13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- Figure 3. (a)A7 crack growth path, (b) A8 crack growth path [8] 3.2. S460N specimens Specimen S7 (amplitude load values: F=27kN; MT=408Nm) under the loading with a out of phase angle of 90° and the corresponding loading phase angle for specimen S13 (amplitude load values: F=22.5kN; MT=272Nm) is 45°. 4 initial corner cracks are inserted into the notch root in specimen S7 because the maximum local tangential stresses are almost equal for sites 1-4. The crack propagation trend for specimen S13 is similar with specimen A8 as shown in Figure 4(b). Figure 4. (a) S7 crack growth path, (b) S13 crack growth path [8] Besides crack growth paths, the fatigue life for each specimen was also calculated based on Paris law. More details and the curves for crack length versus number of cycles are shown in reference [8]. 4. Discussion 4.1. Crack propagation behavior of specimen A7 Crack paths are marked as ①, ②, ③ and ④ corresponding to the crack initiation sites as shown in Figure 2(b). The coordinate system is illustrated in Figure 2(a), the centre point of specimen is considered as the origin. The crack propagation trajectory (path ①) for specimen A7 is plotted in Figure 5(a). The solid line represents the simulated crack growth path in FRANC3D. The path labelled by squares is calculated based on the MTS criterion. It can be seen that when the crack reaches to a certain length (the length of this crack is from the notch root to point A), the crack growth path will deviate from the prediction of MTS criterion. From point A, MSS criterion predicted path is marked by triangle symbols. Obviously, the crack path starting from point A does
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