Analysis of forming limits based on a new ductile damage criterion in St14 steel sheets

Analytical and numerical analyses of forming limit in sheet metal hydraulic bulging test under combined internal pressure and independent axial feeding are researched in this paper. To predict the initiation of fracture, a new normalized ductile damage criterion based on strain hardening exponent, stress triaxiality and strain lode parameters are adopted. Eventually, elastic modulus is chosen as a characterization parameter to measure the ductile damage during the process of plastic deformation of the material. In addition, the explicit expressions of elastoplastic constitutive equations related to this damage criterion are compiled and implemented in ABAQUS/CAE software as the user subroutines. After compared against the analytical and the experimental forming limit diagrams (FLDs), the simulative FLDs demonstrate to be reasonable so that this model can be extended to predict a wide range of sheet metals' forming processes.