Examination of Mode I Loading on Resistance Spot Weld Groups in Tailored Hot Stampings

In this work, Mode I fracture of single and grouped resistance spot welds in hot stamped steels for automotive applications were examined. Fully quenched and 400oC tailored Usibor® 1500-AS samples were used to create flat sheet and hat channel specimens which were resistance spot welded. To characterize the material constituent distribution throughout the parts, hardness measurements were taken. While a large amount of work has been done to characterize tailored hot stampings, spot weld failure is not well understood. The problem is particularly acute for weld failure in structural components where groups of welds may fail in an unstable unzipping mode. To that end, coupon and structural Mode I testing was conducted where force, displacement, and visual data were sampled throughout the test events. While ductility appeared to have little effect on the strength of a single weld, it largely affected the structural response.