In this study, we investigate the interactions of Lamb wave A0 mode with different sizes of delaminations in composites using finite element code Abaqus®. According to Lamb wave dispersion curves, the group velocity of A0 mode increases rapidly as the frequency-thickness increases in the relatively low frequency region. In the delamination region, the frequency-thickness product decreases compared to the healthy laminate since the damage causes ply separation at the lamina interface. In the current study this observation is investigated in detail using finite element simulations. The resulting phase delay is analyzed by Empirical Mode Decomposition (EMD) and instantaneous phase approach. Finite element simulations are performed using Abaqus® and signal processing is performed in joint time-frequency domain using Hilbert-Huang Transform (HHT) method. The unwrapped instantaneous phase difference is correlated with the extent of delamination (quantitative level of damage).

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