Effects of welding defects on the fatigue properties of spot welded automobile steel sheets and the establishment of a fatigue life evaluation method

The welded areas of spot welding of actual vehicles are confirmed welding defects such as blowholes between steel plates. However, most of studies on the strength reliability of spot welded structures do not consider welding defects, and it is necessary to clarify the effects of weld defects on the strength reliability of spot welded structures. This study investigated the effect of the size and location of through holes simulating welding defects on the fatigue properties of tensile-shear-type spot welded joints using automobile steel sheets. Moreover, the effect of the loading type both tensile-shear and cross-tension type on the fatigue properties of the spot welded joints was investigated, and a unified evaluation of the fatigue life for different loading type joints was established. The size and location of a welding defect do not affect the fatigue strength or the fatigue fracture morphologies of tensile-shear-type spot welded joints. This is because the slit tip of spot welded joints is in the singularity stress field under mixed-mode condition, regardless of the welding defect of the joint. Therefore, the equivalent stress intensity factor at the slit tips of joints can uniformly evaluate the fatigue life of joints with different loading types.