Research Papers

Coupled Field Analysis of a Gas Tungsten Arc Welded Butt Joint—Part I: Improved Modeling

[+] Author and Article Information
D. Sen

e-mail: sen@vt.edu

K. S. Ball

Department of Mechanical Engineering,
Virginia Tech,
Blacksburg, VA 24061

1Corresponding author.

Manuscript received May 25, 2012; final manuscript received October 10, 2012; published online March 18, 2013. Assoc. Editor: Lili Zheng.

J. Thermal Sci. Eng. Appl 5(1), 011010 (Mar 18, 2013) (11 pages) Paper No: TSEA-12-1072; doi: 10.1115/1.4007860 History: Received May 25, 2012; Revised October 10, 2012

Thermally induced residual stresses due to welding can significantly impair the performance and reliability of welded structures. From a structural integrity perspective of welded structures, it is necessary to have an accurate spatial and temporal thermal distribution in the welded structure before stress analysis is performed. Existing research has ignored the effect of fluid flow in the weld pool on the temperature field of the welded joint. Previous research has established that the weld pool depth/width (D/W) ratio and heat affected zone (HAZ) are significantly altered by the weld pool dynamics. Hence, for a more accurate estimation of the thermally induced stresses it is desired to incorporate the weld pool dynamics into the analysis. Moreover, the effects of microstructure evolution in the HAZ on the mechanical behavior of the structure need to be included in the analysis for better mechanical response prediction. In this study, a three-dimensional numerical model for the thermomechanical analysis of gas tungsten arc (GTA) welding of thin stainless steel butt-joint plates has been developed. The model incorporates the effects of thermal energy redistribution through weld pool dynamics into the structural behavior calculations. Through material modeling the effects of microstructure change/phase transformation are indirectly included in the model. The developed weld pool dynamics model includes the effects of current, arc length, and electrode angle on the heat flux and current density distributions. All the major weld pool driving forces are included, namely surface tension gradient induced convection, plasma induced drag force, electromagnetic force, and buoyancy. The weld D/W predictions are validated with experimental results. They agree well. The workpiece deformation and stress distributions are also highlighted. The mathematical framework developed here serves as a robust tool for better quantification of thermally induced stress evolution and distribution in a welded structure by coupling the different fields in a welding process.

Copyright © 2013 by ASME
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Fig. 1

(a) Coupled fields in a welding process and (b) strongly coupled weld pool dynamics-thermal fields

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Fig. 2

Schematic diagram of a moving GTA welding process, highlighting the symmetry condition

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Fig. 3

Surface tension gradient variation with surface active agent content and weld pool surface temperature

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Fig. 4

Variation of (a) heat flux distribution parameter and (b) current density distribution parameter with arc length and welding current [46]

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Fig. 5

Structural analysis boundary conditions definition

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Fig. 6

Magnified view of the meshed computational domain near the weld line

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Fig. 7

Flow diagram of the main solution steps

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Fig. 8

Temperature dependent thermophysical properties for stainless steel [47] (a) density, (b) thermal conductivity, (c) specific heat, and (d) viscosity

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Fig. 9

Variation of mechanical properties with temperature for austenitic stainless steel [49]

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Fig. 10

Validation of (a) heat flux distribution and (b) current density distribution on the workpiece

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Fig. 11

Variation of heat flux distribution with (a) current, (b) arc length, and (c) electrode angle

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Fig. 12

Variation of plasma induced shear stress on weld pool surface with current

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Fig. 13

Weld D/W validation

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Fig. 14

Temperature distribution (in K) in the weld region, and the corresponding velocity vectors (in m/s) due to the weld pool convection

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Fig. 15

Variation of weld D/W ratio with current under welding speed of 2 mm/s, 3 mm arc length, and 150 ppm of surface active agent

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Fig. 16

Residual stress distribution on the top of the weld—(a) longitudinal stress SZ and (b) transverse stress SX. Results are plotted on a xy-plane in the middle of the workpiece.

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Fig. 17

Contours of (a) total deformation and (b) von-Mises stress distribution in the workpiece




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