Effect of Non-Uniform Fibre Distribution along Thickness and Non-Uniform Ply Thicknesses on Frequencies of Symmetric Angle-Ply Laminates

Present study investigates the effect of the fibre volume ratios and the ply thicknesses on the fundamental frequencies and the frequency gaps of simply supported and symmetric angle-ply laminates. The elastic constants of the fibre reinforced composite are determined by using micromechanical relations. The laminate is defined as having three layers with different fibre volume fractions in the surface and middle layers. The thicknesses of the surface and middle layers are also taken as different to improve design efficiency in terms of using the reinforcements effectively. Thus, the problem parameters affecting the fundamental frequency and the frequency gaps are the fibre orientations, ratio of the thickness of the surface plies to total laminate thickness and the fibre contents of the layers. Numerical results identify the optimal values of the layer thickness ratios and the fibre orientations with respect to the fibre volume of outer layers and aspect ratios. It is observed that these problem parameters affect the fundamental frequency and the frequency gaps at varying degrees depending on the relative fibre volume fractions of the surface and the middle layers as well as on the relative layer thicknesses and the aspect ratios. Numerical results are given for carbon and glass fibre reinforced laminates to examine their differences with respect to various problem parameters.