Wrinkling limit curves with consideration of anisotropic behaviour for the deep drawing of aluminium sheet alloys

In this work, a combined experimental and finite-element (FE)-based approach was introduced for determining the wrinkling limit curves (WLCs) of sheet metals during forming processes. Aluminium sheets of grade AA5052-O and AA5052-H32 with different formabilities and anisotropic behaviours were investigated. Modified Yoshida buckling tests were carried out for aluminium sheets in both the rolling (RD) and transverse direction (TD). In parallel, FE simulations of the buckling tests were conducted, in which the Hill’48 (both r- and stress-based) yield criteria and Swift strain hardening law were incorporated. Local principal strain histories of observed wrinkle areas on both surfaces of samples were gathered from the simulations and the state of wrinkling initiation was then identified at the inclination of these strain paths. The calculated strain values were verified with developed compressive stresses as well as corresponding strains measured by a digital image correlation technique. The influences of material anisotropies and used yield functions on the determined WLCs were discussed. Subsequently, the determined WLCs were applied for evaluating non-flange wrinkling formation during a rectangular cup drawing test. The forming tests were experimentally and numerically performed for the examined aluminium sheets in both RD and TD. It was found that strain distributions of critical side wall areas at predicted wrinkling onset and severe wrinkle states were well correlated with the WLCs. Thus, WLCs based on the r-based criterion could more accurately describe the non-flange wrinkling incidents of the cup-drawn samples than those of the stress-based model.