PSI - Issue 28

Dimos Triantis et al. / Procedia Structural Integrity 28 (2020) 502–510 D. Triantis, I. Stavrakas, A. Kyriazopoulos, E. D. Pasiou, S. K. Kourkoulis / Structural Integrity Procedia 00 (2019) 000–000 5

506

10000

40

90 days

3 days

28 days

1000

30

14 days

100

20

3 days

14 days

PSC [pA]

10

10

Axial stress [MPa]

28 days

90 days

0

1

0.0000 0.0015 0.0030 0.0045 0.0060

0.00 0.25 0.50 0.75 1.00

f t t

Axial strain

Fig. 3. Plots of the time evolution of the PSC for characteristic specimens of all classes tested.

Fig. 2. Characteristic axial stress-axial strain plots for specimens of all classes tested.

background noise of the PSC for the early aged specimens is attributed to their increased moisture. For all four classes of specimens the PSC is initially almost constant. After a specific time limit, which is a function of the specimens’ age, the PSC value starts increasing. The increase is initially rather smooth but gradually the increase becomes more abrupt and the PSC attains a peak value (also a function of the specimens’ age) just before (or a little before) macro scopic fracture of the specimens occurs. 4. Results and discussion In an attempt to correlate the mechanical response of the specimens with the electric emissions a typical specimen of the “14 days” class is considered. The axial stress-axial strain curve (Fig.4a) is studied in juxtaposition to the time evolution plots of both the axial strain developed and the PSC recorded (Fig.4b). Ignoring initial non linearities due to bedding error (unavoidable in uniaxial compression tests), it is evident from Fig.4 that the axial stress-axial strain curve is linear (recall that the experiments were implemented under stress control

1200

0.0045

37.5

14 days

14 days

Β

A

Β

800

0.0030

25

Axial strain

A

400 PSC [pA]

0.0015

12.5

Axial stress [MPa]

Β΄

A΄

ε L

0

0

0.0000

0.0000 0.0015 0.0030 0.0045

0

150

300

450

Time [s]

Axial Strain

(a) (b) Fig. 4. The axial stress-axial strain curve of a typical specimen of the “14 days” class (a) and the respective plots of the time evolution of both the axial strain developed and the PSC recorded (b).