Effect of oxidation on the tension-tension fatigue strength was examined for a fine-grained isotropic nuclear graphite Grade IG-110. Specimens were oxidized in air at 500°C to a burnoff level of 3.5 and 7.0%. Fatigue tests were carried out at room temperature at a frequency between 0.5 and 10Hz. The conclusions are:
(1) On the basis of all the data points both for the oxidized specimens and the unoxidized, the following relationship was obtained between applied stress σ
a and number of cycles to fracture N
f:
log[(σ
a/σ
t0)(σ
0/σ)
6.24]=-0.00831-0.00988 log N
f,
where σ
t0, ρ
0 and ρ are the mean of the tensile strength of unoxidized specimens, bulk densities before and after oxidation, respectively.
(2) Combination of the fatigue strength curve for the unoxidized and the data on the tensile strength loss due to oxidation made it possible to estimate the fatigue strength of the oxidized with 99% survival probability 95% confidence, which was found to be close to the value calculated from the results of the fatigue test on the oxidized specimens.
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