Microtensile testing of open-cell metal foams — Experimental setup, micromechanical properties

Abstract

Metal foams are cellular materials often used for lightweight construction or as energy absorbers. Coating of open-cell foams improves the mechanical properties by the formation of Ni/Al hybrid foams. The properties are determined by the microstructure, the properties of the strut material and its geometry. The properties of bulk materials significantly differ from those measured at single struts. For meaningful simulations, the determination of micromechanical properties on single struts is necessary. According to the small dimensions and the strut curvature, the micromechanical testing is challenging and has not been performed on struts of the new multi-phase Ni/Al hybrid foams, yet.In this study, a microtensile setup for aluminium and Ni/Al hybrid foams is developed. A challenging aspect was the small sample dimensions and the large discrepancy between the yield strength of aluminium and nickel. To determine true stress–strain curves, an optical system based on CCD cameras was used to calculate the strut cross section by means of a non-contact measurement. Local strains were evaluated using digital image correlation. A method to produce speckle pattern on single struts in an appropriate size was developed. The study outlines the evaluation of micromechanical strut properties of aluminium foams and Ni/Al hybrid foams.