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FE Modelling of Mechanical Tensioning for Controlling Residual Stresses in Friction Stir
D.G. Richards, P.B. Prangnell, P.J. Withers, S.W. Williams, A. Wescott, E.C., Oliver
In: 6th Int. Friction Stir Welding Symposium; 10 Oct 2006-13 Oct 2006; St Sauveur, Canada on 10-13 October 2006. UK: TWI; 2006.
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Abstract
Although Friction Stir Welding (FSW) avoids many of the problems encountered whenfusion welding high strength Al-alloys, it can still result in substantial residual stressesthat have a detrimental impact on service life and induce distortion. An FE model hasbeen developed to investigate the effectives of the mechanical tensioning technique forcontrolling residual stresses in FSWs. The model purely considered the heat input and themechanical effects of the tool were ignored. Variables, such as tensioning level, heatinput, and plate geometry, have been studied. Good general agreement was foundbetween modelling results and residual stress measurements, justifying the assumptionthat the stress development is dominated by the thermal field. The results showed aprogressive decrease in the residual stresses for increasing tensioning levels and,although affected by the heat input, a relatively low sensitivity to the welding variables.At tensioning levels greater than ~ 50% of the room temperature yield stress, tensilestresses were replaced by compressive residual stresses within the weld. Subsequentlythe modelling has been used to examine how mechanical tensioning can be applied inpractical applications.