Fatigue Strength Predictions of Notched Specimens of Spring Steel

Abstract

This paper presents the study on fatigue strength and fatigue life predictions of surface notched specimens of spring steel. The validity of the fatigue limit prediction and the fatigue crack growth prediction based on Haddad's equation, where the hardness of material and stress ratio were taken into considerations, were studied, compared with the experimental results. The specimens with semicircular notch by electrical discharge machining were prepared. The conditions of tests were without decarburization, with decarburization and with shot peening. The main results can be summarized below:(1) The calculated fatigue limits were slightly smaller than the experimental results for the without decarburization specimens. It can be said that the fatigue limit prediction is evaluated within the safe side in this case.(2) The calculated fatigue limits were between the experimental fracture and non-fracture results for the decarburized specimens. Therefore, the fatigue limit prediction can be said to be effective.(3) The fatigue limit prediction for the shot peeed specimens was evaluated within the safe side. It can be said that the prediction is effective.(4) The calculated fatigue crack growth behavior with da/dN-ΔK diagrams showed good agreements with experimental results.(5) The calculated fatigue life was slightly shorter than the experimental fatigue life without decarburization on the S-N curves. The calculated fatigue life showed good agreements with the experimental results with decarburization. Therefore, it can be concluded that the fatigue crack growth prediction is very effective.