多結晶アルミナの微小き裂進展挙動および架橋現象に及ぼす繰返し荷重と結晶粒径の影響

概要

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Crack propagation tests of polycrystalline alumina with average grain size of 1 μm and 19 μm were carried out under static and cyclic load. The alumina with 1 μm and 19 μm are designated as 0D and 5D, respectively. Small specimens with a semi-elliptical surface crack of 200 μm or 340 μm were used. The results were compared with those obtained using CT specimens. The main results obtained are as follows : (1)Cyclic load enhanced the crack propagatin rate as compared with that under static load. (2)The order of the crack propagation resistance under static load is same as that under cyclic load, as shown hereunder. 0D-200>50D-CT>0D-340>5D-340>0D-CT The notation 0D-200 means the specimen of 0D with 200 μm crack. It is to be noted that the bridging effect, which varies depending on grain size, bring difference in crack propagation resistance. (3)Crack opening displacement COD increased as the number of stress cycles increased. This means that cyclic load reduced bridging effect. Stress intensity factor at crack tip K_<Itip> was calculated in terms of COD. (4)The value K_<Itip> was shown to be a good fracture mechanics parameter to describe the crack propagation behavior.
1994-02-15