PSI - Issue 2_A

Hide-aki Nishikawa et al. / Procedia Structural Integrity 2 (2016) 3002–3009 Author name / Structural Integrity Procedia 00 (2016) 000–000

3004

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Table 1. Chemical compositions. Material C Si Cr

Mn P N A 0.07 <0.01 0.51 1.51 0.006 0.003 <0.01 0.025 0.003 B 0.07 <0.01 0.01 1.50 0.006 0.003 0.21 0.026 0.003 C 0.15 0.02 0.54 1.51 0.007 0.001 - 0.019 0.002 S Mo Al

Table 2. Heat treatment conditions for each materials. Cooling rate ( ℃ /s) A B C 1400~1000 ℃ 10 60 50 1000~800 ℃ 4 40 30 800~500 ℃ 1 20 500~350 ℃ 0.5 12

Fig. 1. Simulated HAZ Microstructures.

2

2

φ 10

R31

(32.5)

16.8

16.8

Fig. 2. Specimen configurations.

3. Experimental results and discussions

3.1. Mean stress effects on S-N diagrams

Figure 2 shows S-N diagram. Fig. 2 (a) is represented with stress amplitude. Solid mark shows results under fully reversed tension-compression condition and open mark shows under tensile mean stress condition. Fatigue lives under tensile mean stress conditions were shorter than that of fully reversed tension-compression results. It is known that mean stress dependency is able to be fixed using Smith-Watson-Topper (SWT) equivalent strain proposed by Smith et al. (1970). SWT equivalent strain ε eq is expressed as: ( ) c c a eq E − = 1 max σ ε ε (1) where ε a is strain amplitude, σ max is maximum stress, E is Young’s modules and c is materials constant which is related to mean stress sensitivity. Fig. 2 (b) shows S-N diagrams represented with SWT equivalent strain. Although mean