The Study On Ductile Fracture Failure Criterion Of Dual Phase Steels Body Panel

Advanced High Strength Steel is the main material for lightweight car body.Compared with ordinary steel,Dual Phase(DP)steel has the advantages of high strength,high impact energy absorption and high forming properties,etc.However,during the stamping process of DP steels,double-phase steel breaks are likely to occur at the corners and sidewalls of the concave and convex die.Experiments show that this fracture phenomenon is shear fracture and neck fracture that are unique to DP steels.The shear fracture of DP steel occurs before the necking fracture,and the fracture form is the result of the competition of shear fracture and necking fracture.Because the DP steel fracture mechanism is more complex,it increases the difficulty in the body stamping,and also limits its application in the sheet metal forming process.In this paper,by studying the material properties and fracture mechanism of DP steels,Combined single pull,shear test and finite element simulation,study the failure criterion of ductile fracture of dual-phase steel.The main work of this article is as follows:1.On the basis of the forming simulation theory including yield criteria,reinforcement criteria and failure criteria,combine Hill'48 Yield Criteria with Modified Mohr-Coulomb Failure Criteria,write the Abaqus VUMAT subroutines using Fortran language to simulate the failure process of high strength dual phase steels.2.Through the single pull test,obtaine the mechanical properties of the advanced high strength dual phase steel.Based on the design of dual phase steel shear test,combining with Abaqus numerical simulation,through deducing the calculation formula of the stress triaxiality and equivalent plastic strain of the dual-phase steel,to establish a practical method for determining the triaxiality of the stress and to overcome the difficulty of directly obtaining the stress triaxiality through the test.3.The VUMAT subroutine is called by the finite element software Abaqus to simulate the deep drawing process of the specimen.Combined with the existing method for determining the forming limit of sheet metal,to construct the forming limit curve prediction model of dual-phase steel.4.Based on the finite element software Abaqus simulation of the dual-phase steel bending process,combined with the stress triaxiality and the forming limit curve of the high-strength dual-phase steel to study the fracture failure wide-stress state of the dual-phase steel.