Passive Damping of Spacecraft Sandwich Panels

Abstract

The damping ratio of a structural system has large influence on the structural response and, thus, on the stress. If the damping factor increases the stress decreases drastically, which is necessary for the operation of future reusable launch vehicles as well as to relax dynamical requirements for conventional spacecraft. In the frame of the here described activities a system of passive friction damping elements has been designed which is placed between the face sheets of large spacecraft relevant composite sandwich panels. Presently, corresponding demonstrators are in manufacturing process. Dynamical and thermal test will be performed in near future. In parallel investigations regarding the mass saving potential as well as the life span extension due to increased damping are performed. The influence on the life span will be clarified by means of S-N-curves [MIL 5H], where the critical stress (crack) is depicted versus the load cycles (= life span in case of continuous vibrating structures). Depending upon the material as well as upon the structure there are empirical results showing a decreasing boundary stress with increasing number of load cycles. Instead of steel which shows a horizontal tangent of critical stress for load cycles composite materials have a steady decreasing S-N-curve. Thus, the life span of those materials are directly affected by the number of load cycles in combination with the vibration amplitude. The degree of life span extension depends strongly upon the material, the structure and the load cases and can be quantified for individual cases only. In any case the impact of long term application, wear and temperature impact have to be considered, too.