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RESEARCH PAPERS

Novel Formulation of the Tightening and Breakaway Torque Components in Threaded Fasteners

[+] Author and Article Information
Sayed A. Nassar, Xianjie Yang

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

J. Pressure Vessel Technol 129(4), 653-663 (Sep 12, 2006) (11 pages) doi:10.1115/1.2767354 History: Received December 10, 2005; Revised September 12, 2006

New formulas are developed for the torque-tension relationship, various torque components, and breakaway torque values in threaded fastener applications. The three-dimensional aspects of the lead helix and thread profile angles and the kinetic and static friction coefficients are all taken into account. Two scenarios of the contact pressure between threads and under the turning fastener head are considered, namely, uniformly distributed and linearly distributed contact pressure scenarios. The effect of thread pitch, lead helix and thread profile angles, friction coefficients, and fastener geometry is discussed. Results from the new formulas are compared with the approximate torque-tension relationship provided in the literature. A percentage difference analysis indicates that the new formulas provide a significant improvement that would enhance the reliability and safety of bolted connections, especially in critical applications.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Rotations of the lines OD and BC with the angle α along OB in the plane parallel to the XOZ plane

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Figure 2

The local geometry of the thread surface by using rotations of the lines OB and DC with the angle β along points O and D, respectively, in the plane parallel to the YOZ plane based on Fig. 1

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Figure 3

Uniform underhead contact pressure

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Figure 4

Linearly decreasing underhead pressure

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Figure 5

Uniform thread contact pressure

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Figure 6

Linear increasing thread contact pressure

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Figure 7

Nut factor K versus kinetic thread friction coefficient μtk

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Figure 8

Percentage difference in thread torque Ttp versus thread pitch p for a uniform contact pressure

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Figure 9

Percentage difference in thread torque Ttp versus thread pitch p for a linearly increasing pressure

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Figure 10

Percentage difference in thread torque Ttp versus thread pitch for the model in Refs. 3,7 under uniform and linearly increasing pressures

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Figure 11

Percentage difference in thread torque Ttp versus thread pitch p for the Motosh model (UN=uniform contact pressure; L=linearly increasing contact pressure)

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Figure 12

Percentage difference in thread torque Ttp versus half the thread profile angle α for the Motosh model under a uniform contact pressure

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Figure 13

Percentage difference in thread torque Ttp versus half the thread profile angle α for the model in Refs. 3,7 under a uniform contact pressure

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Figure 14

Percentage difference in thread torque Ttp versus half the thread profile angle α for the model in Refs. 3,7 under a linearly increasing pressure

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Figure 15

Percentage difference in thread torque Ttp versus half the thread profile angle α for the model in Refs. 3,7 while rmt and rt have the same definitions under uniform and linearly increasing pressures

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Figure 16

Difference in Ttp versus p for the Motosh model while rmt and rt are effective ones under uniform and linearly increasing pressures

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Figure 17

Difference in Ttp versus μtk while rmt is the mean one and rt is the effective radius under uniform and linearly increasing pressures

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Figure 18

Difference in Ttp versus μtk for the model in Refs. 3,7; rmt and rt are defined as the effective radii for uniform and linearly increasing pressures

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Figure 19

Difference in Ttp versus μtk for the model in Refs. 3,7; rmt and rt are the mean and effective radii, respectively, under uniform and linearly increasing pressures

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Figure 20

The ratio of the breakaway audit torque to the tightening one versus the ratio of the static thread friction coefficient μts to the kinetic value μtk

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Figure 21

Ratio of loosening torque to tightening torque versus thread pitch p under uniform and linearly increasing thread and bearing contact pressures

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Figure 22

Ratio of loosening torque to tightening torque under uniform and linearly increasing thread and bearing contact pressures

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Figure 23

Ratio of loosening torque to tightening torque versus thread friction coefficient μt under uniform thread and bearing contact pressures

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Figure 24

Ratio of loosening torque to tightening torque versus thread friction coefficient μt under linearly increasing thread and bearing contact pressures

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Figure 25

Ratio of loosening torque to tightening torque versus thread friction coefficient μt under uniform and linearly increasing thread and bearing contact pressures

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