Investigation on forming limit properties of dual phase steel

The accurate representation of the forming limit properties in the material model is very important for predicting the onset of failure. In this study, the FLCs for two dual phase steels DP780 and DP600 were experimentally obtained. The FLSCs were derived numerically by setting up stretching models in ABAQUS in which experimental FLD data were employed as failure criteria. The results of FLSCs showed in good agreement with that transformed from theoretical calculation. A new type of forming limit diagram based on Polar representation of EPS (Effective Plastic Strain) which proposed by Stoughton and Yoon was conducted to analyse the difference of result caused by FLD and FLSD criteria. The forming processes of a special cup-type part drawing were modelled and simulated by utilizing FLD and FLSD as failure criteria, respectively. According to analysis, the Polar EPS diagram can intuitively describe formability problems in forming processes. To avoid the occurrence of failure, it was found that if strain path for the final stage in Polar EPS diagram can be controlled to locate in some safe zones which can be expressed by function related to some parameters, certain required EPS could be achieved without failure during forming. The results indicated that Polar EPS Diagram seemed to be a good tool to analyse formability in complex strain paths condition and could be used to strengthen formability by designing nonlinear paths.