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 5×10
8. 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)=p
1F
1(N)+p
2F
2(N), p
1+p
2=1,
is well fitted to the fatigue life distributions at the stress levels around σ
w. The parameters
m1,
a1 and γ
1 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 γ
2 have different linear relationships on log
a2-σ and log γ
2-logσ diagrams.
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