Influence of Stress Change on the Fatigue Behavior and Fatigue Life of Aluminum Oxide-Dispersion-Strengthening Copper Alloy at Room Temperature and 350℃
Norio KAWAGOISHI, Hironobu NISITANI, Eiji KONDO, Atsunori SHIMAMOTO and Rieko TASHIRO
Abstract:In order to investigate the influence of stress change on the fatigue behavior and fatigue life of an aluminum oxide-dispersion-strengthening copper alloy at elevated temperature, rotating bending fatigue tests were carried out under two-step loading at room temperature and 350℃. Both of static strength and fatigue strength decreased at 350℃. However, at the same relative stress σa/σB, fatigue life was longer at 350℃ than at room temperature. Although the cumulative ratios Σ(N/Nf) were nearly unity for both the low to high and the high to low block loadings at room temperature, Miner's rule did not hold at 350℃. These results were related to the stress dependence on the log l - N/Nf relation. That is, the crack length initiated at the same N/Nf was larger in higher stress level at 350℃, whereas there was no stress dependence in the relation at room temperature. The stress dependence on the relation at 350℃ was caused by the suppression of crack initiation due to the surface oxidation. Key Words:Fatigue, Aluminum oxide-dispersion-strengthening copper alloy, Elevated temperature, Two-step loading, Crack initiation, Crack propagation