Noise Reduktion in the Design of Structural Members made of Layered Polymer Composites Utilizing Finite-Damping-Elements

Abstract

The dynamic behaviour of structures depends on stiffness, mass, geometry and damping. Due to the high difference in damping ratios of fibre and viscoelastic resin, the damping ratio of composites varies with the mode of vibration. For a unidirectional reinforced specimen, the damping for a torsional mode is much higher than for a bending mode in the fibre direction. There are well-known methods available in the literature to determine the modal damping ratios of composites. They are based either on energy balancing or on complex modulus. Using classical laminate theory, one needs three independent input-values in addition to the elastic properties to describe the damping behaviour of a unidirectional reinforced layer. A first order shear deformation theory for transversally isotropic material requires one additional damping ratio corresponding to the interlaminar shear stresses in (2-3)-direction. Based on the Whitney-Pagano laminate theory, an energy-based method has been developed to determine all four damping-ratios from Finite-Element calculations and measurement results. In that way a full set of damping-ratios is determined. Using these values as input, a Finite-Element tool to optimize the modal damping behaviour of complex shell structures made of multilayer laminate has been developed.