MetFoam 2007 Conference on Porous Metals and Metallic Foams September 5-7, 2007, Montreal, Canada Mechanics of Semi-Expanded Hollow Sphere Foams T. Daxner[1], R.W. Tomas Vienna University of Technology, A-1040 Vienna, Austria. Confined expansion of polymer spheres coated with a metal slurry is a way of producing cellular micro-structures that range from sintered hollow spheres in the unexpanded case to sintered polyhedra with nearly flat cell walls in the fully expanded case. In this paper we investigate whether intermediate, semi-expanded configurations offer superior mechanical properties. Finite element unit cell models are employed as idealized mechanical models of the real micro-structure. These models represent a spatially periodic subregion of a regular, quasi-infinite cellular structure. Because the models offer full control over geometrical and bulk material properties they are excellent tools for obtaining qualitative, and, to some extent, quantitative, information on the mechanical behaviour. A special challenge regarding the investigated cellular material is the necessity of a simulation of the actual expansion process of the polymer spheres and their coating in order to obtain realistic geometries and wall thickness distributions for the subsequent study of the sintered end product. Therefore, highly nonlinear simulations of this expansion process are performed. Intermediate, deformed configurations representing different degrees of expansion are extracted from these simulations for producing realistic models for the unit cell analyses. In dependence on the initial thickness of the coating and the degree of confined expansion, the mechanical properties are then predicted in terms of the effective elastic constants and the macroscopic yield stresses for different load cases. An assessment of the buckling behaviour is also presented. The results allow the choice of an optimal degree of expansion for the considered route of production. ----------------------- [1] Corresponding author: Email: daxner@ilsb.tuwien.ac.at. Address: Vienna University of Technology, Gusshausstr. 27-29 (E317), A-1040 Vienna, Austria.