Modelling of the mechanical properties of strengthened metal foams on different scales

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Open-cell metal foams are available for several decades. They are designed as bionic materials inspired by trabecular bones. Usually they are used in lightweight construction or for absorption of kinetic energy, e.g. in crash applications. Up to now metal foams are not well established in the applications because the strength and energy absorption of the usual aluminum foams are not outstanding and their properties are badly reproducible. This can be changed by a new coating technique where a nanocrystalline Nickel is deposited by electrodeposition. Such coatings allow for a significant increase of the plateau stress (strength) and of the energy absorption. If these innovative materials are accepted in the applications it becomes necessary to understand the material behaviour of the hybrid foam (Aluminum foam + Nickel coating). Theoretical models and numerical tools for the description of the material behaviour are still missing. The electrochemical coating of open-pore aluminum foams with nanocrystalline Ni in different thicknesses and with different microstructures as well as with other metals and with metal alloys yields a rich basis of samples for the mechanical experiments. This large variation of samples is essential for the reliable validation of the mechanical models to be developed.The aim of the project is the experimental characterization of such hybrid foams under tensile, compressive, shear and torsional load conditions. Based on these results, the material behaviour will be simulated on the micro and macro scale. The applicants expect a deeper understanding from the simulations of the complex micromechanical behaviour during the deformation of such hybrid foams. The simulation gives information on the relations between structure and properties of the foams and can be used to specifically examine the influence of the coating on the properties. Based on these results the structure of the foam shall be optimized by modifying the geometry of the struts and the coating thickness. Micromechanical tests on single struts of the foam are needed to relate the local processes as bending, fracture and contact with the global deformation of the foams determined from the macroscopic tests. The micro-macro transfer will be performed by a homogenization on the micro scale. As a result of the homogenization it is possible to determine the macroscopic model parameters by a numerical simulation of the microstructure.