Rail Longitudinal Stress Measurements Based on Guided Wave Propagation Characteristics

Guided wave testing can provide an effective method for nondestructive measurements of the longitudinal stress in rails to ensure smooth and safe railway operation. In this paper, a reliable method for determining the longitudinal stress in rails from the propagation characteristics of ultrasonic guided waves is presented. First, the semianalytical spectral element method is adopted to investigate the dispersion properties of guided waves propagating in rails, and the characteristic equation for the dispersion properties is constructed with consideration of the longitudinal stress in rails. From the characteristic equation, the dispersion properties such as wavenumber, phase velocity, and group velocity are obtained, and a mode selection index is proposed for appropriately choosing guided wave modes for measuring rail longitudinal stress. Then, a relation between the change in rail longitudinal stress and the change in guided wave dispersion properties is developed, which provides accurate predictions for the rail longitudinal stress. Finally, guided wave experiments were undertaken for the rail specimens under various stress levels, and the measured data were utilized to verify the effectiveness of the proposed method. The results show that the change in the rail longitudinal stress has approximately a linear relation to the change in group velocity, and the proposed method can effectively determine the rail longitudinal stress with the average absolute relative error of 0.44%.