Fatigue analyses for swept friction stir spot welds in lap-shear specimens of alclad 2024-T3 aluminum sheets

• Three failure modes of Swept-FSSWs under cyclic loading conditions were found.
• Dominant fatigue cracks of Swept-FSSWs under different load ranges were identified.
• Effects of alclading on the fatigue behavior of Swept-FSSWs were observed.
• The fatigue crack growth model provides well life estimations for Swept-FSSWs.

Failure modes of swept friction stir spot welds (Swept-FSSWs) in lap-shear specimens of alclad 2024-T3 aluminum sheets are first investigated. Micrographs of the welds before and after failure under quasi-static and cyclic loading conditions are examined. Three failure modes are found. A fatigue crack growth model based on the paths of the dominant kinked fatigue cracks is developed to estimate the fatigue lives of Swept-FSSWs. The global and local stress intensity factors for finite kinked cracks and the Paris law for crack propagation are used. The fatigue life estimations based on this model agree well with the experimental results.