Abstract
Carbon fiber reinforced polymer (CFRP) composites are high sound attenuation materials. When conducting the phased array ultrasonic total focusing method (TFM) defect detection on them, the detection depth is limited and noise is severe. To solve this problem, a nonlinear frequency modulation (NLFM) waveform with a concave quadratic frequency function is provided, which combines the TFM to increase signal noise ratio (SNR) and detection depth of CFRP composites. The second-order total generalized variation (TGV) and Butterworth high pass filter are introduced to denoise and enhance defect features in the strong background noise in CFRP composites. Experimental researches are conducted to compare the TFM imaging performance with single-pulse excitation (Pulse TFM), linear frequency modulation excitation (LFM TFM), Barker coding excitation (Barker TFM), and nonlinear frequency modulation excitation (NLFM TFM). The results show that NLFM TFM has the optimal SNR and depth resolution. With second-order TGV and Butterworth algorithm, the defect information submerged in the background noise is highlighted, and the clarity and SNR of the detected image are enhanced.
Published Version
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