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1188-LL05-03

Metallic sandwich structures with hollow spheres foam core. Pierre Lhuissier, Alexandre Fallet, Luc Salvo, Yves Bréchet, Marc Fivel. SIMaP-GPM2 - Grenoble Institute of Technology-CNRS-UJF, 101 rue de la Physique , BP46, 38402 Saint-Martin d'heres, France. ABSTRACT Sandwich structures and foamed materials are typical architectured materials. Their combination provides potentially very performant solutions combining stiffness, strength, energy absorption and acoustic damping. The present contribution deals with the integration of a special type of foams, namely hollow spheres stackings, into sandwich structures. Stainless steel hollow spheres main advantage relies on their smooth stress-strain curves and their very good repeatability, compared to other closed cell metallic foams. Therefore these foams are interesting alone but also in sandwich design. A parametric study of the macroscopic behaviour of random stainless steel hollow spheres packing in uniaxial compression was carried out. Scaling laws for the Young's modulus, and for yield strength were established, and they are used to calculate sandwich properties. Then one of the studied metallic hollow spheres packing has been integrated in a sandwich structure with stainless steel faces. Four point bending tests have been performed on various sandwich structures with four core thicknesses and three face thicknesses up to large deflection. We obtained thus the stiffness, the critical load where first damage occurs, the maximum load as a function of the sandwich parameters (core and face thickness). We compared this to classical analytical models. INTRODUCTION The integration of metallic foams in sandwich structures is of major interest when one is looking for a combination of properties such as stiffness, lightness, energy absorbed during damaging, high temperature working conditions and acoustic damping. Prior to the investigations of these properties, the ability to predict the behaviour of such structures where shown under various loading conditions : 3 and 4 points bending with clamped or simply supported boundaries conditions on beams [1-3] and indentation on plates. Various authors proposed failure modes maps [4]. Nevertheless few experiments have been done with hollow spheres foams core sandwich structures. In order to predict the failure mode of such structures an accurate knowledge of the core material properties is necessary. Some models have been developped to predict the behaviour of regular hollow spheres packing [5-7], but except for some works on few spheres [8] or purely experimental investigation [9], it seems that there is up to now a lack of quantification of the overall evolution of the properties of random hollow spheres stacking with the density. Thus compressive tests have been performed on stainless steel hollow spheres foams of various densities. Then four points bending tests have been performed on sandwich beams with hollow spheres foam core and with variable face thicknesses. Comparison between analytical predictions and exp