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Research Papers: Design and Analysis

Proposition of Helical Thread Modeling With Accurate Geometry and Finite Element Analysis

[+] Author and Article Information
Toshimichi Fukuoka

Faculty of Maritime Sciences,  Kobe University, 5-1-1 Fukaeminami, Higashinada, Kobe 658-0022, Japanfukuoka@maritime.kobe-u.ac.jp

Masataka Nomura

Faculty of Maritime Sciences,  Kobe University, 5-1-1 Fukaeminami, Higashinada, Kobe 658-0022, Japannomura@maritime.kobe-u.ac.jp

J. Pressure Vessel Technol 130(1), 011204 (Jan 17, 2008) (6 pages) doi:10.1115/1.2826433 History: Received September 01, 2006; Revised December 08, 2006; Published January 17, 2008

Distinctive mechanical behavior of bolted joints is caused by the helical shape of thread geometry. Recently, a number of papers have been published to elucidate the strength or loosening phenomena of bolted joints using three-dimensional finite element analysis. In most cases, mesh generations of the bolted joints are implemented with the help of commercial software. The mesh patterns so obtained are, therefore, not necessarily adequate for analyzing the stress concentration and contact pressure distributions, which are the primary concerns when designing bolted joints. In this paper, an effective mesh generation scheme is proposed, which can provide helical thread models with accurate geometry to analyze specific characteristics of stress concentrations and contact pressure distributions caused by the helical thread geometry. Using the finite element (FE) models with accurate thread geometry, it is shown how the thread root stress and contact pressure vary along the helix and at the nut loaded surface in the circumferential direction and why the second peak appears in the distribution of Mises stress at thread root. The maximum stress occurs at the bolt thread root located half a pitch from nut loaded surface, and the axial load along engaged threads shows a different distribution pattern from those obtained by axisymmetric FE analysis and elastic theory. It is found that the second peak of Mises stress around the top face of nut is due to the distinctive distribution pattern of σz.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Thread cross section along the bolt axis

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Figure 2

Profile of the cross section of external thread perpendicular to the bolt axis

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Figure 3

Accurate cross section profile of metric coarse thread

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Figure 4

Mesh patterns of cross sections of bolt model

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Figure 5

One-pitch model of external thread and cross section of nut model

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Figure 6

Fienit element model of entire bolted joint

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Figure 7

Mises stress distributions at the bolt thread root along the helix

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Figure 8

Normalized maximum Mises stress occurred at the bolt thread root

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Figure 9

Circumferential contact pressure distributions at the nut loaded surface

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Figure 10

Axial load distributions along engaged threads

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Figure 11

Effect of the chamfering of the nut top thread

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