A Study on the Applicability of Ultrasonic Guided Waves for Monitoring Damage Development in the Foot of In-Service Railway Rails

Railway rails are safety components whose failure can lead to dramatic consequences. Due to the very high number of in-service pieces, the generally adopted strategy for assuring in-service structural integrity is to run diagnostic trains all along the lines and send teams of operators only to those sites showing possible anomalies. On the other hand, one of the main open points of inspections carried out by diagnostic trains is that the foot cannot be inspected at all because it is not accessible from the rolling surface, where the adopted sensors are usually located. The present research focuses on the implementation, based on experimental and numerical activities carried out in the lab on rail chunks containing artificial defects with different shapes and sizes, of a permanent structural health monitoring system devoted to the evaluation of the integrity of the rail foot. The approach uses ultrasonic guided waves actuated and sensed by piezoelectric sensors along with a post-processing procedure defining a simple, but relevant, damage index. Both the cases of free and constrained rail are considered, studied and discussed. Results seem encouraging, so the next step of the research is going to be the on-field application.