PSI - Issue 33

Dimos Triantis et al. / Procedia Structural Integrity 33 (2021) 330–336 Dimos Triantis et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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5

10000

9

10000

9

y = 2977.7x - 0.30

y = 916.65x - 0.37

a o =2 cm

a o =4 cm

1000

6

1000

6

Axial force [kN] 100

3

100

3

Axial force [kN]

Cumulative counts

Cumulative counts

Cumulative counts Power Law Axial force

cum. counts power law force Cumulative counts Power Law Axial force

10

0

10

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0.001

0.1

10

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0.001

0.1

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1000

t f -t [s]

t f -t [s]

(a)

(b)

10000

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9

9000

10000

10000

9

9

9000

a 0 =6 cm

a 0 =6 cm

a o =4 cm

a o =4 cm

Cumulative counts Power Law Axial force Cumulative counts Power Law Axial force

1000

1000

6

6000

6

1000

1000

6

6000

y = 2287.60x - 0.32 y = 2287.60x - 0.32

Axial force [kN] 100 Axial force [kN] 1 0

100

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3000 Axial force [kN] Axial force [kN] 3000

100

3

Cumulative counts

Cumulative counts Cumulative counts

Cumulative counts

Cumulative counts Power Law Axial force Cumulative counts Power Law Axial force

y = 278.60x - 0.44 y = 278.60x - 0.44

a o =8 cm

a o =8 cm

10

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0 0

0. 01

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t f -t [s]

t f -t [s]

t f -t [s]

t f -t [s]

(c) (d) Fig. 4. The time evolution of the acoustic activity described in terms of the cumulative counts versus the time-to-fracture (t f -t) parameter for typical specimens with (a) a ο =2 cm; (b) a ο =4 cm; (c) a ο =6 cm; (d) a ο =8 cm. In order now to comparatively consider the acoustic activity recorded by the sensors attached close to the crowns of the two notches, the cumulative counts recorded for a specimen with a 0 =8 cm, are plotted in Fig. 5, against the “time to- fracture” parameter. It is concluded (besides the expected fact that the activity is stronger in the vicinity of the notch from which crack propagation started) that the power law y=cx - m starts governing the response of the notch from which crack propagation begins (continuous lines) much earlier (almost nine seconds earlier for the specific specimen con sidered here) in comparison with the other notch (dotted lines). 4. Discussion As it was mentioned in the introduction, besides the study of acoustic activity at the stage of impending fracture, the present study aims to comparatively consider this activity against the respective electric one. In this direction, the electric current (PSC), recorded by the proper electric sensor, is plotted in Fig. 6 versus the normalized test’s duration, in juxta-