HIGHER MODES OF LONGITUDINAL WAVE PROPAGATION IN THIN RODS

The propagation of the higher modes of longitudinal wave propagation in a dispersive elastic rod was investigated, both analytically and experimentally. The Pochhammer Chree equation was solved for the mode shapes and group velocities as a function of wavenumber for the axisymmetric modes of longitudinal wave propagation. By integration of the axial displacement across a cross section, an indication of the planeness of the waves was obtained. In the experimental investigation, elastic waves generated in a colored glass pressure bar by absorption of luminous energy from a Q switched laser were measured using a thin piezoelectric crystal sandwiched in the pressure bar. The gross experimental results showed good agreement with the response as predicted by Love's modified wave equation. Higher modes of wave propagation not predicted by the one dimensional theory were evident in the experimental record. These effects were related to the results obtained from the Pochhammer Chree equation. © 1968, Acoustical Society of America. All rights reserved.