単軸引張りの Pre-Strain を受けた銅材の組み合わせ応力下の疲労について

抄録

This paper aims to present evidences for the changes of work hardening phenomena that can occur in tensile pre-strained coppers when they are subjected to fatigue combined stresses.
The present author believes that the phenomena are the result of the origination and propagation of micro-crack. From the fact that the intrusions are found along the slip bands, the author surmises that they develop into persistent slip bands and fissures, and that these bands and fissures are kinds of micro-cracks.
Changing the grade of tensile pre-straining (K), the fatigue stage of the first origination of slip band was studied in connection with the generation of the intrusion, and that of the first origination of the persistent slip band was investigated in relation to the occurrence of the micro-crack.
The main conclusions from this study are as follows:
(1) In the case of uniaxial tensile pre-strained copper the changes of the work hardening phenomena appeared slowly during the fatigue test. These results differ remarkably from that obtained by Professor Wood with regard to the fatigue of complex pre-strained copper.
(2) In the case of the fatigue of the tensile pre-strained copper the work hardening was saturated at an early stage of the fatigue test, and the appearance of the stage of saturation was delayed by the increase of pre-strained grade K. Concerning the fatigue of annealed copper, the saturated fatigue stage was about 20 to 30% of its life.
(3) The occurrence of the initial and decisive fatigue damages was delayed by pre-straning and also by the increase of the normal stress σ_x caused in the longitudinal direction of the specimen.
(4) In view of the fact that in the case of the pre-strained copper the number of cycles from the origination of the micro-crack to the failure of the specimen is less than in the case of the annealed copper, it is believed that the micro-crack in the former case propagates faster than in the latter.