Technological background of viscoelastic damping for space applications

One of the most important themes of the structural analysis is the vibration reduction. At present there are different devices which can be used to improve structural damping based on the use of active or passive dampers. Many studies on reduction and/or suppression of vibrations in LFSS and SFSS (Large/Small Flexible Space Structure) have been carried out in last decades. In this work a special smart structure will be proposed for the vibration suppression of composite panels. In particular the viscoelastic properties of a composite panel-structure will be changed opportunely in order to modify the elastic damping characteristics of the material which constitutes the panel. It is well known that these viscoelastic materials are characterized by the complex modulus. These moduli depend on two main parameters, the temperature T that material operates in and more interesting on the magnitude of the oscillating frequency ω the composite structure can be subjected at under a dynamic environment. In this study the determination of the complex modulus and the effect of above mentioned parameters on a composite panel for space applications are investigated. The sandwich panel here is made up of two carbon fibre skins and a polymeric core in analyzed. This core is constituted by an epoxy adhesive containing some silver conducting stripes opportunely distributed inside it. By applying a voltage to the ends of the silver stripes it is possible to produce a current which in turn generates heating, the epoxy resin and carbon skins, by Joule effect. The temperature acts on chemical bonds by increasing the molecular mobility and producing relaxation of the material which in turns varies the mechanical and thermal characteristics of the core and the resin matrix reducing the storage modulus, increasing the loss modulus and the loss factor. It's worth to note that this loss factor is directly related to the damping ratio of the panel. The viscoelastic parameters of the adhesive and of the carbon fibre will be experimentally estimated and evaluated using DMTA (Dynamic Mechanical and Thermal Analysis) Mathematical models and finite element simulations of this Heated Damping Sandwich Panel (HDSP) will be presented in order to study the coupling related to the thermal and structural interaction between the core, the skins and the silver electrical conductors. The stripe's cross section, the geometrical in-plane disposition and the electrical feeding will be found in order to have the minimum transitory time or the minimum necessary power for vibration suppression.