Abstract
This article presents a new, combined ‘integrated’- ‘multiphysics’ model of friction stir welding (FSW) where a set of governing equations from non-Newtonian incompressible fluid dynamics, conductive and convective heat transfer, and plain stress solid mechanics have been coupled for calculating the process variables and material behaviour both during and after welding. More specifically, regarding the multiphysics feature, the model is capable of simultaneously predicting the local distribution, location and magnitude of maximum temperature, strain, and strain rate fields around the tool pin during the process; while for the integrated (post-analysis) part, the above predictions have been used to study the microstructure and residual stress field of welded parts within the same developed code. A slip/stick condition between the tool and workpiece, friction and deformation heat source, convection and conduction heat transfer in the workpiece, a solid mechanics-based viscosity definition, and the Zener-Hollomon- based rigid-viscoplastic material properties with solidus cut-off temperature and empirical softening regime have been employed. In order to validate all the predicted variables collectively, the model has been compared to a series of published case studies on individual/limited set of variables, as well as in-house experiments on FSW of aluminum 6061.
Highlights
Friction Stir Welding (FSW), a solid state joining method developed and patented by TWI Ltd., Cambridge, UK in 1991 [1], has attracted significant interest from aircraft and car manufacturers for joining high strength aluminum alloy components
If we introduce a high volume of partial melting during FSW intentionally, it will generate a weld with low mechanical properties which is not desired
The model was successfully applied to predict the distribution of microstructure and residual stress around the pin [40, 41], as it predicts temperature distribution at mid thickness with an acceptable tolerance
Summary
Friction Stir Welding (FSW), a solid state joining method developed and patented by TWI Ltd., Cambridge, UK in 1991 [1], has attracted significant interest from aircraft and car manufacturers for joining high strength aluminum alloy components. The fluid dynamics models normally consider a solid mechanics-based definition of viscosity and non-Newtonian incompressible flow of the softened solid. They can predict strain rate distributions and not the strain distribution; there have been some more other models which have used post processing techniques to compute strain on streamlines. In the multiphysics model in this article, based on a solid mechanics definition of viscosity we applied strain rate integration over time to compute plastic strains in all points of fluid dynamics model for the first time (not limited to few streamlines)
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