Experimental study on the behavior of mismatched butt welded joints of high strength steel

Abstract

An experimental study on the load carrying capacity and deformation capacity of 108 mismatched butt welded joints of high strength steel (HSS) under tension load is performed, to investigate the strain distribution development over the specimen along the whole loading process by using digital image correlation technique (DIC). Three simplified hardness distribution patterns were identified based on the existence of hardened HAZ zone (HHZ) and softened HAZ zone (SHZ). For butt joints with Pattern I or Pattern II hardness distribution (92 specimens), the maximum load increases almost linearly with increasing values of mismatch ratio until mismatch ratio reaches 1.0, while for the specimens (42 specimens) with Pattern III hardness distribution, the strength are significantly lower than the estimated value from EC3, which shows the unsafety of EC3 with wide SHZ. In almost all the cases, mismatch (undermatch or overmatch) leads to a decrease in joint ductility because of strain localization inside the weaker zone, which varies depending on the failure location and the hardening properties in these failure zone. It is noted that the loss of material strength in SHZ can only be mitigated with thin SHZ due to the constraint provided by the unyielded adjacent material.