Extraction Of Lamb Wave Dispersion Curves By Using The Conventional Finite Element Method

The Lamb wave method is one of the most common non-destructive methods in the engineeringfield. To ensure that the generated Lamb waves can be received in good conditions after long distancepropagation in materials, the waves should be efficiently transmitted. In addition, the Lamb wavesmay change their modes when the structure is damaged. This chracteristic of Lamb waves brings extradifficulty in signal processing and analysis. Therefore, extracting reliable dispersion curves of Lambwaves quickly is very important in the damage detection by the Lamb wave based method. In thisthesis, conventional finite element method is used in the extraction of Lamb dipersion curves. Firstly,the basic theory and process of the use of finite element method are introduced. In this work,structures should be assimilated to a set of identical periodic elements or cells. Then, the finiteelement mehod is used in the extraction of Lamb dipersion curves of isotropic plate and tube. Theresults for the plate are almost the same as those directly obtained by numerical simulations. For thetube, both3-D model and2-D axisymmetric model are tried to extract the dispersion curve.Numerical results indicate that the2D model can simplify the extraction process greatly. Then thestandard finite element method is used to extract the dispersion curves for composite structures. Theresults of a composite palte are compared well with thosed obtained from the Mindlin plate theory andsimilar trends and numbers are obtained. Due to the complex modes existing in the composite tube, itsdispersion curves are not well drawed by the conventional finite element method and need researchfurthe.Finally, the free vibration of rhombic plates with free edges is analyzised by the standard finiteelement codes, the results match well with the data obtained by the differential quadrature method inmost cases.