Spot Weld Failure Loads under Combined Mode Loading Conditions

Failure loads of spot welds are investigated under static and impact loading conditions. A test fixture was designed and used to obtain maximum loads of spot welds under a range of combined opening and shear loads with different loading rates. Optical micrographs of the cross sections of spot welds before and after failure were obtained to understand the failure processes under various loading rates and different combinations of loads. The experimental results indicate that under nearly pure opening loads, the failure occurs along the nugget circumferential boundary. Under combined opening and shear loading conditions, the failure starts from the tensile side of the base metal near the nugget in a necking/shear failure mode. The effects of sheet thickness and combined load on the load carrying behavior of spot welds are investigated under static and impact loading conditions based on the experimental results. An engineering failure criterion is proposed to characterize the failure loads of spot welds under combined opening and shear loads for both static and impact loading conditions. The engineering failure criterion is expressed as a function of the nugget size, the sheet thickness, the loading angle for characterization of combined loads, and an empirical coefficient for a given loading rate.