1975 年 24 巻 263 号 p. 753-760
The changes in mechanical properties of carbon steel fatigued ultrasonically at 17kHz have been investigated. The results were compared with those fatigued by the rotary bending test at 3000rpm.
The following conclusions are obtained:
(1) The fatigue life of carbon steel cycled at 17kHz is longer than that of the same material fatigued at 3000rpm. This is more pronounced in annealed (An.) materials than in low-temperature quenching (LTQ) ones.
(2) The variations of hardness Hv and residual stress σi during the fatigue test are smaller at 17kHz than at 3000rpm fatigue.
(3) The variations of both Hv and σi for S10C (0.1%C) during the faigue test at 17kHz are slightly smaller than those for S45C (0.42%C). In the case of 3000rpm fatigue, however, these variations values for S10C are fairly larger than those for S45C.
(4) In both 17kHz and 3000rpm tests, the amounts of change in Hv, σi and E become larger as the stress amplitude increases.
(5) In the fatigue process at 3000rpm, the amount of change in Hv of LTQ specimen is larger than that in Hv of An. specimen. However, there is no significant difference between them in the process of 17kHz fatigue.
(6) The number of slip lines produced on the specimen surface fatigued at 17kHz is far fewer than that at 3000rpm, especially in LTQ materials. However, the number of cracks is not so different between them. It is confirmed that those characteristics may influence the hardness and Young's modulus.
(7) The relationship between the hardness and the residual stress can be expressed as follows:
where k is a constant which depends upon the kind of materials, working conditions and fatigue testing conditions. This equation, however, is not applicable to the later stage of the fatigue test nor to the quenched materials.
(8) The relationship between the residual stress and Young's modulus can be expressed as follows:
(σi>0.5kg/mm2 in carbon steel)
where ΔE=Est-Et; Est being Young's modulus in saturation magnetization and Et being Young's modulus in non-magnetization.