Investigations of friction-relevant parameters to ensure reliable bolted joints

Abstract

During the process of torque-controlled tightening of bolted joints, the reliability of load transmission is limited by the achieved accurate preload. The preload is mainly influenced by head‐ and thread friction. The knowledge of reliable coefficients of friction and the dependence on assembly parameters are essential. Although a variety of friction coefficients were published but the overall ranges ask for more precision. So called windows of friction coefficients are available in known guidelines, to define permissible scattering. However, there are practical doubts about useful friction coefficients, especially if newly developed lubricants, corrosion‐resistant coatings and securing devices against bolt-loosening are used. In this study, different parameters of a bolted joint connection, such as lubrication, the surface protection of the screw connection or used security systems, have been investigated on their frictional influence. To make a reliable conclusion about the coefficients of friction, only a measured examination like DIN EN ISO 16047:2013-01 can help. By means of a designed test bench those values could be detected by measurement and supplemented with the collected data of vibration test results at the TH Koln. On this way practically useful coefficients of friction and their scattering have been made available.