Crack Paths 2009

Test Results

The a-N readings from the travelling microscope are shown in figures 7 and 8. The

transition of the crack from the virgin material into the boundary of the peened region

occurs at a crack length of 20mm.

Crackgrowthdata -SpecimenA

40

35

m m )

30

lne g th (

25

20

15

c r a c k

10

5

0

0

50000

100000

150000

200000

N u m b e orf cycles

Figure 7- Fatigue crack growth data (a- curve) for specimen A

Crackgrowthdata - SpecimenB

35

30

m m )

25

lne g th (

20

15

c r a c k

10

5

0

0

10000

20000

30000

40000

50000

N u m b e orf cycles

Figure 8- Fatigue crack growth data (a- curve) for specimen B

A A L Y S I S

The results of the tests were not as expected. Based on the experience from shot peened

specimens, a sudden halt in the growth of the crack was expected in the boundary of the

treated region.

From the figures of stress distribution in the specimens (figures 4 and 5) it is evident

that a tensile core of material exists in the midsection of the specimens. These tensile

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