Abstract: Delamination damage can severely weaken the strength and stability of composite structures, so it is very important to monitor and identify it to ensure the structural safety. This paper proposes an approach to continuously monitor delamination growth in composite structures by using Lamb waves and time-frequency analysis. First, the propagation characteristic of Lamb waves in composite laminate containing delamination damage is studied, and the relationship between time of flights (TOFs) and the length of delamination is established to provide theoretical basis for delamination growth monitoring. Then the wavelet transform is applied to analyze the Lamb waves signal acquired by piezoelectric sensor in time and frequency domain to measure the TOFs between two sensors to determine the length of delamination. Numerical simulation and experimental results have demonstrated that the TOFs of Lamb waves between two sensors increase with the increase of the delamination length which is basically linear. And, through the TOFs extracted by wavelet transform, the delamination growth can be monitored, verifying the effectiveness of the proposed approach.

Key words: composite structures, monitoring of delamination growth, Lamb waves, time-frequency analysis