Correlation between the Existence of Fatigue Limit and Non-Propagating Micro-Crack

概要

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The purpose of this paper is to make clear the reason why the fatigue limit and the coaxing effect exist in steel, using 0.13%C steel and copper specimens. The main results obtained are as follows. In 0.13%C steel specimens ; (1) The incipient fatigue cracks, revealed by light electro-polishing (1〜2μ) after 10^7 cycles under the stress repetitions of the fatigue limit of the specimen, exist in the ferrite not only at the surface but also in the inside and the tip parts of those cracks become 24〜34% harder than in the virgin state. (2) This incipient fatigue crack appearing by the stress of the fatigue limit is the starting point of fracture, when the specimen fails by a stress greater than the fatigue limit. In copper specimens ; (3) The tip parts of the incipient fatigue crack in copper, appearing after 10^7 cycles of the stress which corresponds to the fatigue strength for 2×10^7 cycles, do not become so hard than the ones in 0.13%C steel. These results show that the existence of the fatigue limit in steel is due to the strengthening of the tip parts of the non-propagating micro-crack.
一般社団法人日本機械学会の論文