Ni-Cr-Mo鋼の高温塑性疲労試験

抄録

With the progress of high effective machinery, the fatigue for the plastic region becomes important.
Herein, it is considered to be significant to detect the correlation between the constant strain cycle fatigue and the constant stress cycle fatigue, and this may make it possible to presume the mechanism of the fatigue for the plastic region.
In the case of the constant plastic strain cycle fatigue, the formula for fracture has been formed and has been confirmed through many experiments.
In the case of the constant plastic stress cycle fatigue, however, the formula for the fracture has not yet been estimated.
This paper deals with the experiment of the constant strain cycle and constant stress cycle fatigues for the plastic region by the method of applying the tension and the compression on a Ni-Cr-Mo steel at a room-temperature, 350°C and 550°C.
The conclusions obtained from the foregoing are as follows.
1) In the process of developing the Yokobori's theory, it was found that the static true strain at fracture corresponded to the range of strain at N=1/2 cycle as proposed by D.E. Martin.
2) The formula for fracture due to the constant stress cycle fatigue has been induced as follows.
Assuming the static tensile stress-strain curve to be expressed by the formula
σ=a+bloge^ε a, b; constant
and using the formula
N^1/2Δε_p=c
then
σ_a=(bloge1/√2+σ_f)-b/2loge^N
σ_f; the true static tensile stress at the fracture corrected by the method of P.W. Bridgman
σ_a; the stress amplitude
N; the cycle till the fracture
3) The calculation on this formula as above was confirmed to coincide with the experimental data at each temperature.
The static tensile true stress at fracture; σf corresponded to the stress amplitude at N=1/2 cycle.
4) Further, the relation between the total energy and the total strain absorbed in the specimen until the fatigue fracture is discussed in the text of this paper.