Author(s)

I. Chekkal, C. Remillat & F. Scarpa

Abstract

Auxetic foams have raised some interest in noise and vibration control applications as they showed unusual acoustic properties compared to conventional ones, particularly at low frequencies. Auxetic foams are porous materials with a negative Poisson’s ratio. They expand in all directions when only pulled in one. In this paper, the acoustic properties of auxetic foams are described both from a numerical and experimental point of view. The acoustic absorption properties of both auxetic and conventional foam samples were measured using a two-microphone impedance tube to provide a comparison between the two types of cellular solids. The acoustical properties of auxetic foams are discussed in terms of the dynamic parameters. A numerical model based on Biot’s theory is derived in which the dynamic coefficients of foams are evaluated. Results are compared and commented to provide explanations on the unusual acoustical behaviour of auxetic foams. Keywords: auxetic foams, dynamic parameters, acoustic properties, porous media, Biot’s model. 1 Introduction Porous materials are commonly used in vibration and noise control applications as they are known for their ability to dissipate acoustic waves propagating in their medium. A porous material consists of a solid phase which is the frame or the skeleton and a fluid phase which is the air or the fluid in pores. Auxetic foams are a subset of porous materials. They can be produced from conventional low density open cell polymer foams by causing the ribs of each cell to permanently protrude inward, resulting in a re-entrant structure. Auxetic foams are characterised by a negative Poisson’s ratio. They expand in all directions when only pulled in one. Such unusual behaviour raised some interest in the modern word due to their unconventional mechanical and acoustic properties.

Keywords

auxetic foams, dynamic parameters, acoustic properties, porous media, Biot’s model.