Fatigue Crack Paths 2003

approximately 28.5 mm.Due to the shadowing effect the crack in the symmetry plane

then stopped. This happened, when Δ K was approximately 5.0 MPa√m.

12.0

CrackPath on Front Side

y = 0.6734x - 11.223

o o r d in a t e [ m m ]

-642.0 Z 102468.0 c

Notch

crack at 0 deg.

crack at -38 deg.

crack at +34 deg.

Linear (crack at +34 deg.)

-1-208.0

y = -0.7759x + 13.461

Linear (crack at -38 deg. )

16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 32.0 34.0 36.0

X coordinate [mm]

12.0

Crack Path on BackSide

y = 0.7172x - 12.367

[m m

Z 108.0 c o o r d in a t e ]

notch

crack at 0 deg.

crack at -41 deg.

crack at +36 deg. Linear (crack at +36 deg. )

-1-202468642.0

y = -0.8828x + 15.513

Linear (crack at-41 deg. )

16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 32.0 34.0 36.0

X coordinate [mm]

Figure 1. Crack Path on the front- and back-side of the CT-specimen tested in

nitrogen at 83 Hz (load increasing test).

DISCUSSION

The situations found in these two specimens have been addressed in the literature as

forked crack geometry. Bilby, et al. [8] has defined the stress intensity factor solution

for the specific case shown in Fig. 3 left. For a fare-field tensile stress, the stress

intensity factor of a crack, which is perpendicular to the stress field, is KI. In this case

the crack is loaded in mode I, the opening mode. If the crack is forked it is in a mix

mode loading condition. The local modeII stress intensity factor is no more zero, see