Fatigue analysis of friction stir welded aluminium profile using critical distance

A friction stir (FS) welded extruded aluminium alloy 6005A, which is used for train wall sides, was fatigue tested. The friction stir weld was a lap-butt joint with a sharp notch (interface between the work pieces) next to the weld nugget. Fatigue cracks and failure appeared at notches in the profile. In most profiles, cracks also initiated at the sharp notch at the weld, but the propagation was slow and complete fracture never took place there. Finite element method (FEM) stress analysis combined with the theory of critical distance was used to estimate the fatigue limit. Results from the analysis for the fatigue limit were within 3–28% of the observations. The stress analysis correctly predicted that failure would not occur in the welds.