Ultimate Strength and Failure Mechanism of Resistance Spot Weld Subjected to Tensile, Shear, or Combined Tensile/Shear Loads

[+] Author and Article Information
Yuh J. Chao

Department of Mechanical Engineering, University of South Carolina, Columbia, SC 29208e-mail: chao@sc.edu

J. Eng. Mater. Technol 125(2), 125-132 (Apr 04, 2003) (8 pages) doi:10.1115/1.1555648 History: Received February 05, 2002; Revised August 12, 2002; Online April 04, 2003
Copyright © 2003 by ASME
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Grahic Jump Location
Optical micrographs showing the stages of failure process of a lap-shear sample: (a), (b), and (c) show the progress of the localized necking and (d) final fracture (reproduced from Zuniga and Sheppard 11)
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SEM fractograph (1000X) of a lap-shear sample: the circular dimple rupture microstructure indicating tensile fracture
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Global deformation pattern (b) and the weld nugget pullout failure (c) of a cross tension sample
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Optical micrograph of the cross section of a failed 1.5 mm specimen showing the pullout failure of the weld nugget around the nugget circumference (reproduced from Lin, et al. 14)
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SEM fractograph (1000X) of a cross tension sample: the “fish scale” rupture microstructure indicating shear fracture
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Assumed stress distribution around the weld nugget in a lap-shear sample
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Assumed stress distribution around the weld nugget in a cross tension sample
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Failure loads normalized with respect to batch A, lap-shear sample (ALS)
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Failure strength of lap-shear and cross tension samples made of cold rolled steels with various ultimate tensile strength 24 and prediction by (7) (The predicted is shifted to the left (Mises) and right (Tresca) for clarity)
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Tensile/shear mixed mode test sample geometry 13
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Tensile/shear mixed mode test data 13 and prediction by (10) Normalized load=failure load/(nugget diameter x sheet thickness)
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Engineering and true stress-strain curves for the HSLA steel tested
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Cross tension and lap-shear test sample geometries
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Schematics showing the load-displacement curves of lap-shear and cross tension samples
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Ultimate strength of the spot welds; batch A,B,C-USC data Batch D, Zuniga and Sheppard 11; batch E, Sawhill and Furr 24 (some data are shifted horizontally for clarity)
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Global deformation and failure process of a lap-shear spot-weld sample: (a) initial configuration, (b) nugget rotation (align first with the loading line); (c) stretching, thinning, and necking, and (d) tensile fracture due to localized necking.
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Fracture initiation site of a lap-shear spot-weld sample. The hairline at the bottom of the nugget is the crack.



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