Fatigue Behavior of Spot Welded High Strength Steel Joints

A new fatigue test specimen configuration has been developed which allows testing of spot welded joints in a fully reversed axial fatigue mode in a life range from 5 × l0³ to 1 × 10⁷ cycles. The specimen, a unique square concentric tube arrangement, tests four spot welds simultaneously. The materials tested in this program included three dual-phase steels, an SAE 940X grade, SAE 1020 steel and a cold rolled, low carbon steel - SAE 1006AK for purposes of comparison. The general results indicate the superiority of the dual-phase steels in the low life region with all steels showing equivalent behavior beyond 5 × 10⁵ cycles. Additionally, beneficial effects of increased steel thickness and increased nugget diameter were observed.