Propagation characteristics of ultrasonic diffusion energy in ballastless track structures with different levels of damage

Abstract

The composition of concrete, being heterogeneous, leads to the randomization and transformation of high-frequency ultrasonic waves into an incoherent field. This incoherent field can be effectively quantified by ultrasonic diffusion energy, which thereby facilitates the detection of micro-damage in concrete structures using high-frequency ultrasonic waves. However, the propagation characteristics of ultrasonic diffusion energy in multi-layer structures, such as ballastless tracks, remain unclear. To address this issue, a finite difference method was utilized to derive both the difference equation and its corresponding stability condition equation for the ultrasonic diffusion equation within ballastless track structures. This was followed by an introduction of a numerical simulation method for the propagation of ultrasonic waves, as well as the proposal of an inversion method for ultrasonic diffusion parameters. On basis of this, the propagation characteristics of ultrasonic diffusion energy within ballastless track structures with global and local damage were analyzed and an experimental validation was conducted. The results indicate that the delay in peak arrival time, as well as the changes in attenuation behavior of the ultrasonic diffusion energy, are respond to the damage of ballastless tracks. It was also noted that damage to components in the lower layer has a minimal impact on the propagation of ultrasonic diffusion energy in the components above. Additionally, as the frequency increases, the sensitivity of ultrasonic diffusion energy to global damage or damage to individual component in ballastless tracks decreases, while the sensitivity to local defects increases.