different boundary conditions demonstrates the contraction and repulsion behaviors. This work investigating the mechanical behavior of twisted ribbons could provide a better guideline for designing twisted actuators with high reliability.