Neutral Temperature Estimation of Continuous Welded Rails using Group Velocity of Ultrasonic Waves

Abstract

This study proposes a neutral temperature estimation technique of continuous welded rails using group velocity of ultrasonic waves. In case of boundary-confined metallic structures, especially civil infrastructures exposed to harsh environmental conditions such as continuous welded rail, thermal stress is one of the critical control factors to avoid structural breakage and buckling. It has been known that the ultrasonic wave propagation is sensitive to target structure’s stress variation, so that the neutral temperature can be determined based on the propagation characteristics of stress-dependent ultrasonic wave. To numerically investigate the stress-dependent ultrasonic wave behavior, a 3D rail model with 1 mm mesh size was constructed using actual material property and dimensions of KR60 rail. Here, the two boundary conditions, i.e., Fix-Free and Fix-Fix boundary conditions, applied to the 3D model so that neutral temperature is extracted. The simulation results showed that the group velocity of ultrasonic waves was consistently decreased on the Fix-Free boundary condition according to temperature increase. Similarly, the group velocity on the Fix-Fix boundary condition was also decreased, but the decrement of group velocity was less than the Fix-Free boundary one due to thermal stress. Based on the observation, the stress-dependent group velocity trends can be estimated using the difference between the Fix-Free and Fix-Fix boundary resultants. Finally, the neutral temperature can be estimated by picking up the cross point of two group velocity trend graphs.