Fatigue Strength and Deformation at Rotating Bending in Program Loading Tests

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Abstract
The manifold program loading tests repeated in five stress levels including those in plastic range were carrid out, of S35C steel by rotating bending at the frequency 20rpm at the large stress range and 1790rpm in the ordinary fatigue tests range. In this fatigue test Kawamoto's rotating beam bending fatigue testing machine was used, which was of uniform moment type, and the specimen could be bent in any direction. During the fatigue tests the change of deflexion from vertical to horizontal and vice versa at the center of the specimen was observed. The main conclusion is as follows. (1) The general theory that fatigue fracture occurs at Σn/N=1 is not applicable to the experimental results. When the minimum step stress is relatively small the value of Σn/N is very small. (2) The ratio of the horizontal and the vertical deflexion of the specimen δn/δv is nearly 1 under large stress loading. (3) The loading under stress will make damage on the fatigue life under the program loading.

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