Predicting residual thermal stresses in friction stir welded metals

A sequentially coupled finite element model of the friction stir welding process has been utilized to study the residual stresses caused by the thermal cycles during friction stir welding of metals. This is a two step simulation process. In the first step, the thermal history is predicted from an input torque based thermal model. The temperature history generated by the thermal model is then sequentially coupled to a mechanical model that predicts the residual thermal stresses. The model does not deal with the severe plastic deformations within the weld nugget and the thermo-mechanically affected regions, a fact that may cause modeled results to deviate from experimentally measured residual stresses. The model is three-dimensional and uses temperature dependent material and thermo-physical properties. Three different materials, AA-2024, AA-6061 and SS 304 L, have been studied.