Ultrasonic bidirectional phase shift migration imaging of wrinkles in carbon/glass hybrid composites

Wrinkles in hybrid composites could significantly affect mechanical properties. Considering their irregular interfaces compared to regular layered structures, a bidirectional phase shift migration (B-PSM) algorithm with vertical and horizontal wavenumber variations is proposed to reconstruct wrinkle images in hybrid composites. A wavefield extrapolation operator based on the bidirectional wavenumber distribution is connected with the Fourier transform of full-matrix capture data to realise the wavefield migration from the surface to a given depth in the material. The obtained wavefield is accumulated and inverse Fourier transformed to realise the image reconstruction. Experiments are performed on carbon/glass hybrid composite specimens with wrinkles. The grey level co-occurrence matrix-based features from B-PSM outperform that of classical PSM by a factor ranging from 1.24 to 8.69, which are also better than those from vertical or horizontal wavenumber PSM. All the wrinkle assessment errors in B-PSM imaging are less than 10%.