Research Papers

Thread Forming in Lightweight Material Joints Using Self-Tapping Screws

[+] Author and Article Information
Zhijun Wu, Shraddha Jagatap, Kshitij Satav

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

Sayed A. Nassar

Fellow ASME
Department of Mechanical Engineering,
Fastening and Joining Research Institute (FAJRI),
Oakland University,
Rochester, MI 48309

Manuscript received November 15, 2015; final manuscript received February 22, 2016; published online June 20, 2016. Assoc. Editor: Matteo Strano.

J. Manuf. Sci. Eng 138(9), 091006 (Jun 20, 2016) (10 pages) Paper No: MANU-15-1591; doi: 10.1115/1.4032972 History: Received November 15, 2015; Revised February 22, 2016

In this study, thread forming performance is evaluated under cyclic heating and cooling of tapped lightweight multimaterial joints in which steel self-tapping screws are used. Joint performance is assessed in terms of residual torque, pullout strength, load transfer capacity (LTC), and failure mode. Cyclic temperature fluctuates between 130 °C and −20 °C in a computer-controlled environmental chamber. Joint coupon materials are steel and Nylon polymeric material. Data analysis and discussion are provided. Analysis of experimental data provides a useful insight into design optimization of self-tapped joints.

Copyright © 2016 by ASME
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Fig. 1

Illustration of the test samples

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Fig. 2

RS torque–tension test machine

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Fig. 3

(a) Thermotron machine, (b) samples arranged in thermal chamber, and (c) one thermal cycle profile

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Fig. 4

(a) pullout test setup on MTS and (b) single-lap joint shear test setup on MTS

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Fig. 5

Tightening torque and bolt tension for different pilot hole diameters

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Fig. 6

Thread stripping failure due to screw tightening

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Fig. 7

Effect of pilot hole diameter on self-tapping screw torques and tension

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Fig. 8

Effect of thermal cycles on residual loosening torque

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Fig. 9

Pullout force–displacement relationship

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Fig. 10

(a) Bending in coupon during pullout test and (b) pullout coupon failure modes by thread stripping and brittle failure

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Fig. 11

Effect of thermal cycle on pullout strength and joint linear stiffness

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Fig. 12

Shear force–displacement relationship for the baseline of single-lap Nylon 6 joint with self-tapping screws

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Fig. 13

Single-lap joint shear test: (a) bolt and Nylon joint bending in the test, (b) screw breakage failure, and (c) Nylon 6 joint breakage failure

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Fig. 14

Effect of thermal cycle on screwed joint LTC and joint linear stiffness




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