Laser Ultrasonics Inspection for Defect Evaluation on Train Wheel

Passengers’ safety and in-service life of wheelset axles play an important role in railway vehicles. For this reason, periodic inspections are necessary. Among non-destructive techniques, ultrasonic ones are widely applied in this field. The main disadvantage of conventional ultrasonic techniques is that the overall inspection of wheels requires the train to be put out-of-service and disassembly each part, which is time-consuming and expensive. In this paper, a non-conventional non-contact laser ultrasonic inspection for train wheels is proposed. The proposed method uses a laser interferometer to receive the ultrasonic wave without contact. The receiving system allows choosing the distance between the surface to be inspected and the interferometer, overcoming any encumbrance issue. The experimental investigation is carried out on standard-reproduced defects in order to evaluate the reliability and the accuracy of the technique and to verify its applicability for railway components, as wheels, which have a complex geometry. The experimental setup consists of a pulsed laser for the ultrasonic wave generation. The receiving unit combines a continuous-wave laser and an interferometer in order to acquire the surface out-of-plane displacements. Surface and internal standard defects are detected by collecting all the A-scans in a B-scan map. The results are promising for the application of the laser technique to detect both surface and internal defects on in-service components.