Applicability of the uncoupled ductile fracture criteria in micro-scaled plastic deformation

Micro-scaled plastic deformation, viz., microforming, has been widely used to fabricate microparts with at least two dimensions in submillimeter. In microforming, ductile fracture significantly affects product quality and the forming limit of materials. It happens when the deformation method, mode and sequence are not reasonable. Although extensive research on ductile fracture and ductile fracture criteria in macroforming domain has been conducted, the applicability of these criteria in microforming scenario has not yet been extensively explored and studied. It is thus necessary to explore and address this issue to support the design of microforming process and quality control of the microformed parts. In this paper, the applicability of the uncoupled ductile fracture criteria's in microforming is investigated and discussed. The hybrid constitutive model developed in prior research is used to study the applicability of ductile fracture criteria in microforming via finite element simulation and physical experiments. The simulation results of each criterion are compared with the upsetting experiment to determine the most suitable criterion for further experimental implementation in flanged upsetting and extrusion processes. The influence of size-effects on the applicability of the uncoupled ductile fracture criteria is explored and the stress-induced fracture map is used to demonstrate this effect. The applicability of ductile fracture criteria in microforming is extensively revealed and analyzed and the research thus provides an in-depth understanding of the applicability of ductile fracture criteria in microforming processes.