Conclusions While material qualification tests are frequently based on similar welding configurations, real car body applications are quite systematically dissimilar configurations. For spot welds failing in plug mode, the strength of the assembly only depends on the weakest material strength. In the case of AHSS+AHSS welded combinations, however, things turn out differently. Similar grade but dissimilar-thickness high-strength-steel configurations have been spot welded and tested in cross-tension. The following main conclusions can be highlighted: 1. For dissimilar-thickness configurations, the cross-tensile strength is above the standard “minimum rule” assumptions, this phenomenon being called a “positive deviation.” 2. Limited thermal and notch location effects can explain part of this positive deviation, but the main reason is mechanical. 3. As evidenced through several analytical and numerical studies, this mechanical effect is due to the less severe local stresses at the notch in case of uneven thickness, and improves the positive deviation when the thickness ratio increases. Although widely used for material qualification and scientific purposes, similar configurations appear as the worst case in terms of cross-tension performance for high-strength steels. Actual vehicle design should consider positive deviation in dissimilar configurations to maximize the potential strength of spot welds in high-strength steels. Acknowledgments The authors would like to thank Savine Henrion, Sylvain Dancette and Florent Krajcarz for their help in this study and ArcelorMittal for granting us permission to publish this work. References 1. Seeger, F., Feucht, M., Frank, Th., Keding, B., and Haufe, A. 2005. An investigation on spot weld modeling for crash simulation with LS-DYNA. LS-DYNA Anwenderforum, Bamberg. 2. 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Engineering Fracture Mechanics 87(6): 48–61. WELDING JOURNAL 43 Table 4 — Average α Levels Configuration Average α (N/mm2) TRIP800 1+1 mm 747 TRIP800 2+2 mm 639 TRIP800 1+2 mm 1146 DP980 LCE 1+1 mm 929 DP980 LCE 1.25+1.25 mm 823 DP980 LCE 2+2 mm 913 DP980 LCE 1+1.25 mm 1014 DP980 LCE 1+2 mm 1220 DP980 LCE 1.25+2 mm 1180 DP980 LCE 1+patch+1 mm 1179 DP980 LCE 1+1+1 mm 1004 DP980 LCE 1+1+0 mm 1039 DP980 LCE 1+++1+1 mm 1277 Dear Readers: The Welding Journal encourages an exchange of ideas through letters to the editor. Please send your letters to the Welding Journal Dept., 8669 NW 36th St., #130, Miami, FL 33166. You can also reach us by FAX at (305) 443-7404 or by sending an e-mail to Kristin Campbell at kcampbell@aws.org.
Welding Journal | January 2014
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