Physical modeling of ductile fracture during metalforming process

Abstract

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 ofplasticine, 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 offracture, 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 ductilefracture as afunction ofinclusion morphology and matrix material characteristics. © 1990 by ASME.