Crack Paths 2009

[56]. Then it is assumed that o-pr : o'mmif 0min >o-Op. The following relation specifying

the crack growth per one cycle was proposed in [19]:

§N—°= Corr. 'r

(20)

where r is length of decohesion zone along the crack growth direction and C, n are the

fatigue parameters obtained from uniaxial tests (or = 90°). In the case Ti-6Al-4V alloys

the fatigue parameters are: 3.5 and 1.712. The comparison of model predictions and

experimental results are shown in Tables 2 and 3. The comparison with predictions of

R-criterion is also presented in tables in the following form

0'" > O,

(21)

where C1,n1 are the fatigue constants for the uniaxial test (or : 90°). In the case Ti-6Al

4V alloys the parameters are l,26-lO’14and 5.4 respectively [57]. In the uniaxial test

equation (21) is equivalent to Paris equation.

RIGTHTIP. (Eq. 21)

RIGHTA N DLEFTTIP. (Eq. 20) RIGHTTIP (Experimental results from [52])

t

1

da/dN

\

1

da/dN

\

r

da/dN

La L N La Z N

La L N

[10'3m]

cykle [10a'7m] [10'3m]

cykle

[10'7m]

[10'3m]

cykle

[10'7m]

0,945

3583

2,64

0,945

1390

6,77

0,91

1390

6,54

1,705

5416

4.15

1,705

2430

6,25

1,70

2430

7,59

l

4,58

8695 l

13.83

4,58

5 400

12,14

4,55

5 400

12

l

6,86

9813 |

24,89

6,86

7 000

18,38

6,86

7 000

18

Table2. Mixedmodefatigue crack growth in titanium alloys for specimen A.

R I G T HTIP. (Eq. 21) R I G H TA N DL E F TTIP. (Eq. 20) R I G H T IP (Experimental results fr6m [52])

1

1

da/dN

a

N da/dN

a

N

da/dN

La Z N

[10'3m] cykle [107m] [103m]

cykle

[107m]

[103m]

cykle

[10'7m]

0,86

3546 1,64

0,86

2 954

2,91

0,30

4 660

1,85

3,575 12862 4,19

3,575

9 804

4,91

3,00

11 490

5,77

4,435 14462 5,72

4,435

11 268

6,15

3,87

13 000

3,91

6,9

17436 10,36

6,9

14 319

9,54

6,33

15960

10,92

Table 3. Mixedmodefatigue crack growth in titanium alloys for specimen B.

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