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In this study, the influence of production-related gaps on the shear tension strength and fatigue performance was investigated for resistance spot welded TRIP steel HCT690. Furthermore, the local strain distribution in shear tension test was calculated by the digital image correlation technique (DIC). The static shear tension strength was found to be almost independent of gaps up to 3 mm. The maximum local strain in the spot weld region however decreases depending on which sample side (deformed or undeformed) is considered. In addition, it has been ascertained that gaps of 3 mm lead to a significant drop in fatigue life compared to gap-free shear tension samples. This fact could be attributed to decreased stiffness, higher transverse vibration and higher rotation (θ) between the sheets as well as increased local stress calculated by 2 dimensional FE simulation.
Spot welding is one of the most important technologies for joining sheet metal. While there are lot of approaches to non-destructive testing, quality assurance still mainly relies on welding parameter monitoring and destructive testing, leading to significant failure rates. In this paper an approach to spot weld testing using flash thermography is presented. The main focus of attention is on the identification of two typical error classes: stick welds and welds at the splash limit. Besides investigating the principal feasibility of thermography for zinc plated samples the results of a series test of spot welds joining 1 mm thick TRIP steel are shown. Based upon these results a statistical criterion is developed which allows a reliable classification of the named error classes.
Numerical simulation of component and assembly behaviour under different loading conditions is a main tool for safety design in automobile body shell mass production. Knowledge of local material behaviour is fundamental to such simulation tests. As a contribution to the verification of simulation results, the local deformation properties of spot-welded similar and dissimilar material joints in shear tension tests were investigated in this study for a TRIP steel (HCT690T) and a micro-alloyed steel (HX340LAD). For this reason, the local strain distribution was calculated by the digital image correlation technique (DIC). On the basis of the hardness values and microstructure of the spot welds, the differences in local strain between the selected material combinations are discussed. Additionally, the retained austenite content in the TRIP steel was analysed to explain the local strain values. Results obtained in this study regarding similar material welds suggest significant lower local strain values of the TRIP steel HCT690T compared to HX340LAD. One reason could be the decrease of retained austenite in the welded area. Furthermore, it has been ascertained that the local strain in dissimilar material welds decreases for each component compared with the corresponding similar material weld.