Interaction Of Lamb Wave With Defects And Study Of High Accuracy Detection For Aluminum Plate

Aluminum plate is widely used in many fields. During the plate production, it is inevitable to generate various defects because of the limitation of processing technique. To eliminate those off-test products, it is necessary to detect the aluminum plate. Due to wonderful detection feature, electromagnetic ultrasonic guided wave detection technology is promising. But the detection device with electromagnetic ultrasonic guided wave cannot detect small defects like a through with a diameter of 1mm, which severely limits the usage of electromagnetic ultrasonic guided wave. Besides, the working points which are chosen to study the propagation characteristic are low frequency working points whose wavelength are too long to detect small defects. To solve the problems mentioned above, the propagation characteristic and the interaction with defects of high-frequency Lamb wave are studied in this paper.To solve the problem of computing three-dimensional(3-D) finite element(FE) models of high-frequency Lamb wave, a 3-D finite element model based on ABAQUS is proposed, after considering the progress of exciting ultrasonic with electromagnetic ultrasonic transducers(EMATs).To study the interaction of Lamb wave and defects, the theoretical basis of scattering parameter matrix is studied. The Lamb waves whose frequency-thick are 0.6MHz·mm and 7.824MHz·mm are chosen. The experiments showed that the scattering field is influenced by the shape of defects. And the acoustic energy is not only distributed in axis of transducer, but also has a strong distribution in other directions.According to the technique of coils and the boundary conditions of Lamb wave, the range of Lamb wave is decided and several working points are chosen. To study the feasibility of detecting a through-hole with a diameter of 1mm and a slot with a depth of 0.4mm in a 4mm thick aluminum plate, a proper working point was chosen according to the results of simulation and experiment. To improve the signal noise ratio(SNR), the tuned circuit was improved.An aluminum plate detection device has been developed. The experiments show that the detection device can detect a through-hole with a diameter of 1mm and a slot with a depth of 0.4mm in a 4mm thick aluminum plate, which satisfy the detection demands of GJB3384.In summary, a high-accuracy detecting method, based on electromagnetic acoustic Lamb wave, is studied in this paper. This method can provide a good foundation for aluminum plate detection with high accuracy.