A Statistical Study on Fatigue Fracture of Spot Welded Joints in Cross Tension Type

In this study, the fatigue test to obtain the L-N characteristics was first performed on the spot welded joints in cross tension type. Then the fatigue life distribution was experimentally examined by assigning a number of specimens at two different levels of applied load. Moreover, SEM observations were made on the fracture surfaces by paying attention to the crack initiation site and the crack propagation path. The main results obtained on this type of welded joints are summarized as follows; (1) The both distributions of the static strength and the fatigue life were well represented by the three-parameter Weibull distribution. (2) The fatigue fracture was classified into several types depending on the combination of crack initiation sites and crack initiation lives at respective sites. (3) The fatigue fracture was caused by the propagation of the second crack which was stimulated by the first crack. (4) A correlation was found between the fatigue life and the crack reflected angle, and this was qualitatively explained by the variation of stress intensity factor in the mixed mode.