Comparative Investigation of the Experimental Determination of AA5086 FLCs under Different Necking Criteria

The construction of a forming limit diagram (FLD) is a conventional approach to obtain limit strains and to evaluate the formability of sheet metal. Appropriate necking criteria should be applied to determine the forming limit curve (FLC) accurately. In recent years, deep research on the determination of the FLC has been carried out; meanwhile, several necking criteria have been proposed. However, the application of inappropriate necking criteria would cause deviations when determining FLCs. In this study, both Marciniak and Nakajima tests were carried out on the AA5086 aluminum sheet to make a comparative investigation of different necking criteria in the determination of FLCs. In the Marciniak test, four existing necking criteria were chosen to construct FLCs, and analyzed in detail. The well-performed time dependent and position dependent methods were selected for the Nakajima test. Meanwhile, the modified Wang method based on the height change of the adjacent points was proposed. The comparative results showed that the time and position dependent methods were relatively conservative in both experiments, while the modified Wang method could identify the onset of localized necking more accurately.

Numerical Investigation of Temperature and Forming Rate Effect on AA5086 Warm Formability

The poor formability of aluminum alloy at room temperature limits its use in some products with complex shapes, hence the warm forming process is intended to overcome this problem by using an elevated temperature. Now, the warm formability of AA5086 has not previously been well investigated in the literatures, especially at a rapid forming rate. In this paper, a numerical method has been developed to investigate the warm formability of an AA5086 sheet. Firstly, the dynamic tensile test was carried out under different forming temperatures and forming rates to identify an appropriate constitutive law for the sheet. The inverse analysis was performed to identify the parameter values in the constitutive law. Then based on the commercial finite element program ABAQUS, the Marciniak test was simulated to evaluate the sheet formability of by implementing a user-defined material subroutine UHARD. The effects of forming temperature and forming rate on sheet formability were investigated and it is shown that the formability of AA5086 seems to be insensitive to the forming temperature and forming rate.