Use of non-axisymmetric specimens in upsetting for determining the workability diagram

Abstract

Ductile fracture criteria are often used to predict fracture initiation in metal forming processes. One of such criteria is based on the workability diagram and an average value of the triaxiality factor over the strain path. An advantage of this ductile fracture criterion is that stress invariants involved in the original criterion can be excluded when fracture occurs at a traction free surface. Thus this reduced criterion is formulated in terms of the in-surface strains. The latter can be found experimentally by means of well documented techniques. Using this property of the ductile fracture criterion under consideration it is possible to obtain points of the workability diagram by means of a series of upsetting tests. Previous studies in this field have mainly focused on axisymmetric specimens. In the present paper, upsetting of non-axisymmetric specimens by flat dies is adopted to study material workability of the steel C45E. Experimental results obtained are combined with the workability diagram determined using basic tests (Rastegaev test, upsetting of cylinder by flat dies, torsion and collar test). The motivation of using non-axisymmetric specimens is to find new strain paths which can be useful for the determination of the workability diagram.