Investigation of Fatigue and Flaw Tolerance Performance of 18CrNiMo7-6 Case-hardening Steel

The aim of this study is to evaluate the effect of small defects on the fatigue life of the 18CrNiMo7-6 material. The evaluations are based on comparisons of S/N curves, which are obtained through coupon-level fatigue testing of pristine and intentionally flawed specimen sets. Fractographic examinations are performed on the failed specimens from both sets in order to investigate the fracture characteristics and discover any potential differences in failure mechanisms of two sets. Experimental findings regarding endurance limit of the flawed set are also compared with analytical evaluations. In these evaluations, the small defect effect is also considered on top of the linear fracture mechanics approach. Finally, the differences between the outcomes of fatigue life evaluations, when different methods are used, are discussed.