Graded open-cell aluminium foam core sandwich beams

We show that the replication process can be extended towards the production of functionally graded porous structures by fabricating and testing structures in which outer layers of dense metal encase a central part made of foam with graded porosity. Samples of this kind are produced by pressing individual layers of NaCl powder of granulometry 60-90 μm, and then stacking these layers between two skins of dense aluminium. The stacked preforms are then infiltrated with pure aluminium and solidified before dissolution of the salt in water. Specimens containing up to five layers of porous Al of different density between two dense outer skins of pure Al are produced; selected samples are tested in three-point bending. Data show good agreement with analysis based on sandwich beam theory and the Deshpande-Fleck yield criterion. Results of this work indicate that whereas lightweight graded metal/metal foam beams show little promise from the standpoint of stiffness-limited design, they may be of interest from the standpoint of load-limited design.