Longitudinal and Torsional Vibration Characteristics of Boron Nitride Nanotubes

Background Boron nitride nanotubes (BNNTs) are new cousins of carbon nanotubes (CNTs), which alternately substitute boron and nitrogen atoms for carbon atoms entirely. Its excellent physical and chemical properties, such as excellent thermal stability, chemical inertness and strong acid corrosion resistance, make BNNTs products be favorable to machine, thus scientific activities focused on them have profound practical significance and great application prospect. However, the vibration characteristics of BNNTs is still the least understood aspects. Method Longitudinal and torsional free vibration of single-walled boron nitride nanotubes are investigated through a coupling atomistic-continuum model with Euler beam model and atomistic simulations. Euler beam model with the involved atomistic-continuum multiscale model is capable of capturing the size effect since physical meanings of the integration for involved higher order gradient tensors are corresponding to size effect. The analytical solutions obtained by the coupling method are compared with atomistic simulation and are found to be in a good agreement. Results Computational results demonstrate that fundamental frequencies are in an order of 1 THz for both cantilevered and clamped boron nitride nanotubes, independent of tubular chirality. The effect of tubular radius on fundamental frequencies of both longitudinal and torsional free vibrations are large when it is small, especially the latter. The error between coupling method and atomistic simulation generally decreases as the length/diameter ratio increases. Conclusions For a given length/diameter ratio, tubular radius have a distinctly decreasing effect on the error no matter what the kind of constraint is. However, a small difference observed in the study of torsional free vibration is that the clamped constraint gives rise to a slight increasing effect on the error as the tubular radius increases, but limited to a small degree. The vibrational modes confirm that the difference is originated from the involved breathing vibration in both torsional and longitudinal free vibration.