Modal Damping Behavior of CFRP-Structures

The dynamic behaviour of structures depends on stiffness, mass, geometry and damping. Due to the high difference in damping ratios between fibre and viscoelastic resin, the damping ratio of composites 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 interlaminar shear stresses. Based on the Whitney-Pagano laminate theory, an energy-based method has been developed to determine the damping-ratios from Finite-Element calculations and measurement results. By this means 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 for further calculations, the modal damping behaviour of complex shell structures made of multilayer laminates becomes predictable through Finite-Element analysis. The theory described in this paper has been completely integrated into the B2000 environment.