Structural health monitoring strategy for detection of interlaminar delamination in composite plates

In this paper, a Structural Health Monitoring (SHM) strategy is proposed in order to detect interlaminar delamination in a Carbon Fiber Reinforced Polymer (CFRP) structure using guided waves. The delamination is simulated by inserting a Teflon tape between two transverse plies and the guided wave generation and measurement is ensured by piezoceramic (PZT) elements. Theoretical propagation and through-the-thickness strain distribution are first studied in order to determine the optimal configuration of the final system in terms of mode and frequency selection and piezoceramic spacing for detection of cross-sectional delamination. Finite element simulation are then used to validate the assumptions and pitch and catch measurements are performed by comparing wave propagation for different frequencies and along damaged and undamaged paths and the analysis of results is performed using Reassigned Short-Time Fourier Transform (ReSTFT). It appears that in the low frequency range (below 300 kHz), A0 mode is sensitive to the damage while in the high frequency range, S1 and A1 modes are both very sensitive to the damage while the propagation of the S0 mode is not much affected.