PSI - Issue 2_A

Y. Nakai et al. / Procedia Structural Integrity 2 (2016) 3117–3124 Author name / Structural Integrity Procedia 00 (2016) 000–000

3121

5

(a) N = 6.00×10 6 cycles

(b) N = 6.80×10 6 cycles

(c) N = 7.10×10 6 cycles

(d) N = 7.50×10 6 cycles

(b) N 6 cycles Figure 7: 3D-images of cracks and inclusions (0.049S mass%, vertical inclusion). f = 7.67×10

the displayed vertical crack, but unfortunately it could not be shown in the same figure. Such horizontal cracks were also previously observed in a specimen with an artificial hole, which simulated an inclusion (Makino et al., 2014).

At N = 7.67 × 10 6 cycles, flaking occurred as a result of the propagation of the horizontal crack. The shape of the flaking was similar to that observed on the surface by SEM as shown in Figure 6. (b) Material with horizontal inclusions Figure 8 shows a surface image of a crack initiation site of specimen with horizontal inclusions ( N = 2.50×10 6 cycles, shortly after crack initiation at the surface). Small cracks, those are almost perpendicular to the ball-rolling direction, can be observed. 3D images of inclusions and cracks observed by SRCL at N = 2.50 × 10 6 cycles, 2.75 × 10 6 and 3.00 × 10 6 cycles are shown in Figure 9, where (A) is a top view, (B) is a side view of the specimen, and (C) is the view from the rolling (a) N i = 2.50×10 6 cycles (b) N = 3.13×10 6 cycles Figure 8: SEM micrograph of surface crack and flaking.