Common lightweight materials are often prone to vibrations, as loss factors of isotropic materials generally decrease with higher specific Young’s moduli. This may reduce the comfort for the user but also increases the fatigue of the material due to unwanted vibrations.
Fiber-metal-elastomer laminates used in this study consist of alternating layers of carbon fibre reinforced plastics, elastomer layers and aluminium sheets. These laminates offer great potential in lightweight structures with adjustable damping properties, while also showing the benefits of conventional fiber metal laminates, with their damage tolerant behaviour. The material behavior is strongly influenced by the viscoelastic properties of the applied elastomer, which damp by the principle of constrained layer damping when the laminate is excited. More specifically, large shear strains are induced in the viscoelastic elastomer layers when the laminates are deformed under bending loads. The characterization in this study is done by modal analysis according to ASTM E756-05, with a cantilever beam under bending vibrations. Different laminate set-ups are investigated to show the influence of layup, fiber orientation, elastomer moduli and elastomer thickness on the modal parameters. Therefore, frequency response functions are recorded and modal loss factors of the natural frequencies are extracted by using the half-power bandwidth method. The results are compared with an analytical model based on the so-called Ross-Kerwin-Ungar-equations (RKU) and numerical studies by using finite element simulations. The different models are compared and their limitations are discussed. In contrast to the general trend of decreasing damping values with higher specific Young’s moduli for isotropic materials, for the studied laminates an increased constraining layer stiffness can also increase the damping due to higher shear strains in the elastomer layers.