Study on the forming of sandwich shells with closed-cell foam cores

Abstract

The efficiency and safety of vehicles represent today one of the most important lines of developing in the automotive industry, for example by the introduction of new materials. In fact, the investment in advanced materials represents one of the most important strategies to reduce injury among vehicle occupants in traffic accidents. Associated with the development of safety systems, there is also the possibility of improving efficiency by the introduction of materials that lead to weight reduction, having a direct impact on fuel consumption and carbon dioxide emissions. Metallic foams are one of these materials, due to the excellent ratio between mechanical properties and density. The main goal of this investigation is to study the mechanical behaviour of aluminium sandwich structures, composed by a metallic foam core with two outer layers of metallic sheets. With this work, the authors intend to contribute to a better understanding and consequently to provide design guidelines for the plastic forming of these composites. In order to correctly characterize the mechanical behaviour of the sandwich structure, the foam core and sheets were tested separately. For the aluminium sheet a series of tensile tests were performed, using samples obtained along three different angles to the rolling direction. For the metal foam core, uniaxial compression tests were used. Finally, with the numerical model defined considering isotropic and anisotropic constitutive models, a set of numerical and experimental bulge tests were performed to evaluate the capacity of forming of these panels, using hydroforming processes.