Bearing Friction Torque in Bolted Joints

• Published in: Tribology transactions Vol. 48; no. 1; pp. 69 - 75
• Main Authors: Nassar, Sayed A., Barber, G. C., Zuo, Dajun
• Format: Journal Article
• Language: English
• Published: Colchester Taylor & Francis Group 01-01-2005; Taylor & Francis; Taylor & Francis Inc
• Subjects: Analysis; Applied sciences; Bearing Friction; Bearing Radius; Bearings; Bolted Joints; Exact sciences and technology; Fastener Underhead Pressure; Friction; Friction, wear, lubrication; Machine components; Mechanical engineering. Machine design; Pitch Torque; Pressure; Thread Friction; Threaded Fasteners; Torque; Torque-Tension Relationship; Tribology; Underhead Friction; Underhead Friction Torque; Underhead Friction; Torque; Mechanical torque; Machining; Bearing(mechanics); Turning; Fastener; Thread Friction; Modeling; Pitch Torque; Contact stress; Bearing Friction; Friction coefficient; Penetration rate; Contact pressure; Fastener Underhead Pressure; Bolted joint; Torque- Tension Relationship; Bearing Radius; Pressure distribution; Threaded Fasteners; Contact surface; Joint clamping; Underhead Friction Torque; Bolted Joints; Reliability; Tribology
• ISSN: 1040-2004; 1547-397X
• DOI: 10.1080/05698190590899967

Formulas are developed for calculation of the effective radius of the bearing friction forces on the rotating contact surface in threaded fasteners. These formulas provide a more accurate estimation of the underhead bearing friction torque component in threaded fastener applications. This enhances the reliability, safety, and quality of bolted assemblies, especially in critical applications. It is well known that the torque-tension correlation in threaded fasteners, and the resulting joint clamping force, is highly sensitive to friction torque components: under the turning head and between threads. This analysis focuses on the bearing friction torque component under the turning head of a threaded fastener. Furthermore, it analyzes the error contained in the current practice when an approximate value, equal to the mean contact surface radius, is used instead of the actual bearing radius. New formulas for the bearing friction radius are developed for a mathematical model of a bolted joint using four different scenarios of the contact pressure distribution under the rotating fastener head or nut. The effect of the radially varying sliding speed over the rotating contact surface is analyzed and compared with a constant-friction-coefficient scenario. Numerical results and error analysis are presented in terms of a single nondimensional variable, namely, the radii ratio between the outside and the inside bearing area.