Influence of bending-twisting and extension-bending coupling on damping of laminated composites

Abstract

This paper describes a three-dimensional finite element-strain energy method for characterizing vibration coupling effects on damping of laminated composites. The analysis was performed on graphite-epoxy laminated cantilever beams in two stacking sequences: (i) 12-ply symmetric laminates [12(θ)], and (ii) 12-ply antisymmetric laminates [6(θ)/6(−θ)]. Thus, the effects of vibration coupling between bending and twisting in symmetric laminates, and between extension and bending in antisymmetric laminates on damping were studied. A modal strain energy method was applied in a finite-element formulation to solve for the natural frequencies, mode shapes and energy dissipation of the laminates. The coupling energy dissipation was separated from the non-coupling energy dissipation by the decomposition of the total energy dissipation in order to study its contribution to damping. The results of the first three modes, which includes two flexural modes and one torsional mode, are presented. The resulting torsional damping data are generally higher than the flexural damping data. The coupling effects on damping in flexural modes were found to be more significant than those in torsional modes, and such effects appear to be dependent upon the fibre angle and the vibration mode of interest. The coupling effects appear to increase damping in flexural modes, and were found to be maximized at a fibre angle around 30°. The non-coupling energy dissipation was found to be more dominant for the flexural modes at a fibre angle of 90°, and it appears to be more dominant at a fibre angle of 0° in torsional modes, however.