Real-time non-invasive measurement and monitoring of wheel–rail contact using ultrasonic reflectometry

Rail stress levels are vital to the lifespan of rail tracks, and are responsible for the safe operation and ride comfort of train services. In particular, wheel–rail contact stress is a dominating factor affecting wear, cracking, fatigue and failure of both wheel and rail. The wheel–rail interaction problem has long been investigated, yet detailed contact information on real cases remains obscure due to the interface complexity, including the varying wheel and rail profiles and lack of effective stress characterisation methods. Ultrasound image study, as an excellent non-destructive evaluation (NDE) method, is widely used in railway systems for defect detection, stress determination and rail profile checking. Specifically, ultrasonic reflectometry has proved successful in making static machine-element contact measurements. This article introduces a novel measuring method for both short-term and long-term dynamic wheel–rail contact monitoring purposes based on ultrasonic reflectometry. The method is investigated in detail, including the study of ultrasound propagation pathways in the rail, and the optimum placement of ultrasonic elements as well as actuator–receiver combinations. The proposed monitoring technique is expected to characterise and monitor the contact behaviour of operating high-speed rail system in real-time.