Ultrasound SAFT imaging for HSR ballastless track using the multi-layer sound velocity model

Abstract

Accurate detection of void defects in ballastless track structures has become a core problem that needs urgent resolution for the maintenance and repair of high-speed railway (HSR) line structures in China. In this study, the root mean squaresynthetic aperture focusing technique (RMS-SAFT) ultrasound imaging method, which is suitable for the void defects of multi-layer structures, is proposed by combining the RMS velocity method and SAFT ultrasound imaging. First, a multi-layer sound velocity model (the relationship model between sound propagation time and sound propagation distance) of the HSR ballastless track is established. The sound propagation time is expressed as a function of the RMS of sound propagation speed as an independent variable. Second, the propagation time of the sound wave in the HSR ballastless track is calculated in accordance with the multi-layer sound velocity model and the obtained propagation time is substituted into the SAFT ultrasound imaging method for imaging. Lastly, the accuracy of the method is verified through a finite element simulation and an experiment. The results show that for the HSR ballastless track with minimal differences in the sound propagation speed at each layer, the sound propagation time calculated by the multi-layer sound wave model has high accuracy. The proposed RMS-SAFT ultrasound imaging method improves the accuracy of traditional SAFT imaging and realises accurate imaging of the void defects of HSR ballastless track.