A "Design of Experiment" Approach to the Performance of Lamb Ultrasonic Wave-Based Structural Health Monitoring of Aeronautical Carbon Fibre Reinforced Polymer Laminates

The present paper investigates, through the Design of Experiment (DOE) methodology, the performance of Lamb wave-based Structural Health Monitoring (SHM) by using PZT transducers which are surface bonded onto aeronautical carbon fibre reinforced polymer (CFRP) laminates. The experiments highlight the chance of exciting a pure A(0) Lamb wave mode, actuating at low frequencies [0;50] kHz; in addition, via a pair of PZT, the magnitude of the diagnostic signal and consequently the signal to noise ratio (SNR) is amplifiable. Hence a rigorous 2(k) factorial design method has been applied to study the influence of the following three factors on the SHM approach: the frequency of excitation, the dimension and the position of delamination defects artificially recreated using Teflon patches. After processing the sampled data with the discrete and continuous wavelet transforms, respectively for denoising and extracting the features of the signal, the SHM approach is shown to be able to detect small delaminations in the range from 8 to 24 mm, regardless of their location in the CFRP laminates. The frequency and the interaction between the position and the dimension of defects are demonstrated to be the most influencing factor.