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RESEARCH PAPERS

Effect of Tightening Speed on the Torque-Tension and Wear Pattern in Bolted Connections

[+] Author and Article Information
Sayed A. Nassar, Saravanan Ganeshmurthy, Ramanathan M. Ranganathan, Gary C. Barber

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

J. Pressure Vessel Technol 129(3), 426-440 (Jun 30, 2006) (15 pages) doi:10.1115/1.2749290 History: Received October 24, 2005; Revised June 30, 2006

In an effort to enhance the reliability of clamp load estimation in bolted joints, this experimental study investigates the effect of tightening speed and coating on both the torque-tension relationship and wear pattern in threaded fastener applications. The fastener torque-tension relationship is highly sensitive to normal variations in the coefficients of friction between threads and between the turning head and the surface of the joint. Hence, the initial level of the joint clamp load and the overall integrity and reliability of a bolted assembly are significantly influenced by the friction coefficients. The effect of repeated tightening and loosening is also investigated using M12, class 8.8 fasteners with and without zinc coating. The torque-tension relationship is examined in terms of the nondimensional nut factor K. The wear pattern is examined by monitoring the changes in surface roughness using a WYKO optical profiler and by using a LECO optical microscope. A Hitachi S-3200N scanning electron microscope is used to examine the contact surfaces under the fastener head after each tightening/loosening cycle. Experimental data on the effect of tightening speed, fastener coating, and repeated tightening are presented and analyzed.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Fastener testing system (courtesy of RS Technologies Ltd.)

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Figure 2

Schematic of torque-tension head (2)

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Figure 3

WYKO NT 1100 optical profiler (courtesy of Veeco Instruments)

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Figure 4

Nut factor versus tightening speed for unlubricated zinc coated fasteners

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Figure 5

Nut factor versus tightening speed for lubricated zinc coated fasteners

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Figure 6

Nut factor versus tightening speed for lubricated plain fasteners

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Figure 7

Thread friction coefficient versus tightening speed for unlubricated zinc coated fasteners

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Figure 8

Thread friction coefficient versus tightening speed for lubricated zinc coated fasteners

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Figure 9

Thread friction coefficient versus tightening speed for lubricated plain fasteners

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Figure 10

Bearing friction coefficient versus tightening speed for unlubricated zinc coated fasteners

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Figure 11

Bearing friction coefficient versus tightening speed for lubricated zinc coated fasteners

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Figure 12

Bearing friction coefficient versus tightening speed for lubricated plain fasteners

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Figure 13

Roughness measurements on fastener underhead and washer surfaces

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Figure 14

Roughness profiles for underhead and washer surfaces showing wear tracks

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Figure 15

Roughness data for unlubricated zinc coated fastener and washer surfaces tested at tightening speed=1rpm

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Figure 16

Roughness data for unlubricated zinc coated fastener and washer surfaces tested at tightening speed=100rpm

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Figure 17

Roughness data for lubricated zinc coated fastener and washer surfaces tested at tightening speed=1rpm

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Figure 18

Roughness data for lubricated zinc coated fastener and washer surfaces tested at tightening speed=100rpm

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Figure 19

Roughness data for lubricated plain fastener and washer surfaces tested at tightening speed=1rpm

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Figure 20

Roughness data for lubricated plain fastener and washer surfaces tested at tightening speed=100rpm

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Figure 21

Optical microscope images of the unlubricated zinc coated washer surface tested at tightening speed=1rpm(magnification=5×)

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Figure 22

Optical microscope images of the unlubricated zinc coated underhead surface tested at tightening speed=1rpm(magnification=5×)

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Figure 23

SEM images of unlubricated zinc coated washer and underhead surfaces (250μm)

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Figure 24

Main effect of variables on the nut factor K

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Figure 25

Main effect of variables on the thread friction coefficient μt

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Figure 26

Main effect of variables on the bearing friction coefficient μb

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Figure 27

Normal probability plot for the nut factor K

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Figure 28

Normal probability plot for the thread friction coefficient μt

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Figure 29

Normal probability plot for the bearing friction coefficient μb

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