Noise reduction in the design of structural members made of layered polymer composites utilizing finite-damping-elements

Due to the large difference in damping ratios between fibre and viscoelastic resin, the damping ratio of CFRP varies with the mode of vibration. Using classical laminate theory, one needs three independent input-values in addition to the elastic properties to describe the damping behaviour of an unidirectional reinforced layer. A shear deformation theory requires two additional damping ratios corresponding to the transverse shear stresses. Based on the Whitney-Pagano [1] laminate theory, an energy-based method has been developed to determine the damping-ratios from Finite-Element calculations and measurement results. By this a full set of damping-ratios is determined, which is well suited for use as initial input for the developed Finite Elements. Using these values as input, the modal damping ratios of complex shell structures made of multilayer laminates can optimised through Finite-Element analysis for noise and vibration reduction purposes. In the present case the optimisation is done by changing the fibre orientations and using stiffness restrictions.