13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- However, near the fatigue limit, the fatigue life of three group specimens is not very different, and the fatigue limit remains the same value of 60 MPa for three cases of pitch difference. 4.3. Investigation of the fractured specimens Figure 8 shows the examples of fractured specimens (σa＝130MPa). For the normal bolts and nuts, it is confirmed that the fracture is always happened at the first thread bottom as shown in Figure 8(a). For the specimens of α=αsmall, the fracture position is between the No.1 thread and No.3 thread of bolt. It should be noted that the fracture surfaces have the different characteristic compared with the (a) α=0 (fatigue life 151,860 cycles) (b) α=αsmall (fatigue life 242,810 cycles) (c) α=αmiddle (fatigue life 184,770 cycles) Figure 8. Fractured specimens (σa=130MPa)
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