Practical failure analysis of resistance spot welded advanced high-strength steel sheets

In this study, a practical numerical procedure to analyze the failure behavior of resistance spot welded structures, especially for structures composed of advanced high-strength steels (AHSS) sheets, was developed for the first time. The root cause of the difference in failure modes between the welded structures of AHSS and conventional mild steel sheets was also elucidated. Given that the characterization of detailed mechanical properties of base sheets and weld nuggets is extremely complex, considerable effort was exerted to identify and properly simplify critical mechanical properties that are essential for failure analysis. This was achieved by developing a simple but effective experimental procedure to characterize the key properties by mainly utilizing standard and miniature-specimen tensile tests that are commonly available in any laboratory. In this study, two AHSS sheet grades, TRIP980 and DP980, as well as a conventional mild steel (GMW2) sheet grade were considered. The study involved the macroscopic characterization of mechanical properties including hardening behavior and fracture criterion. Furthermore, electron backscattered diffraction analysis of the base sheets and weld nuggets was also performed. The failure mode and strength of the lap-shear and U-shape tension tests were then analyzed for similar welded sheets under quasi-static loading conditions.