We establish the physics and understanding of nonlocal nanoscale wave propagation
in carbon nanotubes (CNTs) based on nonlocal elastic stress field theory.
This is done by developing an analytical nonlocal nanotube model based
on the variational principle for wave propagation in CNTs. Specifically, we
successfully derive benchmark governing equations of motion for analyzing
wave propagation based on an analytical nonlocal shear deformable model.
The physical insights of the analytical nonlocal stress model are presented
through examples. Analytical solutions with significant observation of wave
propagation have been predicted and the prediction compares favorably
with molecular dynamic simulations. Qualitative comparisons with other
non-nonlocal approaches, including the strain gradients model, the couple
stress model and experiments, justify the stiffness enhancement conclusion as
predicted by the new nonlocal stress model. New dispersion and spectrum
relations derived using this analytical nonlocal model bring an important focus
onto the critical wavenumber: stiffness of CNTs and wave propagation are
enhanced below the critical wavenumber, while beyond that a sharp decrease in
wave propagation is observed. The physics of nanoscale wave propagation in
nanotubes are further illustrated by relating the nanoscale and the phase velocity
ratio.