CRACK INITIATION IN METALWORKING : EXPERIMENTAL AND THEORETICAL INVESTIGATION Gouveia B. P. P. A., Rodrigues J. M. C., Martins P. A. F., Atkins A. G * . Instituto Superior Técnico, Departamento de Engenharia Mecânica, Av. Rovisco Pais, 1049-001 Lisboa, Portugal (*) Department of Engineering, University of Reading, Whiteknights, Reading RG6 6AY, UK SUMMARY An important concern in metalworking is whether the desired deformation can be accomplished without failure of the material. This paper describes the utilization of ductile fracture criteria in conjunction with the finite element method for predicting surface and internal failures in cold metalworking processes. Previously published ductile fracture criteria are selected, and their relative accuracy for predicting and quantifying fracture initiation sites is investigated. Two of the ductile fracture criteria are then utilized to predict the initiation site and the level of deformation at which surface or internal cracking will occur during three different types of metalworking processes; radial extrusion, open-die forging and blanking. A rigid-plastic/viscoplastic finite element technique is utilized and the theoretical analysis is made in conjunction with metal experiments. Ring, cylindrical, tapered and flanged upset test samples are utilized for providing the experimental values of the critical damage at fracture under several different loading conditions. The paper concludes with a discussion on plastic flow and crack initiation during double wedge indentation into a strip. Keywords: Metal working, ductile fracture, finite element method