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Conference Article: Acoustic emission from polycrystalline graphites

Ioka, I.; Yoda, S.; Oku, T.; Miyamoto, Y. (Japan Atomic Energy Research Inst., Tokai, Ibaraki. Tokai Research Establishment)

Abstract

Acoustic emission was monitored from polycrystalline graphites with different microstructure (pore size and pore volume) subjected to compressive loading. The graphites used in this study comprised five brands, that is, PGX, ISEM-1, IG-11, IG-15, and ISO-88. A root mean square (RMS) voltage and event counts of acoustic emission for graphites were measured during compressive loading. The acoustic emission was measured using a computed-based data acquisition and analysis system. The graphites were first deformed up to 80 % of the average fracture stress, then unloaded and reloaded again until the fracture occured. During the first loading, the change in RMS voltage for acoustic emission was detected from the initial stage. During the unloading, the RMS voltage became zero level as soon as the applied stress was released and then gradually rose to a peak and declined. The behavior indicated that the reversed plastic deformation occured in graphites. During the second loading, the RMS voltage gently increased until the applied stress exceeded the maximum stress of the first loading. There is no Kaiser effect in the graphites. A bicrystal model could give a reasonable explanation of this results. The empirical equation between the ratio of sigmaAE to sigmaf and sigmaf was obtained. It is considered that the detection of microfracture by the acoustic emission technique is effective in macrofracture prediction of polycrystalline graphites.

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key words: acoustic emission testing; fracture properties; graphite; htgr type reactors; microstructure; polycrystals; acoustic testing; carbon; crystal structure; crystals; gas cooled reactors; graphite moderated reactors; materials testing; mechanical properties; nondestructive testing; testing
Reference:
Specialists' meeting on graphite component structural design, JAERI Tokai (Japan), September 8-11, 1986
International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors
IWGGCR--11, pp:227-232