Fatigue Damage of Electropolished Carbon Steel Specimens with a Shallow Groove under Two Stress Levels

概要

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Fatigue tests of S 20 C electropolished specimens were conducted with a rotating bending testing machine under double repeated stress in two stress levels. The results are as follows. (1) The values of accumulated cycle ratio based on the initiation of crack (length of 0.1 mm) are between 0.9 and 1.1 and independent of the loading order of stress amplitudes. This may imply that the fatigue damage before the initiation of crack is accumulated in a linear way and mainly at the same places. (2) In the process of crack propagation, the values of accumulated cycle ratio based on the fracture of specimen depend on the loading order of stress amplitudes. This may be explained from the fact that the crack lengths at the same cycle ratio under different stress amplitudes do not coincide. (3) The repetition of the second stress increases the density of slip traces mainly in the grains whose slip traces appear under the repetition of the first stress. (4) French's damage curve is close to the crack (length of 0.1 mm) initiation curve.
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