焼なましおよび表面圧延低炭素銅の疲労き裂発生機構

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In order to clarify the fatigue crack initiation mechanism of the annealed and the surface-rolled low carbon steels, the fatigue deformation and crack initiation processes in both the materials have been observed by the X-ray microbeam technique and the electron microscopic replica method, and discussion has been made on the experiment. The following results have been obtained. (1) The behaviors of crystal deformation during fatigue are various in each crystal grains, according to their crystal orientations. But generally, in annealed specimens. total misorientation and micro lattice strain increase highly in the initial stage of fatigue process, and keep on increas-ing slightly till 80% is reached in fatigue life, but in surface-rolled specimens on the contrary, they decrease. They show also quite different surface structural changes in both the specimens. (2) The formation of distinct subgrain is found after the increase of total misorientation and of micro lattice strain and before fatigue crack initiation in annealed specimens, and is found after their decrease and before fatigue crack initiation in surface-rolled specimens. And in the case of low stress fatigue the presence of subgrain is not so evident as in high stress fatigue. (3) The fatigue crack initiation mechanism is the same both in annealed specimens and in surface-rolled ones. The fatigue crack in both the specimens is formed by jointing the pores in the slip band region on the specimen surface which are considered to have been generated by the diffusion of vacancies. and this jointing action is accelerated by the stress concentration due to the notch-peak formed in the slip band region. On the other hand, the distinct subgrain becomes clear in both the specimens at the fatigue crack initiation. And this fatigue crack is considered to run along the distinct subgrain boundary.
社団法人日本材料学会の論文
1970-09-15

焼なましおよび表面圧延低炭素銅の疲労き裂発生機構

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