Sound absorption of cellular metals with semiopen cells

TLDR

The study evaluates the feasibility of aluminum foams with semiopen cells for sound‑absorption and seeks to guide processing by linking absorption to pore size, opening, and porosity. Foams were fabricated by negative‑pressure infiltration of a water‑soluble spherical particle preform, and an analytical model was developed to relate pore connectivity to infiltration pressure, particle size, wetting angle, and surface tension, while measurements of sound‑absorption coefficient and static flow resistance were taken for samples with varying porosity, pore size, and opening, and a theory based on the acoustic impedance of apertures and cylindrical cavities in a hexagonal hollow‑prism unit cell was constructed. The model’s predicted sound‑absorption coefficients closely matched the measured values, confirming the correlation between morphological parameters and acoustic performance.

Abstract

A combined experimental and theoretical study is presented for the feasibility of using aluminum foams with semiopen cells for sound-absorption applications. The foams are processed via negative-pressure infiltration, using a preform consisting of water-soluble spherical particles. An analytical model is developed to quantify the dependence of pore connectivity on processing parameters, including infiltration pressure, particle size, wetting angle, and surface tension of molten alloy. Normal sound-absorption coefficient and static flow resistance are measured for samples having different porosity, pore size, and pore opening. A theory is developed for idealized semiopen metallic foams, with a regular hexagonal hollow prism having one circular aperture on each of its eight surfaces as the unit cell. The theory is built upon the acoustic impedance of the circular apertures (orifices) and cylindrical cavities due to viscous effects, and the principle of electroacoustic analogy. The predicted sound-absorption coefficients are compared with those measured. To help select processing parameters for producing semiopen metallic foams with desirable sound-absorbing properties, emphasis is placed on revealing the correlation between sound absorption and morphological parameters such as pore size, pore opening, and porosity.