13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Fracture surface for T-386G specimen failed at 1400 a MPa with a short life of 4 1.8 10 N in rotating bending is shown in Fig.11(a), where the top is the result observed at low magnification and the bottom the result at high magnification. In this case, the fatigue crack took place on the specimen surface and it propagated inside the specimen. Figure 11(b) gives another example of the fracture surface at 950 a MPa with a life of 8 8.8 10 N in the interior-induced fracture modewith a clear fish-eye. In this case, the fatigue crack took place around the interior inclusion at the center of the fish-eye and the fine granular area[FGA] was found around the inclusion. These pairs of results give examples of the fracture surface in rotating bending. However, Fig. 11(c) gives other examples of the fracture surface at 700 a MPa with a life of 6 7.7 10 N in the interior- induced fracture mode in axial loading. No inclusion was found at the crack initiation site at the center of the fish-eye in this case, but the fine granular area[FGA] can be observed at the crack initiation site. The fine granular area in Fig.11(c) was again carefully observed by inclining the sample 5deg., after which 3-D image of the fracture surface around the FGA was reconstructed by means of stereo-projection analysis[A Software of Mex supplied by Alicona Co. Ltd.]. Based on this analysis, it was found that a plane of the FGA inclined 60deg. against the macroscopic fracture surface and the gap of the local surface levels at both ends of the FGA is about 10 m. Several examples of fracture surfaces for SWOSC-V steel in rotating bending are indicated in Fig.12, in which the top is the result observed at low magnification and the bottom the result at high magnification. In the case of Fig.12(a), the fatigue crack took place at a shot-peened dimple on the specimen surface and it propagated inside the material resulting the final fracture. In Fig.12(b), the fine granular area[FGA] was formed at an interior site along a inclined plane. According to the stereo-projection analysis, this plane was inclined 60deg. against the macroscopic fracture surface similar to the previous result obtained for SUP7 steel. Figure 12(c) gives another example of the fracture surface in interior-induced fracture and a defect was found at the crack initiation site. However, any inclusion was not observed here regardless of careful EDS-analysis. Thus, no inclusion was found at the crack initiation site in every series of SWOSC-V steel. It is supposed that this fact comes from high cleanliness of the present steel. (a) Surface-induced fracture (b) Interior-induced fracture (c) Interior-induced fracture [ 1050 a MPa, 8 1.6 10 N ] [ 1100 a MPa, 7 2.7 10 N ] [ 1050 a MPa, 8 2.1 10 N ] Figure 12. Typical examples of fracture surfaces for SWOSC-V steel in rotating bending
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