Achievement of acoustical properties of foam materials by tuning membrane level: Elaborations, models and experiments

Abstract: This work presents a combined numerical and experimental approach to characterize the macroscopic transport and acoustic behavior of foam materials with a membrane cellular structure. A direct link between the sound absorption behavior of a membrane foam-based layer and its local microstructural morphology is also investigated. To this regard, we first produce a set of foam samples having the same density and the same monodisperse pore size but different values of the closure rate of the windows separating the foam pores. Then, the morphology of pore connectivity with membranes is measured directly on SEM together binocular images. The obtained morphological information is used to reconstruct the representative unit cell for computational performance. The knowledge of the computational model of acoustic porous materials obtained by a hybrid approach based on the scaling laws and the semi-phenomenological JCAL model. For validation purpose, the numerical simulations are further compared with the experimental data obtained from a set of three-microphone tube tests, a very good agreement is observed. In acoustic terms, the obtained results point out that for the given high porosity and cell size, we can archive a high sound absorbing ability of based-foam layer by controlling the membrane level at a range of 45-85$\%$. To elaborate these foams, a gelatin concentration in a range of 14-18$\%$ should be used in the foam making process. In addition, we can obtain for instance the peak and the average values of acoustic absorption of a foam layer in a specific frequency range of interest by varying its membrane content. Methodologically, our work proposes (i) a systematic approach to characterize directly macroscopic properties from the local microstructure, and (ii) a manufacturing technique that can be used to make foams with the desired microstructure.