On the Existence of Zero Group Velocity Modes in Rails

Abstract

Ultrasonic guided waves are of practical interests for nondestructive evaluation (NDE) and structural health monitoring (SHM) since users can promote desirable wave modes for damage detection, thickness measurement, surface condition characterization, stress measurement, and so on. This study focuses on demonstrating the existence of zero group velocity (ZGV) modes for guided waves in free rails. First, the team computed dispersion curves of AREMA standard rails to identify ZGV points through semi-analytical finite element analysis (SAFE). Second, finite element models were established to spatially sample wave propagation in free rails for wavenumberfrequency domain analysis. The results of finite element simulations were compared with dispersion curves produced by SAFE, and multiple points were identified with vanishing group velocity at non-zero wavenumbers. And resonances with positive and negative wavenumbers revealed that the observed standing waves phenomenon results from the interference of two traveling waves propagating with opposite directions. Our observation and developed methodology have potential applications for rail defect detection, support condition assessment, and rail stress measurement.