Role of Residual Stresses on Fatigue Crack Propagation of FSW 6056-T78 Aluminium Joints under Various Technologies


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Residual stress fields may be rather frequently observed in several mechanical and structural parts, usually as a result of the manufacturing and joining techniques adopted. Their effects on material performances can be quite different, going from highly detrimental to beneficial, according to their distribution and to the acting material damage mechanisms (fatigue fracture, brittle or ductile failure, corrosion,…). Residual stresses are produced in welded structures by thermal expansion, plastic deformation and shrinkage during cooling. The amount of constraints determines the level of residual stress. Friction Stir Welding (FSW) is a quite new joining technique particularly for aluminium alloys difficult to fusion weld. Since conventional FSW showed its limits, Bobbin Tool technology has been developed. These both types of welds produce low-distortion of high quality (even no postweld distortion) and relevant residual stresses. The residual stresses of the aerospace material 6056-T78 aluminium alloy Friction Stir Welded sheets have been analysed on various tempers in accordance with these two different technologies. The effects have been investigated parallel and orthogonal to the weld direction. By means of local or global heat treatments, the residual stress state can be generally reduced or changed from tensile to compressive stresses on surface; in that way, the different heat aging conditions T78 as-welded and post-welded are checked in this study. This paper presents the method used, the measurements of this fatigue damage and their consequences on the fatigue life performance of structural materials.



Materials Science Forum (Volumes 519-521)

Edited by:

W.J. Poole, M.A. Wells and D.J. Lloyd




A. L. Lafly et al., "Role of Residual Stresses on Fatigue Crack Propagation of FSW 6056-T78 Aluminium Joints under Various Technologies", Materials Science Forum, Vols. 519-521, pp. 1089-1094, 2006

Online since:

July 2006




[1] Asserin-Lebert A, Bron F, Besson J, Gourges AF, Rupture of 6056 aluminium sheet materials: Effect of sheet thickness on strain localization and thoughness, in: Proceedings of the 14 th Biennal Conference on Fracture - ECF 14. EMAS publishing; (2002).

[2] Schindler H.J., Cheng W. and Finnie I.: Experimental Mechanics, 37, 3, 1997, pp.272-277.

[3] Schindler H.J. and Landolt R.: Proc. Of the 4th European Conference on residual stresses, 1996, pp.509-517.

[4] Dalle Donne C., Raimbeaux G.: Residual stress effects on Fatigue Crack Propagation in Friction Stir Welds., ICAF10, Haiwaii, USA, 3-7 December (2001).

[5] Masubushi K.: Analysis of Welded Structures, Pergamon press, United Kingdom, Chapter 6 (1980).

[6] Whang X-L, Spooner S., Hubbard C.R., Feng Z., Taljat B.: Characterization of Welding Residual stresses with Neutral Diffraction", pp.491-494 in "Proceedings of the 1998 SEM Spring Conference on Experimental and Applied Mechanics, Society for Experimental Mechanics, Bethel, Connecticut (1998).


[7] Lafly A-L, Alléhaux D, Marie F, Dalle Donne C, Döker H: Impact of Friction Stir Welding Techniaues on microstructure changes and mechanical properties, 58th Annual Assembly and International Conference of International Institute of Welding (IIW), Prague, 10-15 July (2005).


[8] Annual book of ASTM standards, Technical Report E561-94. Philadelphia: American Society for Testing and Materials; (1998).

[9] Afgrow Manual Use.

[10] Elber W.: Damage Tolerance in Aircraft Structures, STP 486, American Society for Testing and Materials, Philadelphia, 1971, pp.230-242.

[11] Nelson D.V.: Effects of residual stress on fatigue Crack Propagation, Residual Stress Effects in Fatigue, ASTM STP776, W. Conshohocken, PA, 1982, pp.172-94.


[12] Parker A. P: Stress intensity factors, Crack profiles, and Fatigue Crack Growth Rates in residual stress fields, Residual stresses effects in fatigue, ASTM STP776, W. Conshohocken, PA, 1982, pp.13-31.