Visco-elastic properties of aligned multi-walled carbon nanotube blocks

Structural components subjected to cyclic stress can succumb to fatigue and fail at stress levels much lower than what is expected under static loading conditions. Such fatigue behavior in nanotube structures has never been reported, albeit its importance in practical devices incorporating nanotube components. In particular, cyclic compression loaded vertically aligned nanotube structures could find various applications as electro-mechanical systems. Here, this work reports the mechanical response from repeated high compressive strains on freestanding, long, vertically aligned multiwalled carbon nanotube membranes and show that the arrays of nanotubes under compression behave very similar to soft tissue and exhibit viscoelastic behavior. Under compressive cyclic loading, the mechanical response of nanotube blocks shows initial preconditioning, hysteresis characteristic of viscoeleastic materials, nonlinear elasticity, stress relaxation, and large deformations. Furthermore, no fatigue failure is observed even at high strain amplitudes up to half million cycles. The outstanding fatigue life and extraordinary soft tissue-like mechanical behavior suggest that properly engineered carbon nanotube structures could mimic artificial muscles, and their added high electrical and thermal conductivity could make excellent candidates for uses as compliant electrical contact brushes, probe cards and electromechanical systems.