Vibro-acoustic properties of auxetic open cell PU foams : numerical and experimental study

Auxetic open cell PU foams have raised some interest in the scientific community for potential engineering and sound management applications due to their unconventional mechanical and acoustic properties. Auxetic cellular materials are characterised by a negative Poisson's ratio expanding in all directions when pulled in only one, therefore behaving in an unusual manner compared to conventional materials. Auxetic open cell foams were shown to have unusual acoustic absorption properties particularly at lower frequencies compared to their conventional counterparts. The main objective of this study is to obtain a better understanding of the acoustic behaviour of auxetic open cell PU foams by performing a combined numerical and experimental analysis. Wave propagation through foams was modelled using a homogenisation approach based on Biot's theory. A method to evaluate Biot's Poroelastic Parameters describing the foam's Static and Dynamic properties was proposed. The structural response of conventional and auxetic foams under loading conditions was studied by evaluating Biot's static poroelastic coefficients. The dissipation mechanism of sound waves propagating in auxetic cellular materials was also examined by evaluating the dynamic parameters of conventional and auxetic cellular solids. Samples of open cell PU-PE foams with negative Poisson's ratio were manufactured and used in the measurements of sound absorption based on ISO 10-534-2 Standard. The acoustic 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. A finite element formulation based on Biot's theory was also proposed to evaluate the acoustic absorption properties of both auxetic and conventional foams. The Numerical and experimental results are compared and commented to provide explanations to the unusual properties of auxetic foams.EThOS - Electronic Theses Online ServiceGBUnited Kingdo