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Metallic foams show some potential for being produced with controlled spatial variations in their density. This suggests employing them as graded materials in space ®lling lightweight structures designed in analogy to cortical bone, a natural cellular material, that displays increased density in regions of high loading. In the present study the in¯uence of the mechanical properties of aluminium foams on the results of an optimisation of the foam density distribution with regard to structural strength and stiffness was examined. Regression formulae for the relationships between stiffness and strength of metallic foams on one hand and effective density on the other hand can be ®tted to the results of uniaxial compression tests of a certain brand of metallic foam. These results and additional assumptions such as overall isotropy and a yield surface suitable for cellular materials can be implemented into a ®nite element program adapted for performing stiffness or strength optimisation on the basis of a density adaptation similar to the remodelling of bone. Some applications are presented that show how foams with gradients in the apparent density may be employed to obtain optimal structural behaviour for classical design problems.MST/4565

Modern materials and material compounds for application in lightweight structures exhibit, in addition to the use of constituents of high specific stiffness and strength, very special micro-and meso-structures. Typical representatives of such material compounds are sandwiches with thin homogeneous or composite face layers and structured core materials (for instance honeycombs and closed or open cell foams). The load carrying capacity of lightweight structures made of such materials and material compounds, respectively, is limited by a considerable number of rather different but interconnected instability modes occurring at length scales which are several orders of magnitude smaller than the size of the structural part. These non-global instabilities are the subject of the presented key-note paper.