The Comparative Analysis and Verification of the Engineering Methods for Considering the Shallow Crack Effect for the Pr
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CTURAL AND TECHNOLOGICAL STRENGTH AND SERVICEABILITY OF MATERIALS
The Comparative Analysis and Verification of the Engineering Methods for Considering the Shallow Crack Effect for the Prediction of the Fracture Toughness of the Materials for Nuclear Reactor Pressure Vessels V. I. Kostyleva, * and B. Z. Margolina aNational
Research Center Kurchatov Institute—CRISM Prometey, St. Petersburg, 191015 Russia *e-mail: [email protected] Received August 30, 2019; revised November 5, 2019; accepted November 22, 2019
Abstract—The key features of the fracture of the specimens with shallow cracks are considered, and a brief analysis of the main methods making it possible to predict the temperature dependence of the fracture toughness KJc(T) for shallow cracks is given. These methods include the DA method, (J–Q) method, (J–T) method, “local” methods utilizing multiparameter probabilistic approaches, GP method utilizing the deterministic “power” approach, as well as two engineering methods—RMSC (Russian Method for Shallow Crack) and EMSC (European Method for Shallow Crack). Detailed verification and comparative analysis of these two engineering methods are carried out in respect of the materials of the VVER and PWR nuclear reactor pressure vessels considering the shallow crack effect on the basis of 13 sets of experimental data for domestic and imported steels. Keywords: VVER reactor pressure vessel, fracture toughness KJc, deep and shallow cracks, brittle fracture resistance, engineering methods for predicting KJc(T) DOI: 10.1134/S2075113320060106
INTRODUCTION It is known that the fracture toughness KJc of a specimen with a relative crack length a/W ≤ 0.2 exceeds the fracture toughness of a specimen with a standard relative crack length a/W = 0.45–0.55, where a is the depth of the crack and W is the width of the specimen [1–15]. By way of example, Fig. 1 presents the experimental data on the fracture toughness KJc with shallow (a/W ≈ 0.1) and deep (a/W ≈ 0.5) cracks for steels of the A533B and 18MND5 brands [12–14]. In publications, such a regularity is called a shallow crack effect, and cracks with a relative length a/W ≤ 0.2 are called shallow. It should be noted that the consideration of the shallow crack effect is very important when evaluating the brittle fracture resistance (BFR) of VVER or PWR nuclear reactor pressure vessels (NRPVs). The point is that the relative size of the postulated cracklike defects in NRPVs generally is a/S ≤ 0.1 (a is the depth of the postulated semielliptical defect, S is the thickness of the NRPV wall) [16–18]. The size S in fact corresponds to the size W in the fracture toughness tests of the standard bend specimens of the SE(B) type or compact specimens of the CT type [19, 20]. Because of this, the postulated defect in NRPVs can be classi-
fied as a shallow crack. Therefore, consideration of the shallow crack effect will lead to a decrease in the excessive conservativism in the calculations for the brittle fracture resistance of NRPVs and, hence, an increase in the service life of NRPVs. The es
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