Relationship between friction parameters in a Coulomb-Tresca friction model for bulk metal forming

The ring compression test was employed to investigate the relationship between Coulomb friction coefficient and Tresca friction factor in a Coulomb-Tresca friction model. The results indicated that the ratio (k) of Coulomb friction coefficient to Tresca friction factor varies under lubricated and dry conditions. The ratio k can be described by a parabolic function under lubricated conditions and by an exponential function under dry condition. There is a transitional region between lubricated and dry conditions.