Effect of Notch Formation Method on Fatigue Resistance for Ck45 Carbon Steel based on the Notch Sensitivity Factor

In this study, the effect of the notch preparation method on the fatigue strength of medium carbon steel (ck45) was studied. Rotational bending samples were used with a stress ratio R = -1, all test were conducted at room temperature.Test samples were divided into three groups, the first group is for the polished specimens without notch, the second group is for rolled notch specimens, and the third group is for machined notch specimens. Stress- life curves were established for all cases, to find Basquin equation thatis, for the investigated material: for Smooth specimens, for rolled notch specimens and for machined notch specimens. The results also indicate a change in the microstructure near the rolled notch from granular structure  to the tissue structure. Perhaps the increase in fatigue resistance is due to this structure, which leads to impeding the growth of the cracks, since the direction of the tissue structure is perpendicular to the direction of the cracks growth.