Frequency maximization of laminated sandwich plates under general boundary conditions using layerwise optimization method with refined zigzag theory

The present paper extends the layerwise optimization (LO) procedure to the maximization problem of the fundamental frequencies of sandwich plates with fibrous composites and low stiffness core layers. Frequencies are calculated by the Ritz method based on a refined zigzag theory (RZT). Polynomial functions which satisfy at least geometrical boundary conditions with boundary indexes are employed as displacement functions, and they enable satisfying arbitrary sets of boundary conditions for rectangular plates. Results of the experimental modal analysis validate the accuracy of the present calculations, and a comparison with results of the classical laminated theory (CLPT) and the first order share deformation theory (FSDT) supports the effectiveness of the present method. Optimized results are compared with other typical sets of lay-up configurations and this shows the LO method as suitable means to the optimization problem for sandwich plates.