PSI - Issue 68

M. Zarazovskii et al. / Procedia Structural Integrity 68 (2025) 391–397 M. Zarazovskii et al./ Structural Integrity Procedia 00 (2025) 000–000

393

3

• The method requires testing at a single temperature, which simplifies the process of assessing the strength of a material under specific conditions. According to the Master-Curve methodology T 0 is determined by solving the following transcendental equation:

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where N – number of specimens; T i – test temperature corresponding to K Jc(i) ; K Jc(i) = K Jc or K Jc(i) = K Jclimit in the case when K Jclimit < K Jc : δ i (Kronecker symbol and takes the value 0 or 1) δ i =1 – when K Jclimit > K Jc , or δ i =0 – when K Jclimit < K Jc . The principal advantages of the Master-Curve approach in comparison to the classical approach are as follows: • This method allows for the direct determination of the crack resistance curve based on experiments conducted on the static crack resistance of the material in its required state (after operating time). This contrasts with the use of correlation methods.; • This method enables the characterisation of fracture toughness over a wide temperature range using a single reference curve. • It is not necessary to use large specimens and corresponding experiments on high-force machines to obtain adequate fracture toughness values in the region of 100 MPa∙m 0.5 and above, in order to obtain a fracture toughness curve. It is possible that as few as six standard or half-size specimens may be sufficient. The Master-Curve approach is the standardised methodology by ASTM E1921, that is widely accepted within the materials science community. This contributes to the consistency and comparability of results from different studies and laboratories. However, this method has been well established and verified only on standard full-size specimens, such as SENB (Single Edge Notched Bend) with dimensions 10×10×5 mm and Compact Tension with sizes (СТ)1Т and (CT)0.5T and naturally on larger dimensions standard specimens. Also, this methodology is employed in certain nuclear power standards, for instance, in the EU’s document for WWER reactor – VERLIFE (2008). The objective of this study is to develop a methodology for experimental determination of crack resistance using half-size SE(B) specimens with a crack (10×10×5 mm) and compact C(T)0.16T specimens (4×5×10 mm). The aim is to assess the possibility of their use for Master-Curve and reference temperature determination.

2. Methodology 2.1. Material

The material selected for testing is unirradiated 15Kh2NMFAA base material steel (WWER-1000). Chemical composition in accordance with the former USSR’s technical conditions document TU 108.765-78 (1978) and the actual as well are given in Table 1. Mechanical properties according to the TU 108.765-78 and defined with tensile tests STRUMAT-LTO Deliverable 1.1 (2023) are presented in Table 2.

Table 1. Requirements for the chemical composition of 15Kh2NMFAA of WWER-1000 RPV Model alloy C Si Mn Cr Ni Mo V Cu S P TU 108.765-78

0.13 0.16

0.17 0.37

0.30 0.60

1.8 2.3

1.0 1.5

0.50 0.70

0.10 0.12

0.10 0.012 0.010

15Kh2NMFAA

Actual

E H

0.12 0.33 0.77 2.16 1.02

0.7

0.1 0.1

0.1 0.1

0.008 0.009

0.12 0.51 1.31 2.07

2

0.69

0.008

0.01