Investigating the spot weld fatigue crack growth proces using X-ray imaging

An x-ray technique was used to investigate the fatigue crack initiation and crack propagation processes of spot welded joints. The fatigue cracks usually initiate 0.2-1.0 mm from the nugget edge of the spot weld. Finite element and theoretical analyses indicated that the maximum stress concentration is away from the nugget root. Three different fatigue crack propagation modes have been observed that correspond to different loading amplitude regimes. Lastly, fatigue crack propagation rates are presented for galvannealed and galvanized metals.