Fatigue Crack Paths 2003

constant, which can be found by fitting fatigue data from simple uniaxial tests to fatigue

data from simple torsion tests.

Application of the Fatemi-Socie model for the six loading cases show the variations

of the F-S parameter on different plane orientations as presented in Fig. 4. For each

loading case, the plane angle è with the maximumF-S parameter can be identified and

they are summarized in Table 5.

0.007-90

-70

-50 Case2 Case3 Case4 Case5 Case6 Case1 -30 -10 10 30 50

70

90

te m i S o c ie P a r a m e te r

0.000123456

F a

Plane angle [º]

Figure 4. Variations of the F-S parameter on different plane.

S-W-TModel

The tensile damage model, proposed by Smith, Watson and Topper [3], predicts that the

fatigue crack plane is the plane orientation è with maximum normal stress (the

maximumprincipal stress):

(3)

()2max1εσθn

where σn is the normal stress on a plane è, ε1 is the normal strain on that plane.

Figure 5 shows the variations of the normal stress σn on the different plane è, under

the six loading cases. For each loading case, the plane angle with the maximumnormal

stress σn can be identified and they are summarized in Table 5.

Case2 Case3 Case4 Case5 Case6 Case1

600

[M P a ]

500

e s s

400

N o r m a l S t r

300

200

100

0

-90

-70

-50

-30

-10

10

30

50

70

90

Plane angle [º]

Figure 5. Variations of the normal stress σn on different plane.