Fatigue performance of spot welded and weld bonded advanced high strength steel sheets

Fatigue properties and failure characterisation of spot welded and spot weld bonded (WB) high strength steels, such as advanced high strength steels (AHSS) DP600 GI, TRIP600, and high strength low alloy (HSLA) steel HSLA340Y GI have been studied. Tensile shear and coach peel specimens were used in the present study. Both constant amplitude sinusoidal loading and random loading fatigue tests were conducted. The results show that the fatigue strength, under constant amplitude sinusoidal fatigue loading, of spot welded DP600 GI and TRIP600 specimens was approximately the same as that of HSLA340Y GI specimens in the case of tensile shear and coach peel type specimens for both low and high cycle fatigue. However, spot WB specimens show significantly higher fatigue strength than that of spot welded specimens, especially at low load condition (high cycles). Fatigue tests were also conducted on wide width DP600 GI and HSLA340Y GI spot welded specimens and no significant difference in fatigue strength between regular size specimens (39 mm in width) and wide specimens ( 125 mm in width) was observed. Random loading fatigue tests show that DP600 GI has a lower fatigue strength compared to HSLA340Y GI. Crack initiation and propagation during the fatigue loading history has been experimentally determined and discussed.