Fatigue strength of tensile shear spot welds made of ST12 steel

Fatigue specimens were made of S2 steel sheets wilh product line welding equipment. Microstructure in different zones was observed and Vicker's hardness around the weld nugget was measured. Constant amplitude fatigue loading was applied on specimens with MTS material testing frame to obtain the S-N curve. According to the constant amplitude fatigue test results, two-stage loading tests were carried out, and then linear damage accumulation rule was used for damage analysis under two-stage loading. Damage accumulation results show that there was loading sequence effect for low carbon S2 steel spot welded joint under two-stage loading, the loading sequence effect under high-low loading sequence was even more explicit.