Observation and prediction of fatigue behavior of spot welded joints with triple thin steel plates under tensile-shear loading

Spot welding is very commonly used for joining two thin plates, which has useful application in the automotive, aerospace and other industries. For having a complex structure with spot welds, it is necessary to study the fracture and fatigue behavior of spot welds with multiple plates. When tensile-shear load applied to the spot welded structure, the spot welded structure may be deformed into an asymmetric shape when using two or more plates of different thickness. In this paper, fatigue behavior of spot welded triple plates is examined experimentally and the prediction of fatigue lifetime is proposed by the crack opening angle (COA) around the spot weld. The COA obtained experimentally is directly related with well-known fracture parameter, i.e. stress intensity factor, and the COA can be used for the prediction of fatigue strength regardless of the thickness of specimen if the geometry of triple plates is the same. The two different types of spot welded structures were considered to determine the difference of fatigue behavior due to the geometry of spot welding of triple plates under tensile-shear loading.