This paper deals with the nonlinear free vibration analysis of in-plane bi-directional functionally graded (IBFG) rectangular plate with porosities which are resting on Winkler–Pasternak elastic foundations. The material properties of the IBFG plate are assumed to be graded along the length and width of the plate according to the power-law distribution, as well as, even and uneven types are taken into account for porosity distributions. Equations of motion are developed by means of Hamilton’s principle and von Karman nonlinearity strain–displacement relations based on classical plate theory (CPT). Afterward, the time-dependent nonlinear equations are derived by applying the Galerkin procedure. The nonlinear frequency is determined by using modified Poincare–Lindstedt method (MPLM). Numerical results are obtained in tabular and graphical form to examine the effects of some system key parameters such as porosity coefficients, distribution patterns, gradient indices, elastic foundation coefficients, aspect ratio and vibration amplitude on the nonlinear frequency of the porous IBFG plate. To validate the analysis, the results of this paper have been compared to the published data and good agreements have been found.

This research aims to design, manufacture, and determine the vibration characteristics of a composite sandwich panel with lattice cores. For this purpose, first, a glass fiber sandwich panel with lattice truss core has been fabricated in the laboratory. In this part, the vacuum-assisted resin transfer molding method has been used to achieve laminates without any porosity. Afterward, the modal tests have been performed to obtain the natural frequencies, shape modes, damping ratio, and frequency responses of the sandwich panel. In addition, a finite element analysis has been developed to calculate the natural frequencies, damping ratio, and mode shapes of the composite sandwich panel. Then the experimental data have been compared to numerical simulation, and good agreement has been found.