Crack Paths 2009

In Figure 4.2, showing da/dN as function of AK, A Kis instead increasing due to

increasing 0"’0

in the interval o'jjmax I140-360 MPa, with aI20000b and lGB1I5000b.

The curves Figure 4.2 show good agreement, especially for the highest growth rates.

T h edifferences in the threshold values of AK,belowwhichno crack growthwill occur,

is also clearly seen in the figure and it was found that the highest growth rates, given a

constant AK, is obtained with o'°°

:80 M P aand the lowest with 03min :20 MPa. This yy min

is because it requires a smaller increase in 0'”

to nucleate further dislocations than

w m m

the required increase in 03m," to annihilate one less dislocation, which leads to an

increase in threshold value with decreasing 0' 0 O yy min ‘

3 0

— 13m,“ = ZOMPa , 3° ______. oj§m=40MPa

,

_____ _-

’

2s _

'

. . . . . . . . . . . . .

. . . . . . . . . . . . 03m," I60MPa

_ ... .- ejm, I8OMPa

25 I _ ... .- 0'“

2 0 *

5

E20

2 3 15.

%

e

s15

10

10 -

5 L

g

5.

_<.°';’

‘ / ~ , "I

. -

coda. .

.

l

l

. . l

l

l-

0 / l

l

.

l

l

l

l

l

0.4 0.5 0.6 0.7 0.8 0.9 l

1.1 1.2 1.3 1.4

0.4 0.5 0.6 0.7 0.8 0.9 1

1.1 1.2 1.3

AK [MPm/m]

AK [MPm/m]

1.

2.

Figure 4.Crack growth rate, da/dN, as function of stress intensity factor, AK. 1. Constant

0'” increasing a. 2. Constant a increasing o'°° yy m a x

yy m a x‘

Also a comparison between the two different ways of increasing AK, by either

(I)

increasing a or increasingo'

has been performed, using 0'” :40 M P aand

' W m w ’

yy min

lGB1I5000b.The result is seen in Figure 5 and it is seen that, for low growthrates, the

two ways of increasing A Kgive similar results. For higher growth rates, however, it is

found that the curves shows different slopes and, by increasing a, results in lower

00 growth rates as comparedto increasing o'yymax. W h e nusing the method of increasing

0'” an almost linear relation betweenA Kand da/dNwas observed as comparedto

what is obtained for long cracks were AK, typically, is of the powerof two and four [1]

in relation to da/dN.

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