Limitations in Measuring the Flow Stress

In designing of plastic metalworking technologies, one determining amount used is the flow stress (kf ) of the material to be formed. A few experimental methods are used to measure it, but in all case it is intended to establish a specific stress and strain state in the whole volume of the specimen, or at least in its majority. In our work the limitations of upsetting in axial symmetrical and plane strain states were investigated by FE modeling and experimental methods within cold working conditions. Both methods were executed on traditional testing machines and Gleeble 3800 thermo-mechanical simulator. It was intended to determine the flow stress up to as high strain values as possible. The processing of the experimental results showed, reliable flow stress values were obtainable in the equivalent strain range of 0 to 3 using the step-by-step upsetting in plane strain, and in the 0 to 1.2 range by cylindrical upsetting.