Study On The Dispersion Characteristics Of Ultrasonic Lamb Wave In The Plate Structure And The Development Of The Transducer

Storage tank is widely used in petrochemical enterprises.Because the tank bottom plate is influenced by the environment,the strength of the bottom plate of the tank is reduced,and even the perforation leakage is produced.Therefore,it is very necessary to accurately test the quality of the tank bottom plate and run safely and steadily.Ultrasonic Lamb wave is a form of ultrasonic guided wave,which is an effective method to detect the damage of plate structure.The ultrasonic Lamb wave is sensitive and economic to the defect of the plate material.In order to effectively utilize the ultrasonic Lamb wave to detect the structure of all kinds of tank bottom plate,in this paper,the dispersion curves of different material tank bottom plate are plotted and the dispersion characteristics are analyzed.The Lamb wave transducer is designed,and its basic properties are tested.The main research contents of this paper are as follows:1)Firstly,the development status of Lamb wave detection technology at home and abroad was reviewed.The main products of the domestic and foreign ultrasonic testing instruments were listed,and the functions and characteristics of the products were introduced.2)According to the Rayleigh-Lamb equation,Lamb wave dispersion curves for infinite plate is solved.The phase velocity and group velocity curves of Lamb wave of tank bottom plate of different materials are plotted by Matlab software and the comparative analysis is carried out.By analyzing and comparing the dispersion characteristics of different materials,the mode and the frequency-thickness products range of each material in the actual test are selected.3)According to the characteristics of Lamb wave,the project finally chooses the oblique transducer.For the transducer,the piezoelectric crystal,the damping block,the oblique wedge and the sound absorbing material are selected respectively.Then,according to the frequency dispersion characteristics of the tested materials,the chip size and the angle of the oblique wedge are calculated.Finally,the designed transducer has been produced by the manufacturers.4)The equivalent impedance of the transducer,the incident point,the refraction angle(K value),the sensitivity margin and the resolution have been tested by Ultrasonic detector,high frequency signal generator,high-frequency millivoltmeter,test block and otherequipment.The DAC curve has been made.Test results show that the technical indicators meet the design requirements.