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Research Papers

Numerical Simulations and Experimental Results of Tensile Test Behavior of Laser Butt Welded DP980 Steels

[+] Author and Article Information
S. K. Panda1

Centre for Advanced Materials Joining, University of Waterloo, Waterloo, ON, N2L 3G1, Canadas2panda@engmail.uwaterloo.ca

N. Sreenivasan, M. L. Kuntz, Y. Zhou

Centre for Advanced Materials Joining, University of Waterloo, Waterloo, ON, N2L 3G1, Canada

1

Corresponding author. Also at E3-3110, Department of Mechanical Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada.

J. Eng. Mater. Technol 130(4), 041003 (Aug 26, 2008) (9 pages) doi:10.1115/1.2969256 History: Received December 31, 2007; Revised July 02, 2008; Published August 26, 2008

Laser welding of advanced high strength steels for fabrication of tailor welded blanks is of increasing interest for continued improvements in vehicle performance and safety without an increase in weight. Experimental results have shown that formability of welded dual-phase (DP) steels is significantly reduced by the formation of a softened region in the heat-affected zone (HAZ). In this study, a finite element simulation of welded DP980 samples undergoing transverse uniaxial tensile testing was used to evaluate the effects of soft zone width and strength on formability characteristics. Both the strength and the ductility of laser welded blanks decreased compared with those of unwelded blanks due to the formation of a softened outer-HAZ, where strain localization and final fracture occurred during tensile testing. The magnitude of softening and the width of the HAZ depend on the laser specific energy. It was observed from tensile test experiments and numerical simulations that both a decrease in strength and an increase in width of the softened HAZ were responsible for a decrease in the overall strength and ductility of the welded blanks.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Subsize tensile test specimen

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Figure 2

Minitensile specimen used to determine the properties of weld (all dimensions are in mm)

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Figure 3

Micrograph of the weldment showing different zones

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Figure 4

Formation of three different zones in laser welding: (a) cross-weld hardness profiles and (b) schematic representation of three different zones in a transverse tensile test

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Figure 5

FE meshes for the quarter model transverse tensile specimen with constraints in the XY plane

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Figure 6

True stress–true strain curve obtained from the experiment for base metal (DP980) and weld

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Figure 7

Log true stress–log true strain curve obtained from the experiment for base metal (DP980) and weld zone

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Figure 8

Comparison of load-elongation curves obtained from experiment and numerical simulation for DP980 steel

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Figure 9

Comparison of the stress-strain behaviors of the base metal and transverse welded blanks

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Figure 10

Localized failure in the softened zone during tensile testing of transverse welded specimens (diode laser weld)

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Figure 11

Comparison of experimental and numerical results for load versus displacement in diode and Nd:YAG laser welds of DP980

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Figure 12

Comparison of experimental and numerical major strain distributions in the transverse welded tensile specimen (diode laser weld)

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Figure 13

Strain localization in the softened zone observed in both experiment and FEM simulation

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Figure 14

Simulated maximum load and displacement with respect to the decrease in the softened zone strength for a welded sample with a 0.5 mm softened zone width of HAZ

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Figure 15

Plastic strain contours in the different weld zones for softened zone strengths of (a) 1300 MPa and (b) 1450 MPa at time=0.1996 s of deformation

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Figure 16

Plastic strain contours in the different weld zones for softened zone strengths of (a) 1300 MPa and (b) 1450 MPa at time=3.1996 s of deformation

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Figure 17

Simulated maximum load and displacement with respect to the softened zone width (with softened zone strength of 1300 MPa) of HAZ

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Figure 18

Y-stress distribution (in GPa) in the softened zone (of 4 mm in width) due to the development of constraint force during deformation

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Figure 19

Comparison of Y-stress developed in the welded specimen

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