Prediction of surface-fracture initiation in the axisymmetric extrusion and simple upsetting of an aluminum alloy

Most bulk metal forming processes may be limited by ductile fracture. such as an internal and surface fracture developing in the workpiece. It is important to predict the conditions within the deforming workpiece which may lead to fracture, as by using this prediction it may be possible to choose appropriate process conditions and to modify the forming processes to produce sound products. This paper suggests a scheme to simultaneously accomplish both the prediction of surface-fracture initiation and the analysis of deformation in the axisymmetric extusion and simple upsetting of an aluminum alloy. The Cockcroft-Latham criterion, which has been applied successfully to a variety of loading situations, is used in the present investigation to estimate if and where surface fracture will occur during the deformation process. The numerical predictions and experimental results for the two types of metal-forming process under consideration are compared, The proposed scheme successfully predicts the site of surface-fracture initiation and the corresponding level of deformation observed experimentally.