Structural-Acoustic Optimization of Sandwich Panels

by Wennhage, Per

With the introduction of more lightweight vehicle structures for railway cars, a great deal of interest is focused on the question of airborne sound reduction, since lightweight structures have a reputation of poor sound insulation properties. Although the high damping of sandwich materials is often pointed out along with the other bene ts of using such materials, the sound reduction capabilities are more strongly in uenced by the geometry and elastic properties of the constituents than by damping. As a result of this, a sandwich panel can be lightweight and designed to carry high mechanical loads, but be really poor when it comes to attenuation of air-borne sound. This thesis deals with the design of sandwich panels with minimum weight under simultaneous sti ness, strength, and acoustic constraints. The acoustic constraints are de ned as a required sound reduction index for air-borne sound. A relatively well documented area of sandwich research is the mechanical behavior of sandwich plates under various loads. Nevertheless a part of the present work is an evaluation of a test-setup which can be used to verify research work regarding sti ness or failure modes of sandwich panels. The material damping and elastic modulus of a certain type of solid foam core is investigated in order to use the core density as a design parameter. Face materials are usually not used as design parameters, since there is a limited selection of materials to choose from, and the choice is often given by factors which are not a part of the detailed design of the sandwich constituents. The acoustic model of sandwich panels are coupled to a weight optimization of sandwich structures. In this optimization, the sound reduction index of various panels in the structure is used as constraints. It is shown that it is possible to use acoustic models as constraints in the optimization of large sandwich structures. The acoustic theories for sound reduction of sandwich panels and the weight optimization under acoustic constraints are veri ed experimentally through full scale tests. The sound reduction index of two sandwich panels, one of which was optimized for minimum weight, are measured and the agreement between theory and experiments is good. The conclusion is that a lightweight load carrying sandwich structure with high enough sound reduction index can be designed using optimization with mechanical and acoustic constraints.