13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- connected joint is rare. In this paper, fatigue tests and finite element analysis (FEA) were employed to study the fatigue properties of 2524-T3 FSW joint and riveted lap joint. Test results show that the fatigue strength of FSW joint is better than that of lap joint. The residual stress of FSW joint and the detailed stress distribution of lap joint were obtained by FEA. Furthermore, the fatigue life of FSW joint was estimated according to the result of residual stress distribution and base metal S-N curve; the fatigue life of lap joint was estimated according to the results of stress-strain distribution and local stress-strain method. 2. Experiments Fatigue tests of FSW joint specimens and lap joint specimens were made by machine MTS-810-500 at room temperature, just as shown in Fig.1 and Fig.2. Figure 1. Fatigue test of FSW joint specimen Figure 2. Fatigue test of lap joint specimen 2.1. Specimens and Fixture Design Two types of specimens, which simulate different connective types of skins in airframe, are shown in Fig.3 and Fig.4. Pieces of specimens are made of aluminum alloy 2524-T3 and rivets are made of titanium alloy TC4. FSW joint specimens were produced by machine FSW2-4CX-006. The tool shoulder diameter is 8mm. The pin is cylindrical with a hemispherical tip, its dimensions are 2.6mm in diameter and in 1.7 mm length. The tool rotation speed is set at 1000 rpm, and the translation speed is fixed at 100mm/min. While the rotating tool moves along the welding line, a forging pressure of 1.5kN is applied. Lap joint specimens are connected by staggered rivets. Figure 3. FSW joint specimen (mm) Figure 4. Staggered riveted lap joint specimen (mm) The weight of lap joint specimen and FSW joint specimen are 297g and 271g separately. This means the FSW technique could reduce structural weight significantly than traditional jointing techniques.
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