One of the most conventional approaches of quality control in metal weldments is the evaluation of residual stresses and distortion. Constraining the structure during welding, is the significant key parameter for optimizing the residual stress. In this research, an attempt was made to obtain the best welding constraint of 5XXX Al alloy lap joints during double pass GTAW. A 3-Dimentional finite element simulation was utilized for determining the effect of three different types of local U-shape Fixture (LUF) on residual stresses distributions and distortion. Considering sequentially coupled thermal-mechanical strategy, double ellipsoidal modelling of heat source and element death and birth technique were used in simulation. Thermocouple and LVDT’s set up were applied to validate thermal and mechanical results, respectively. Results provided by simulation show acceptable agreement with experimental values. According to results obtained from simulation, suitable LUFs selected based on optimum residual stresses and distortion in welding the aluminium structure.

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