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Technical Briefs

True Cross Sectional Area of Screw Threads With Helix and Root Radius Geometries Taken Into Consideration

[+] 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 131(2), 024501 (Dec 10, 2008) (5 pages) doi:10.1115/1.2967884 History: Received December 27, 2006; Revised June 12, 2007; Published December 10, 2008

When evaluating the strength of threaded fasteners under external loads, stress area is commonly used. However, in order to elucidate the mechanical behavior of bolted joints more rigorously and extensively, it is desired to derive an analytical expression of the true cross sectional area of screw threads, with the effects of the helix and root radius taken into account. In this paper, a series of closed-form algebraic equations, which can calculate true cross sectional areas of internal and external screw threads, is derived. The equations obtained can be applied to both metric and inch screw threads with a coarse or a fine pitch. Then, the equivalent diameter of the true sectional area is defined and compared with the pitch diameter and stress area diameter.

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Copyright © 2009 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 the external thread perpendicular to the bolt axis

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Figure 3

Thread root geometry of external threads

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Figure 4

Geometry of the internal thread

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Figure 5

Profile of the cross section of the external thread for metric coarse screw threads

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Figure 6

Profile of the cross section of the external thread for metric fine screw threads

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Figure 7

Effect of the root radius on the equivalent diameter

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