Acoustic properties of air-saturated porous materials containing dead-end porosity

Abstract

This study examines the acoustic properties of materials with complex micro-geometry containing partially open or dead-end (DE) porosity. One of these kinds of materials can be obtained from dissolving salt grains embedded in a solid metal matrix with the help of water. The solid matrix is obtained after the metal, in liquid form, has invaded the granular material formed by the salt particles at negative pressure and high temperature, and after cooling and solidification of the metal. Comparisons between theoretical and experimental results show that the classical Johnson-Champoux-Allard model does not quite accurately predict the acoustic behavior. These results suggest that the assumptions of the Biot theory may not all be fulfilled and that cavity resonators and dead ends can be present in the material. The first part of the study proposes a simple model to account for this geometry. Based upon this model, two acoustic transfer matrices are developed: one for non-symmetric and one for symmetric dead-end porous elements. It is thought that this model can be used to study the acoustic absorption and sound transmission properties of the type of material previously described. In the second part, a series of simplified samples are proposed and tested with a three-microphone impedance tube to validate the exposed model. Finally, the third part compares the predictions of the exposed model to the impedance tube results on a real aluminum foam sample containing dead-end pores. These first results are encouraging and show that this simple model also provides a good prediction for these materials with more complicated microstructure.