Zero Group Velocity Modes in Rails: a Numerical Study

Ultrasonic guided wave propagation along a free rail was simulated to understand the existence of intrinsic zero-group velocity (ZGV) modes. A finite element model was established to spatially sample the complex wave disturbance in the rail to study its dispersion relationships. The sharp resonant phenomenon of ZGV modes was observed in the frequency domain, and multiple ZGV points were identified at finite wavenumbers in the wavenumber-frequency domain. The resonances with positive and negative wavenumbers revealed that the observed ZGV modes result from the interference of two propagating modes traveling in opposite directions. ZGV modes in free rails have the potential for rail defect detection, support condition assessment, and stress-free temperature measurement.