PSI - Issue 19

Shota Hasunuma et al. / Procedia Structural Integrity 19 (2019) 194–203 Shota Hasunuma, Ogawa Takeshi/ Structural Integrity Procedia 00 (2019) 000 – 000

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(b)

(a)

(c)

(b)

Loading direction 500  m

300  m

(c)

(e)

(d)

(d)

3.5  m

(f)

100  m

300  m

 3.5

(f)

(g)

(h)

500  m

100  m

(h)

(i)

(i)

300  m

100  m

Fig.9 Optical micrographs of No.1-AM at N / N f,EP = 0 (a), 0.1(e) and 0.2(g). (b) , (c), (f), (h) and (i) are close up image of (a), (b), (e), (g) and (h) , respectively. (d) is height distribution result observed laser micrograph, where N f , EP is number of cycle to failure of EP specimen. Crack growth behavior was observed to examine the effect of the machined surface layer on the crack growth characteristics. Fig. 9 shows observations of the No.1-AM specimen. Many cracks initiated in the scratch. Red arrows indicate tip of scratch. Scratch length is about was about 1500  m. Black and blue arrows indicate crack tip. There were many cracks in the scratch. Cracks grew almost as large as scratch in early stage of fatigue life because of crack coalescence. Fig. 10 shows observation results for No.4-AM specimen. Crack initiated in the scratch on the No.4-AM specimen; i.e., crack initiation and growth behavior of No.4-AM specimen was similar to that of No.1 AM specimen. In addition, in the case of No.4-AM specimen, there were cracks which initiated form line scratch