Perforated closed-cell aluminium foam for acoustic absorption

Abstract

Closed-cell metal foams are lightweight and durable materials resistant to high temperature and harsh conditions, but due to their fully closed porosity they are poor airborne sound absorbers. In this paper a classic method of drilling is used for a nearly closed-cell aluminium foam to open its porous interior to the penetration of acoustic waves propagating in air, thereby increasing the wave energy dissipation inside the pores of the perforated medium. The aim is to investigate whether it is possible to effectively approximate wave propagation and attenuation in industrial perforated heterogeneous materials with originally closed porosity of irregular shape by means of their simplified microstructural representation based on computer tomography scans. The applied multi-scale modelling of sound absorption in foam samples is confronted with impedance tube measurements. Moreover, the collected numerical and experimental data is compared with the corresponding results obtained for perforated solid samples to demonstrate a great benefit coming from the presence of an initially closed porous structure in the foam.