FREE-VIBRATION ANALYSIS OF COMPOSITE BEAMS

Methods for predicting the natural frequencies and mode shapes of composite beams are presented. The sectional elastic constants are determined from two qualitatively different methods: simple analytical methods in which the stiffnesses are given in closed form and a detailed cross-sectional finite element method. The equations of motion are also solved in two ways: by an essentially exact integration method and by a mixed finite element method. All the methods are validated for the types of problems considered by comparison with previously published experimental data and numerical results. Predicted elastic constants based on the methods considered are presented, and differences between the results are discussed. Numerical results are also presented showing the effects of these differences on the predicted natural frequencies. It is shown that predicted free-vibration characteristics of composite beams can be sensitive to the assumptions used in determining the stiffnesses. Finally, the influence of ply layup on the natural frequencies and mode shapes is studied for thin-walled beams with circular cross sections.