13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- type specimens were obtained by group test method, the formulas of S-N curves are, FSW specimen: N=1.89×1011(S-122)-3.36, (1) Lap joint specimen: N=1.18×108(S-72.9)-1.84. (2) S-N curves are illustrated in Fig.7. Figure 7. S-N curves of two type specimens The S-N curves show 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 joint (195MPa) is about 61% higher than that of lap joint(120MPa). 3. Finite element analysis In order to reveal the fracture mechanism of two jointing techniques, three-dimensional elasticplastic FEA for two types of specimens was conducted by ANSYS 14.0 software. Through FEA, the residual stress of FSW joint and detailed stress distribution of lap joint were obtained, and both of them provide necessary conditions for life prediction. 3.1 FEA of FSW joint FSW is a coupled-field (structural-thermal) process. The temperature field affects the stress distribution during the entire process. Also, heat generated in structural deformation affects the temperature field. In this paper, a direct FEA of coupling is developed using a coupled-field element SOLID226. The simulation occurs over three load steps, representing the dwell, traverse and cool phases. The schematic diagram of FEA model is shown in Fig.8.
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