Crack Paths 2012

The calculated KI and KII values are normalized with respect to the crack size, a, and

a nominal normal stress acting at the crack mouth location in an uncracked specimen.

The nominal bending and tensile stresses are given by (see notations in Figure 1)

F , 3 0 6 12 2 B W Fs B W x M m V

V

b

(1)

B W

for the SE(B) and SE(T) specimens, respectively. In Eq. (1) the coordinate x = 0

indicates the horizontal position of the initial notch (crack mouth) in the SE(B)

specimen. The respective dimensionless stress intensity factors for both mode I and

modeII are expressed as follows

F K a F K a m III III b III III S V S V ,

,

,

(2)

,

,

for the SE(B) and SE(T) specimens, respectively.

The numerical results in Figure 3 demonstrate that mode I loading dominates the

crack propagation behaviour. For the SE(B) specimens, the mode II stress intensity

factor is almost zero, except for the very beginning stage of crack growth starting from

the mode I pre-crack, as well as at shifting from the asymmetric to symmetric roller

position for the specimens SEB4and SEB8. Besides, the final stage of crack growth

prior fracture is also influenced by mode II. Similar conclusions hold for the SE(T)

specimens which show a moderate increase of modeII crack tip loading either for deep

cracks of a/W>0.7 (SET1, SET2) or at the onset of ligament break through (crack

running in the bore in the SET3 specimen).

-101234567

4

FI (SEB5, SEB6, SEB7)

FI (SET1, SET2)

3

FI (SEB4)

FI (SET3)

2

FI (SEB5, SEB6, SEB7)

FII (SET1, SET2)

FI (SEB4)

FII (SET3)

, F

, F

F

F

1

0

-1

0.0

0.2

0.4

0.6

0.8

0.0

0.2

0.4

0.6

0.8

Normalizedcrack depth, a / W ( ) SE(B)

Normalizedcrack depth,a / W

(b) SE(T)

Figure 3. Dimensionless stress intensity factors for mixed modespecimens.

In all cases considered, except for the deepest crack in bend specimens, the absolute

ratio of modeII to modeI stress intensity factor, KII/KI, is well below 0.2. Assuming an

equivalent stress intensity factor range according to [5]

' '

(3)

eq ' '

2 K K

21

K

34.5

K

,

I

I

2

II

2

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