In-situ and ex-situ microtensile testing of individual struts of Al foams and Ni/Al hybrid foams

Abstract

Metal foams are cellular materials, offering a strong structure-property relationship. Their global properties are strongly connected to the local micromechanical properties of the struts and to the microstructure of the foams. The mechanical properties of individual struts differ widely from the bulk matrix material as a result of differences in solidification conditions and the surface-to-volume ratio. A robust micromechanical understanding and knowledge of micromaterial parameters is essential to design components made of foams e.g. supported by numerical simulations. However, up to now, micromechanical charaterisation of individual struts is very challenging but an emerging field of research. The present contribution deals with the microstructural and micromechanical characterisation of individual struts of open-cell aluminium foams and Ni/Al hybrid foams. The crystallographic texture is investigated by electron backscatter diffraction. Microtensile testing is performed on individual struts to determine real micromechanical material properties by ex-situ testing using a specially developed device and a digital image correlation method. Furthermore, in-situ microtensile tests using scanning electron microscopy are conducted for high-resolution investigation of the micromechanical deformation and damage mechanism occuring under loading of individual struts. The experimentally determined Young's modulus of the nickel coating is compared with theoretical calculations based on the grain orientation data.