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Materials Technology

The Influence of Mechanical and Laser Cutting on the Fatigue Strengths of Square Hollow-Section Welded T-Joints

[+] Author and Article Information
R. Moazed

Department of Mechanical Engineering,  University of Saskatchewan, Saskatoon, SK S7N 5A9, Canadareza.moazed@usask.ca

R. Fotouhi1

Department of Mechanical Engineering,  University of Saskatchewan, Saskatoon, SK S7N 5A9, Canada

1

Corresponding author.

J. Offshore Mech. Arct. Eng 134(3), 031401 (Feb 10, 2012) (12 pages) doi:10.1115/1.4005186 History: Received June 18, 2010; Revised August 07, 2011; Published February 10, 2012; Online February 10, 2012

T-joint connections are commonly encountered in many machine components and load carrying members. The T-joint connections can be fabricated using traditional cutting (machine or flame) or by laser cutting techniques. The present study investigates the feasibility of using laser cutting to produce welded square hollow-section T-joints with similar or higher fatigue strengths than their conventional mechanical cut counterparts. A total of 21 full-scale T-joint samples, typical of those found in the agricultural industry, were included in this study. Nineteen of these samples were examined with the intention of forming a fatigue crack of approximately 3.8 cm (1.5 in.es) in length, and two samples with strain gauges attached for strain measurements. The experimental results of the full-scale T-joints subjected to cyclic loads showed that the fatigue strength of the samples that were manufactured with laser cutting were higher than those fabricated with mechanical cutting. A finite element analysis (FEA) of the T-joints was also performed, and the FEA results were verified with the experimental strain measurements.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Test specimen: (a) schematics of traditional mechanical cut edge (b), (c) schematics of laser cut edge and (d) the cuped T-joint connection

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Figure 2

Test rig and loading mechanism (a) and (b) for in-plane loading conditions and (c and d) for general loading conditions (out-of-plane loads)

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Figure 3

Simulink program developed for the control of the hydraulic actuator

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Figure 4

Locations 1 to 8 of the strain gauges installed

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Figure 5

(a) Couped sample and (b) weld profile shown for the cut made along line A3

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Figure 6

(a) Conventional sample and (b) weld profile shown for the cut made along line A2

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Figure 7

(a) Geometry of krouse specimen for the fatigue testing of the weld and parent materials and (b) plates used for the preparation of the welded samples

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Figure 8

S-N curves of the weld and parent materials

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Figure 9

(a) in-plane loading, and (b) general loading conditions

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Figure 10

Measured strains in the X-direction for conventional sample for (a) in-plane loading and (b) general loading

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Figure 11

Comparison of the strain readings at location 6 in the X-direction for the conventional and couped samples

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Figure 12

FE solid element model of the welded T-joint

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Figure 13

Modeled cross-section and corresponding nodes in FEA for (a), (b) conventional and (c), (d) couped T-joint

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Figure 14

Stresses along the path BA (shown in Fig. 1) for the top surface of the tube: (a) normal stress and (b) shear stress components

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Figure 15

Stresses along the path BA (shown in Fig. 1) for the mid-thickness of the tube: (a) normal stress and (b) shear stress components

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Figure 16

Membrane and bending stresses in the X-direction for the couped and conventional samples for (a) general and (b) in-plane loading conditions

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Figure 17

T-joint sample with fatigue crack initiated (a) at the weld toe close to location 6 and (b) at the weld itself close to location 6

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Figure 18

Load-life diagram to failure for 3.8 cm (1.5 in.) fatigue crack for loads ranging from 4500–12,000 lbs (20,017 to 53,379 N)

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