Crack Paths 2009

of the R-curve. In this case the homogenous model with parent material strength

underestimates the resistance curve

Homogenou (spare material strength nt

),[10] Heterogenous(local

()N

0

1

2

weld strength) 3 4

5

6

F o r c e

24000 6000

D

a (mm)

180

Experimental Homog nou(sparen material strength), [10] Heterogen us(local w ld str gth)

12305050505

Fig. 4: values of C T O Acalibrated on

δ5 (mm) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Fig. 3: calibration of C T O Aby comparison.

Δ

of F E Mand experiment - Kahntear test.

Kahntear test.

In the case of the 750mm-wide specimen the situation is the opposite that is the

homogenous model overestimates the R-curve. This is due to the different

representation of crack growth given in the two diagrams. In Fig. 5 the x-axis reports

the real crack propagation because the dimensions of the specimen were too small to

use the effective crack propagation [11], used instead in Fig. 8:

2 1 2 e fK f a ⎛ a⎞ Δ = Δ + ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ y σ

π

(1)

The good correlation between the FE model with local weld strength and the

experiment shown in Fig. 6 is obtained using the σy =205MPawhich is an average of

the yield strength of nuggett and T M A Zmeasured in [7]. The point of crack instability

in the experiments corresponds to 5-9mmof real crack propagation which is also well

matched by the experiments (Δa=6mm).

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