Friction Compensation in the Upsetting of Cylindrical Test Specimens

This manuscript presents a combined numerical and experimental methodology for determining the stress-strain curve of metallic materials from the measurements of force and displacement obtained in the axial compression of cylindrical test specimens with friction between the specimens and the platens. The methodology is based on minimizing the error between the average surface pressure obtained from the experimental measurements of the force and displacement and that obtained from the slab method of analysis of metal plasticity. Three different friction models based on Coulomb friction, the constant friction model or combined friction models are utilized. Experimental results obtained from cylindrical and Rastegaev test specimens with different lubricants combined with the experimental determination of friction by means of ring compression tests allows compensating the effect of friction in the determination of the material flow curve. Comparison with the flow curves determined without friction compensation shows the viability of the proposed methodology. The proposed methodology is a simple and effective alternative to other solutions available in the literature and the pseudo-code supplied in the Appendix is provided for those readers interested in utilizing the associated numerical algorithm for determining the stress-strain curves of metallic materials.