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Research Papers

A Novel Prevailing Torque Threaded Fastener and Its Analysis

[+] Author and Article Information
H. N. Vikranth

Centre for Product Design and Manufacturing,
Indian Institute of Science,
Bengaluru-560012, India

Ashitava Ghosal

Department of Mechanical Engineering,
Indian Institute of Science,
Bengaluru-560012, India
e-mail asitava@mecheng.iisc.ernet.in

We have used r and s as equal to ensure slope continuity between two successive cubic helix profiles along the nut or bolt.

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanical Design. Manuscript received August 30, 2012; final manuscript received June 11, 2013; published online September 5, 2013. Assoc. Editor: James Schmiedeler.

J. Mech. Des 135(10), 101007 (Sep 05, 2013) (9 pages) Paper No: MD-12-1435; doi: 10.1115/1.4024977 History: Received August 30, 2012; Revised June 11, 2013

We present a novel concept of a threaded fastener that is resistant to loosening under vibration. The anti-loosening feature does not use any additional element and is based on modifying the geometry of the thread in the bolt. In a normal nut and bolt combination, the axial motion of the nut or bolt is linearly related to the rotation by a constant pitch. In the proposed concept, the axial motion in the bolt is chosen to be a cubic function of the rotation, while for the nut, the axial motion remains linearly related to the rotation. This mismatch results in interference during the tightening process and additional torque required to overcome this interference gives rise to the enhanced anti-loosening property. In addition, the cubic curve is designed to ensure that the mismatch results in stresses and deformation in the elastic region of the chosen material. This ensures that the nut can be removed and reused while maintaining a repeatable anti-loosening property in the threaded fastener. A finite element analysis demonstrates the feasibility of this concept.

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References

Figures

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Fig. 6

Meshing of model and boundary conditions used in FEA

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Fig. 7

Stresses in composite tubes [40]

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Fig. 8

(a)-(b) von-Mises stress and contact pressure of the interference fit from FEA

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Fig. 5

Sectional view at θ = 76.07 deg corresponding to maximum interference

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Fig. 4

V-profile for ISO general-purpose metric screw threads

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Fig. 3

(a)–(b) Examples of cubic profiles with varying r and s

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Fig. 2

Variation of lead angle for regular helix and cubic curves

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Fig. 1

Comparison of the z coordinate in cubic and linear helical curve for M10 (r = s = 0.01)

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Fig. 9

(a)-(b) von-Mises stress from FEA (for r = s = +0.17)

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Fig. 10

Centroid of the nut thread in sectional view

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Fig. 11

Fy versus interference plot (for steel)

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Fig. 13

von-Mises stress versus interference for steel and titanium alloy

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