Hybrix: Experimental characterization of a micro-sandwich sheet

The development of new micro-sandwich sheets (i.e. two metallic skins separated by a composite core), which can be shaped by conventional sheet metal forming processes, became one of the most interesting materials and promising automotive applications in the past few years. However, due to the lack of understanding of certain fundamentals related with the mechanical behavior of micro-sandwich sheets during forming processes, the transfer and scale-up of this promising material to industry has been hindered. To overcome problems concerning the formability of these new materials and make the conventional sheet forming process more adapted, the experimental characterization of the micro-sandwich sheets is absolutely necessary. In this work, a new approach to experimentally characterize micro-sandwich sheets, with the mechanical properties of the core unknown, is presented. Firstly, for the characterization of stress-strain curves and anisotropy, uniaxial tensile tests in 3 different orientations with respect to rolling direction are performed on total micro-sandwich specimens and skin-only specimens. Secondly, the mechanical properties of the core are then deduced from micro-sandwich and skins’ mechanical properties, and the constitutive parameters established. Additionally, 5 different Nakazima geometries were punched according to ISO 12004 for formability assessment. Experimental Forming Limit Curves (FLC), punch forces and principal strain data were recorded during the tests using high resolution cameras and system GOM ARAMIS. Finally, the experimental mechanical tests were numerically reproduced. The systematic excellent agreement between numerical and experimental results is a good validation of the methodology proposed in the present work to identify the constitutive properties of the micro-sandwich materials.