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RESEARCH PAPERS

Clamp Load Loss due to Elastic Interaction and Gasket Creep Relaxation in Bolted Joints

[+] Author and Article Information
Sayed A. Nassar, Ali A. Alkelani

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

J. Pressure Vessel Technol 128(3), 394-401 (Jul 30, 2005) (8 pages) doi:10.1115/1.2218343 History: Received June 27, 2005; Revised July 30, 2005

An experimental study is presented in order to determine the clamp load loss due to elastic interaction and gasket creep relaxation in bolted joints. Studied parameters include the gasket material and thickness, bolt spacing, tightening sequence, fastener grip length, and level of the fastener preload. The joint is composed of two steel flanges and a gasket made of styrene butadiene rubber or flexible graphite. The flanges are fastened together using M12x1.75 Class 10.9 fasteners. Force washers are used to monitor bolt tensions in real time. Four different gasket thicknesses of styrene butadiene rubber (1/16, 1/8, 3/16, and 1/4 in.) and two thicknesses of flexible graphite (1/16 and 1/8 in.) are considered. For the same bolt circle of the flange, the bolt spacing is varied by using a different number of bolts; spacing that corresponds to using three, five, or seven bolts is considered in this study. The effect of the tightening strategy is studied by using sequential, star, or simultaneous tightening patterns. Bolt tightening is accomplished by using either an electric digital torque wrench with various control options or by using a production-size multiple spindle fastening system that is capable of simultaneous tightening of all fasteners. Experimental data is presented and analyzed, in order to study the effect of the various parameters on the clamp load loss due to the combined effect of elastic interaction and gasket creep relaxation at room temperature.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 8

(a) Effect of flexible graphite gasket thickness (1∕16in.). (b) Effect of flexible graphite gasket thickness (1∕8in.).

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Figure 9

(a) Tension loss in the joint for three levels of fastener preload. (b) Tension loss in the joint for three levels of fastener preload.

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Figure 10

Relaxation versus initial stress for red rubber of various thicknesses

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Figure 11

Tension loss for two different fastener grip length L

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Figure 12

Clockwise sequential tightening (1-2-3-4-5)

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Figure 13

Star tightening pattern (1-3-5-2-4)

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Figure 14

Normalized tension versus time (simultaneous tightening)

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Figure 1

Experimental test setup

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Figure 2

Simultaneous tightening test setup (five-spindle fastening system)

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Figure 3

Sequential and star tightening patterns

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Figure 4

Bolt tension versus time (single-bolt joint)

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Figure 5

(a) Behavior of bolted flange: no gasket. (b) Behavior of bolted flange: 1∕8in. red rubber. (c) Behavior of bolted flange: 1∕8in. flexible graphite.

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Figure 6

(a) Effect of red rubber gasket thickness (1∕16in.). (b) Effect of red rubber gasket thickness (1∕8in.). (c) Effect of red rubber gasket thickness (3∕16in.). (d) Effect of red rubber gasket thickness (1∕4in.).

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Figure 7

Gasket stress versus compression: red rubber

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