窒化けい素における長いき裂と短いき裂の疲労き裂伝ぱ挙動

概要

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Fatigue crack growth tests of silicon nitride specimens with long cracks were carried out to investigate the effects of wave form of loading, stress ratio and frequency. The crack growth rate was independent of the wave form of loading and frequency. The effective stress intensity factor range afforded a unique crack growth curve regardless of stress ratio in the range of low growth rate. The fatigue crack growth rate in cyclic fatigue was higher than that in static fatigue. Fatigue tests of smooth specimens with small surface cracks induced by grinding were also carried out in the high frequency range. The S-N curve was predicted by using the both cyclic and static Crack growth curves, where the initial surface crack size was defined on the basis of the strength of the specimen and the fracture toughness value. The s-N curve predicted using the cyclic crack growth curve was not in agreement with the experimental results. On the other hand, the predicted S-N curve using the static crack growth curve was in good agreement with the experimental results. Therefore, it is clear that as ma11crackterlds to grow in a static fatigue manner even in the range of high frequency and low Crack growth rate, where the cyclic crack growth is dominant for long cracks.
社団法人日本材料学会の論文
1991-05-15