PSI - Issue 2_A

Ido Simon et al. / Procedia Structural Integrity 2 (2016) 205–212

209

I. Simon et al. / Structural Integrity Procedia 00 (2016) 000–000

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Table 2: Load and displacement ratios, total number of cycles and the test frequency for each fatigue test. specimen no. R d R P N f (cycle)

test frequency

FTG-4-02 FTG-4-03 FTG-4-04 FTG-4-05

0.10 0.33 0.50 0.75

0.08 0.31 0.47 0.72

1,770,600 2,581,500 2,700,000 3,000,000

4 Hz 5 Hz 5 Hz 6 Hz

calculated for ∆ a = 5 mm using a G R - curve obtained from fracture toughness tests of specimens from other batches. The G R -curve as calculated in the fracture toughness tests is given by

0 . 14 .

G R = 508 + 340( ∆ a )

(4)

In eq. (4), ∆ a = a − a 0 is the length of the current delamination a relative to the initial delamination length a 0 . In Fig. 4b, the delamination propagation rate da / dN is presented as a function of ∆ G Ie f f = G Imax − G Imin 2 . (5) In eq. (5), G Imin and G Imax are the minimum and maximum energy release rates, respectively, which occur during a fatigue cycle. For each one of the representations, G Imax and ∆ G Ie f f , a power law was fitted through the data. The power law may be written as

da dN =

D [ f ( G )] m .

(6)

10 -2

10 -2

FTG-4-02 (R d FTG-4-03 (R d FTG-4-04 (R d FTG-4-05 (R d

= 0.10)

FTG-4-02 (R d FTG-4-03 (R d FTG-4-04 (R d FTG-4-05 (R d

= 0.10)

= 0.33)

10 -3

10 -3

= 0.33)

= 0.50)

= 0.50)

= 0.75)

= 0.75)

10 -4

10 -4

࣡ IR

, ɧ a =5mm

10 -5

10 -5

10 -6

10 -6

10 -7

10 -7

࣡ Imax (N/m)

୼࣡ eff (N/m)

10

100

1000

10

100

1000

(a)

(b)

Fig. 4: (a) Delamination propagation rate da / dN versus G Imax for the di ff erent displacement ratios, together with the fracture toughness G R -curve value at ∆ a = 5 mm. (b) Delamination propagation rate da / dN versus ∆ G e f f given in eq. (5) for the di ff erent displacement ratios.