A new evaluation to friction analysis for the ring test

A non-constant shear friction approach is proposed to evaluate the friction in ring test. The distribution of shear friction is derived and found to be dependent on the ratio (called F-coefficient) of the second derivative and first derivative of velocity at the z-direction. An upper bound method combined with the F-coefficient is used to simulate the processes of ring test. The calibration curves are reconstructed according to the F-coefficient and show good agreement compared with the literature. A relation between the F-coefficient, neutral line and constant friction factor m are also shown for discussion.