PSI - Issue 42

S. Lindqvist et al. / Procedia Structural Integrity 42 (2022) 42–49 Author name / Structural Integrity Pro edia 00 (2019) 000–000

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Table 1. Key parameters. J integral

Total time of the measurement

Cooling rate. Depth = 10 mm

Final temperature

Crack growth

before cooling starts

[kJ/m 2 ]

[°C]

[s]

[mm]

[°C/s]

5.2 5.3 5.4 5.5 5.6 5.7 8.1 8.2 8.3 8.4

48 94

11 22 32 34 26 28 19 13 20 18

598 670

2,1 2,6 3,7 3,9 6,2 2,6 4,5 5,6 4,2 5,9

-2,1 -1,9 -1,9 -1,6 -1,6 -2,0 -1,9 -2,2 -2,2 -2,0

558 978

1390 2053 2101 1582 1358 2281 1629 2375

1005

704 528

1132

733

1163

3.2. Fracture surfaces Figures 15 to 17 show the fracture surfaces of the specimens. The fatigue pre-crack, crack growth in 300 °C (dark blue areas) and crack growth during the cooling transient can be distinguished from the fracture surface. A special feature on the fracture surface is the splitting (delamination of the ligament) of the fracture surface as explained in section 2.1. The split always occurs at the center of the specimen.

Crack growth during cooling Splitting

Crack growth at 300 °C

Fatigue pre-crack

Figure 4. Fracture surface.

3.3. The effect of thermal transient on load-displacement raw data Figure 18 shows the effect of a cooling rate of 2 °C/s on the red load-CMOD curve, when the specimen is cooled from 300 °C to room temperature. The decrease in temperature is also marked into the Figure. The discontinuities (pop-ins) observed in the load-CMOD record are connected to splitting. During isothermal testing, splitting occurs only at room temperature. The splitting phenomena is not a result of the