Research On The Propagational Characteristics Of Lamb Waves In Structures

Choosing narrowband Lamb waves as the research objects, the dispersive curves of Lamb waves used in active structural health monitoring were mainly discussed in this thesis.Firstly,the modeling methods of Lamb waves existing were compared in this paper. According to the purpose of the research in this paper, 3D elastic theory was chosen. The propagational characteristics of Lamb waves in isotropic and antisotropic materials were modeled and the dispersive curves of Lamb waves in an aluminum plate and a carbon fiber composite lamina were calculated separately through the given parameters of certain plate. The phase and group velocities of Lamb waves in the aluminum plate related to the frequency and the thickness of the plate because of the material characters. However, for the carbon fiber composite lamina, the situation was of difference, in which the velocities were with regarded to the frequency and thickness as well as the propagational direction and the fiber orientation. Combined with the transfer matrix method, the dispersive curves of Lamb waves in a composite laminate could be got.Secondly,Lamb waves were experimental discussed in this paper, the Gabor wavelet function was used to compute the wavelet transform coefficients of Lamb wave signals in order to obtain the time and the phase angle delay of Lamb waves'propagation. Based on these processes, the experimental dispersive curves were illustrated at last, which proved the theory curves correct and was appropriate for other applications.This research is important and will be useful in structural health monitoring.