長寿命域の疲労寿命分布に関する統計的一考察

抄録

The main purpose of the present study was to investigate the fatigue life distribution at stress levels around the endurance limit σ_w. Three multiple-type rotating bending testing machines were manufactured, each of which can test eighteen specimens simultaneously. Approximately twenty specimens were tested at each respective stress level around the endurance limit σ_w with the maximum number of stress cycles of about 5×10⁸. The specimens used were heat treated rimmed steel CH10R bars. The results were analyzed using the Weibull distribution of mixed type.
The major conclusions are as follows;
(1) In the stress range above σ_w, there are fixed relationships between the parameters of Weibull distribution and the stress, that is, the shape parameter m is constant, and the scale and location parameters, a and γ, have linear relationships on log a-σ and log γ-log σ diagrams.
(2) The Weibull distribution of mixed type
F(N)=p₁F₁(N)+p₂F₂(N), p₁+p₂=1,
is well fitted to the fatigue life distributions at the stress levels around σ_w. The parameters m₁, a₁ and γ₁ of F₁(N) are given by extending m-σ, log a-σ and log γ-log σ relations in the stress range well above σ_w to the stress range around σ_w. And F₂(N) appears only at the stress levels around σ_w, whose parameter m₂ is constant and parameters a₂ and γ₂ have different linear relationships on log a₂-σ and log γ₂-logσ diagrams.