13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- series: 775MPa, T-386EP series: 625MPa and T-386SP series: 725MPa, respectively. Variation of the fatigue limit and the fracture mode depending on the surface finishing is quite similar to the trend in the case of rotating bending. Figure 9 indicates S-N diagram obtained for SWOSC-V steel in rotating bending. The fatigue limit for T-363G specimen is higher than that for T-395G specimen depending the hardness realized by the tempering at the respective temperatures. The interior-induced fracture was not observed even for the gigacycle regime in the case of low temperature tempering. The slope of the inclined portion in T-395G specimen is fairly steep comparing with that in T-363G specimen. Figure 10 is S-N diagram obtained for the respective series of T-386 specimens. The fatigue limit for T-363EP series is decreased due to the removal of the surface layer with the compressive residual stress. This trend is very common to the case of SUP7 steel as shown in Fig.7(b) and Fig.8(b). (a) T-395G series and T-363G series (b) Various series of T-363 specimens Figure 9. S-N diagrams for SWOSC-V steel in rotating bending 3.3. SEM observations of fracture surface (a) Surface-induced fracture (b) Interior-induced fracture (c) Interior-induced fracture in rotating bending in rotating bending in axial loading [ 1400 a MPa, 4 1.8 10 N ] [ 950 a MPa, 8 8.8 10 N ] [ 1200 a MPa, 4 7.0 10 N ] Figure 11. Typical examples of fracture surfaces for SUP7 steel in both loading types 300m 20m
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