Research On Defect Imaging Of Composite Plate Based On Air-coupled Lamb Wave

Air-coupled Lamb wave scanning imaging is a new detection technology for composite plate defects,which has the advantages of non-destructive testing and rapid visualization of defects.It provides an convenient method for quantitative analysis of the location,shape and damage of composite plate defects.Studying air-coupled Lamb wave defect imaging is beneficial to timely discovering composite plate damage and taking measures to reduce economic losses.For composite plate defect imaging,study on air-coupled Lamb wave scanning imaging is carried out in this paper,including air-coupled Lamb wave detection principle,finite element simulation of Lamb wave propagation characteristics,imaging algorithm and scanning experiment.The major research contents can be summarized as follows:(1)According to the transfer matrix method,the Lamb wave dispersion equation in the composite plate is analyzed.The Lamb wave dispersion curve is drawn by numerically solving the dispersion equation.The relationship between the incident angle of air-coupled transducers and the excitation mode of Lamb wave is studied,and the optimal incident angle of air-coupled transducer is determined.(2)The finite element simulation model of Lamb wave propagation in composite plate has been established.The variation of the amplitude of air-coupled Lamb wave received signal is studied,by adjusting the distance between the defects and the Lamb wave propagation path.The effects of different types of composite plate defects on the attenuation characteristics of air-coupled Lamb wave are analyzed.(3)The probabilistic damage algorithm in air-coupled Lamb wave scanning imaging is studied and the relationship between the defect damage probability and the Lamb wave signal difference coefficient is discussed.The selection basis of the eigenvalue is analyzed,and the calculation method of eigenvalues of Lamb wave signals based on discrete wavelet decomposition is obtained.An improved probability damage algorithm based on skewed energy distribution is proposed.The skewed energy distribution is used to replace the normal energy distribution in the traditional algorithm,which improves the recognition of defect edges.Some evaluation method of the defect reconstruction image are developed for evaluating the imaging effect of the imaging algorithm.(4)The experimental system of air-coupled Lamb wave scanning detection is built.The carbon fiber composite experimental plate with different types of defects are fabricated.The experimental scheme of air-coupled Lamb wave scanning detection is implemented,and the experimental results show agreement with the finite element model.The reconstructed images of composite plate defects are obtained by using the traditional algorithm and the improved algorithm respectively.According to the image evaluation index,the imaging quality of the two imaging algorithms is compared.The results show that the improved algorithm can effectively improve the contrast of the image while effectively reducing the defect imaging error.