Baseline-free Lamb Wave Damage Monitoring Technology Based On Time Reversal Process

Lamb wave based active damage monitoring method is widely used due to its sensitivity tosmall defects in plate-like structures. Damage scattering signal was regarded as importantinformation and widely used for damage monitoring, locating and identification technologies inLamb wave based structural health monitoring. However, traditional damage scattering signalscollection based on baseline and difference process had poor practicality in applications. Timereversal focalization of Lamb wave and probability-based damage imaging method are adopted inthis paper to focus on baseline-free Lamb wave damage monitoring methodology.Firstly, the research about Lamb wave based structural damage monitoring and its problemswere introduced, and direction of research was confirmed. Lamb wave propagation characteristicswas analyzed based on its dispersion equation. Lamb wave actuating and sensing models usingpiezoelectric elements were discussed. After that, the principle of Lamb wave time reversalprocess was analyzed.Secondly, time reversal theory based baseline-free Lamb wave damage monitoring methodwas proposed. Method and process for getting damage scattering signals from time reversalfocalized Lamb waves were analyzed theoretically. Signal processing technologies used to obtainthe time information of damage were introduced, including wavelet transform, Hilbert transformand cross-correlation function. The damage locating and monitoring were realized using theellipse equations and intuitionistic probability-based damage imaging method which could reduceinfluence of noises on the monitoring results.Thirdly, both single and multi-damage models were analyzed to put forward theimplementation procedure of the proposed baseline-free damage monitoring method and validateits accuracy and practicability experimentally.The experimental results showed that the method can identify and locate the damage justusing the current structure responses without the dependence of any baseline or reference signals.It indicated that the proposed method could improve the practicality and stability of Lamb wavehealth monitoring technology with high accuracy and precision. It was meaningful for theapplications of structural health monitoring.Finally, the existed problems in the research and further work were also presented.