Structural components subject to cyclic stress can succumb to fatigue, causing them to fail at stress levels much lower than if they were under static mechanical loading. However, despite extensive research into the mechanical properties of carbon nanotube structures for more than a decade, data on the fatigue behaviour of such devices have never been reported. We show that under repeated high compressive strains, long, vertically aligned multiwalled nanotubes exhibit viscoelastic behaviour similar to that observed in soft-tissue membranes. Under compressive cyclic loading, the mechanical response of the nanotube arrays shows preconditioning, characteristic viscoelasticity-induced hysteresis, nonlinear elasticity and stress relaxation, and large deformations. Furthermore, no fatigue failure is observed at high strain amplitudes up to half a million cycles. This combination of soft-tissue-like behaviour and outstanding fatigue resistance suggests that properly engineered nanotube structures could mimic artificial tissues, and that their good electrical conductivity could lead to their use as compliant electrical contacts in a variety of applications.

A macroscopic block ͑ϳ9 mm 3 ͒ of aligned carbon nanotubes ͑CNTs͒ was grown by chemical vapor deposition and its simultaneous electrical conductivity and compressive strain responses were measured parallel and perpendicular to the CNT alignment. The block exhibits elastic moduli of 0.9 and 1.6 MPa for compressive strain of Ͻ20% in parallel and perpendicular configurations, respectively. The electrical conductivity increases with increasing compressive strain in both configurations. The reversible electrical conductivity and compressive strain responses of block is attributed to elastic bending of CNTs. These excellent properties of CNT block can be used in compressive strain sensing applications.

Acoustic emission signals are known to exhibit a high degree of reproducibility in time and show correlations with the growth and shrinkage of martensite domains when athermal martensites are subjected to repeated thermal cycling in a restricted temperature range. We show that a recently introduced two dimensional model for the martensitic transformation mimics these features. We also show that these features are related to the shape memory effect where near full reversal of morphological features are seen under these thermal cycling conditions.

We have studied the electronic properties and the band structure of copper nanowires for various diameters using first principles density functional methods and a supercell approach. The resistances of copper nanowires were computed on the basis of the Landauer formalism and compared with those obtained from an empirical approach. The fundamental resistances of small copper nanowires (∼60 nm diameter) are found to be larger than those predicted by Ohm's law. In parallel, we have computed the fundamental resistances for bundles of single walled carbon nanotubes and compared them with that of a single copper wire of similar dimensions. We find that the resistance of carbon nanotube bundles is smaller than that of the copper wires for dimensions below 60 nm. Our results are discussed in light of recent experiments.

We have studied the behavior of band gap and effective mass of both the electrons and the holes in small diameter zigzag single-walled carbon nanotubes under uniaxial mechanical strain by using first-principles density-functional theory. The band gap of these nanotubes is modified by both compressive and tensile strain and all zigzag single-wall carbon nanotubes show a semiconductor-metal transition with strain. We also find that both compressive and tensile strains have a similar effect on the effective mass of the electrons and holes in these nanotubes. Our studies also show that the response of the changes in band gap and effective mass to the uniaxial strain could be grouped into three categories, depending on their chirality.