Fatigue Strength under Multiple Repeated Stress : (In the Case of Double Change of Amplitude in Two Stress Levels)

Abstract

The problems of the fatigue of materials have been studied by many investigators, but there still remain many unknown factors, especially on the damaging effects due to the repeated stress with varying amplitude. In this study, we carried out the fatigue tests on the medium carbon steel by supperposing the higher stress reversals upon the fundamental repeated stress levels in order to discuss the process of fatigue stressing, and investigated the influence of the cycle ratio of the primary stress, the secondary higher stress level, and its reversals on the cumulative cycle ratio to failure. As a result, it has been found that the more the cycle ratio of the primary stress amplitude is and the lower the secondary stress level is, the greater the cumulative cycle ratio to failure becomes. Besides, we have interpreted these test results by the use of the cycle ratio-damage curves (D-R curves).