Damage Detection in Bounded Fluid Loaded Plates UsingPiezoelectric Fiber Composite Generated LambWaves

This paper focuses on damage detection in a bounded plate while damage reflection andboundary reflections arrive at the sensor simultaneously. The plate is assumed to be fluidloaded, so a proper Lamb mode, excited and received by piezoelectric fiber composite (PFC)transducers, is selected such that it is not affected by fluid loading. A dispersion and wavestructure study is done in order to select the Lamb mode, which is S1 at f.d=3.8 MHz.mm,with zero out of plane displacement. Having selected the proper mode, an experimental setupwhich is a 6.25 mm thick steel plate is prepared and equipped with a four element PFC transducer.It is experimentally shown that the excited S1 mode is not affected by fluid loadingwhile other excited modes are affected and attenuated. Two notches are placed on the platesuch that wave reflections from notches interfere with boundary reflection, thus a suitablesignal processing method is needed. It is shown that a correlation followed by signal differencecalculation can be used for detecting the notch reflection from boundary reflection.Moreover, Continuous Wavelet Transform (CWT) based signal processing can clarify the damage reflection from transducer response peaks in experiments, successfully.

Keywords:

Structural health monitoring , Lamb waves , Dispersion curves , Wave structures , Fluid loaded , Wavelet Transform