Predicting Sheet Forming Limit of Aluminum Alloys for Cold and Warm Forming by Developing a Ductile Failure Criterion

In this study, the forming limit of aluminum alloy sheet materials are predicted by developing a Ductile Failure Criterion (DFAC). In the DFAC, the damage growth is defined by Mclintock formula, stretching failure is defined at Localized Necking (LN) or Fracture without LN, while the critical damage is defined by a so-called effect function, which reflects the effect of strain path and initial sheet thickness. In the first part of this study, the DFAC is used to predict Forming Limit Curves of six different aluminum sheet materials at room temperature. Then, the DFAC is further developed for elevated temperature condition by introducing an improved Zener-Hollomon parameter (Z′), which is proposed to provide enhanced representation of the strain rate and temperature effect on limit strain. In warm forming condition, the improved DFAC is used to predict the FLCs of Al5083-O and failure in a rectangular cup warm draw process on Al5182+Mn. Comparison shows that all the prediction matches quite well with experimental measurement. Thanks to the proposal of effect function, the DFAC only needs a calibration at uniaxial tension and thus provides a promising potential to predict forming limit with reduced efforts.