Damage detection method based on continuous wavelet transform of second harmonic Lamb waves

The nonlinear Lamb waves are sensitive to closed micro cracks and have a great potential for the detection of damage to prevent the catastrophic failure of entire structure. A five-stage closed micro crack localisation method based on time of flight (ToF) of the second harmonic Lamb waves is proposed in this research. The first step is frequency analysis of the received signals to ensure the generation of second harmonic wave. The second step is to extract second harmonic wave component in frequency range. The third step is to obtain wave signals in time domain. The fourth step is to extract ToF of second harmonic wave. The fifth step is to locate damage with ToFs. The method provides an effective strategy based on wavelet transform to extract the second harmonic Lamb waves from the dynamic response signals for the detection of closed micro crack. The numerical and experimental results indicate that the proposed method can accurately locate the closed micro crack in plate-like metallic and composite structures.