The fatigue life of the specimens depended on the applied load amplitude, the ratio of shear to the normal loading, and spot weld nugget diameter.
The lower load amplitudes or the high loading ratio had longer fatigue lives, as did the cases which contained a higher amount of shear loading (lower normal loading) and specimens with a larger nugget diameter.
The effect of the combined loading, shear and tensile loading on the fatigue life of spot weld have been studied. The bigger weld nugget provides the higher fatigue life.
The strength of the joint depends on the weld nugget diameter and the ratio of the shear to the normal loading (tensile).
Finite element analysis has been used to validate the results.
Stress intensity factor is a measure of fatigue strength. Therefore, the KI parameter is a combination of superposed stress intensity factors for Mode I and Mode II loading.
The initiation of fatigue cracks were observed at the edge of the weld nugget in the sheet metal, and propagation of the cracks depended on the loading directions and amplitudes according to the linear elastic approach.
X-ray computed tomography during interrupted fatigue testing of the spot welds shows that the main fatigue crack initiates at the edge of the weld nugget at the facing interface and penetrates through the sheet thickness.
It was found that the quality of the spot weld is a function of the weld nugget size formed as a result of current flow and pressure of the welder's electrode. However, weld time and some other different parameters also effecting the weld nugget quality and strength.
The linear elastic fracture mechanics approach requires an accurate determination of the stress intensity factors at the spot welds. In addition, an initial crack length has to be determined. There is no information about the initial crack length of the spot weld.