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Charpy V-notch specimens are widely used within the nuclear industry to monitor the effects of neutron damage to the reactor pressure vessel (RPV) beltline region. There is an ever-increasing need to obtain more notched bar impact data as plants age. Many plants will require more specimens for surveillance during the license renewal period. Other plants have experienced more embrittlement than originally anticipated, and it will be necessary to develop plant-specific Charpy shift trend curve models to ensure continued safe operation. Since physically based trend curves have not yet been validated, the use of plant-specific data will save the utilities operations costs since overly (arbitrarily) conservative models are no longer needed. Miniature specimens have also been used to characterize the material condition after vessel annealing. The use of miniaturized specimens which can be fabricated from previously tested full sized specimens offers one solution to this need for more fracture data.
Experiments performed using side-grooved miniaturized notch test (MNT) specimens have demonstrated that 1/16 scale miniature specimens can be designed to yield transitional fracture behavior and that the fracture appearance and energy-temperature curves can be quantitatively related to the conventional ASTM E23 specimen data. This paper presents the results of a study focused on designing an optimized MNT specimen and test machine. A combination of literature review, metallurgical analysis, and finite element analysis was used to consider such design parameters as minimum specimen cross-section, specimen length, notch acuity, the use of side grooves, side groove geometry, support span, and striker geometry. Two dimensional and three dimensional, elastic-plastic, large deformation, finite element analyses were used to compare stress/strain fields for standard and miniaturized specimens. Specimen and test machine geometries have been developed to ensure continuum requirements are met, the MNT specimen stress fields simulate those of the conventional specimen, and scatter for the miniature data is minimized.
Charpy, miniaturized specimen testing, impact test, fracture appearance, lateral expansion, ductile-brittle transition temperature, upper shelf energy
President, MPM Research & Consulting, Lemont, PA
President, Computational Mechanics, Inc., Julian, PA
Consultant, Jamesville, NY
Program Manager, ESEERCO, New York, NY