LFM-Golay coding excitation anisotropy TFM with Canny operator second-order TGV for detecting deep defects in CFRP...

Carbon fiber reinforced polymer (CFRP) composites exhibit highly anisotropic multilayer heterogeneity material properties. When conducting the phased array ultrasonic total focusing method (TFM) defect detection on them, the detection depth is limited and the noise is severe. To solve this problem, the COMSOL finite element simulation was initially employed to examine the anisotropic acoustic velocity characteristics of CFRP composites, and a relationship curve between the group velocity of quasi-P waves (QP waves) and the sound wave propagation direction was established; the sources and laws of noise in the ultrasonic propagation structure of CFRP composites were also clarified. On this basis, to address the problem of high sound attenuation in CFRP composites, an anisotropic coded excitation TFM based on linear frequency modulation and Golay code composite modulation waveform (LFM-Golay TFM) was proposed to enhance detection depth. To resolve the problem of high noise in CFRP composites, a second-order total generalized variation (TGV) detection image denoising technique based on the Canny operator was proposed. Experimental research was conducted, the results show that compared to single pulse, Barker, and LFM TFM, the LFM-Golay TFM has the best imaging resolution and signal-to-noise ratio (SNR). This algorithm improves the effective detection depth by more than twice compared to single pulse TFM. The proposed Canny operator second-order TGV denoising technique can comprehensively denoise the detection image.