Wave propagation in sandwich structure

by Sander Tavallaey, Shiva

Abstract (Summary)
An analytical model for wave propagation in a three-layered sandwich structure with different boundary conditions was developed. The sandwich material that was treated, consisted of a thick lightweight core, and two thin and stiff laminates. Both laminates and core were assumed to be homogeneous and isotropic. The governing equations were derived partly by applying the general field equations (2-D theory) to the core and, partly by utilizing the thin plate/ beam theory (1-D) to the laminates. The dispersion equation for the structure was derived and solved using the winding-integral technique. The boundary conditions across the thickness of the structure were then satisfied at a finite number of the points. The calculated natural frequencies were shown to converge with respect to the number of collocation points and included modes. Comparisons with alternative models, i.e. the Euler-Bernoulli, the Timoshenko, and a complete layered media model, were made. The latter comparison, concerned only the eigenvalues and eigenfunctions for the infinite structure. The first two models are shown to diverge, to a great extent, with the present theory while a good agreement is obtained between modal wave numbers calculated by the present theory and the complete layered media model, respectively. Moreover, measurements, using modal analysis, were carried out on a sandwich beam with two different boundary conditions, i.e., clamped-clamped and free-free. The results of the analytical model, as well as measurements, suggest that the boundary conditions have a considerable effect on the apparent bending stiffness of the sandwich beams. In other words, there is a great discrepancy between the natural frequencies for the sandwich beam with fixed and free ends, respectively. The agreement between the predicted and the measured results is found to be quite satisfactory. Furthermore, a restricted parameter study was carried out. The results of the parameter study indicate that the stiffness relation between laminates and core is of great importance as regards the dynamic behavior of the sandwich structure.
Bibliographical Information:


School:Kungliga Tekniska högskolan

School Location:Sweden

Source Type:Doctoral Dissertation

Keywords:Sandwich structure- wave propagation- dynamic behavior


Date of Publication:01/01/2001

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