Periodic unit cell reconstruction of porous media: Application to open-cell aluminum foams

Copyright 2007 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.International audienceIn this article, the issue of reconstructing an idealized periodic unit cell (PUC) to represent a porous medium is examined by means of microcomputed tomography (μCT). Using μCT, three-dimensional images of open-cell foam are collected and used to characterize the representative parameters of its cellular morphology. These parameters are used in order to reconstruct the porous medium by means of an idealized PUC: a tetrakaidecahedron with ligaments of triangular cross sections, whose characteristic dimensions have been measured on the μCT images. The proposed reconstruction of the idealized PUC is applied to four aluminum foams. The averaged macroscopic properties of the foams (open porosity and thermal characteristic length) are deduced from their respective PUC model and compared to experimental measurements and literature data. Good correlations are obtained. For each of the foams, this provides a parameterized idealized periodic unit cell on which the partial differential equations governing sound dissipation and propagation in foams can be solved with a view to studying the microphysical basis of the acoustical macrobehavior

Computation of the dynamic thermal dissipation properties of porous media by Brownian motion simulation: Application to an open-cell aluminum foam

Copyright 2007 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.International audienceThis paper reports simulation results of frequency dependent heat conduction through three-dimensional reconstructed unit cells of an open-cell aluminum foam under acoustic excitations. First, a three-dimensional random walk based algorithm is proposed to calculate the dynamic thermal permeability or dynamic bulk modulus of periodic complex porous geometries. Second, the error and convergence of the implemented calculation algorithm are quantified in terms of the random walk population, normalized trapping distance, and type of geometry. Finally, the algorithm is applied to the calculation of the dynamic bulk modulus of an aluminum foam and compared to laboratory measurements. Good agreement is obtained between simulations and measurements

Computation of the dynamic bulk modulus of acoustic foams

International audienc

Linking microstructure with acoustic properties of open-cell foams

Structured session: "New materials and systems in building acoustics"International audienceA research program has been initiated in January 2002 in order to link microstructure of high porosity open-celled foams with their acoustic properties. This paper is intended to highlight the main results of this study. The general objective of this work is the determination of the acoustical macro-behavior at the local scale of real rigid-framed porous media. In this purpose, one needs first to determine the local geometry of the media, and second to solve in it the partial differential equations which govern dissipation phenomena by thermal and viscous effects. The first step has been overcome by the modern technique of Computed Micro Tomography (CMT). This leads to experimental identification of the parameters of an idealized periodic unit-cell. The second step, the resolution of the linearized heat and viscous fluids equations under harmonic regime, is performed using Brownian motion simulations and finite element methods respectively, in three-dimensional and equivalent two dimensional unit-cells. Macroscopic behavior is obtained by spatial averaging of the local and frequency-dependant thermal and velocity fields. Results are presented in terms of only two frequency-dependant functions, taking into account the long-wavelength sound absorption and propagation properties of an air filled media; and compared with standing waves tube measurements. This computational methods combined with physically realistic cellular models will make optimal design of real open-celled foams a reality in the future

Periodic Unit Cell Reconstruction of Porous Media: Acoustic Properties of an Open Cell Aluminum Foam

National audienc

Bottom-up approach for microstructure optimization of sound absorbing materials

International audienceA major issue in building acoustics concerns the need to increase or adapt the absorption spectrum of commonly used sound absorbing materials. However, the most advanced models used to characterize and predict sound absorbing material performances are based on macroscopic parameters, which are inter-dependant, and do not take explicitly into account the local geometry description of the porous media, i.e. microstructure. For these reasons, optimizing sound absorbing material performances firstly relies on our ability to predict acoustic properties of porous media from the description of their local geometry, and secondly to propose pertinent physically realistic modifications of the microstructure having predictable impacts on the absorption spectrum. Starting from an open-cell foam sample having poor sound absorption properties, this paper exposes how the link between microstructure and macro-behavior is achieved, and how its sound absorption is increased from the optimization of its microstructure

Mesostructural approach for characterising macroscopic parameters of open cell foams with computed microtomography

International audienc

Microscopic and mesoscopic approaches for describing and building sound absorbing porous materials

International audienc