Prediction of fracture in hub-hole expanding process using a new ductile fracture criterion

A hole expansion process is an important process in producing a hub-hole in a wheel disc of a vehicle. In this process, the main parameter is the formability of a material, which is expressed as the hole expansion ratio. As the hole is expanded during the process, a crack tends to occur in the upper edge of a hole. Since prediction of the forming limit by hole expansion experiments needs tremendous time and effort, an appropriate fracture criterion has to be developed for finite element analysis to define the forming limit of materials. This paper newly proposes a modified ductile fracture criterion to consider the deformation characteristics of a material accurately in a hole expansion process. In order to verify the validity of the proposed criterion, the hole expansion process of a hub-hole is studied by finite element analysis with ABAQUS/standard considering several ductile fracture criteria. The fracture mode and hole expanding ratio are compared with respect to the various facture criteria. While existing criteria do not predict the fracture mode or hole expansion ratio adequately and show deviation from experimental results of hole expansion, the newly proposed fracture criterion predicts the fracture mode and the hole expanding ratio accurately.