PSI - Issue 68

M. Zarazovskii et al. / Procedia Structural Integrity 68 (2025) 391–397

394

4

M. Zarazovskii et al./ Structural Integrity Procedia 00 (2025) 000–000

Table 2. Requirements to mechanical properties of 15Kh2NMFAA of WWER-1000 RPV

20°C, not less ! , MPa "#,% , MPa & , % , % ! , MPa "#,% , MPa & , % , % TU 108.765-78 350°C, not less

Model alloy

15Kh2NMFAA

608

490

15

55

539

441

14

50

Actual

E H

578.5 635.5

451.5 479.5

20.8 22.0

– –

502 560

393 412

15.7 15.1

– –

2.2. Experimental equipment To conduct the experiments and maintain cryogenic temperatures, cryo chambers for three-point bending and the FT testing were manufactured. The schemes of the cryo chambers are presented in Fig. 1. These chambers are designed to carry-out the experiments of structural materials in the temperature range of 77 К...173 К.

a

b

Fig. 1. Diagram of cryochambers. (a) for three-point bending; (b) for mini-CT testing. (1) Upper movable rod; (2) Nitrogen supply pipe; (3) Foam cover; (4) Nitrogen vapour; (5) Metal body; (6) Foam; (7) Thermocouple; (8) Specimen; (9) Thermal gaskets; (10) Extensometer; (11) Liquid nitrogen; (12) Support; (13) Lower fixed rod; (14) Glue; (15) Sleeve; (16) Hetinax support; (17) Nut; (18) Thermal gasket; (19) Frame. The crack opening during mini-CT samples testing was recorded using extensometer mounted 2mm out of the front face (FF) with conversion to load-line displacement (LLD) using equation FRACTESUS (2021):

(

)

%%& DD&

( ) " $# " ! " $# " + ! + ! +

=

(5)

where r =0.352 – the rotation factor, x – the distance from LL to the FF, a – crack length and W is the specimen width. The mini-CT specimen was subjected to FT testing, with the use of a low-temperature extensometer that had been calibrated at room temperature in liquid nitrogen. The calibration was conducted utilising a mechanical calibrator from Instron, with an absolute error of 0.38 µm. Given that the discrepancy in calibration coefficients at the extremes of the temperature range is 6.1%, a linear relationship between the strain gauge calibration coefficient and temperature was assumed for temperatures within the range of 77 to 293 Kelvin. The temperature during the three-point bending tests was measured using copper-constantan thermocouples, which have the highest sensitivity in this temperature range Samsonov G.V. et al. (1972). The thermocouple signal was fed to an HP 3456A millivoltmeter with the ±1 µV accuracy. The thermocouple was calibrated at seven fixed temperature