Brittle failure of metallic foams under tensile and cyclic loading - experimental studies and standardization

Based on a series of tensile and cyclic testing on various cellular materials including open porous metal sponges, aluminum foam with and without foaming skin (Alulight, Alporas, Foamtech), aluminum foam sandwiches (AFS), and syntactic metal foams, the tendency to brittle fracture in tension and fatigue was shown. By means of scanning electron microscopy of fracture surfaces and cross-sections, this tendency was attributed to a brittle behavior of the cell strut material that is caused by casting porosity and large Si precipitates in the Al-Si eutectic of aluminum cast alloy. The general objective of the work is the derivation of robust and reliable mechanical testing procedures and an improved understanding of the damage mechanisms of cellular metals under monotonic and cyclic loading conditions. The results have served as the basis for the definition of a draft standard for tensile testing of cellular metals (German Institute for Standardization DIN 50099) which is outlined in the present paper