Vibration and sound radiation of sandwich beams with honeycomb truss core

The vibrations of and the sound radiation from sandwich beams with truss core are analyzed. The structure of the core is composed of a sequence of identical unit cells repeating along the beam length and across the core thickness. Each cell is composed of beam elements assembled to form a frame structure. Layouts with the typical honeycomb pattern arranged through the thickness of the core are here considered. This design represents an alternative with respect to the traditional application of honeycombs in sandwich construction. The proposed configuration provides sandwich beams with interesting structural as well as acoustic characteristics. A finite element model is developed to evaluate the structural and the acoustic behavior of the considered class of sandwich beams. The model is formulated by employing dynamic shape functions, derived directly from the distributed parameter model of beam elements. This formulation, often denoted as spectral, allows an accurate evaluation of the dynamic behavior of the considered structures at high frequencies and with a limited number of elements. In addition, the spectral model can be easily coupled with a Fourier transform based analysis of the sound radiated by the fluid-loaded structure. The model is used to analyze the performance of beams with various core configurations. The comparison is carried out in terms of structural response and sound transmission reduction index. In addition the sound pressure levels and distributions resulting from the beam vibration in an unbounded acoustic half-plane are evaluated and compared. Hexagonal and re-entrant configurations are considered in an effort to study the effects of core geometry on structural response and acoustic radiation. (C) 2003 Elsevier Ltd. All rights reserved.