PSI - Issue 2_B

T. Šarac et al. / Procedia Structural Integrity 2 (2016) 2405–2414

2413

Author name / Structural Integrity Procedia 00 (2016) 000–000

9

1.00

450 Gy/h, 40 0 C 1400 Gy/h, 40 0 C 2780 Gy/h, 70 0 C

0.75

0.50

0.25

b)

0.00

1.0

106 kGy/h, 70 0 C 250 kGy/h, 25 0 C 455KGy/h, 55 0 C 1390 KGy/h, 40 0 C

0.8

0.6 Relative elongation

0.4

0.2

a)

0.0

0

1000

2000

3000

Ageing time, h

Fig. 8. The relative elongation as a function of the ageing time for a) industrial EPDM and b) Nordel.

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24

25 0 C EPDM 40 0 C EPDM 55 0 C EPDM 70 0 C EPDM 85 0 C EPDM 40 0 C Nordel 70 0 C Nordel

Kirr (1/h)

0

1000

2000

3000

Dose rate (Gy/h)

Fig. 9. Radiative reaction rate constant as a function of the dose rate.

elongation at break of industrial EPDM is mainly governed by the oxidation process. On the contrary, the K irr value of the neat polymer as a function of dose seems to be dependent on the temperature, especially for the lowest and the highest dose rates. The value of K irr of NORDEL samples is higher in comparison with industrial EPDM, and the di ff erences increases by increasing the dose rate. NORDEL samples aged at samples aged at 40 0 C and 70 0 C exhibit linear dependence of K irr as a function of the dose in contrast to square rood dependence observed for industrial EPDM. This indicates that that there is a di ff erence in the degradation mechanisms of industrial and neat polymer. While irradiation and temperature assisted oxidation e ff ect play the major role in EPDM, the chain scission caused by irradiation seems to be main degradation mechanism in neat polymer (NORDEL). The dose rate e ff ect is less observed in elongation at break data in comparison with the ultimate tensile stress, possibly because both cross-linking and chain scission have the same e ff ect on the elongation at break via destruction of network structure which is responsible for elongation properties. Because of that, the total elongation can be used as the relevant parameter for the cable life time prediction.