PSI - Issue 16

Eugene Kondryakov et al. / Procedia Structural Integrity 16 (2019) 43–50 Eugene Kondryakov et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction

Impact bending tests of Charpy specimens arise as the primary type of tests in the modes of surveillance specimens performed to monitor the material conditions of structural elements of reactor units. A limited number of tests for surveillance specimens, especially at high fluences, and deficiency of irradiated metal lead to significant discrepancies in the prediction of operation ability of NPP equipment elements for the required operation time. The solution to a given problem involves the development of new test procedures and enhancement of the known test procedures for the investigation of the crack nucleation and propagation, as well as the improvement of informative nature of the test results. The standard impact toughness tests provide limited information for the analysis of the influence of different factors on the material behaviour. The energy on the specimen fracture (Kobayashi (2001), Böhme (1999), Schindler et al. (2002)) is determined, while the percentage of the ductile component in the fracture or the value of lateral expansion of the specimen with the fracture zone is evaluated by the fracture type (Tanguy et al. (2001)). The volume of the information obtained in the process of testing for its further analysis can be increased via equipping the testing facilities with the modern system of high-speed data registration, which allows one to record a complete diagram of strain and fracture of the specimen with a sufficient resolution (Kondryakov et al. (2005), Zhao et al. (2019)). For this purpose, apart from Charpy specimens, sub-sized specimens and side-grooved specimens are used. Modern procedures and high-speed registration systems can increase the amount of information for these tests and, therefore, obtain additional possibilities for the investigation of the processes of crack initiation and propagation. At present, the nuclear industry employs sub-sized specimens for the assessment of the level of metal degradation, which makes it possible to save the deficient metal and have more information on the process of testing. The issue of re-calculation of the test results for sub-sized specimens and the development of the correlation dependencies remains to be open. As is seen from the investigations Margolin et al. (2009), the formation of shear lips in Charpy specimens might affect the test results, which leads to the inaccurate assessment of the critical brittle temperature and moment of the crack initiation. Thus, the main focus is on the development of the test procedures for Charpy specimens with edge notches (side-grooved specimens). However, the task of the interpretation of such test results and development of the correlation dependences is also unsolved.

Nomenclature Т

temperature

P

force time

t

s

impact tester displacement

E S

energy

area under diagram P(s)

KCV specific energy V

crack propagation velocity

L

length of the specific regions of the crack propagation within the specimen macrofracture