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RESEARCH PAPERS

Thread Friction Torque in Bolted Joints

[+] Author and Article Information
Sayed A. Nassar, Payam H. Matin, Gary C. Barber

Fastening and Joining Research Institute, Department of Mechanical Engineering, Oakland University, Rochester, Michigan 48309

J. Pressure Vessel Technol 127(4), 387-393 (Feb 23, 2005) (7 pages) doi:10.1115/1.2042474 History: Received November 04, 2004; Revised February 23, 2005

In this paper, formulas are developed for the calculation of the effective thread friction radius in fasteners, in order to determine the thread friction torque component. Due to the lack of exact formulas in the literature, current practice uses the average value of the minor and major thread radii, as an approximation, for determining the thread friction torque component. Results provided by these formulas are compared with those given by the current practice that uses the average value of the minor and major thread radii, instead of the exact value. It is well known that the torque-tension relationship in threaded fastener applications is highly sensitive to the friction torque components: between threads, and under the turning fastener head or nut. Even moderate variations or inaccuracies in determining the friction torque components would significantly impact the fastener tension and the joint clamp load. High accuracy in the estimation of the friction torque components is critical, as it directly affects the reliability, safety, and the quality of bolted assemblies. This analysis focuses on the thread friction torque component. The new formulas for the thread friction radius are developed for a mathematical model of a bolted joint using five assumed scenarios of the contact pressure between male and female threads. Because of the fact that the variation in the sliding speed of various points on a thread surface is insignificant, a uniform thread friction coefficient is used in the analysis. However, a contact area weighted average value is used for the thread friction coefficient. Numerical results and error analysis are presented in terms of a single nondimensional variable, namely, the ratio between the major and minor thread radii.

FIGURES IN THIS ARTICLE
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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Bolted joint model

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Figure 2

Effect of γ on the average thread friction coefficient

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Figure 3

Scenario 1: uniform thread contact pressure

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Figure 4

Percent error for a constant thread contact pressure model

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Figure 5

Scenario 2: convex parabolic thread contact pressure

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Figure 6

Percent error for a convex thread parabolic contact pressure

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Figure 7

Scenario 3: concave parabolic thread contact pressure

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Figure 8

Percent error for a concave parabolic thread contact pressure

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Figure 9

Scenario 4: linear increasing thread contact pressure

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Figure 10

Percent error for a linear increasing thread contact pressure

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Figure 11

Scenario 5: linear decreasing thread contact pressure

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Figure 12

Percent error for a linear decreasing thread contact pressure

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