PSI - Issue 81

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ScienceDirect

Procedia Structural Integrity 81 (2026) 123–128

© 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers Keywords: biaxial loading; cruciform specimen; constraint; fracture toughness, stress triaxiality, Master curve. 1. Introduction Integrity assessment of VVER-type reactor pressure vessels based on fracture toughness characteristics obtained under uniaxial loading in plane strain conditions demonstrates a pronounced level of conservatism. In accordance with the regulatory documents applied in the nuclear industry, it is recommended to account for the biaxially of loading acting on the faces of a postulated crack, with due consideration of crack depth, which allows the accuracy of the assessment to be improved and its conservatism to be reduced. A fundamental study devoted to the investigation of the effect of biaxial loading on static fracture toughness characteristics is the work by Bass et al. (1999), in which experimental data obtained using a large-scale cruciform specimen subjected to five point bending were analyzed. For reactor pressure vessel steels in the unirradiated condition (base material), the influence of the shallow crack effect under biaxial loading close to that realized in the reactor vessel wall on the fracture toughness parameter K Jс was demonstrated. Similar trends were subsequently observed for small-scale cruciform specimens (Kim et al. (2016), Hohe et al. (2011), Pokrovs’kyi et al. (2022), Pokrovskyi et al. (2023)). Subsequently, it was shown that the application of two-parameter Abstract The assessment of the structural integrity of reactor pressure vessels is performed in accordance with regulatory documents based on fracture mechanics criteria. In doing so, it is necessary to account for the effects of shallow cracks, biaxial loading, and crack front length, as these factors alter the in-plane and out-of-plane constraint and influence the fracture toughness. In this study, a series of small-scale cruciform specimens made of 15Kh2NMFAA steel with shallow cracks was used to investigate the influence of biaxial loading on static fracture resistance, to determine the reference temperature T ₀ , and to compare it with T ₀ ref obtained from standard CT-1 specimens in accordance with the ASTM 1921 standard. Experimental results indicate that biaxial loading of cruciform specimens with shallow cracks reduces the reference temperature T ₀ and consequently decreases the conservatism of residual lifetime assessments for nuclear reactor pressure vessels. The influence of biaxial bending on fracture toughness were analyzed based on finite element analyses of stress triaxiality and the constraint parameter derived from crack-tip opening. VIII International Conference “In - service Damage of Materials: Diagnostics and Prediction“ (DMDP 2025) Fracture assessment of a cruciform bending specimen using a two-parameter fracture criterion based on crack tip opening displacement V. Sidyachenko*, A. Zhovtobriukh G.S. Pisarenko Institute for Problems of Strength of the NAS of Ukraine, 2 Sadovo-Botanichna str., Kyiv-014, 01014, Ukraine

* Corresponding author. Tel.: +380 44 281 63 39 ; fax: +380 44 286 16 84. E-mail address: Sydiachenko@ukr.net

2452-3216 © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of DMDP 2025 organizers 10.1016/j.prostr.2026.03.022