Affiliations: IDMEC/IST – Instituto Superior Tecnico, Av.
Rovisco Pais, Lisbon, Portugal | Aeronautical Laboratory, Portuguese Air Force Academy,
BA1, Granja do Marques, Pero Pinheiro, Sintra, Portugal
Note: [] Corresponding author. Professor, University of Victoria,
Victoria, Canada. E-mail: suleman@uvic.ca
Abstract: The paper presents a structural health monitoring system based on
propagation of tuned Lamb waves and their interference with discontinuities.
The dispersion curves are studied to determine the appropriate type and
dimension of transducers and to select the optimum scanning frequencies and
relevant propagation modes. A piezoelectric sensor network was implemented in
an aluminum plate in order to generate and to sense the wave propagation and
associated reflections. The algorithm developed for damage detection relies on
the comparison of undamaged and damaged responses of the structure.
Combinations of filters and statistical methods were applied to detect
differences in the sensor signals acquired for the two different states
(damaged and undamaged), corresponding to damage reflections. In order to
eliminate the false positives due to noise, a probability analysis is performed
to obtain the final damage position. The software designed for the current
application allows the automatic calculation of dispersion curves, it executes
the scans, performs data processing, executes the detection algorithm and
presents the probable damages and their positions in a graphical form.
Experiments were performed with the introduction of cumulative damages in the
plate such as surface and through-the-thickness holes and cuts, ranging from 7
mm to 1 mm in diameter. Additionally, a stringer was attached to the plate by a
single rivet line to simulate an aircraft skin structure. Cuts originating from
rivet holes and connecting adjacent rivets, as well as loosened rivets were
detected by the system. The introduction of the stringer resulted in a loss of
precision in the determination of the radial position of the damages near it.
Also, the network revealed significant difficulties in the detection of damages
beyond the stringer.
Keywords: Structural health monitoring, non-destructive testing and evaluation, lamb waves, piezoelectric networks
