In this paper, free vibration characteristics of laminated composite plates are investigated. A model is developed for a composite layer based on the consideration of non-linear terms in von-Karman's non-linear deformation theory. The governing partial equation of motion is reduced to an ordinary non-linear equation and then solved using LIM method. The variation of frequency ratio of the Isotropic and composite plates is brought out considering parameters such as aspect ratio, fiber arrangements (orientation), number of layers, and modal ratios. Laminated composite plates, due to their high specific strength and stiffness have been increasingly used in a wide range of aerospace, mechanical, and civil applications. By tailoring the sequence of the stacks and the thickness of the layers, composite laminates' characteristics can be matched to the structural requirements with no difficulty. To use composite laminates efficiently, an accurate knowledge of vibration characteristics is essential. Vibration not only creates excessive noise and wastes energy but also may result in catastrophic failures. These phenomena, when the system operates around its natural frequencies, would be even more disastrous.
Key wordsMany publications have dealt with the linear vibrations of laminated composites. In these cases, the equation of motion is obtained easily and then by a reduction into a generalized eigenvalue problem, frequencies and mode shapes are determined. However, in many working conditions, plates are subjected to large amplitudes, so a nonlinear frequency analysis is required as a result. Obtaining an exact solution for the nonlinear free vibration of composite plates is very difficult due to the complexity of the equation of motion. The first approximate solution developed by Chu and Herman[1] in 1956, was the start point for so many other numerical methods introduced in the following years such as the finite element method (FEM) [2], the discrete singular convolution method (DSC), the strip element method, and the Ritz methods [3].
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