Modelling and simulation of ultrasonic inspections in welded rails subjected to practical environmental conditions

A permanently installed Ultrasonic Broken Rail Detection system monitors the Sishen-Saldanha railway line in South Africa. The system detects complete rail breaks at long-range using guided wave ultrasound. For the system to be reliable, its damage detection performance must be evaluated under actual environmental and operational conditions (EOCs). However, obtaining monitoring data containing damage reflections is virtually impossible since detected defects in operational rail track sections are immediately removed and replaced with new rail. Laboratory experiments are also not possible since end reflections from short sections of rail dominate the response. Therefore, damage signals can only practically be obtained from numerical simulations. The simulated damage signals should be realistic and include varying EOCs, especially temperature variations. This paper aims to demonstrate a procedure to model temperature variations in ultrasonic signals. The temperature model and the modelling framework developed are used to simulate reflections from welds. The framework models the excitation, propagation and scattering of guided waves from discontinuities by employing a hybrid model based on the 3D Finite Element method (FEM) and the 2D Semi-Analytical Finite Element (SAFE) method. The simulated results are validated using experimental measurements collected from an operational rail at different temperatures.