Abstract
The value of ΔKeff, th for a medium carbon steel (0.46%C) was measured by a rotating bending fatigue test using specimens which were annealed after introducing fatigue cracks. Since the fatigue cracks become ideal cracks after annealing, ΔKeff, , th can be determined by finding the critical stress under which no crack growth occurs. The values of Kop/Kmax for a stationary fatigue crack in the rotating bending fatigue test(R=-1) were estimated by the Dugdale model as Kop/Kmax=-1.0 over a wide range of stresses. The values of ΔKeff, th obtained in this study were 3.4∼3.6 MPa·m1/2 and were approximately independent of crack size in the range from 100 μm to 1 000 μm. The importance of this value for short cracks is emphasized from the view point of fatigue under varying loads which include both high and low stress amplitudes.
