Damage Detection Research For Aluminum Alloy Structure Based On Time-frequency Analysis Of Lamb Wave Signal

As an effective real-time online detection method, structural health monitoring technology based on Lamb wave has become a hot spot at home and abroad in the recent decade. With the analysis of the data sent by the sensor embedded or attached in the structure under test, the technology can monitor the overall situation of the structure in real time, discover internal damage of the structure, identify and locate the damage. Structural health monitoring has a wide application prospect in areas such as aerospace, large civil structure. Combined with time-frequency analysis technology, the theory of Lamb waves in thin plate is studied for the damage detection on aluminum-alloy sheet. Main content of this paper is as follows:First of all, the propagation characteristic of Lamb wave is theoretically studied, the calculation of dispersion equation is solved through the numerical method, and dispersive curves and vibration amplitude of Lamb wave are drawn out,which provides theoretical basis for effective utilization of Lamb waves to detect structural damage. Based on above and combined with experiments, the optimizing analysis of Lamb wave excitation signal is performed through several aspects: the center frequency, the number of the wave’s peak, incentive form of the wave and so on.Secondly, the overall design of structure health monitoring system is introduced, including hardware composition of system and part of the software implementation. In view of the limitations of time domain analysis on the Lamb wave signals, HHT and wavelet packet decomposition are introduced. Combined with frequency-domain analysis, these signal processing techniques are used to extract damage characteristic information in the signal. Signal preprocessing and wavelet multi-scale decomposition are used to reduce the noise in the detected signal. The effectiveness of HHT and wavelet packet decomposition technique to deal with the detection signal is further demonstrated through the example analysis.Finally, we set up experimental platform of structural damage detection based on Lamb wave, in order to identify the damage for aluminum alloy structure and study preliminarily damage location. With 1 millimeter thick 7050 aluminum-alloy plate as detection object, we receive Lamb wave signals propagating in plate structure which is intact or with the crack damage and aperture defects. The energy of the fundamental and second harmonic components is extracted by fast Fourier transform to identify the existence of damage in the experiment. As the characteristic parameter characterizing damage, energy peak of the signal is extracted with HHT to estimate the extent of damage. Combined with ellipse positioning principle, HHT and wavelet packet decomposition technique are used to obtain the arrival time of energy peak of received signal and realize preliminary location of damage in aluminum-alloy structure. Experimental analysis results show that damage detection method used can identify damage and determine the approximate location of damage, obvious experiment results have been achieved.