Research On Lamb Wave Time Reversal Haracteristics In Structural Damage Etection

Ultrasonic Lamb waves has the advantages of propagation attenuation small, widedetection range,sensitive to small defects in plate-like structures, such as crack, andhaving been applied for a long time in the field of non-destructive testing,technology isrelatively mature;So Lamb wave based active damage monitoring method is widelyused in Structural Health Monitoring (SHM). Damage scattering signal was regarded asimportant information and widely used for damage monitoring, locating andidentification technologies in Lamb wave based structural health monitoring. However,the analysis and interpretation of Lamb waves are complicated due to their dispersiveand multimodal natures.Because of the complicated structures, especially the composite,it is difficult to analyze the structural character and its damage, its application inengineering had been greatly limited. Main contents as follows:Firstly,this paper introduces the theory of Lamb wave dispersion equation analysisprocess and principle of Lamb wave detection;focuses on the dispersion characteristicsof Lamb wave propagation and multi-mode dispersion characteristics. On the basis ofLamb wave propagation analysis,on the basic principle of time reversal method andLamb wave time reversal process made the theoretical analysis.Time reversal timereversal focusing performance evaluation indexes are put forward by the analysis ofthese problems to understand the characteristics of Lamb wave.Secondly,finite element model of Lamb wave propagation characteristics wasestablished by applying the finite element analysis software ABAQUS;Lamb wavepropagation characteristics of plate structures was carried on the detailed study;Then,the correctness of the theory and the related parameters settings used in theprocess of model was verified by numerical simulation.By numerical simulation vividlyreflect the different condition of the Lamb wave propagation in plates of the finiteelement model,it would greatly help to identify direct wave,reflected wave and theboundary damage reflected wave，etc.Theoretical analysis for the method of timereversal processing to extract the damage scattering signal process,and put forwardbased on the time reversal method without baseline Lamb wave damage monitoringmethod; according to the response signal when the focus of each wave packet in therelation between each position and a moment, corresponding time-frequency analysismethod is applied to extract the information related to the damage of damage location, this method is verified by numerical simulation to the damage location and under thecondition of no benchmark.Finally, using the method of time reversal when the structure response signalreconstruction,Lamb wave time reversal focusing performance were investigated inisotropic aluminium plate and the anisotropy of composite laminated plate structure,and making use of the time reversal focusing performance evaluation index analysis indetecting the defect board of Lamb wave focusing performance. The results show thatthe method can determine the occurrence of structural damage, and the extent ofstructural damage identification.