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Research Papers: Coatings & Solid Lubricants

Effect of Coating Thickness on the Friction Coefficients and Torque-Tension Relationship in Threaded Fasteners

[+] Author and Article Information
Sayed A. Nassar, Amro M. Zaki

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

J. Tribol 131(2), 021301 (Mar 09, 2009) (11 pages) doi:10.1115/1.3085941 History: Received July 10, 2008; Revised January 29, 2009; Published March 09, 2009

This paper experimentally investigates the effect of coating thickness on the thread, bearing friction coefficients, and torque-tension relationship in threaded fasteners, as well as an investigation into the effect of coating thickness on surface roughness properties. The torque-tension relationship is highly sensitive to frictional changes. Two different coating thicknesses are investigated using two bolt thread pitch; test data are collected for a preselected level of bolt tension. The experimental setup collects real-time data on the tightening torque, bolt tension, and the corresponding reaction torque. Test data are used for calculating the thread and bearing friction coefficients, as well as the overall torque-tension relationship for two different coating thicknesses. The study would provide an insight into the variation in the torque-tension relationship, which is a key factor that significantly affect the reliability and safety of bolted assemblies in many mechanical and structural applications.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Linearly decreasing underhead contact pressure model

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Figure 2

Fastener testing system (Courtesy of RS Technologies Ltd.)

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Figure 3

Schematic of torque-tension head

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Figure 4

Real-time test data for M12×1.25 bolts with thin coating

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Figure 5

Real-time test data for M12×1.25 bolts with thick coating

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Figure 6

Real-time test data for M12×1.75 bolts with thin coating

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Figure 7

Real-time test data for M12×1.75 bolts with thick coating

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Figure 8

Thread friction data of thin versus thick coatings for M12×1.25 bolt/nut

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Figure 9

Thread friction data of thin versus thick coatings for M12×1.75 bolt/nut

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Figure 10

The effect of coating thickness on the thread friction coefficient μt for fine and coarse M12 bolts

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Figure 11

Bearing friction data of thin versus thick coatings for M12×1.25 bolt/nut

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Figure 12

Bearing friction data of thin versus thick coatings for M12×1.75 bolt/nut

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Figure 13

The effect of coating thickness on the bearing friction coefficient μb for fine and coarse M12 bolts

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Figure 14

Nut factor K data of thin versus thick coatings for M12×1.25 bolt/nut

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Figure 15

Nut factor K data of thin versus thick coatings for M12×1.75 bolt/nut

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Figure 16

The effect of coating thickness on the nut factor K for fine and coarse M12 bolts

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Figure 17

Average surface roughness Ra measurement results for bolts before tightening

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Figure 18

Coating thickness effect on the average arithmetic height Ra before and after the tightening process

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Figure 19

Coating thickness effect on the skewness Rsk of the surface profile before and after tightening/loosening

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