PSI - Issue 19

Yukitaka Murakami et al. / Procedia Structural Integrity 19 (2019) 113–122 Yukitaka Murakami et al. / Structural Integrity Procedia 00 (2019) 000–000

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the goal. In order to share a common understanding of fatigue performance among AM researchers, it may be convenient to define the grade of AM materials from the viewpoint of fatigue performance as follows. Fatigue-Grade 5: Fatigue limit  w > ~ 90% of the ideal fatigue strength, 1.6 HV (see Fig. 1 and Eq. (1)).

Fatigue-Grade 4: Fatigue limit  w = ~ 70% - 90% of the ideal fatigue strength. Fatigue-Grade 3: Fatigue limit  w = ~ 50% - 70% of the ideal fatigue strength. Fatigue-Grade 2: Fatigue limit  w = ~ 30% - 40% of the ideal fatigue strength. Fatigue-Grade 1: Fatigue limit  w = ~ 10% - 30% of the ideal fatigue strength.

Fig. 1 Relationship between Vickers hardness HV and fatigue limit.

800

800

Surface polish without HIP (HV=369) Surface polish with HIP (HV=345) As built without HIP (HV=369) As built with HIP (HV=369)

Surface polish without HIP ( =378) Surface polish with HIP ( =340) As built without HIP ( =378) As built with HIP ( =340) New machine Surface polish without HIP( =384) HV HV HV HV HV

700

700

600

600

500

500

σ a （ MPa ）

σ a （ MPa ）

a

400

400

300

300

200

200

100

100

0

0

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

N f （ cycles ）

N f （ cycles ）

(a) EBM (Electron Beam Melting)

(b) DMLS (Direct Metal Laser Sintering)

Fig. 2 S - N data for EBM and DMLS (Masuo et al (2018) and additional data).

(a)EBM (√ area = 357 μ m )

(b)EBM (√ area = 245 μ m)

(c)DMLS (√ area = 41 μ m)

(d)DMLS (√ area = 55 μ m)

Fig. 3 Defects at fatigue fracture origins.