Study on residual stresses caused by underwater friction stir welding: FE modeling and ultrasonic measurement

Predicting residual stresses arising from the thermal and mechanical loading history during engineering processes including welding would be a viable tool to reach the optimum process parameters. In the present article, an elasto-thermo-visco-plastic model has been employed to estimate the residual stress caused by the underwater friction stir welding, which are resulted by large thermo-mechanical deformations on one hand and rapid cooling arising from the enormous non-uniform boiling heat convention of water on the other hand. Finally, the numerical results are compared with experimental data acquired by the ultrasonic method to evaluate the accuracy of the simulation process. Regarding the low temperature during underwater friction stir welding, the employed constitutive equations result in acceptable residual stress fields, while for in-air case, the amount of error increases significantly due to experience of high temperatures and intensification in hardening precipitation phenomena