Crack Paths 2006

(b)

(a)

102 34 567 8

105 6 7

E m =0.05 std 69

G=0, OWV=0.29

E m =-0.4 std 0.56

G=0,OWV=0.29

G=0, OWV=0.44

G=0,OWV=0.44

G=0, OWV=0.68

G=0,OWV=0.68

G=S/2, O WV =0.50

G=S/2, OWV=0.50

G=S/2, OWV=0.62

G=S/2,O WV =0.62

G=S/2, OWV=0.71

G=S/2, OWV=0.71

var.amp.-torsionvar.amp.-bending

var.amp.-torsion

var.amp.-bending

4

10

3

10

u3

u3

u3

u3

2

10

10 2

10 4

10 6

2

4

6

8

8

10

10

10

10

10

Texp, s

T

, s

8

exp

(c)

(d)

108

1056 7 8

G=0, O WV =0.29

E m =-1.14 std 0.46

G=0,OWV=0.29

G=0, O WV =0.44

G=0,OWV=0.44

E

=-0.58

7

m

10

G=0, O WV =0.68

E

=0.32

G=0,O WV =0.68

std

G=S/2, O WV =0.50

G=S/2, OWV=0.50

6

10

G=S/2, O WV =0.62

G=S/2,O WV =0.62

G=S/2, O WV =0.71

G=S/2, OWV=0.71

5

var.amp.-torsion

var.amp.-torsion

10

var.amp.-bending

var.amp.-bending

1023 4

4

10

3

10

u3

u3 u3

u3

2

10

108

10 2

104

10 6

108

2

4

6

10

10

10

T

, s

T exp , s

exp

Figure 2. Comparison between the experimental fatigue lives T exp and the calculated

fatigue lives T

cal: (a) the maximumnormal stress criterion, (b) the maximumshear stress

criterion (the Findley criterion Eq. 5 for k = 0), (c) the Matake criterion Eqs 8 and 10,

(d) the max{Vn,Wns} criterion.

From the engineering point of view, the material fracture behaviour is not known

before the material fatigue failure and therefore this feature cannot be used as a key in

the selection of the proper fatigue criterion. It was assumed that this selection could be

made by the maximumdamage degree computed by two simple criteria, i.e. the

maximumnormal stress criterion (Eq. 13) and the maximumshear stress criterion (Eq.

(5) for k=0). For each specimen, the damage degree on the critical plane is computed by

these two criteria (max{Vn,Wns}) and than the fatigue life T cal

is determined by the

highest damage degree (Fig. 2 d).