The Study And Application On Ductile Fracture Criterion Of Dual Phase Steels During Forming

Advanced High Strength Steels(AHSS) are increasingly used in automotive industry due to their superior strength and good plastic property. During stamping process, the unique fracture phenomenon of advanced high-strength steel appears due to the competition of shearing and necking, which affects the forming process of car plate design, prevents the dimensional accuracy and further improvement of forming quality of dual phase steel parts.Based on the research of shear fracture mechanism in dual phase steel panels forming, a ductile fracture criterion put forward,the shear fracture of advanced high strength steels is studied combine the single tensile shear test with finite element simulation,proposed a fracture criterion which is a failure envelope combine triaxial stress degree with ultimate fracture strain, Achieve the purpose of predicting the stamping fracture of dual phase steel.In this paper, the main research contents include:1. Summarize the basic theory of finite element analysis for sheet metal forming, Discuss the theory of anisotropic elastic-plastic constitutive, provide theoretical basis for choosing an accurate constitutive integration algorithm.2. The specimen of shear and tensile are used in the performance test and simulation analysis of Advanced High Strength Steels and researching the shear fracture mechanism of DP780 steel.3. Studies on the ductile fracture criterion which is commonly used in engineering, the applicability used to predict the fracture of DP780 steel has carried on the detailed comparison and evaluation, choosing a ductile fracture criterion which is unified the phenomenon of tensile and shear, and the unknown parameters are calibrated by the experiment of tensile shear. To accurately predict the competition behavior of necking fracture and shear fracture for dual phase steel forming.4. The fracture characteristics of DP780 steel was studied under the condition of tensile and shear, the fracture strain decreased when the triaxial stress degree increase in the process of tensile, and the fracture strain increase when the triaxial stress degree increase In the process of shear, A criterion for predicting the material forming was proposed Based on the combination of limit fracture strain and triaxial stress degree.