Experimental investigation by laser ultrasonics for high speed train axle diagnostics

• A laser-ultrasonics procedure for train axles ultrasonic inspection is reported.
• A FE model for the design of experiments based on laser-ultrasonics is described.
• A sensitivity analysis to the angular position and distance was performed.
• The experimental tests was able to identify the presence of defects.

The present paper demonstrates the applicability of a laser-ultrasonic procedure to improve the performances of train axle ultrasonic inspection. The method exploits an air-coupled ultrasonic probe that detects the ultrasonic waves generated by a high-power pulsed laser. As a result, the measurement chain is completely non-contact, from generation to detection, this making it possible to considerably speed up inspection time and make the set-up more flexible. The main advantage of the technique developed is that it works in thermo-elastic regime and it therefore can be considered as a non-destructive method.The laser-ultrasonic procedure investigated has been applied for the inspection of a real high speed train axle provided by the Italian railway company (Trenitalia), on which typical fatigue defects have been expressly created according to standard specifications. A dedicated test bench has been developed so as to rotate the axle with the angle control and to speed up the inspection of the axle surface. The laser-ultrasonic procedure proposed can be automated and is potentially suitable for regular inspection of train axles.The main achievements of the activity described in this paper are:–the study of the effective applicability of laser-ultrasonics for the diagnostic of train hollow axles with variable sections by means of a numerical FE model,–the carrying out of an automated experiment on a real train axle,–the analysis of the sensitivity to experimental parameters, like laser source – receiving probe distance and receiving probe angular position,–the demonstration that the technique is suitable for the detection of surface defects purposely created on the train axle.