13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- For the purpose of simulating the actual force condition, anti-bend fixtures were designed for lap joint specimens, just as shown in Fig.5. The anti-bend fixture I and II are designed to prevent out-of-plane bending and the function of shims is to ensure specimens loaded in the same plane. In order to reduce the friction between specimens and fixtures during test, some effective measures were applied such as injecting lubricant oil or inserting plastic films between contact surfaces. Figure 5. Configuration of anti-bend fixtures 2.2 Fatigue test All specimens were subjected to constant amplitude loads; the stress ratio R=0.06 and the load frequency f=10. In order to obtain S-N curves, each type of specimens were divided into three groups, which loaded under different stress levels (illustrated in Table 1). Table 1. The maximum stress endured by different types of specimens during fatigue test (MPa) FSW specimen Lap joint specimen 1 240 150 2 210 120 3 180 100 2.3 Test results Fig.6 shows the fracture forms of specimens. The fracture position of FSW specimens locates on the thermomechanical affected zone and the lap joint specimens break on the line of the first row of rivets. Figure 6. Fracture forms of two type specimens Chauvenet criterion was used for all test results to abandon dubious data. And S-N curves of two
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