Referenzfreies ultraschallbasiertes Verfahren zur Zustandsüberwachung rotierender Bauteile - Anwendung auf Radsätze von Schienenfahrzeugen

In this research work a baseline-free method for Acousto-Ultrasonics (AU)-based Structural Health Monitoring (SHM) of mechanically loaded and rotating axles is proposed, which can be used for condition monitoring of wheelset axles of railway vehicles. The novel “Dynamic Reference Method” utilizes the difference that is generated in the ultrasonic wave propagation due to the crack breathing mechanism of a mechanically loaded and rotating axle.

Due to their physical properties, ultrasonic waves can propagate through a structure and interact with discontinuities within the material, making them particularly suitable for permanent condition monitoring with SHM methods. In order to extract the changes due to damage, most SHM systems first need to collect data from the structure in healthy condition to build the so-called baseline. With the help of signal processing and feature extraction, the structural health condition is assessed through the comparison of the baseline and the newly acquired data. In real operation, structures are exposed to varying Environmental and Operational Conditions (EOCs), especially wheelset axles of railway vehicles, which are considered in this thesis. Different studies on the stability and the influence of EOCs on AU-based SHM methods using a previously collected baseline have shown that these lead to errors in the results of condition monitoring. This is due to the fact that it is difficult or impossible to distinguish the effects due to EOCs from the effects of structural damages. It is in some cases not economically feasible to collect data and to construct a baseline model for each combination of all possible EOCs for each structure. In consideration of such a practical limit, the development of a baseline-free SHM method is necessary and is focused in this thesis.

The results of the condition monitoring during the crack initiation and propagation in wheelset axles of railway vehicles demonstrate the effectiveness of the proposed baseline-free SHM method. Cracks can be detected, the crack propagation can be observed during fatigue tests and the approximate circumferential position of the crack can be localized by the proposed method. In addition, it is proved that the introduced SHM method is able to detect a fatigue crack during measurement runs on a full-scale roller test rig for railway vehicles without a previously collected baseline.

The proposed baseline-free SHM method could be used to complete the safety level of the periodically performed non-destructive inspections during the operation of wheelset axles, as the permanent condition monitoring prevents unforeseeable damages. This innovative technology contributes to the climate-friendly mobility of the future by increasing the acceptance of rail transport.