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Effect of properties of metallic foams on stiffness and strength of sandwich beams

Polymer foam core sandwich beams typically have many cells through the core thickness so that cell size effects are negligible. In some proposed applications of metallic foam core sandwich beams (for instance, aircraft components) this is not the case. Metallic foams have larger cells than polymer foams (2-5 mm rather than 0.2-1 mm) and the thickness of the structural components may be restricted to roughly 5-15 mm. In this study, we examine cell size effects on the structural response of sandwich beams. Metallic foam cores may be subject to substantial normal as well as shear stresses. We begin by considering three possible yield criteria for metallic foams, comparing them to biaxial yield data. The most appropriate yield criterion has been used to determine the loads at which sandwich beams fail in a variety of modes (face yield, core yield and core indentation). The effect of the ratio of cell size to specimen size on core shear strength and core indentation strength is studied next. Finally, the effect of cell size to specimen size on the stiffness and failure of sandwich beams is presented. Thesis supervisor: Lorna J. Gibson Title: Matoula S. Salapatas Professor of Materials Science and Engineering