高強度鋼SUJ2におけるFish-eye破壊過程の観察

概要

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Long-term fatigue tests have been conducted on a high strength steel, SUJ2,in order to clarify the fatigue behaviour in long life region, more than 10^7 cycles. The fatigue failure at the stress level under the ordinary fatigue limit occurred in long life region. Fracture mechanism in this region is fish-eye type, i. e. inner defect induced failure, while surface slip type fracture is found in short fatigue life region. At the center of fish-eye non-metallic inclusion is recognized, which is surrounded by an indefinite and grainy region. However, the fish-eye without grainy region was also observed exceptionally. Therefore, a fish-eye is divided usually into three parts, i. e. inclusion, grainy region and inner crack. Most of the inclusions generating the fish-eye were located within 0.1mm from the specimen surface. The sizes of inclusions calculated by the √<area> method are almost constant to the stress level and the number of cycles. The initial stress intensity factor range, ΔK_<ini>, at which crack was generated from the inclusion, is almost the same with increasing fatigue life, i, e. 2.3〜3.5 MPa √<m>. On the other hand, the sizes of fish-eyes calculated by the √<area> method are scattered to the stress level and the number of cycles. Based on the results, a model of the fatigue failure at the stress level under the fatigue limit is proposed.
一般社団法人日本機械学会の論文
1999-12-25