Effect of strength of steel sheets on tensile shear strength and failure mode of dissimilar joint of spot welds

Abstract

Advanced high strength steel sheet (AHSS) is widely used in the automotive body for weight reduction and the improvement of crash performance. For example, TS1500 MPa class hot stamped steel (1500HS steel) sheet is applied to many vehicle models. However, there is a concern that performance of spot welded joints will decline as steel strength increases. In order to further expand the application of AHSS, it is very important to have knowledge about the characteristics of spot welded joints. In this report, we investigated the tensile shear strength (TSS) of the 1500HS steel sheet. Then, we compared the joint strength and failure position of the same kind material joints and the dissimilar material joints with the 1500HS steel sheet in case of the plug failure. As a result, it was found that TSS of dissimilar material joints depend on base metal strength on lower strength steel side. However, fracture occurred on the 1500HS steel side except for joints with large difference of base metal strength. The mechanism is thought that the effect of strain concentration at the edge of nugget on the 1500HS steel side due to the increase of rotational deformation around the nugget.