An elastoplastic analysis of flange wrinkling in deep drawing process

Abstract

The onset of flange wrinkling of a deep drawing cup is analyzed as an elastoplastic bifurcation problem. The flange is modeled as an elastoplastic annular plate subject to axisymmetric radial tension along its inner edge. As observed in the laboratory as well as practical industrial applications, aluminum alloy sheets usually wrinkle in the plastic range. Therefore, the critical condition governing the onset of elastoplastic wrinkling is formulated within the context of the general bifurcation theory. A closed-form solution for the critical drawing stress is developed based on an assumed nonlinear plastic stress field and the deformation theory of plasticity. The theory properly accounts for the plastic anisotropy of the aluminum sheets and the critical drawing stress at the onset of wrinkling is also compared against the one employing the flow theory of plasticity. The predicted critical bifurcation stress and the wave numbers are compared to those obtained by Senior's one-dimensional theory. It is demonstrated that there is a strong dependency of the critical bifurcated stress at the onset of wrinkling on the shear stress induced on the flange. The effects of flange width, drawing ratios, material properties, strain hardening on the onset of wrinkling are investigated. The differences between the present theoretical approach and Senior's theory are emphasized.