The Inspection Technology Of Composite Thin Plate With Air-Coupled Lamb Wave

Carbon fiber composite sheets can cause a certain degree of damage or defects during the manufacture,processing and use,which adversely affect the safety and stability of the system.It is necessary to use non-destructive testing methods for quality inspection to ensure the safety of production and use.In this paper,air coupling Lamb wave was used on carbon fiber composites testing.At the same time,the time-frequency analysis method was used to accurately identify and locate the defects,and achieve good detection results.The main contents of this paper are as follows:(1)The numerical solution of the dispersion equation was realized by computer programming using the dichotomy.The group velocity and phase velocity curves of the carbon fiber composite sheet were plotted and compared with the group velocity and phase velocity extracted by the simulation model.The results were basically the same.(2)The finite element method was used to simulate the air-coupled ultrasonic Lamb wave detection.It is verified that the A0 mode amplitude is much larger than the S0 mode amplitude under air-coupling conditions.The simulation studies on different defects and the interaction between guided waves and defects were carried out.The results show that the mode transition effect is related to the defect type when the A0 and S0 mode is reflected.The groove type defect reflection will produce obvious S0 mode guided wave,while the through hole defect reflection effect is not obvious.The self-built air-coupled ultrasonic testing system is used to detect the guided waves of carbon fiber composites with different defects.The experimental results show that the air-coupled Lamb wave has a good detection effect on the groove defect and the through hole defect which were basically consistent with the theoreticaland simulation results.(3)The matching pursuit algorithm is studied.According to the characteristics of air-coupled Lamb wave,the Chirplet atom is used to construct an over-complete dictionary library,which realizes the accurate reconstruction of the signal.The Wigner-Will time-frequency analysis method is used to process the experimental and simulation data,and the characteristic information of the signal is effectively extracted.The results show that the proposed method can effectively distinguish different modal scattering signals and realize the determination and localization of the defects,and achieved high positioning accuracy.