The process of ductile fracture during metalforming was modeled by deforming plasticine specimens which contained steel-wire segments to simulate the inclusions in a fully plastic matrix. Due to the strain-rate-sensitive characteristics of plasticine, slant shearing from inclusion was found to be the dominant mechanism in fracture initiation at deformation rate of 10−4 s−1. As strain rate increased to 10−1 s−1, this shearing crack transformed into tearing cracks normal to the maximum tensile stress. These two basic modes of fracture, slant shearing and normal tearing, were further substantiated by the process of void coalescence, depending on inclusion morphology and matrix characteristics. These fracture behaviors were explained by a predictive model based on plastic instability of the deforming matrix and were evidenced by real metallic material. A qualitative criterion is proposed to depict the mode transition in ductile fracture as a function of inclusion morphology and matrix material characteristics.

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