Stress wave propagation in Boron-Nitride nanotubes

PK Patra and RC Batra, COMPUTATIONAL MATERIALS SCIENCE, 130, 144-151 (2017).

DOI: 10.1016/j.commatsci.2017.01.008

The propagation of axial stress waves in Boron-Nitride nanotubes of different chirality and length under adiabatic conditions has been studied using molecular dynamics (MD) simulations. The velocities of the axial stress waves are found using three methods - (i) direct MD simulations, (ii) harmonic approximation of the nanotubes, and (iii) one-dimensional (1-D) wave equation. The MD simulation results indicate a small dependence of the wave velocities on the nanotube chirality and the excitation frequency - in armchair and zigzag nanotubes waves travel faster than that in chiral nanotubes, and wave velocities decrease with an increase in the frequency of excitation. The wave speed obtained from the harmonic approximations is 20-25% higher than that found from the MD simulations. Likewise, the frequencies of vibrations from the two approaches differ by 15-20% for most of the cases. The computation of the wave speed from 1-D equation requires a prior knowledge of the elastic modulus and the nanotube wall thickness. The values of these parameters are found from MD simulation results - axial tensile tests provide an estimate of the wall thickness scaled elastic modulus and the transverse vibration data relates the standard deviation of the tip displacement with material properties of the nanotube. The wave speed predicted from the 1-D wave equation agrees with that obtained from the MD simulations at low excitation frequencies. The contribution of the anharmonicity to the dynamics during wave propagation is found by matching the response of the anharmonic Fermi-Pasta-Ulam chain with the MD simulation results. (C) 2017 Elsevier B.V. All rights reserved.

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