Fatigue Crack Paths 2003

Drill collar NC26

φe=89 m m

φi=38.1 m m

Drill collar N C 5 0

φe=168.3 m m

φi=69.8 m m

d

e

H

Figure 1. Twodifferent sizes of Drill collar.

Figure 2. Resonant test device

for D CNC26.

Tests were conducted up to complete failure of the specimen or to 107 cycles. In a few

tests a beach marking technique was applied in order to obtain a registration of

subsequent crack fronts.

110

PINFailure

100

Crack Detection in PIN

90

(M P a )

Pin failure

80

S t r e s s

70

60

50

40

1E+05

1E+06

1E+07

1E+08

Cycles

Figure 3. S-N curve for D CNC26.

To this end, applied load was lowered to 30%of test load for 104 cycles periods.

Results of full scale tests are reported in Fig. 3. Failure analysis occurred on Pin for

NC26TJ, while it was also observed on Box for NC50TJ.

Basic Material Characterisation Tests

The following basic material characterisation tests were conducted:

- Tensile tests