Crack Paths 2006

Table 2. Scatter assessment of delay time after 100%overload.

100%overload application

End of delay

Delay cycles

Specimen 1

17606

62606

45000

Specimen 2

19001

104001

85000

Specimen 3

45101

125101

80000

Delay cycles mean value

70000

Delay cycles standard deviation

21794

Delay cycles coefficient of variation

31.1 %

The propagation data related to the second 50 % overload and to the specimens N. 4-7

are shown in Fig. 3. This time the data from four specimen are available for statistical

regression (Table 3).

10

9

8

7

6

specimen #4

specimen #5

5

specimen #6

4

specimen #7

3

5000

10000

15000

20000

25000

30000

35000

40000

45000

0

N cycles

Figure 3. Crack length vs. cycles for the specimens N. 4-7 after the second overload.

Table 3. Scatter assessment of delay time.

Delay

End of delay at

cycles:

cycles

50%overload application at cycles:

6000

Specimen 4

6001

12001

Specimen 5

10001

19001

9000

Specimen 6

18001

27001

9000

Specimen 7

15001

24001

9000

Delay cycles mean value

8250

Delay cycles standard deviation

1500

Delay cycles coefficient of variation

18.1 %

After complete recovery from the transient behaviour associated to the second overload,

a third 40%overload was applied for one cycle (Table 1) whenthe crack length is about

11.5 mm.The propagation data related to specimen N. 4-7 are shown in Fig. 4. Again

the data from four specimen are available for statistical regression (Table 4).