Predicted and Measured Anisotropic Acoustic and Elastic Properties for Open Cell Porous Material and Their Influence on Acoustic Performance in Typical Train Applications

Invited paper

Eva Lundberg

MWL/KTH Royal Institute of Technology

Wednesday 3 june, 2015, 15:00 - 15:20

0.7 Lisbon (47)

Abstract:
Multilayer panels, as used in train floors, walls and roofs must be designed to fulfil many requirements, including acoustic and structural demands derived from global vehicle requirements. In order to maintain or increase the acoustic performance with reduced weight, porous materials are often used as an integrated part of the panels. The acoustic and elastic properties of the open cell foam are determined by the micro geometry. Modelling the full actual geometry for the foam is still computationally too demanding, and therefore a representative unit cell on micro level can be used to describe the overall behaviour in the long wavelength region, provided the micro-geometry can capture the most important characteristics of the foam. The influence of an anisotropic micro-structural geometry on the acoustic and elastic properties is discussed, and compared to corresponding anisotropic properties measured for real materials. The directional dependence of the flow resistivity, with respect to the rise direction and the in-plane properties, is studied. The possibility of the appearance of a negative Poissonís ratio in industrially produced foam is discussed. The acoustic and elastic properties obtained from the micro models are used in typical multilayer arrangements for vehicles and global measures for the panel, such as for example sound and vibration transmission, are calculated and the influence of the directional properties is discussed.

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