Bottom-up approach for microstructure optimization of sound absorbing materials

• Published in: The Journal of the Acoustical Society of America 2008-08, Vol.124 (2), p.940-948
• Main Authors: Perrot, Camille, Chevillotte, Fabien, Panneton, Raymond
• Format: Article
• Language: English
• Subjects: Acoustics; Computer Simulation; Construction Materials; Engineering Sciences; Equipment Design; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Materials Testing; Mechanics; Models, Theoretical; Noise - prevention & control; Noise: its effects and control; Particle Size; Physics; Porosity; Sound; Sound Spectrography; Structural acoustics and vibration; Surface Properties; Temperature; Triazines - chemistry; Viscosity
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.2945115

Results from a numerical study examining micro-/macrorelations linking local geometry parameters to sound absorption properties are presented. For a hexagonal structure of solid fibers, the porosity ϕ , the thermal characteristic length Λ ′ , the static viscous permeability k 0 , the tortuosity α ∞ , the viscous characteristic length Λ , and the sound absorption coefficient are computed. Numerical solutions of the steady Stokes and electrical equations are employed to provide k 0 , α ∞ , and Λ . Hybrid estimates based on direct numerical evaluation of ϕ , Λ ′ , k 0 , α ∞ , Λ , and the analytical model derived by Johnson, Allard, and Champoux are used to relate varying (i) throat size, (ii) pore size, and (iii) fibers' cross-section shapes to the sound absorption spectrum. The result of this paper tends to demonstrate the important effect of throat size in the sound absorption level, cell size in the sound absorption frequency selectivity, and fibers' cross-section shape in the porous material weight reduction. In a hexagonal porous structure with solid fibers, the sound absorption level will tend to be maximized with a 48 ± 10 μ m throat size corresponding to an intermediate resistivity, a 13 ± 8 μ m fiber radius associated with relatively small interfiber distances, and convex triangular cross-section shape fibers allowing weight reduction.