Research On High-resolution Small Damage Monitoring Based On High Frequency Lamb Wave Spectral Warping

Small damage monitoring with high-frequency Lamb waves is very important to the accurate evaluation of aircraft structural residual life,early warning of structural health states and the preventing the catastrophic structural failures caused by the severe damage growth in the late stage.However,in the practical small damage detection,besides the dispersion characteristic,the signal wavepackets can be also elongated and deformed by the amplitude-frequency response of high-frequency Lamb waves.This can seriously decrease the resolution and signal-to-Noise Ratio(SNR)of high-frequency Lamb wave diagnostic signals.As a result,the final small damage detection results would be badly affected.In the dissertation,to resolve the problem of dispersion characteristic and amplitude-frequency response influence in high-frequency Lamb wave small damage monitoring,high-frequency Lamb Wave Spectral Warped(LWSW)is mainly studied and applied for high-resolution quantified small damage imaging in the aircraft plate-like structures.The main contents and innovations are as follows:(1)Based on the established sensing model of high-frequency Lamb waves,the dispersion and amplitude-frequency response effects of high-frequency Lamb waves on the diagnostic signals are analyzed.The influences of Lamb wave frequencies on the small damage detection ability are also discussed.The results of analysis and discussion are validated by the numerical simulations and experiments.(2)The dispersion and amplitude-frequency response compensation theory of high-frequency LWSW is investigated.The fast realization of high-frequency LWSW is discussed.According to the problem that the travelling properties of high-frequency Lamb waves are hard to be accurately computed in theory during the practical high-frequency LWSW,the measuring methods of relative wavenumber curves and amplitude-frequency response curves of high-frequency Lamb waves are developed.The high-frequency LWSW with measured travelling properties is validated by the experiments on an aluminum plate and a carbon-fiber composite plate,respectively.(3)The high-resolution small damage imaging method with high-frequency LWSW,and the flaw information quantified extraction method based on high-frequency Lamb wave imaging are developed.Applying the developed methods,the high-resolution quantified imaging for the adjacent dual small holes and single hole growth in an aluminum plate is accomplished.