Based on multi-layer gradient threshold CFRP plates defects detection system

Carbon fiber reinforced plastic (CFRP) is widely used in fields such as aircraft and construction due to its advantages of light weight, high hardness, wear and corrosion resistance. To quantitatively detect internal defects in CFRP panels, a THz reflective defect detection system was built. A defect analysis algorithm based on multi-layer gradient threshold is proposed. Based on the manufacturing process of CFRP, a THz wave echo function model for multi-layer CFRP structures was derived. A CFRP plate containing debonding defects and crack defects was trial produced, to obtain its THz time-domain spectrum. The experiment completed the reconstruction of THz two-dimensional images of CFRP plates. The test results show that three different depths of test data can be detected, and the calculated diameters of the debonding defect areas are 9.12, 9.86, and 9.93 mm, respectively, with a relative error mean of 3.63%. Crack defects can also be effectively identified, but the quality of their test images will decrease with increasing pre-embedded depth. The linearity between defect depth and testing frequency is 0.98, which verifies the possibility of quantitative calculation. The test results of power spectral density and defect depth show that it has good uniformity.