Investigations of propagating wave types in railway tracks at high frequencies

At low frequencies waves propagate in a rail as bending, extensional or torsional waves. At higher frequencies, above about 1.5 kHz, the rail cross-section deforms and many higher order wave types exist. This cross-section deformation has to be taken into account for an accurate evaluation of the dispersion properties at high frequencies. Simulation results in the literature show that a multiplicity of wave modes is possible within this high-frequency range. In this work, wave types that propagate primarily through separate regions of the rail cross-section are investigated for frequencies up to 80 kHz. Two numerical methods are applied to obtain the dispersion properties for a railway track model including rail pads as a continuous foundation. These are a conventional finite element (FE) method and a wavenumber finite element (WFE) method, each of which can include the effects of cross-sectional deformation. In order to validate the predicted results, experiments were performed on a short test track using an impact hammer and accelerometers. Additional measurements used piezoceramic transducers to excite the rail at higher frequencies. The results are compared with simulations in terms of the group velocity and they present very good agreement. From this comparison, it is identified which wave types predominantly propagate on various regions of the rail cross-section.