Crack Paths 2012

loading of two R ratios i.e. R = 0.06 and 0.5. For R = 0.06, the maximumapplied

norminal stress

max = 90 M P aand 170 MPa, and the resulted .-levels is in a35

M P a mFo.r R = 0.5,

max = 110 MPa, and the . values in a17 M P a. m

The second kind of loading condition, stated as LC2, is obtaind by adding a high

peak load to LC1, see in Fig. 2(a). The C A loading is R = 0.06,

m a x = 110 MPa, and the

peak load is

m a x = 170 MPa. The minimumloading in the spectrum is kept constant at

the level of

m i n = 6.6 MPaDŽThreeintervals (n), cycles between two peak loads, i.e. n =

2100, 4200 and 8400, are selected in this study.

The third kind of loading conditions, stated as LC3, which is slightly different from

LC2, is achieved by adding a negative amplitude load,

min = -17 MPa, also called

underload, immediately after the overloads, see Fig. 2(b). The interval n is 4200.

Table 1. Specimen and loading condition listing

Load ratio(R)

Specimen ID

( MPa x K m )

(mm) Frequency

(MaPax' K m )

Crack Length at MaxK (mm) a 0

(Hz)

0.06

24.0

22.5

16.6

2.0

10

LC1-0.06-90-1

0.06

25.5

24.0

17.8

2.0

10

LC1-0.06-90-2

0.06

26.4

24.8

18.5

2.0

10

LC1-0.06-90-3

0.06

33.1

31.1

10.7

2.0

LC1-0.06-170-1

5

0.06

37.4

35.1

12.9

2.0

LC1-0.06-170-2

5

0.5

27.6

13.8

15.4

2.0

LC1-0.5-110-1

5

33.2

16.6

19.0

2.0

LC1-0.5-110-2

0.5

5

25.5

24.0

6.8

3.2

LC2-2100-1

0.06

5

31.0

29.0

9.4

2.0

LC2-4200-1

0.06

5

28.0

26.5

8.2

2.0

LC2-4200-2

0.06

5

36.8

34.6

12.6

LC2-8400-1

0.06

3.2

5

34.3

32.2

11.3

3.2

LC2-8400-2

0.06

5

24.5

23.0

6.3

2.0

LC3-4200-1

0.06

5

23.0

21.5

5.6

2.0

LC3-4200-2

0.06

5

(a)

(b)

Figure 2. Constant amplitude loading with overloads and underloads

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