Research Of Metal Plate Damage Detection Based On Lamb Wave Frequency Tuning And Phased Array

Thin plate-like structures?aircraft shell,industrial containers,etc.?is one of the most common forms of structures in the engineering application,but due to the internal defects caused by improper operation in the manufacturing process,the impact of the external load and the environment erosion during the working process.All these will have a harmful effect on production safety and the national economy.So,the research of nondestructive testing technology on plate-like structures has important practical significance.This paper aims at typical damage identification of plate-like structure,S₀ modal of ultrasonic Lamb wave was applied to study linear phased array damage detection,and the research work includes:Firstly,the basic theory of ultrasonic Lamb wave was derived,and the transmission characteristics of the ultrasonic Lamb wave were analyzed.The ultrasonic Lamb wave dispersion effect and multiple modal characteristics were studied,and the ultrasonic Lamb wave dispersion curves were also obtained.The coupling mechanism between piezoelectric sensor and plate structure was studied to stimulate ultrasonic Lamb wave.By using the theory of frequency tuning,the relationship between the amplitude distribution of each ultrasonic Lamb wave mode and excitation frequency was obtained.By numerical modal and the experiment test validation,selection basis and selection method of S₀ mode with lower ultrasonic Lamb wave dispersion effect were established.Secondly,based on the fast propagation speed,long propagation distance and small energy attenuation of ultrasonic Lamb wave,the adaptable one-dimensional linear phased array were researched,also we explored the influence of linear array parameters on linear array spatial orientation?element number,array type,the array spacing and element size,etc.?and designed the best linear phased array structural parameters to enhance main lobe acoustic beam energy and to curb beam side lobe and the grating lobe,which improved the accuracy of damage detection and phased array imaging quality.The exciting principle of phased array and the calculation of delay are deduced.The detection and imaging principle of ultrasonic phased array were also introduced and explained.A linear phased array point-by-point focusing scanning damage imaging algorithm based on ultrasonic Lamb wave is established.Finally,by employing the COMSOL Multiphysics software,we set up a numerical simulation model and located and imaged the preset damage to verify thevalidity of the point-by-point scanning damage imaging algorithm.Based on the research results of numerical simulation,an experimental test platform was built.By uniting one-dimensional linear phased array and ultrasonic Lamb wave frequency tuning technology,we detected damages of different sizes and locations of thin aluminum plate,and located and imaged the preset damage.Comparing the results of experiments with the results of numerical simulation,the difference between experiment and simulation modal was summarized and the sources of error were investigated.