13th International Conference on Fracture June 16–21, 2013, Beijing, China -11- 4. Conclusion Based on the calibrated Gologanu material models and failure criteria of Thomason and Brown and Embury for the different material zones of resistance spot welded joints between the hot-stamped ultra-high strength steel and the microalloyed HSLA steel, the joints’ behavior in terms of force vs. displacement curves, load bearing capacities, fracture mode and fracture locations can be calculated using detailed finite-element models according to the joints geometry. In the cases investigated pull-out fracture of the joints under shear loading took place inside the softened HAZ of 22MnB5 due to localization of plastic deformation. Under combined axial and shear loading as well as under pure axial loading situations a change in fracture location can be observed. In these cases fracture occurred as pull-out fracture in the coarse grain HAZ of 22MnB5 directly adjacent to the weld nugget. Fracture initiation of all joints is calculated due to the Thomason criterion. The evolution of axial and shear forces acting on the weld during different loading situations could be obtained by decomposing the applied loads into their axial and shear components according to their true loading angles. Such results can be used for the adjustment or the identification and construction of simplified force based failure criteria used for simplified spot weld models in crash simulations. Furthermore, factors influencing the load bearing capacity of the joints, as e.g. sheet thickness, weld nugget diameter or other geometrical quantities can be investigated by means of detailed finite-element modeling of spot welded joints between the investigated materials without further experimental effort. Acknowledgements The results presented are part of the research project P806/A262. The research project was conducted with professional supervision and financial support of the Research Association for Steel Application (FOSTA), Düsseldorf, Germany and the Research Association of the Working Group of the Iron- and Metal-processing Industry e.V. (AVIF), Ratingen, Germany by the Stiftung Stahlanwendungsforschung. Sincere thanks are given for the sponsorship. References [1] LS-DYNA Keyword User´s Manual, Version 971, Livermore Software Technology Corporation (LSTC), 2010. [2] PAM-CRASH/SAFE Solver Notes Manual, ESI Software GmbH, 2004. [3] ABAQUS Analysis user’s manual, Version 6.9. Hibbit, Karlsson & Sorensen Inc., 2004. [4] J.H. Song, H. Huh, Failure characterization of spot welds under combined axial-shear loading conditions, International Journal of Mechanical Sciences, 53 (2011) 513 – 525. [5] S.-H. Lin, J. Pan, S.-R. Wu, T. Tyan, P. Wung, Failure loads of spot welds under combined opening and shear static loading conditions, International Journal of Solids and Structures, 39 (2002) 19 – 39. [6] S. Aslanlar, The effect of nucleus size on mechanical properties in electrical resistance spot welding of sheets used in automotive industry, Materials & Design, Vol. 27 (2006), 125 – 131. [7] S. Sommer, S. Burget, F. Klokkers, D. Hein, D. Krätschmer, H.-J. Wink, Charakterisierung und Ersatzmodellierung des Bruchverhaltens von Punktschweißverbindungen aus ultrahochfesten Stählen für die Crashsimulation unter Berücksichtigung der Auswirkungen der Verbindung auf das Bauteilverhalten, Final report FOSTA/AVIF P806/A262, to be published [8] V.H. Baltazar Hernandez, S.K. Panda, M.L. Kuntz, Y. Zhou, Nanoindentation and microstructure analysis of resistance spot welded dual phase steel, Material Letters, 64 (2010), 207 – 210. [9] O. Hahn, D. Gieske, A. Rhode, Probe und Probenspannvorrichtung zum Einsatz in
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