"Development of an automated measurement and evaluation system for PWAS-based damage identification methods"
Development of an automated measurement and evaluation system for PWAS-based damage identification methods
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The following master thesis deals with the development of an automated measurement and evaluation system for damage detection and localization methods, based on
Piezoelectric Wafer Active Sensor (PWAS). The methods used focus on the propagation of guided waves (GW) packets in thin-walled structures and on the electromechanical impedance (EMI) of a structure under
continuous excitation by a PWAS. For the development process of this automated system, a square aluminum plate with homogeneous material properties was used as a test structure. After the creation of an experimental
setup for the automated measurements, consisting of a unit for the GW measurements, a unit for the EMI measurements, a switching unit for controlling the PWAS measurements and a computing unit for the evaluation of
the determined measurement data with the help of the damage detection and localization methods, the system was implemented on the target structure, a composite aircraft spoiler featuring a system of sensors.
Subsequently, tests were carried out with two different artificial damages, a magnet and a clay lump to simulate a punctual mass change, at different positions within the investigated area of the structure.
The investigations showed that by using damage detection methods based on both GW propagation and EMI measurements, the damage present could be detected very well. However, it was found that due to the conservatively
chosen parameters, they sometimes detect damage even when no damage is present. This problem was solved very well by introducing a recheck of the detection results based on data from the localization methods.
Damage localization using methods based on the propagation of wave packets proved to be more challenging on the composite aircraft spoiler than on the simple aluminum structure due to the special material properties
(e.g. strong material damping). Nevertheless, good localization results could be achieved for the majority of the simulated damage cases using these methods. For damage localization using EMI, the material properties
of the spoiler, in contrast to those of the aluminum plate, proved to be advantageous and enabled the applicability of this method. In tests with different artificial damages and different positions, adequate
localization results could be achieved in the most cases. In summary, the implementation of the automatic damage detection and localization system and the use of simple evaluation methods generally produced good
results despite this complex composite structure. Furthermore, valuable knowledge was gained for future work on damage detection and localization using PWAS arrays. However, in order to be able to guarantee reliable
operation and high accuracy of the localization results, further improvements of the system are necessary.