Effect of Thread Pitch and Initial Tension on the Self-Loosening of Threaded Fasteners

[+] Author and Article Information
Sayed A. Nassar, Basil A. Housari

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

J. Pressure Vessel Technol 128(4), 590-598 (Jul 30, 2005) (9 pages) doi:10.1115/1.2349572 History: Received June 27, 2005; Revised July 30, 2005

A mathematical model and an experimental procedure are presented to study the self-loosening phenomenon of threaded fasteners that are subjected to cyclic transverse loads. The study investigates the effect of thread pitch, initial bolt tension, and the amplitude of the external excitation on the loosening of a single-bolt joint. The rate of drop in the joint clamp load (fastener tension) per cycle, as well as the total number of cycles that would cause the complete loss of clamp load, are monitored. In the mathematical model, the differential equations of linear and angular motion of the bolt are formulated in terms of the system properties and the external cyclic transverse excitation. Numerical integration of the equation of angular motion provides the bolt rotation in the loosening direction, which causes the partial or full loss of the clamp load. An iterative MATLAB code is developed and used for the calculation of tension loss in the fastener tension due to the self-loosening. Analytical and experimental results are discussed.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Bolt-free body diagram

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Figure 2

Bolt motion under external transverse force

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Figure 3

Forces on the bearing surface

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Figure 4

Thread contact force components

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Figure 5

Thread friction force components

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Figure 6

Effect of thread pitch on the self-loosening

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Figure 7

Tension-rotation relationship for 1∕2in.-13 and 1∕2in.-20 bolts

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Figure 8

Flow chart for the MATLAB algorithm

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Figure 9

Self-loosening test setup

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Figure 10

Typical self-loosening curve

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Figure 11

Effect of thread pitch on the self-loosening

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Figure 12

Effect of initial bolt tension on the self-loosening

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Figure 13

Effect of the excitation amplitude on the self-loosening



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