ECCM15 - 15 TH EUROPEAN CONFERENCE ON COMPOSITE MATERIALS, Venice, Italy, 24-28 June 2012 1 ELASTIC BEHAVIOUR OF CELLULAR POLYURETHANE MATERIALS AS CORE MATERIAL IN SANDWICH PANELS B. Buffel 1* , F. Desplentere 1 , B. Dekeyser 2 , M. Moesen 3 , I. Verpoest 3 1 KHBO Expertise Centrum Kunststoffen, Department IW&T, KHBO, Zeedijk 101 B-8400 Oostende 2 Recticel International Development Centre, Recticel, Damstraat 2 B-9230 Wetteren 3 Department of Metallurgy and Materials Engineering, Catholic University Leuven, Kasteelpark Arenberg 44 - bus 2450 B-3001 Heverlee *bart.buffel@khbo.be Keywords: sample size effect, cellular materials, surface evolver, FE-modelling Abstract Within this work the linear elastic properties of a cellular sandwich core material are investigated. This core material is a complex of two different types of polyurethane foams. Compression tests were performed on the complex material and on both constituents separately. After accounting for a significant sample size effect, in the case of the open cell foam constituent, all materials revealed a primary bending deformation mechanism and a high dependency on foam density. Finite Element modelling was used to evaluate the elastic response of the open cell foam. The surface energy of the Kelvin cell geometry was minimised using surface evolver software [7]. The influence of foam density and shape anisotropy are analysed in a parametric study. 1 Introduction Because of their efficient use of structure and material, sandwich panels are often used in applications where weight-saving is critical: aerospace, automotive, sport equipment, etc. [1,2]. Cellular materials are one of the possibilities when selecting an appropriate core material. Next to the compression and shear properties, polymer foams exhibit excellent thermal insulation properties. Due to the direct link between foam density and all other relevant core properties, (stiffness, strength, thermal insulation) an optimization of the sandwich panel design is possible. Therefore the focus of this research is to understand and characterise the elastic behaviour of these cellular materials. The complete characteristic compressive response of cellular materials is defined by a linear elastic zone followed by a collapse plateau and finally densification of the material (Fig. 1). Modelling the initial elastic zone has been subject of many different researches. The power law model developed by Gibson & Ashby [1,3] is based on a cubic structure which deforms primarily by in plane deformation of the cell wall of a closed cell structure or by bending of the cell edges in the case of an open cell structure. These two deformation mechanisms can be identified by the value of the power law exponent which is respectively 1 or 2. Warren and Kraynik [4] confirmed this simplified model by applying its principles on the Kelvin Cell geometry.