EFFECT OF VARIABILITY IN MICRO-GEOMETRY OF POLYURETHANE FOAMS ON THE DOUBLE WALL TRANSMISSION LOSS

摘要

Propagation of waves in elastic porous media, e.g. polymeric foams, is described by Biot-Allard's theory [1]. Two classes of characteristic parameters are needed to describe the porous media in this theory. First, non-acoustic parameters: porosity φ, thermal characteristic length Λ', viscous characteristic length Λ, flow resistivity σ, and tortuosity α_∞ which are used in Johnson-Champoux-Allard (JCA) semi-phenomenological model [1]. Second, mechanical parameters, which in the case of isotropic material, are: bulk density ρ, Young's modulus E, loss factor η, and Poisson coefficient ν. The mechanical and non-acoustical properties are inherently dependent on the micro-structure of these materials. But, the internal structure of most porous material, e.g. polyurethane (PU) foam, is too complicated to be studied quantitatively. Therefore, the lattice of PU foams with low relative density (ρ_r) is commonly idealized by a tetrakaidecahedral, periodic unit cell (called PUC) and the macroscopic behavior recovered from a dedicated micro-macro approach. Furthermore, the cell windows can be randomly or partially closed, and cells are elongated in the rise direction. Measurements of such lattice results in variability in micro-structure properties of PUC. Hence, a clear understanding of the impact of variability associated with micro-structure properties measurement, and macroscopic Biot's parameters on vibro-acoustical performance of PU foams is of great importance in the design and optimization of such foams.