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|저자명||N. Park, H. Huh|
|Name||2014 KSTP fall conference|
This paper is concerned with prediction of fracture strains for DP980 steel sheets at a wide range of loading paths. The usage of DP980 steel is significantly increasing in automotive industries for enhanced safety and high fuel efficiency. The material behavior of advanced high-strength steels (AHSSs) sheets show unpredictable and sudden fracture in sheet metal forming processes. A modified Lou–Huh ductile fracture criterion is utilized to predict the formability of AHSSs because the conventional forming limit diagram (FLD) constructed based on necking is unable to evaluate the formability of AHSSs. Fracture loci were extracted from three dimensional fracture envelopes by assuming the plane stress condition to evaluate equivalent plastic strains at the onset of fracture at a wide range of loading paths. Three different types of specimens such as pure shear, dog-bone and plane strain grooved specimens were utilized for tensile tests to calibrate the fracture model of DP980 steel sheets. Fracture strains of each loading path were evaluated to show that there is little deviation between fracture strains predicted from the fracture model and experimentally acquired ones. Through the comparison, it is clearly shown that the three dimensional fracture envelopes can accurately predict the onset of the fracture of DP980 steel sheets in complicated loading conditions from compressive loading, and shear to equi-biaxial tension.