1979 Volume 48 Issue 7 Pages 482-488
The spot welding of low carbon steel sheets was carried out using an electrode tip of a rectangle in shape. The specimen obtained had a uniform and cylindrical weld nugget in the direction of the width of the sheet, so that the welded structure was observed on the side of the specimen and the structural changes in the fatigue process were examined without cutting the specimen.
The fatigue test was performed under the pulsating tension-shear load, and the initiation and the propagation of a crack were examined by an optical microscope. The microcracks were initiated in the slip bands formed near the edge of the junction in the heat affected zone and developed into the macrocrack along the cross section of the specimen perpendicular to the direction of the loading.
Furthermore, it was found that the bending moment in the longitudinal direction of the specimen resulted from the offset of the overlapped part decreased considerably at a quarter cycle of the cyclic loading with an increase of a plastic deformation in the base metal.