Buckling Assisted Fatigue of Spot-Welded Box Beam under Bending

Fatigue cracks initiated at the spot-welded points or edges of the flange are observed on spot-welded box beams under repeated bending moment in the plane of the spot-welded flange. This fatigue fracture caused by buckling of the spot-welded flange is an inherent characteristic in discontinuous thin sheet structures, which we designate “buckling assisted fatigue.”

A two-dimensional buckling model is analyzed in order to clarify the mechanism of this kind of fatigue fracture. The load-stress curves and stress distribution of the spot-welded flange obtained from this theoretical analysis closely coincide with experimental results.

Finally, a new method used on this theory is proposed for predicting the failure mode of spot-welded box beams by applying the plane bending Δε -N curves of a single spot-welded specimen and the base metal.