Crack Paths 2009

scale yielding but also for gross-section yielding condition. The findings are consistent

with the results presented in [18]. It simplifies the prediction of unknown parameter C

that is a function of stress concentration factors and net-section peak stress level as

shown in Figure 9(b), for given material and loading condition.

5

HLioghw Kt

1.00E-04

y = 1E-06e0.0097x

4

2

R

= 0.9973

m

erte , C

y = 5E-07e0.0032x

x,ponent

1.00E-05

3

2

R

= 0.9282

amra

2

E

1.00E-06

P

High Kt

1

Low Kt

Expon. (Low Kt)

Expon. (High Kt)

0

Peaknet-section stress level (MPa)

1.00E-07

100

200

300

400

500

100

200

300

400

500

Peaknet-section stress level (MPa)

(a) the effect on

(b) the effect on C

m

Figure 9. The effect of and t K

peakn_σ on F C Grate parameters.

From Figure 9(b), an empirical equation can be derived to predict unknown

parameterC for different stress concentration factor at different net-section stress as

follows:

p e a k A K A A t e C 2 1 0 + + =

(3)

where ,

and are constants determined by multiple regression. From the low

0 A 1 A t K

2 A

t K

ttKK

and high

F C G datasets, the constants are -1.71E+01, 1.6E+00 and 6.40E-03

respectively for the mid . To validate “ Eqs 1 - 3”, the mid F C Gdata were used.

Figure 10 demonstrated that the predictions of F C Gfor the mid specimens at the net

peak levels of 180 and 200 M P aare consistent with the experiments. It indicated that

both tested and predicted F C G rates for the mid specimens are weakly stress t K

dependent.

1.0E-021

/SFH )

1.0E-03

m

t ( m

1.0E-04

d a / d

Tested Mid Kt at200 M P a

1.0E-05

Predicted Mid Kt at 200 Mpa

Test Mid Kt at 180 M P a

1.0E-06

Predicted Mid Kt at 180MPa

1.0E-07

1.0E+00

1.0E+01

1.0E+02

Kn_peak ( M P a √ m )

Figure 10. Validation of F C Gprediction for Mid . t K

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