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 is predicted by developing a ductile failure criterion (DFC). In the DFC, 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 DFC is used to predict forming limit curves (FLCs) of six different aluminum sheet materials at room temperature. Then, the DFC is further developed for elevated temperature conditions 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 DFC 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 predictions match quite well with the experimental measurements. Thanks to the proposal of effect function, the DFC needs calibration only in uniaxial tension, and thus, provides a promising potential to predict forming limit with reduced effort.