Bifurcation analysis of plastic wrinkling formation for anisotropic laminated sheets (AA2024-Polyamide-AA2024)

Laminated aluminum sheets sandwiched with a polymeric core (Al2024/Polyamide 6/Al2024) are increasingly being used for automotive applications to boost vehicle's vibration-damping performance without adding additional weight. Wrinkling has been a major limiting failure mode in sheet metal forming which can be eliminated with an increase in the blank holder force (BHF). Because of the significant difference in material properties between the polymer core and the aluminum skin, it has always been a great challenge to predict their wrinkling onset and wrinkling pattern in deep drawing process. This contribution presents an efficient analytical model as well as an FE computation of the blank holder force leading to controlled local stability failure (wrinkling) and achieved optimum BHF in sandwich sheets forming. In the analytical model, plastic bifurcation based on the large deformation theory for an anisotropic sheet is used to predict the wrinkling onset. The results of the FE calculations and the analytic model are in good agreement with the experimental data.