Wrinkling Determination in Sheet Metal Loaded by Shear Stresses

Lightweight concept approach in sheet metal forming requires, among others, thickness reduction and geometry complexity. This combination dramatically promotes the wrinkling occurrence, which can be considered as one of main failure mode that toolmakers must consider. The sheet metal wrinkling determination research usually considers the wrinkling in flange and conical area of a cylindrical cup. For complex geometries the loadings are more diverse than in the deep drawing of a cylindrical cup involving shear stress states. In this context, the present work proposes the application of two different wrinkling determination methodologies in an experimental sheet metal specimen loaded by shear in an aluminum alloy. One of the methodologies involves geometrical parameters to trigger the onset of wrinkling and the other methodology is physically based and considers the evolutions of the in-plane minor strain and its strain rate. The experimental formability test requires a dedicated clamping apparatus to allow its kinematics to be similar to a tensile test. Results allowed the identification of the stress state that triggered the wrinkling occurrence, and the determination of the critical strains that allow plotting the wrinkling limit curve of the sheet material.