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|저자명||Yanshan Lou, Hoon Huh|
The paper is concerned with the mechanism, modelling and numerical prediction of ductile fracture for a dual phase steel sheet of DP980 in a wide stress state at low stress triaxiality in shear and at intermediate stress triaxiality between uniaxial tension and plane strain tension. The mechanism of ductile fracture is investigated based on scanning electronic microscope (SEM) images of fracture surfaces for central hole, in-plane shear and notched specimens, which reveal that voids link up along the direction of the maximum shear stress for all these specimens. Shear linking-up of voids was assumed as the mechanism for void coalescence by a newly proposed micro-mechanism-motivated ductile fracture criterion. This criterion is utilized to construct the fracture locus of DP980 using fracture strains measured from in-plane shear, central hole and plane strain tensile specimens. The constructed fracture locus is implemented into numerical analysis to predict the onset of ductile fracture of these three specimens as well as three types of notched specimens and three shear tensile specimens. The predicted fracture strokes are demonstrated to be close to experimental results with high accuracy from comparison of predicted load-stroke curves with those measured from experiments. High accuracy of the proposed fracture criterion guarantees satisfactory predictability not only in failure prediction for sheet metal forming but also in blanking and cutting.