Stretchbending is a typical method for sheet stamping forming. Different fracture failure modes occur on advanced high strength dual phase steel based on different stress state. For example, shear fracture occurs under tight radius stretchbending condition. In this paper, a stretchbending ratio α was introduced to indicate different stress states to determine the failure mode: necking or shear fracture. Stretchbending experiments of DP steels were conducted and fracture morphology was observed. The results show that shear fracture still belongs to ductile fracture, and tighter punch radius or higher DP strength leads to shear fracture much more easily.

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