Damage Identifation Of Metal Sheet Based On Lamb Waves Using Piezoelectric Array

Lamb wave of damage identification method due to its sensitivity to small defect inmetal thin plate-like structures,such as cracks,holes and delamination,So it has receiveda great deal of attention and has been an attractive topic of structural health monitoring(SHM).At present,there also existed some problems in the applications of the Lambwave based diagnosis method,including low signal-to-noise rate,weak damagesignals,low monitoring effective.By means of theoretical analysis,numerical simulationand experimental verification,some problems of structural health monitoring anddamage location based on piezoelectric array in thin plate are researched based on Lambwave propagation theory in this paper.The researches mainly focus on the followingaspects:By researching of Lamb wave propagation characteristics and derivation of thetheoretical modeling of Lamb wave in thin metal, some problems about multiple modalsand dispersion characteristics of Lamb wave are discussed based on the dispersion curveequation; By means of analysis the feasibility of using single mode, optimize theexcitation frequency, control the product of the thickness and the frequency,the A0mode is regarded as the focus of this paper research through the analysis of thecharacteristics of A0and S0mode. this paper focus on scattering wave and analyzes theamplitude attenuation and the time delay caused by damage, at the same time by meansof the time-frequency domain analysis method to extracted the direct wave of time delay,the detection of damage can be acquired by using piezoelectric multi-channeltechnology.The propagation of Lamb waves in thin plates is studied by finite element methodusing Comsol with a2-D and3-D model.Compared with theoreticalexpectation,analysis the single mode amplitude under the optimal frequency. Based onthe narrow band of five cycles excitation signal selected, numerical simulation about themulti-channel piezoelectric array damage location is accomplished based on singlemode by arranging piezoelectric array.A synchronous data acquisition system of four-channel response signals based onLabview virtual instrument is constructed, PZT can be used as actuator or sensor in turnthrough multi-channel switch.The original response signal can be filtered and denoised by the signal processing method, the time of flight(TOF)of the response signal isextracted based on the single fixed scale continuous wavelet transform(CWT).Throughartificial simulation drilling damage on aluminum plate, the effectiveness of thepiezoelectric array damage identification methods is verified,the positioning accuracy issimilar with the numerical simulation.Finally the passive monitoring platform isbuilted,the performance of aluminium plate was studied by impact of the steel ball andthe location of impact source is positioned by the method of four-point arc positioning.