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The integrity of the wheel is very important for the safety of railway. In this paper a laser-ultrasonic diagnostic measurement procedure has been designed for the inspection of the train wheels with the aid of a FE-model simulating the ultrasound propagation within the wheel itself. The laser-ultrasonic method exploits an air-coupled ultrasonic probe that detects the ultrasonic waves generated by a high-energy pulsed laser. As a result, the measurement chain is completely non-contact, from generation to detection, this making it possible to considerably speed up the testing set-up time and make it more flexible. This is an important advantage with respect to the conventional NDT technologies currently applied to train component diagnostics, as contact phase array methods. Laser ultrasonics is a complete remote technique since both the laser source and the receiving probe are installed in the proximity of the wheel directly on the bogie and therefore it is a more flexible technology with respect to standard techniques applied for wheel train diagnostics, as phased array. The applications of laser-ultrasonic technique available in the state-of-the-art work with high energy ultrasonic waves to guarantee good signal to noise ratio. Therefore, conventional laser-ultrasonic systems operates under ablative regime that assures high energy ultrasonic waves generation. On the other hand, the ablation produces damages on the surface of the component inspected. In this paper, it has been demonstrated that it is possible to work with lower energy waves, i.e. in the limit between ablative and thermo-elastic regime, if the experiment is properly designed on the basis of a numerical model. This operation regime allowed to guarantee a material removal below the threshold admitted in rail wheel application. The diagnostic procedure developed has been applied for the inspection of train wheels provided by the Italian railway company Trenitalia, on which dominant wheel failure cracks have been expressly created. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Laser Ultrasonics NDT for train wheelset inspection. • Axle standard defects investigated. • FEM model developed to drive experiments and set optimal measurement set-up. • Experimental parameters identified to improve the contrast between sound and damaged area. Laser-Ultrasonics Testing (LUT) is a Non-Destructive Technique (NDT) with good potential for application in the railway sector, nevertheless this technique is not yet used in practice because there are some practical difficulties to overcome. The possibility of measuring on a complete wheelset by bypassing the keying of the wheel will allow drastically reducing the inspection time but it has not yet been demonstrated. In fact, the attenuation of the signal in the path makes complex the interpretation of the generated waves. This paper aims at illustrating how the combination of simulated and experimental data allows to optimize the test setup for having output data of unambiguous interpretation. The main innovations presented in this paper are: (i) the possibility to work with low energy waves in the thermoelastic-ablative limit while maintaining satisfactory contrast levels for the purpose of defect detection and (ii) the implementation of a complete Finite Element Model (FEM) including the generation and propagation of waves in the solid domain and the propagation in air. This last step has not considered before in previous papers. The model allows to define the optimal experimental conditions to have a measured signal with an adequate signal-to-noise ratio (SNR > 6 dB) and to define an experimental procedure for defect detection reliable and comparable with current standards. This study lays the foundations for an innovative approach for train axle diagnostics which can be used during train extraordinary maintenance interventions. The laser ultrasonics system presented in this paper can be likely integrated in the pit lathe and exploited to monitor the railway wheels during their re-profiling phase, without having to remove them from the vehicle. [ABSTRACT FROM AUTHOR]