Workability limits in cold forging: Investigation of the deformation mechanics through FEA

This paper investigates the effectiveness of theoretical failure criteria in the estimation of workability limits in cold forging through Finite Element Analysis (FEA), by incorporating them into the commercial software ABAQUS 6.3.1. Universal applicability of the threshold values of these criteria functions, at the location and instant of fracture, represents their overall performance. FEA of various cold working processes involving typical materials was carried out up to the experimentally observed limit for fracture. Threshold values of all failure criteria depended on the stress-state resulting from geometry and loading conditions of the process. Poor scalability of the failure criteria across stress-states is attributed to the transition in modes of fracture, from global ductile - local brittle to shear depending upon the level of hydrostatic stress at fracture sites. There exists a race between the types of fracture in the deformation zone and failure occurs by the mechanism reaching the threshold first. Among the existing failure models, Kuhn's fracture locus successfully delineates the safe and unsafe regions in plastic strain-space, irrespective of the mode of fracture.