PSI - Issue 19

Akira Ueno et al. / Procedia Structural Integrity 19 (2019) 494–503 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 2 Piping system.

Fig. 3 Surface roughness of the thin hole.

Fig. 4 Stress distribution on a thick wall of the specimen.

Because of an electric discharge machining, thin hole surface was rough. For case of fatigue tests, surface roughness of thin hole decreases a fatigue life. Therefore, the inside of thin hole of fatigue specimen are fine finished by special polishing procedure as shown in Fig. 3(a) and (b). Specimen dimensions were designed for avoiding effect of hoop stress   that is generated on a specimen wall. Also, in this study, diameter of thin hole was designed that the hoop stress   to axial stress ratio was below 10% for avoiding effect of bi-axial stress. As shown in Fig.4 (a) and (b), for case of 1.0 mm diameter thin hole, maximum hoop stress   , max generated on thin hole surface are always below 10% of stress amplitude of fatigue tests.

2.2. Material

Material used in this study was an austenitic stainless steel JIS SUS316L. As different in manufacturer, 3 different Lot were used in this study (Table 1(a)-(c)). The Ni equivalent, that is a profitable to measure a stability of the austenite phase, were calculated by Eq. (1) reported by Yamada, T. et. al .(2012). The Ni eq of three Lot are listed in Table 2.