Ductile fracture in metalworking: experimental and theoretical research

An important concern in metalworking is whether the desired deformation can be accomplished without failure of the material. This paper describes the utilisation of ductile fracture criteria in conjunction with the finite element method for predicting surface and internal failures in cold metalworking processes. Four previously published ductile fracture criteria are selected, and their relative accuracy for predicting and quantifying fracture initiation sites is investigated. Ring, cylindrical, tapered and flanged upset test samples are utilised for providing the experimental values of the critical damage at fracture under several different loading conditions. Two of the ductile fracture criteria are then utilised to predict the initiation site and the level of deformation at which surface or internal cracking will occur during finite element simulation of three types of metalworking processes, namely, radial extrusion, open-die forging and blanking. The analysis is made in conjunction with metal experiments, good agreement being found to occur.