Formability prediction of aluminum sheet alloys under isothermal forming conditions

The forming limit diagram (FLD) is a tool that is used by automotive engineers to assess and compare the formabilities of sheet metals. The FLD is experimentally determined by portraying the biaxial strain distribution in the plane of the sheet under proportional loading paths. However, experimental determination of the FLD is time consuming. With increasing interest in warm forming of aluminum sheets, the process for determining the forming limit diagram is further complicated and more cumbersome as the forming limits change with increasing temperatures. Accordingly, a process for predicting the FLD based on the material constitutive model is of interest. This paper presents a finite element based criterion for predicting the FLD under isothermal conditions. The paper provides experimental validation for the predicted results using select automotive 5xxx series aluminum alloys. The findings indicate that the developed criterion can adequately predict the forming limit for each strain path.