Low cycle fatigue tests of isotropic fine-grained graphite IG-11 were performed at the stress combination of pull-pull, pull-push and push-push. The best fit
S-N curves obtained by several statistic analysis methods, were compared and the effect of stress ratio and specimen size on fatigue strength were discussed. Following conclusions were obtained:
(1) The best fit
S-N curves obtained by Price's method showed comparatively better in data fitting than the other methods.
(2) The fatigue strength decreased as decrease of stress ratio
R. The drastic decrease of fatigue strength was observed in the case of
R=-3.5. This is because that the effect of pre-compressive stress in first fatigue cycle induced the decrease of tensile strength.
(3) The effect of specimen size on fatigue strength in the case of
R=+∞ and compressive strength were observed.
(4) The mechanism of fatigue in graphite was well understood assuming that fatigue fracture were occurred when the stress intensity reach to the fracture toughness value in the process of crack extension.
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