PSI - Issue 5

Maria Paarmann et al. / Procedia Structural Integrity 5 (2017) 869–874 M. Paarmann et al./ Structural Integrity Procedia 00 (2017) 000 – 000

873

5

a)

b)

4

4

point A point C

3

3

 K /  K th,RT [ ]

 K /  K th,RT [ ]

2

2

ΔK th,500 ΔK

1

1

th,400

ΔK th,300

ΔK th,600

0

0

10

20

30

40

10 20 30 40 50

a [mm]

a [mm]

Fig. 5. Crack growth start at front point A and C depending on temperature for (a) position F and (b) position E

The curves are based on the FORMAN/METTU equation and the parameters determined from the experimental data. Another base of the lifetime prediction is the SIF-solution numerically determined in FRANC3D (chapter 3). In the current case the SIF for the largest crack size does not exceed the critical SIF. Nevertheless, the curves underline faster crack growth on the surface point than on the deepest point of the crack front. The figure also shows that high temperatures result in a smaller number of cycles N at the critical crack size c crit of T = 600°C. For room temperature for example N is about thirteen times higher than at T = 600°C. It underlines the importance of investigating temperature dependent residual lifetime in power plant components.

a)

0 10 20 30 40 50 60 0 10 20 30 40 50 60

RT

300°C

400°C

500°C

600°C

a [mm]

0

0.5

1

1.5

2

2.5

3

3.5

4 x 10 6

N [ ]

b)

c crit

c [mm]

0

0.5

1

1.5

2

2.5

3

3.5

4 x 10 6

N [ ]

Fig. 6. Comparison of temperature dependent crack growth curves in the ball-shaped part for scenario 2 at (a) the deepest crack front point A and (b) the surface point C of position F