Estimation of Fatigue Life on Notched High-Strength Aluminum Alloy Plate under Two-Step Loading by Epuivalent Stress Amplitude
Toru TAKASE , Atsuhiro KOYAMA and Ryo YONEDA
Abstract:All tests were performed for high-strength aluminum alloy plate with a notch on both sides. Firstly, the proposed simplified method for estimating the stress and strain at the notch root was investigated.@The strain at the notch root was measured by a strain gage. The estimated strains and strain ranges were in good agreement with the experimental results. Next, fatigue tests were carried out under constant amplitude loading and two-step loading. In two-step loading, two stress 1eve1s were used as the primary stress amp1itude and three cycle ratios were combined. The cycle ratio was defined as the ratio of cycles at the primary stress amplitude to the corresponding fatigue life. Fatigue test results were discussed using the equivalent stress amplitude, which was estimated by the stress amplitude and the mean stress at the notch root. Both the fatigue life and the fatigue limit under the secondary stress amplitude tended to lower, as the cycle ratio under the primary stress amplitude increased. However, the fatigue life under the secondary stress amplitude did not depend upon the magnitude of the primary stress amplitude, if the cycle ratio was same. Hence, the fatigue life under the secondary stress amplitude can be estimated by the equivalent stress amplitude without the @effect of the primary stress amplitude. Key Words:Fatigue, Two-step loading, Equivalent stress amplitude, Aluminum alloy, Notch