Methodical Approach to Studying Growth Kinetics for Short and Long Fatigue Cracks in Irradiated Reactor Materials: Part
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ING, DIAGNOSTICS AND QUALITY CONTROL OF MATERIALS
Methodical Approach to Studying Growth Kinetics for Short and Long Fatigue Cracks in Irradiated Reactor Materials: Part 1. Problem Definition. The Effect of Initial Notch Acuity on the Fatigue Crack Rate in Small-Sized Samples V. I. Smirnova, *, A. J. Minkina, B. Z. Margolina, and V. I. Kokhonova aNational
Research Center Kurchatov Institute—Central Research Institute of Structural Materials Prometey, St. Petersburg, 191015 Russia *e-mail: [email protected] Received February 8, 2019; revised March 12, 2019; accepted March 18, 2019
Abstract—The main methodological features of the studies on the kinetics of fatigue crack growth in the course of testing of irradiated small-sized samples are considered. The effect of the initial notch acuity on the long crack growth rate is studied. On the basis of experimental studies, the size of stress concentration zone is estimated depending on the notch type in the small-sized samples. A brief literature review of the main problems in the studies on the growth kinetics for short fatigue cracks is performed. The tasks for further research are formulated. Keywords: austenitic steel, neutron irradiation, cyclic crack resistance, fatigue crack growth, short and long fatigue crack DOI: 10.1134/S2075113320060222
INTRODUCTION The Purpose and Objectives of the Study The problem of the neutron irradiation effect exerted on the growth rate of fatigue cracks in chromium-nickel austenitic steels at present is becoming increasingly more and more urgent, since such information is necessary to assess the durability of critical elements in the equipment for nuclear power plants (NPP) and to resolve the issue of extending the service life thereof. The relevance of such studies can also be explained by the fact that, for Russian domestic materials, the experimental data on cyclic crack resistance (the fatigue crack growth rate depending on the amplitude of change in the stress intensity factor under cyclic loading) are rather limited [1–3]. The requirement for placing the largest number of samples in testing assemblies for subsequent irradiation in research reactors (BOR-60, VVR-M, etc.) or operating reactors at nuclear power plants has determined the choice for studying the kinetics of fatigue crack growth in small prismatic lateral-notched samples for bending tests. Such samples 10 × 10 × 55 mm in size have a short (shallow-depth) mechanical notch (Fig. 1) and can also be used to study the crack resistance of irradiated materials composing the retrievable parts of NPP equipment via testing for three-point bending [3].
To study the kinetics of fatigue crack growth in highly irradiated materials with the use of small-sized nonstandard bending samples, a special testing technique and experimental data processing procedure was developed. The testing methodology was developed as applied to the specific testing equipment, namely, to that for testing irradiated samples according to a threepoint bending scheme using a SCHENCK PSB-100 servohydraulic machin
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