Study On Damage Imaging Method Using Global Phased Array Beamforming And Local Time-reversal Based On Lamb Wave

Ultrasonic Lamb wave has features of far propagation capability,low energy attenuation and sensitive to small damage.It is widely used in the field of structural health monitoring(SHM)such as aerospace,unclear power plant,shipbuiding and automobile.However,there are some affects on the accuracy of the damage imaging positioning in the structure due to the inherent dispersion and mult-modal characteristics of Lamb wave.Therefore,the research on damage imaging method based on Lamb wave precise localization has become an overriding concern in the field of SHM.In this dissertation,ultrasonic Lamb wave method is used to image and locate the damage in aluminum thin plate,the propagation characteristics of Lamb wave in the plate structure are analyzed theoretically,and the improved linear mapping dispersion compensation method is proposed.Lamb wave structure response signal is processed by wavelet time-frequency distribution and moving time window function method.Then the existence area of damage in the aluminum plate is globally and quickly located based on phased array sum-delay imaging method using Lamb wave.Secondly,the localized damage area is used as the target area,and the local damage is analyzed accurately based on time reversal imaging method in frequency-wavenumber(f-k)domain.The effectiveness of the damage detection method proposed in this paper is verified by comparing the two aspects of the numerical simulation and experiment to the results of the Lamb wave detection of the damage results of the aluminum plate,which provides a theoretical guidance for the actual damage detection of the engineering structure.The specific research work of this dissertation is as follows:Firstly,the background and significance of the damage detection method based on ultrasonic Lamb wave in the field of SHM are introduced.The research progress of Lamb wave in dispersion compensation is reviewed.By studying the basic theory of Lamb wave,the propagation characteristics of the Lamb wave in the plate are clarified.On this basis,signal processing methods used in this research work are discussed and studied.Secondly,aiming at the problems such as dependence on theoretical wavenumber curve,material parameters and calculation complexity in traditional linear mapping dispersion compensation method,a linear mapping method based on group delay is proposed in this paper.The ridges are extracted by analyzing the Wigner-Ville-time-frequency-distribution of the signals,and the estimation of the mapping parameters is completed.And a 2D non-destructive model was built using COMSOL to study the removal of Lamb wave dispersion.Numerical simulation results verify the effectiveness of the proposed method.Compared with the traditional method,the method does not depend on the material property and the theoretical wavenumber curve,and the calculation is simple,which extends the application range of the linear mapping method.Finally,the principle of Lamb wave phased array beamforming and damage imaging based on delay-sum and time reversal imaging in frequency-wavenumber domain based on Mindlin plate theory are analyzed and studied.The 3D damage model was established by using COMSOL software,and the damage of aluminum plate was accurately located by extracting the damage wave field data based on the imaging method in this paper.In order to verify the results of the numerical simulation,a PZT-SLDV hybrid scanning detection system was built in the experiment.The system includes a piezoelectric transducer(PZT)for generating guided waves and a non-contact scanning laser Doppler vibrometer(SLDV)for acquiring guided wave data.Through the processing of experimental data,firstly,the location of the damage in the aluminum plate was quickly and globally located by the Lamb wave phased array beamforming and damage imaging method,then an accurate imaging of the local damage was achieved based on the time-reversal imaging method in the damage area,and complete the location process of the damage from the global to the local.The comparison between numerical simulation and experimental results shows that the proposed imaging method can identify not only the damage location,but also the size and shape of the damage.