Effect of Artificial Defects on Fatigue Limit of S38C Axle Steel

Two kinds of artificial defects including indentation and electro-discharge machined crater were introduced into the fatigue specimen of S38C axle steel by Brinell hardness tester and electric spark ablation. The fatigue limits of specimens with different sizes of artificial defects were studied and compared with calculation by Murakami equation. The results show that the fatigue crack originated from the bottom of the artificial defects. The fatigue limit of specimens with artificial indentation and electro-discharge machined crater showed a linear decreasing trend with the increase of the defect projection in the study scope. Under the same projection area condition on the cross section of defects, the tested fatigue limit of the specimen with the electro-discharge machined crater was about 30 MPa smaller than that of the specimen with the artificial indentation; the tested fatigue limit of the specimen with the artificial indentation was about 50 MPa larger than the calculated value; the tested fatigue limit of the specimen with the electro-discharge machined crater was only 20 MPa higher than the calculated value, indicating the fatigue limit of specimen with such defect could be predicted approximately by Murakami equation.