13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- estimate error is 8.2%, which satisfies engineering demands. The coincidence of estimate result and test result prove that the failure of lap joint is mainly caused by stress concentration of hole edge. 5. Conclusions This paper has studied the fatigue properties of aerial aluminum alloy 2524-T3 FSW joint and lap joint by fatigue tests and FEA. The S-N curves of different specimens have been obtained by fatigue tests to compare the fatigue strength of them. It has been shown that the fatigue strength of FSW joint is better than that of lap joint. At the fatigue life of 1×105 cycles, the fatigue strength of FSW joints is about 61% higher than that of lap joint. The three-dimensional elasticplastic FEA for two types of specimens have been developed to explore the fracture mechanism of two jointing techniques. The residual stress of FSW joint were obtained by a nonlinear direct coupled-field analysis, and the detailed stress distribution of lap joint which under pulling force were simulated. The maximum residual stress of FSW joint is 115MPa at the point of 2.5mm from the weld center, and the maximum stress concentration of lap joint locates on the right hole’s edge of the first rivets row. Finally, fatigue lives of specimens have been estimated, and both estimated results agree with that of experiment. Results show that the residual stress is the main factor affecting the fatigue life of FSW joint and the failure of lap joint is mainly caused by stress concentration of hole edge. References [1] W.M. Thomas, E.D. Nicholas, J.C. Need ham, M.G. Murch, P. Templesmith, C.J. Dawes, Friction Stir Welding, International Patent Application No. PCT/GB92102203 and Great Britain Patent Application No. 9125978.8, 1991 [2] Alves de Sousa RJ, Yoon JW, Cardoso RPR, Fontes Valente RA, On the used of a reduced enhanced solid-shell finite element for sheet metal forming applications. Int J Plasticity, 23(2007) 490-515. [3] H.W. Zhang, Z. Zhang, J.T. Chen, The finite element simulation of the friction stir welding process. Materials Science and Engineering A, 403 (2005) 340-348. [4] Zhu X.K.,and Y.J.Chao, Numerical Simulation of Transient Temperature and Residual Stresses in Friction Stir Welding of 304L Stainless Steel. Journal of Materials Processing Technology, 146.2(2004)263-272. [5] Z. Feng, X.L. Wang, S.A. David, et al, Modelling of residual stresses and property distributions in friction stir welds of aluminium alloy 6061-T6. Science and Technology of Welding and Jointing, 4(2007)348-356. [6] G.J. Bendzsak, C.B. Smith, An experimentally validated 3D model for friction stir welding, Proceedings of the Second International Symposium on Friction Stir Welding. Gothenburg, Sweden: TWI, 2000. [7] T. li, Q.Y. Shi, H.K. Li, Residual stresses simulation for friction stir welded joint. Science and Technology of Welding and Joining, 8(2007)634-640. [8] Zhou Caizhi, Yang Xinqi, Luan Guohong, Research Progress on the Fatigue Behavior of
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