Comparative Fatigue Life Study on the Indentation Levels of Resistance Spot Welds with Dual Phase Steel

This project is focused on the critical parameters affecting nugget formation through both electrical-thermal analysis and thermal-mechanical analysis during resistance spot welding (RSW) process. The object of this study is three stacked up sheets instead of conventional two sheets assemblies because of its wide application in automobile industry. It is analyzed that the nugget and the plastic ring region localized around nugget are more inclined to have fatigue failure such as cracks and fracture. Local indentation levels comprising of 10%, 30% and 50% of a sheet thickness are investigated under tensile shear load and cross tension load by fatigue experiments. It is proved that higher indentation level weld is more likely to have longer fatigue life than that of lower indentation level weld at the same load condition for both tensile shear loads and cross tension loads. Moreover, comparing with the results derived from DP material welds, it is obtained that the indentation levels for mild steel welds shows similar results on fatigue lives.