Issue 77

V. Antonchenko et alii, Fracture and Structural Integrity, 77 (2026) 247-264; DOI: 10.3221/IGF-ESIS.77.15

Figure 2: Parameters of the considered defect, with point representation.

The average shape functions are obtained from the following relations:

1







4  



(3)

i

i

i

i

6 point

point

point

1

2

3

The WWER-1000 reactor pressure vessel has anticorrosion cladding, which significantly complicates the accurate determination of stress polynomials. Due to the abrupt change in material properties within the cladding region, substantial errors arise when approximating the stress field. Fig. 3 presents the distributions of the actual stresses obtained from the finite element analysis as well as their interpolated representations. The analysis of the stress plots clearly demonstrates the pronounced influence of the anticorrosion cladding on the stress distribution. The solid blue line corresponds to the actual stresses, while the red dashed line represents the interpolated function. During the interpolation process, a significant error is observed near the cladding, due to the inability of a smooth polynomial function to capture the steep stress gradients adequately. This error may lead to either overestimation or underestimation of the stress level near the crack tip, thereby affecting the accuracy of subsequent fracture mechanics parameter calculations. In Fig. 3, we can see a stress discontinuity in the cladding zone, making accurate polynomial selection impossible with this distortion. Therefore, we applied the stress decomposition method presented in VERLIFE [4]. It consists of separating the stresses in the base metal and the cladding. We obtain two smooth functions. The stress decomposition process is schematically shown in Fig. 4. Then SIF can be found using equation:

   

   

j

j

4

1

a r h r  

a r h r  

  

  

  

  













a r 







(4)

K

i

i

j j

jr jr

1





j

j

0

0

Stress intensity factor analysis is based on the linear elastic fracture mechanics, thus we decompose the complex stress distribution to compute the SIF separately for each type of polynomial loading. The most convenient way is to apply different polynomial loading on the crack surface.

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