PSI - Issue 2_B

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

2411

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

7

10.0

70 0 C

7.5

5.0

2.5

b)

non-aged Nordel 450 Gy/h Nordel 1400 Gy/h Nordel 2780 Gy/h Nordel non-aged EPDM 455 Gy/h EPDM 1390 Gy/h EPDM 2760 Gy/h EPDM

0.0

10.0

7.5

Ultimate tensile stress (MPa)

40 0 C

5.0

2.5

a)

0.0

0

500

1000 1500 2000

Dose (kGy)

Fig. 5. The comparison of the ultimate tensile stress values for industrial EPDM and NORDEL aged at a) 40 0 C b) 70 0 C . The full line is a guide for an eye.

1.2

55 0 C, 106 Gy/h 70 0 C, 106 Gy/h 85 0 C, 106 Gy/h 25 0 C, 250 Gy/h 55 0 C, 455 Gy/h 70 0 C, 455 Gy/h 85 0 C, 455 Gy/h 25 0 C, 720 Gy/h 40 0 C, 1390 Gy/h 70 0 C, 1390 Gy/h 40 0 C, 2760 Gy/h 70 0 C, 2760 Gy/h

1.0

0.8

high dose rate

0.6

0.4

low dose rate

0.2

Relative elongation

0.0

0

200 400 600 800 1000 1200

Dose (kGy)

Fig. 6. The change of elongation at break in industrial EPDM. The lines are guide for an eye.

stress increase for dose rates higher than 500 Gy / h Gueguen et al. (1994.). Similar observation is also reported by Pinel and Boutaud Pinel et al. (1999., 1994.). Our results rather show that the crossover gradually changes, while e ff ect of interplay of dose rate and ageing temperature is confirmed. While increase of the temperature shifts the transition to lower dose, an increase of dose rate shifts the transition to higher dose. The existence of a crossover is essentially observed in entire dose range considered in this study. Change of elongation at break as a function of dose for the industrial EPDM is presented on the Figure 6. Dose rate e ff ect is found to be less pronounced, as it has been observed earlier, Seguchi et al. (1981.). Still, for extreme ageing conditions clear di ff erence in elongation at break decrease is evidenced. So, for the samples aged at high ageing temperatures and low dose rates elongation at break decreases much faster in comparison with samples aged for very high dose rates. The comparison of the elongation at break of the industrial EPDM with those of NORDEL (Fig7.) as a function of dose shows that elongation at break decreases faster for neat EPDM. Once again this e ff ect can be assigned to the absence of fillers and stabilisers which make NORDEL less chemically stable. Dose rate e ff ect is observed to be stronger at high temperatures. The fact that the elongation at break is less sensitive to the dose rate e ff ect could be