Towards Continuous Railway Monitoring: A Concept for Surface Crack Assessment Based on Surface Acoustic Waves

Sebastian Fichtenbauer

Research output: ThesisMaster's Thesis

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This master's thesis employs an experimental approach to evaluate the feasibility of a surface acoustic wave (SAW) based monitoring concept for depth assessment of surface cracks. The focus of this work is on a potential application for monitoring of rail cracks. To date, no measurement principle has been found that offers both precise sizing of gauge corner cracks in rails, commonly termed head checks, and compatibility with permanent rail installation. Such a technique holds the potential to be the key to continuous in-situ condition monitoring of railway infrastructure, ensuring a cost-efficient, yet safe operation of rail tracks. The primary objective of this thesis is to determine if surface acoustic waves can be used for a quantitative assessment of head check depth. The SAW transmission coefficient was selected as the representative wave feature for crack examination. Rail samples that exhibit varying degrees of head check damage were collected. An experimental setup was established to determine the SAW transmission coefficient for different crack depths. A Laser Doppler vibrometer was used to measure the out-of-plane displacement of the propagating SAWs, which were excited by piezoelectric transducers affixed to the rail specimens. Characteristic measurement signals were analyzed in both time and frequency domains. A signal processing algorithm was developed and implemented to extract the amplitudes of the incident and transmitted SAW. Subsequently, the transmission coefficients were calculated from these values. The extensive number of measurements allowed for an evaluation of the statistical scatter of the obtained transmission coefficients. Based on the obtained results, a linear correlation between head check depth and transmission coefficient is hypothesized for low crack depth and high-frequency surface acoustic waves. Consequently, sizing head checks using the SAW transmission coefficient is deemed potentially feasible under these specific conditions. Moreover, mechanisms impeding a quantitative assessment of deeper head checks have been identified. To apply the evaluated sensor concept in railway tracks, many challenges still need to be overcome, given the prevailing harsh environment.
Translated title of the contributionBewertung eines Zustandsüberwachungskonzepts zur Abschätzung der Risstiefe in Eisenbahnschienen mittels akustischer Oberflächenwellen
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • O'Leary, Paul, Supervisor (internal)
  • Gänser, Hans-Peter, Supervisor (external)
Award date15 Dec 2023
Publication statusPublished - 2023

Bibliographical note

no embargo


  • condition monitoring
  • head checks
  • crack detection
  • surface acoustic waves
  • rails

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