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Experimental characterization of residual stress fields in T-joints
welded by Friction Stir Welding
R.A.S. Castro 1 , V. Richter-Trummer 2 , S.M.O. Tavares 2 , P.M.G.P Moreira 1 ,
P. Vilaça 3 , P.M.S.T. de Castro 2
1 Optics and Experimental Mechanic Laboratory, National Institute of Mechanical Engineering and
Management, University of Porto.
2 Mechanical Engineering Department, Faculty Engineering, University of Porto.
3 Mechanical Engineering Department, Superior Technical Institute, Technical University of Lisbon.
The advent of the Friction Stir Welding (FSW) technique allowed a more intense use of
aluminum welded structures. Since this is still a relatively new process, there is lack of
information concerning its joints mechanical behavior. The knowledge of the residual stress
field derived from a manufacturing process is a key factor for the safe operation of structural
components; they may be detrimental with a predominant contribution to fatigue and other
structural failures [1].
Therefore, the main goal of this work is to characterize the residual stress field in T-joints
welded by FSW. The T-joints were composed of two aluminium 6056 sheets in the flanges and
an aluminium 7075 sheet in the web. Two residual stress measurement techniques were used:
in a first workpiece it was used the Sectioning method [2] while in the second it was used the
Hole Drilling method [3].
The results obtained show that the residual stress field along the thermo-mechanically affected
and heat affected zones can be modeled by a logarithmic curve. The maximum tensile stresses
obtained were in the order of 100 MPa while the compressive ones reached the value of -40
MPa. Both values were obtained in the flanges as the stresses in the web are much lower than
these ones. There are no significative differences between the advancing and retreating sides of
the work pieces while between the welding (crown) and root ones no conclusions could be
effectively made.
This work was carried at the Institute of Mechanical Engineering and Industrial Management
(INEGI) under the specifications of the Research Integration Program (BII) promoted by the
Foundation for Science and Technology (FCT), Portugal.
References:
[1] Bussu, G. and Irving, P. E., (2003), The role of residual stress and heat affected zone properties on
fatigue crack propagation in friction stir welded 2024-T351 aluminium joints. International Journal of
Fatigue. 25(1): p. 77-88.
[2] Galatolo, R. and Lanciotti, A., (1997), Fatigue crack propagation in residual stress fields of welded
plates. International Journal of Fatigue.
[3] ASTM, International, Standard Test Method for Determining Residual Stresses by the Hole drilling
Strain-Gauge Method - E837. 2008.
206 3 rd meeting of young researchers at UP