Effects Of Stress Gradient and Test Frequency on the Rotating Bending Fatigue Strength of Annealed Carbon Steel Specimens Containing Small Artificial Defects

Rotating bending (RB) fatigue tests have been conducted frequently to obtain fatigue data. Historically, however, the factors that affect the results obtained by this testing method have yet to be discussed well. This study aims to reveal the effects of stress gradient χ and test frequency f on the RB fatigue strength. The annealed 0.37% carbon steel specimens containing an identical drilled hole of √area = 93 μm in size were used. The influences of the factors of χ and f were systematically investigated, changing the shape and diameter of specimens and loading type so that the stress gradient at the specimen surface was χ = 0 mm -1 , 0.2 mm -1 , or 0.4 mm -1 , and setting the test frequency as either f = 1 Hz or 67 Hz. The experimental data were compared with the S-N curve predicted based on Murakami and Endo’s sc S-N prediction model. The effect of χ was small for the present test conditions. However, the fatigue life was longer than the prediction when the f was high because of the high inertia force of the testing machine’s shaft rotating at high speed.