Research On Damage Detection For Composite Material Based On Lamb Wave And HHT Technology

Composite damage detection is an important research content of structural health monitoring. The paper proposed a method that combining the Lamb wave with time-frequency domain analysis technology for the damage detection of composite materials.Firstly, the multiple modes and dispersion nature of ultrasonic Lamb wave are investigated in theory. Furthermore, optimization of excitation signal is performed experimentally with the four parameters: the transport mode, the center frequency, the amplitude and the number of the wave's peak value.Secondly, HHT that is one of the Time-frequency representations (TFRs) is introduced in aspects of not only the theoretical analyses but also the programmer in Matlab, including how to compute the instantaneous frequency, how to process the EMD and how to dispose Hilbert spectrum, after that bring forward the resolve to the problems during the processing of EMD.Finally, Damage detection system for composite materials based on lamb wave active detection technique using HHT method is discussed in detail. Whether there is damage in composite material or not is determined by four methods: the damage detection method based on extreme value theory, the damage detection method based on ellipse technique, the damage detection method based on four points arch technique and the damage detection method based on nerve net. Different characteristic parameters fitting for different damage detection methods are extracted from the filtered sensors signal by HHT technology. At last, the location and the degree of damage in the composite material can be determined by using defferent damage detection methods.This study adopts active detection technique based on Lamb wave to monitor damage in composite materials. PZT ceramics are bonded on the surface of fiberglass-reinforced composite materials acting as both actuators and sensors to generate and collect Lamb wave. Characteristic parameters are extracted from the filtered sensors signal by HHT method. Using these parameters in different methods for damage detection, the location and the degree of damage in the composite material can be determined.