Bearing Friction Torque in Threaded Fasteners With Non-Flat Underhead Contact

Abstract

This study provides experimentally validated formulation of underhead bearing friction torque component during tightening of threaded fasteners with non-flat contact with the joint. Motosh model is utilized for spherical and conical contact surfaces for various scenarios of contact pressure. For each pressure scenario, a single non-dimensional 3-D graph is generated for the corresponding values of an effective bearing friction radius. A rotating sliding speed-dependent friction coefficient model is also investigated for its impact of the results of bearing friction radius. Torque-Tension testing is used to measure the bearing friction torque and the corresponding bearing friction coefficients using Motosh model, in which the newly formulated bearing friction radius expressions are entered. Obtained bearing friction coefficient values are then compared with those published by the threaded fastener manufacturer.