岩石の疲労寿命に及ぼす平均応力および応力振幅の影響

抄録

In this paper the authors report the results of the test of andesite respecting its fatigue failure under pulsating compressive stress. The discussion has been made on cases where fatigue lives have been observed as of wide fluctuation, on the assumption that fatigue failure takes place in stochastic process.
Using a graphical method in which the logarithms of probability of survival are plotted against fatigue lives, the authors show that the probability of survival is given by
p=ξ_jexp(-λ_jN)+ξ₂exp(-λ₂N)
where p: the probability of survival,
ξ_i: the probability that failure of the test piece occurs by the fracture process with the rate constant λ_i, and ξ₁+ξ₂=1,
N: the number of loading cycles.
This result means that fatigue failure in the rock takes place in either of the two disjunctive Poisson's processes of the first order. Of these two processes the one with the smaller rate constant would correspond to the intergrannular fracture of the rock structure, while the other with the greater rate constant would correspond to the intergrannular fracture of the rock structure.
Based on these test results, the rate constants λ_i are evaluated for various mean stresses and stress amplitudes. The effects of the mean stress and stress amplitude on the rate constants are discussed, and expressed as
λ_i=A_i·σ_m^mi·σ_aⁿⁱ
where σ_m: the mean stress,
σ_a: the stress amplitude.
Using the method of least squares, the unknown parameters in this equation are evaluated.