Shear Fracture Criterion On Advanced High Strength Dual-Phase Steels During Forming

Advanced High Strength Steels(AHSS) are increasingly used in automotive industry due to their superior strength and substantial weight advantage. However, shear fracture observes on tight radii during stamping processes. Since traditional approaches, such as the Forming Limit Diagram(FLD), are unable to predict this type of fractures. In this paper, based on the research of the shear fracture mechanism, using Modi?ed Mohr–Coulomb(MMC) to study the shear fracture process of Advanced High Strength Dual Phase Steels based on the elastic-plastic constitutive theory. The new model is applied to analyze forming process, a new shear fracture criterion are proposed to predicting shear fracture of Advanced High Strength Dual Phase Steels.Firstly, Hill’48-MMC damage models are established, the plasticity and ductile fracture of the present sheet are fully characterized by a Hill’48 orthotropic model and a MMC fracture model, respectively. The corresponding constitutive equation and numerical expression are deuced.Secondly, because the implicit iterative stress update algorithm is inefficient and converge difficultly when solving the questions of sheet metal forming rupture problem. The constitutive integration algorithm of numerical method is improved. Stress compensation updating algorithm based on elasticity tensor is introduced into the explicit dynamic solver. It is not only ensuring the accuracy and stability of the algorithm, but also improving the computational efficiency.Thirdly, based on material subroutine VUMAT in the finite element software ABAQUS/Explicit, the material subroutine VUMAT of Hill’48-MMC damage models was coded using Fortran. The visualization of the damage evolution in the process of sheet metal forming is realizing.Finally, referring to other forms of fracture criterion, a prediction shear fracture criterion of Advanced High Strength Dual Phase Steels based on Hill’48-MMC is proposed by combining with the results of Advanced High Strength Dual Phase Steels stretch bending forming numerical simulation, the main influence factors of shear fracture are analyzed further, we can see that this prediction criterion is feasible and applicable. Then the shear fracture criterion is then used on predicting shear fracture in automobile panel forming processes, and compared with the analysis of the simulation results by Dynaform, which confirms that the newly proposed shear fracture criterion more accurately predicts shear fracture of Advanced High Strength Dual Phase Steels compared with forming limit diagram(FLD).