Nondestructive determination of longitudinal rail stress from guided wave dispersion properties

Abstract

The determination of the longitudinal stress in continuous welded rails is essential for the safe operation of high-speed railways. Guided wave inspections have many advantages, and can provide an effective tool for non-destructive measurements of the longitudinal stress in rails. This paper provides a new method for determining longitudinal rail stress using ultrasonic guided wave dispersion properties. First, the characteristic equations of guided waves propagating in a waveguide with existing longitudinal stress are constructed, generating the dispersion properties of the waveguide such as the wavenumber, phase velocity and group velocity. The sensitivity of the dispersion properties of propagative modes to the longitudinal rail stress is investigated, which is then used for selecting appropriate modes for guided wave inspections. On the basis of the perturbation method, the relationship between the change in longitudinal rail stress and the change in dispersion properties is developed, which can be used for determining the longitudinal rail stress from dispersion properties. Furthermore, a mode selection index considering both the stress sensitivity and mode shape characteristics is employed for selecting appropriate propagative modes for guide wave inspections. Finally, a numerical example for CHN60 rail is adopted to demonstrate the effectiveness of the proposed method. From the results, the proposed method can accurately determine the longitudinal stress in the rail by using the dispersion properties available.