Determination of forming limit curve in two-layer metallic sheets using the finite element simulation

Forming limit curve (FLC) is a suitable method for determining the formability of the metallic sheet. The purpose of the present research is to expose a simulation-based approach to predict the FLC in two-layer metallic sheets. In this paper, the formability of two-layer (AA3004-ST12) metallic sheets, with an aluminum inner layer (in contact with the punch) and a steel outer layer (in contact with the die) was numerically investigated. Two distinct criteria, including the acceleration (i.e. the second time derivatives) of thickness, and major strain extracted from the strain history information of finite element software, were applied to determine the commencement of local necking in FLCs. It shows that the localized necking starts when the acceleration of the thickness or major strain, is maximized. The published experimental results for AA3004/ST12 two-layer metallic sheets were employed in order to evaluate the simulation results. It is shown that the presented methods are noticeably aligned with the published experimental data. By the grace of present methods, the effects of some process parameters on the FLC have been investigated. It is shown that process parameters such as thickness and lay-up of each layer will have significant influences on FLC of two-layer metallic sheets.