In this study, a 3D finite element simulation is utilised to analyse the uniaxial tensile deformation behaviour of AA6082-T6 defective and defect-free friction stir welds. For the first time, the non-uniform distribution of material strength and the root defect are simultaneously considered. It is found that, compared to the defect-free weld which fractured generally at the heat affected zone, the presence of the root defect in the weld boosts the rate of strain accumulation at the root of the weld nugget zone (WNZ), resulting in failure in the WNZ during tensile. This study shed new lights on the underlying mechanism on how the welding defects weaken the strength of friction stir welds.
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