PSI - Issue 19

Yasuhiro Yamazaki et al. / Procedia Structural Integrity 19 (2019) 538–547 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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and lower temperature conditions becomes more significant. Further investigations about the effects of oxidation on the propagation behavior and crack closure of the fatigue small crack are needed. The relationships between the d a /d N and the ∆ K eff / E are shown in Fig. 8. As shown in Fig. 8, even if the crack closure and the temperature dependence on the deformation resistance take into consideration, the short crack growth rates under the higher temperature condition are still higher than those under the lower temperature condition.

a

b

Fig. 4. Typical hysteresis loops during the TMF test, (a) at 500-900°C, (b) at 200-600°C.

Fig. 5. Typical short cracks initiated and propagated by the TMF test, (a) at 500-900°C, (b) at 200-600°C.

Fig. 7. Crack opening ratio as a function of the half-length length evaluated by the FE analysis.

Fig. 6. Short crack propagation rates correlated with the stress intensity factor range.

The microstructures around the crack tip are shown in Fig. 9. As shown in Fig. 9(a), under the higher temperature condition, the crack tip and crack wake were covered with oxidation products. In addition, the micro-cracking in the