Effect of Sheet Thickness on Fatigue Behavior of Friction Stir Spot Weld of Al 6061-T6 Lap-shear Configuration

Document Type: Original Article


Mechanical Engineering Department, K.N. Toosi University of Technology, Tehran, Iran.


The effect of three different sheet thicknesses of friction stir spot welding on lap-shear specimens of Al 6061-T6 alloy was experimentally analyzed. Different fatigue life evaluation models were applied to estimate the fatigue behavior of the friction stir spot welding in different thicknesses. Experimental results show a clear correlation between static strength and fatigue behavior of different welding conditions. Results of tensile and fatigue tests demonstrated the sheets with 2mm indicated the optimum thickness which were studied in this research. At the same cycles, fatigue results of different thicknesses showed considerable differences in the low cycles in comparison with the higher ones. The evaluation models of Pook, Zhang and three-dimensional finite element models were investigated in the different sheet thicknesses. The three-dimensional finite element model evaluated fatigue behavior better than the other models at different sheet thicknesses.


[1] T. Rosendo, B. Parra, M.A.D. Tier, A.A.M. Da Silva, J.F. Dos Santos, T.R. Strohaecker, N.G. Alcântara, Mechanical and microstructural investigation of friction spot welded AA6181-T4 aluminium alloy, Mater. Des., 32(3) (2011) 1094-1100.
[2] Z. Zhang, X. Yang, J. Zhang, G. Zhou, X. Xu, B. Zou, Effect of welding parameters on microstructure and mechanical properties of friction stir spot welded 5052 aluminum alloy, Mater. Des., 32(8-9) (2011) 4461-4470.
[3] Y. Tozaki, Y. Uematsu, K. Tokaji, Effect of processing parameters on static strength of dissimilar friction stir spot welds between different aluminium alloys, Fatigue. Fract. Eng. Mater. Struct., 30(2) (2007) 143-148.
[4] G. Matsoukas, G.P. Steven, Y.W. Mai, Fatigue of spot-welded lap joints, Int. J. Fatigue., 6(1) (1984) 55-57.
[5] A.H. Ertas, F.Q. Sonmez, A parametric study on fatigue strength of spot‐weld joints, Fatigue. Fract. Eng. Mater. Struct., 31(9) (2008) 766-776.
[6] M.M. Rahman, R.A. Bakar, M.M. Noor, M.R.M. Rejab, M.S.M. Sani, M.S.M., Fatigue life prediction of spot-welded structures: a finite element analysis approach, Eur. J. Sci. Res., 22(3) (2008) 444-456.
[7] Y. Zhang, D. Taylor, Sheet thickness effect of spot welds based on crack propagation, Eng. Fract. Mech., 67(1) (2000) 55-63.
[8] P.C. Lin, Z.M. Su, R.Y. He, Z.L. Lin, Failure modes and fatigue life estimations of spot friction welds in cross-tension specimens of aluminum 6061-T6 sheets, Int. J. Fatigue., 38 (2012) 25-35.
[9] Z.M. Su, R.Y. He, P.C. Lin, K. Dong, Fatigue analyses for swept friction stir spot welds in lap-shear specimens of alclad 2024-T3 aluminum sheets, Int. J. Fatigue., 61 (2014) 129-140.
[10] V.X. Tran, J. Pan, Fatigue behavior of dissimilar spot friction welds in lap-shear and cross-tension specimens of aluminum and steel sheets, Int. J. Fatigue., 32(7) (2010) 1167-1179.
[11] H.M. Rao, J.B. Jordon, M.E. Barkey, Y.B. Guo, X. Su, H. Badarinarayan, Influence of structural integrity on fatigue behavior of friction stir spot welded AZ31 Mg alloy, Mater. Sci. Eng. A, 564 (2013) 369-380.
[12] A.M.S. Malafaia, M.T. Milan, M.F. Oliveira, D. Spinelli, Fatigue behavior of friction stir spot welding and riveted joints in an Al alloy, Procedia. Eng., 2(1) (2010) 1815-1821.
[13] S.R. Ahmadi, S. Hassanifard, M.M. Pour, Fatigue life prediction of friction stir spot welds based on cyclic strain range with hardness distribution and finite element analysis, Acta Mech., 223(4) (2012) 829-839.
[14] A.H. Ertas, F.O. Sonmez, Design optimization of spot-welded plates of maximum fatigue life, Finite Elem. Anal. Des., 47(7) (2011) 413-423.
[15] P.C. Lin, J. Pan, T. Pan, Failure modes and fatigue life estimations of spot friction welds in lapshear specimens of aluminum 6111-T4 sheets. Part 2: Welds made by a flat tool, Int. J. Fatigue., 30(1) (2008) 90-105.
[16] L.P. Pook, Fracture mechanics analysis of the fatigue behaviour of spot welds, Int. J. Fract., 11(1) (1975) 173-176.
[17] S. Zhang, Stress intensities at spot welds, Int. J. Fract., 88(2) (1997) 167-185.
[18] S. Zhang, Fracture mechanics solutions to spot welds, Int. J. Fract., 112(3) (2001) 247-274.
[19] J.A. Newman, N.E. Dowling, A crack growth approach to life prediction of spot‐welded lap joints, Fatigue. Fract. Eng. Mater. Struct., 21(9) (1998) 1123-1132.
[20] S.H. Lin, J. Pan, P. Wung, J. Chiang, J., A fatigue crack growth model for spot welds under cyclic loading conditions, Int. J. Fatigue., 28(7) (2006) 792-803.
[21] B.A. Bilby, G.E. Cardew, I.C. Howard, Stress intensity factors at the tips of kinked and forked cracks, Anal. Mech., 3 (1978) 197-200.
[22] B. Cotterell, J. Rice, Slightly curved or kinked cracks, Int. J. Fract., 16(2) (1980) 155-169.
[23] D.A. Wang, S.H. Lin, J. Pan, Stress intensity factors for spot welds and associated kinked cracks in cup specimens, Int. J. Fatigue., 27(5) (2005) 581-598.
[24] N. Pan, S.D. Sheppard, Stress intensity factors in spot welds, Eng. Fract. Mech., 70(5) (2002) 671-684.
[25] D.A. Wang, J. Pan, A computational study of local stress intensity factor solutions for kinked cracks near spot welds in lap-shear specimens, Int. J. Solids. Struct., 42(24-25) (2005) 6277-6298.
[26] ASM Handbook, Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, ASM International 2 (1990).
[27] SAE. Welding: Resistance, Spot and Seam, AMSW 6858. Pennsylvania, USA: SAE, (1999).
[28] ASM Handbook, Heat Treating. ASM International, 4 (1991).
[29] ISO14324, Resistance Spot Welding–Destructive Tests of Welds-Method for the Fatigue Testing of Spot Welded Joints. The International Organization for Standardization, (2003).
[30] D.A. Wang, C.H. Chen, Fatigue lives of friction stir spot welds in aluminum 6061-T6 sheets, J. Mater. Proces. Tech., 209(1) (2009) 367-375.
[31] D.A. Wang, P.C. Lin, J. Pan, Geometric functions of stress intensity factor solutions for spot welds in lap-shear specimens, Int. J. Solid. Struct., 42(24-25) (2005) 6299-6318.
[32] B.F. Jogi, P.K. Brahmankar, V.S. Nanda, R.C. Prasad, Some studies on fatigue crack growth rate of aluminum alloy 6061, J. Mater. Process. Technol., 201(1-3) (2008) 380-384.