Parametric study on interply tracking in multilayer composites by analytic-signal technology.

Recently, researchers proposed the use of ultrasound combined with analytic-signal concepts for the reconstruction of the internal ply structure of composites. Optimal parameters for the pulse-echo mode ultrasonic testing are determined by modeling the analytic-signal response. The internal structure can be reconstructed by instantaneous metrics based on the interaction of the multilayer structure and the ultrasonic wave. However, there are certain drawbacks associated with the use of instantaneous metrics. The phase-derived interply track tends to be sensitive to the inspection conditions. This paper analytically studies the errors of the interply tracking for a wide range of parameters, including (i) signal-to-noise ratio, (ii) bandwidth, (iii) interply thickness, and (iv) attenuation, amongst others. It provides a guideline on how to improve the performance of the interply tracking procedure in real measurements. An experimental study combining the analytic-signal procedure with a standard log-Gabor filter in the frequency domain is performed to derive the interply tracks of a 24-layer composite laminate in a robust way. The bandpass filter selects the appropriate frequency band of the analytic-signal response from the composite. It shows a good ability for frequency and bandwidth selection, and can efficiently cope with noise features. The reconstructed ply tracks in A-scan, B-scan, and C-scan modes are analyzed to verify the performance of this procedure.