Elastic wave propagation and vibrations are fundamental in applications technologically relevant, including the nondestructive evaluation and structural health monitoring, which have a strong impact on infrastructure safety and reliability. Indeed, the current research activities focus on finding novel strategies to detect imperfections and cracks in infrastructures, especially for the applications based on visual inspection or more conventional strategies less-practical or not-usable in real-time monitoring.
To this end, the Department of Mechanical Engineering of Politecnico di Milano is carrying out research activities in collaboration with RFI – Rete Ferroviaria Italiana. The activities focus on the analysis of wave propagation in railway systems at sonic and ultrasonic frequencies to detect cracks and defects developed over time due to multiple causes, such as corrosion and fatigue, among others. While there are established tools to study and characterize such phenomena at laboratory level, the on-field implementation has been so far elusive from the practical perspective. The experimental campaign is located in Bologna and consist in a railway system equipped with one input site, in which a set of smart piezoelectric devices is bonded on the rail to generate a wave. Several output sites are then placed at difference distances from the input in order to measure the transmitted and reflected waves. It is expected that the scattering pattern contains information about defect size and coordinate. This, in combination with a suitable management system can be employed as a new platform to foresee failures in railway systems or, in general, in mechanical and civil structures.
At the current progress of the activity, the reflection pattern without the presence of defects has been successfully acquired up to a distance of 350 m from the input source. The following steps will be thus focused on the generation of different types of defects and on the study of their influence on the dynamic behavior of the rail.