Free vibration study of sandwich plates using a family of novel shear deformable dynamic stiffness elements: limitations and comparison with the finite element solutions

In this paper, the dynamic stiffness matrix of a completely free rectangular multi-layer plate element based on Reddy's higher-order shear deformation theory is derived. The reduction of the proposed model to the first-order shear deformation theory-based formulation is presented. Three coupled Euler-Lagrange equations of motion have been transformed into two uncoupled equations introducing a boundary layer function. The proposed model enables free transverse vibration analysis of rectangular multi-layer plates with (transversely) isotropic layers having arbitrary combinations of boundary conditions. The influence of transverse shear deformation is discussed along with the applicability of two shear deformable dynamic stiffness elements. Moreover, the influence of the boundary conditions on the free vibration characteristics of sandwich panels has been discussed. The natural frequencies obtained using different dynamic stiffness multi-layer plate elements have been validated against the solutions from the commercial software Abaqus and the previously verified numerical solutions using layered finite elements. The limitations of the model regarding the differences between material properties of the face and core layers within a sandwich plate are highlighted. The influence of face-to-core thickness ratio on natural frequencies is illustrated, while a variety of new results is provided as a benchmark for future investigations