An investigation on determination of flow curves at room temperature and under forming conditions

The bulge correction factor method (BCFM) is used for determination of the flow curve of a metal by means of a compression test under forming conditions. Since in this test the interfacial friction causes a non-homogeneous deformation, a correction factor is employed to calculate the actual flow stress. However, for high frictions and axial strains, this method unreasonably overestimates the flow stress. In the present investigation, using finite-element simulations of the compression test, more realistic correction factors were obtained. Despite the bulge correction factor, the numerical correction factor was considerably affected by the strain hardening behavior of the material, interfacial friction and the initial height/diameter ratio of the sample. But the strength coefficient did not influence the numerical correction factor. When suitable numerical correction factors were applied to the experimental results of the compression tests with lead and tin, compared with the factors obtained from BCFM, the subsequent finite-element simulations provided more accurate load-displacement curves.