Failure modes of single resistance spot welded joints subjected to combined fatigue loading

Combined loading fatigue tests were conducted on spot welded coupons of a galvanized sheet steel for proportional, constant amplitude loading conditions. The factors that influence the failure modes of the coupons are described and photographs of typical failure modes are presented in addition to the fatigue life results of the tests. The fatigue crack initiation sites for all of the tests were at the edge of the spot weld nugget at the sheet interface. The applied load amplitude and nugget diameter had the most significant effect on the final fatigue life of the coupons. The main factors that determine the final failure mode of the fatigue specimens are the ratio of shear and normal force (i.e. the applied loading angle), the applied mean load, and nugget diameter. The observations are related to common spot weld fatigue damage parameters.