Damage Detection Technology For Composite Material Based On Lamb Wave And Time-frequency Domain Analysis

Because of the excellent performance, composite material is used in various domains, and its damage inspecting becomes an austere challenge. Development of the damage detection becomes a key technology for the extent of the application of composite material. The paper proposed a method that combining the Lamb wave with time-frequency domain analysis technology for the damage detection of composite materials.At first, the multiple modes and dispersion nature of ultrasonic Lamb wave were theoretically investigated with the dispersion equations and its numerical solution. That provided a theoretical base for the optimal design of the form of excitation signal. Furthermore, optimization of excition signal was performed experimentially with the excition function form and four parameters: the transport mode, the center frequency, the amplitude and the number of wave.Secondly, STFT, Wavelet and HHT, the three Time-frequency representatio ns(TFRs) were introduced, including not only the theoretical analyses but the p rogramme in Matlab.In which, HHT is the most important method,including ho w to compute the instantaneous frequency , how to process the EMD and how to dispose Hilbert spectrum, after that bring forward the resolvent to the probl ems during the processing of EMD.Finally, tests and analyse about damage detection were processed, including judgement the occurring of damage, judgement the sensitivity of different damage form and different damage position, the elementary damage orientation and estimate the degree of damage,. The results verified that the TFRs of signal have difference results between the health and damage structure;the sensitivity is different to different damage form and damage position, so PZT's distributing is very important;damage orientation can come true by the ellipse method and TFRs, the mirror change of mirror damage do not lead the severe influence on composite material. All the results verify HHT is a more effective method comparing to the STFT and wavelet at the same time.