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Conference Article: Bending fatigue behavior of nuclear-grade graphite under impact loading

Futakawa, M.; Kikuchi, K.; Muto, Y. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Dept. of High Temperature Engineering); Shibata, H. (Tokyo Univ. (Japan). Inst. of Industrial Science)

Abstract

The graphite components in HTR (High Temperature gas-cooled Reactor) are subjected to impact force due to an earthquake. It is important from the viewpoint of seismic safety design to investigate the difference of strength under impact loading and non-impact loading. Both bending strength and bending fatigue strength tests, therefore, were carried out under impact non-impact loading on two kinds of graphite materials: isotropic and near-isotropic. The impact of response analyses, which used a beam model taking account of the contact behavior between specimen and tup, were performed to evaluate the relationships between impact energy, impact force and stress. The main conclusions obtained are summarized as follows:

  1. A beam model taking account of the contact behavior through the Hertzian theory is applicable to describe the impact behavior.
  2. The bending strength of graphite is independent of strain rate in the range from 10-6 to 5 l/s.
  3. Despite both specimen volume and kind of graphite the strength of graphite is lower in impact fatigue than in non-impact fatigue.

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key words: bending; earthquakes; fatigue; graphite; htgr type reactors; impact strength; mathematical models; reactor components; carbon; deformation; gas cooled reactors; graphite moderated reactors; mechanical properties; reactors; seismic events
Reference:
Specialists' meeting on the status of graphite development for gas cooled reactors. Tokai, Ibaraki (Japan). 9-12 Sep 1991
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--690, pp:87-95