Ring Compression Test for High‐Temperature Glass Using the Generalized Navier Law

Glass‐forming processes such as high viscosity extrusion and Precision Glass Molding take place at temperatures where slip between the glass and mold/die surfaces is known to occur. Characterization of the frictional forces that accompany interface slip are essential in computational simulations of these processes for prediction of pressing time or force, distortion of the part and possible wear of expensive mold surfaces. In this study, the generalized Navier law, where the interface shear stress, τ, is related to the relative sliding speed of the glass on the mold surface, v s , by τ =  kv s e , is used in simulations of the ring compression test to produce friction calibration curves. Contrary to the nonlinear form of the Navier law, the linear form, just like the Coulomb friction model, leads to calibration curves that are loading rate and material behavior independent. This independence is achieved by normalizing the Navier friction coefficient with the viscosity. Friction calibration curves for the normalized coefficient are characterized for the full range of interface conditions from no‐slip to no friction. The results showed an approximate one‐to‐one correspondence between the normalized Navier coefficient and the Coulomb friction coefficient for the full range of axial deformation in the ring compression test.