A Sobel-enhanced total focusing method using an ultrasonic linear array transducer for detecting wrinkles in multidirectional CFRPs

Carbon-fiber reinforced plastics (CFRP) are increasingly used in the aerospace industry. Wrinkles are common defects of complex curved CFRP parts, severely damaging the mechanical performance. The ultrasonic technique is an effective tool for detecting wrinkle defects in complex curved CFRP parts in the aerospace industry. We propose a Sobel-enhanced total focusing method using an ultrasonic linear array transducer for detecting wrinkles in multidirectional CFRPs. The total focusing method (TFM) imaging wrinkles loses some ply geometry information due to the non-zero local mean when extracting the cosine of the instantaneous phase of a synthetic depth trace from its associated analytic signal for amplitude normalization. The proposed Sobel-enhanced TFM method combines the aperture-angle limitation and the vertical Sobel operator to relieve the non-zero local mean in this paper. The proposed method can extract almost all ply geometry information of a 32-ply CFRP sample when the limited angle, θ max = 10° or 5°.