Earing prediction of 2090-T3 aluminum-cups using a complete homogenous fourth-order polynomial yield function

Abstract

Earing can be described as difference in cup wall height due to planar anisotropy of the sheet metals, and both prediction and minimization of this defect are critical steps of drawing process design to save material and production costs due to additional trimming operations. The finite element (FE) method is a practical design tool in this context. The accuracy of FE analyses is directly dependent on modeling material deformations using an effective plasticity model. In this study, a homogeneous orthotropic fourth-order polynomial stress function is presented and implemented into Ls-Dyna FE software by a user-defined material subroutine to predict the earing evolution of a strongly anisotropic aluminum alloy (AA2090-T3) in cup drawing. Primarily, the parameters of the function were calibrated using test data. The effects of element size, number of through-thickness integration points, and time-step size were investigated separately on the drawn cup's earing profile and thickness strain distributions. It was observed that mass scaling factor related to time step size has a significant impact on the cup height and profile. Finally, simulations were repeated with optimum parameters to assess the performance of the plasticity model. The yield criterion successfully predicted the cup profile, earing amplitude, and thickness strain distributions.