Feasibility study of new Structural Health Monitoring solutions for crack localization

Student thesis: Master's Thesis


Structural Health Monitoring (SHM) techniques are an essential prerequisite of
condition based maintenance philosophies for industrial applications. These philosophies have the potential to increase the operational safety level while also reducing the direct operating cost of structures and components. A new SHM system was recently patented, using vacuum galleries that are embedded in the component by means of additive manufacturing techniques. Based on pressure monitoring inside these vacuum galleries, information about the health of the
component can be derived. The expansion of the patented SHM system with crack localization capabilities is the main subject that has been investigated in this thesis.
The thesis starts with an extensive literature study on Structural Health Monitoring techniques and leak detection and localization techniques for pipelines. Especially the acoustical localization techniques are deeply studied from the literature.
Extensive studies on these subjects have been performed in order to be able to use them
in the particular application of embedded galleries. A generalized theoretical formula for the prediction of the amplitudes of Negative Pressure Waves in the galleries was derived. Also, a simulation is presented for simulating the pressure change inside the galleries after a leak event.
Measurements were performed on large scale test set-ups (Tube diameter 16:9mm) and on a small scale test set-up (Capillary diameter 1:6mm) in order to evaluate the derived theoretical models. The leak localization capabilities of the dierent proposed methods are investigated using measurements on the dierent test set-ups. All properties (such as the gallery geometry, the leak position and the initial pressure level) were varied in order to evaluate their
eects. The gallery pressure was recorded at both ends of the gallery by means of piezo-resistive sensors.
The measurements on the large scale test set-up show the presence of Negative Pressure Waves, which contain a large amount of leak localization information. Especially the difference between the Time Of Arrival (TOA) at both tube ends can be used to locate the crack. Also the reflections of the Negative Pressure Waves at the gallery ends were recorded, allowing for crack localization with only one sensor. Crack localization is possible within millimetre accuracy.
The small scale measurements on the capillary test set-up do not show the presence of Negative Pressure Waves as a consequence of friction. Leak localization was still possible, but by using a transmissibility technique on the pressure signals. The accuracy of the leak localization dropped to the centimetre range.
It was concluded that crack localization is feasible on the basis of the newly developed SHM system. Further studies are still required to improve the localization accuracy.
Date of Award27 Jun 2015
Original languageEnglish
Awarding Institution
  • Vrije Universiteit Brussel
  • Université libre de Bruxelles
SupervisorPatrick Guillaume (Promotor) & Dieter Jens De Baere (Co-promotor)


  • Structural Health Monitoring
  • Leak localization
  • Vacuum galleries
  • Negative Pressure Waves
  • Transmissibility

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