Research On Impact Damage Localization Method Of Thin Metal Plates

As load-bearing structures,thin metal plates are widely used in engineering fields.When the thin metal plates are damaged by external impact or collision,the surface quality of the parts will be seriously threatened,and even catastrophic accidents will be caused.Nowadays,there are many health monitoring methods for metal sheet structures,among which piezoelectric monitoring technology is widely used.Based on the research of structural health monitoring,the signal characteristics,propagation characteristics,signal de-noising,time delay estimation and location algorithm are deeply studied through theoretical analysis,data simulation and experimental verification when impact damage occurs on metal sheet structural parts,and the paper has completed the design and experimental analysis of damage location on thin metal plates.The main contents are as follows:1?Firstly,the characteristics of Lamb generation and propagation in metal sheet parts are introduced.According to the signal characteristics generated by impact damage,the Lamb wave and S₀?A₀ modal components in the signal are determined,and the dispersion curves of each modal wave propagation in 3 mm sheet metal parts are drawn.Based on the multi-mode characteristics and dispersion curves,the following two damage localization schemes are determined.2?Aiming at the interference of white noise and mechanical noise in damage signal propagation,the de-noising technology of damage signal is mainly studied.In this paper,the wavelet packet transform(WPT),empirical mode decomposition(EMD),ensemble empirical mode decomposition(EEMD),variational mode decomposition(VMD)are introduced respectively,and the denoising algorithm of WPT-EEMD is proposed.In this method,the original signal is denoised by improved wavelet packet threshold,and the useful signal and noise are further subdivided by EEMD modal decomposition,the useful information and noise are further subdivided,and the signal component containing damage information is selected for reconstruction by using the energy ratio and correlation criteria between the modal component and the original signal,so as to achieve the purpose of noise reduction.The simulation results show that compared with other denoising methods,WPT-EEMD denoising signal has higher SNR and smaller distortion.Finally,combined with the delay superposition algorithm,the energy threshold detection of the denoising signals of WPT-EEMD is proposed to obtain the time-delay damage source localization scheme.The real experimental results show that the average error of damage source localization in this way is 2.55cm in the range of 50cm×50cm steel plate.3?In view of the multi-mode characteristics of damage signal propagation,the delay estimation method of damage signal is mainly studied.In this paper,an optimal time difference algorithm based on VMD is proposed by referring to the time delay estimation methods such as cross-correlation and short-time energy threshold.In the case of low SNR,the VMD was used to obtain the modal components,and the effective information of the damage signal and the noise signal were placed in different IMF components.Then,the time delay was estimated by cross-correlation band by band,and the frequency band with the least fluctuation and the least standard deviation was selected from the frequency band for location analysis.The simulation results show that with the reduction of SNR,the optimal time difference algorithm has more stable performance and smaller delay error than other methods.Finally,combined with the delay superposition algorithm,a damage source localization scheme based on the VMD decomposition of the damage signals and the optimal time difference estimation is proposed.The real experimental results show that within the range of 50cm×50cm steel plate,the lateral and vertical coordinate errors of the proposed scheme are within 9.4%and 3.4%.4?In order to meet the practical needs,the damage location test system of steel plate is designed and built,which mainly includes important modules such as signal conditioning,data acquisition and Lab VIEW data processing,etc.,and the damage location test experiment and result analysis are carried out on the damage location test system.