Crack Paths 2009

Constant amplitude loading

As forged

shot blasted

Shotblasted As forged

16

12

14

points

10

n s

12

i n i t i a t i o

o n

8

10

N u m b e r o f c r a c k i n i t i a t i

N u m b e r o f c r a c k

8

6

6

4

4

2

2

0

0

30

35

40

45

50

55

60

65

20

25

30

35

40

45

50

Load(KN)

Equivalent load level, K N

a) Constant amplitude loading

b) Variable amplitude loading

Figure 10: Numberof crack initiation points vs. maximumload.

Shot blasted

12

As forged

points

10

N u m b e r o f c r a c k i n i t i a t i o n

8

6

4

2

0

40

45

50

55

60

65

70

Maximumload,KN

Figure 11: Numberof crack initiations vs. maximulmoad in variable amplitude loading tests

Crack propagation

The depth of fatigue crack propagation in all cases (as it is shown in Figure 8 and 9)

decreases with increasing load level. The beach marks can be seen in variable amplitude

specimens tested in lower loads but they gradually disappear by increasing the

maximumload. Figure 12 shows that for both shot blasted and as forged components

the depth of fatigue crack propagation decreases with increased maximumload. This

trend is, however, more pronounced in shot blasted specimens. Figure 12b shows the

same trend but for variable amplitude loading condition.

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